In a world-first achievement published in ("An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets"), scientists from the RIKEN Center for Emergent Matter Science in Japan, along with colleagues from the National Institute of Material Science and the University of Tokyo, have developed a new hydrogel whose properties are dominated by electrostatic repulsion, rather than attractive interactions. According to Yasuhiro Ishida, head of the Emergent Bioinspired Soft Matter Research Team, the work began from a surreptitious discovery, that when titanate nano-sheets are suspended in an aqueous colloidal dispersion, they align themselves face-to-face in a plane when subjected to a strong magnetic field. The field maximizes the electrostatic repulsion between them and entices them into a quasi-crystalline structure. They naturally orient themselves face to face, separated by the electrostatic forces between them. To create the new material, the researchers used the newly discovered method to arrange layers of the sheets in a plane, and once the sheets were aligned in the plane, fixed the magnetically induced structural order by transforming the dispersion into a hydrogel using a procedure called light-triggered in-situ vinyl polymerization. Essentially, pulses of light are used to congeal the aqueous solution into a hydrogel, so that the sheets could no longer move. By doing this, they created a material whose properties are dominated by electrostatic repulsion, the same force that makes our hair stand end when we touch a van generator. Up to now, manmade materials have not taken advantage of this phenomenon, but nature has. Cartilage owes its ability to allow virtually frictionless mechanical motion within joints, even under high compression, to the electrostatic forces inside it. Electrostatic repulsive forces are used in various places, such as maglev trains, vehicle suspensions and noncontact bearings, but up to now, materials design has focused overwhelmingly on attractive interactions. The resultant new material, which contains the first example of charged inorganic structures that align co-facially in a magnetic flux, has interesting properties. It easily deforms when shear forces are applied parallel to the embedded nano-sheets, but strongly resists compressive forces applied orthogonally. According to Ishida, "This was a surprising discovery, but one that nature has already made use of. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, based on inspiration from articular cartilage, will open new possibilities for developing soft materials with unusual functions. Materials of this kind could be used in the future in various areas from regenerative medicine to precise machine engineering, by allowing the creation of artificial cartilage, anti-vibration materials and other materials that require resistance to deformation in one plane."
Review of studies on exotic superfluids in spin-orbit coupled Fermi gases
Ultracold atomic gases have been widely considered as ideal platforms for quantum simulation. Thanks to the clean environment and the highly tunable parameters in these systems, many interesting physical models can be simulated using cold atomic gases, and various novel many-body states have been prepared and probed experimentally. The recent experimental realization of synthetic gauge field in ultracold atomic gases has significantly extended the horizon of quantum simulation with cold atoms. As a special form of synthetic gauge field, synthetic spin-orbit coupling has attracted much attention recently. Professor YI Wei from University of Science and Technology of China, Professor ZHANG Wei from Renmin University of China, and Professor CUI Xiaoling from Chinese Academy of Sciences reviewed the recent theoretical studies on various novel pairing superfluid phases in spin-orbit coupled ultracold Fermi gases. They showed that spin-orbit coupling modifies the single-particle spectra, which gives rise to exotic few-body correlations and interesting pairing states. The review article was published in ("Pairing superfluidity in spin-orbit coupled ultracold Fermi gases"). 
Schematic illustration of the single-particle spectra modified by spin-orbit coupling. The Rashba-type spin-orbit coupling can lead to a degenerate ring in momentum space for the lower branch of the single-particle dispersion spectra (left). The lower-branch dispersion spectrum under the NIST-type spin-orbit coupling (right) is less symmetric. These differences, as well as the hyperfine-spin dependence of the single-particle dispersion under spin-orbit coupling, give rise to rich physics in these systems. (© Science China Press) In condensed-matter materials, spin-orbit coupling plays a key role in many interesting phenomena, such as quantum spin Hall effects, topological insulators, and topological superconductors. With the availability of synthetic spin-orbit coupling as a tool of quantum control, people hope to simulate various topological phases, the topological superfluid state in particular, in the highly controllable environment of ultracold Fermi gases. Indeed, recent theoretical studies have suggested that exotic superfluid phases and novel phenomena can be engineered with carefully designed configurations. By reviewing these theoretical studies, YI et al. discuss the exotic superfluid phases in systems with different spatial dimensions and with different forms of spin-orbit coupling. A fundamentally important effect of spin-orbit coupling is the modification of single-particle dispersion spectra. The review focuses on how this effect leads to interesting pairing phases such as the topological superfluid state, various gapless superfluid states, the spin-orbit-coupling-induced Fulde-Ferrell state, and the topological Fulde-Ferrell state. Besides many-body physics, the change in the single-particle dispersion can also induce novel few-body correlations, for example, a three-body bound state in the absence of any stable two-body bound state. These interesting few-body states, if observed, should no doubt give rise to even more exotic many-body properties.
Schematic illustration of the single-particle spectra modified by spin-orbit coupling. The Rashba-type spin-orbit coupling can lead to a degenerate ring in momentum space for the lower branch of the single-particle dispersion spectra (left). The lower-branch dispersion spectrum under the NIST-type spin-orbit coupling (right) is less symmetric. These differences, as well as the hyperfine-spin dependence of the single-particle dispersion under spin-orbit coupling, give rise to rich physics in these systems. (© Science China Press) In condensed-matter materials, spin-orbit coupling plays a key role in many interesting phenomena, such as quantum spin Hall effects, topological insulators, and topological superconductors. With the availability of synthetic spin-orbit coupling as a tool of quantum control, people hope to simulate various topological phases, the topological superfluid state in particular, in the highly controllable environment of ultracold Fermi gases. Indeed, recent theoretical studies have suggested that exotic superfluid phases and novel phenomena can be engineered with carefully designed configurations. By reviewing these theoretical studies, YI et al. discuss the exotic superfluid phases in systems with different spatial dimensions and with different forms of spin-orbit coupling. A fundamentally important effect of spin-orbit coupling is the modification of single-particle dispersion spectra. The review focuses on how this effect leads to interesting pairing phases such as the topological superfluid state, various gapless superfluid states, the spin-orbit-coupling-induced Fulde-Ferrell state, and the topological Fulde-Ferrell state. Besides many-body physics, the change in the single-particle dispersion can also induce novel few-body correlations, for example, a three-body bound state in the absence of any stable two-body bound state. These interesting few-body states, if observed, should no doubt give rise to even more exotic many-body properties.Introducing Graphene Study 2015
As part of its extensive education and outreach activities, Europe’s Graphene Flagship will soon stage a second Graphene Study week. This will take place from 23-28 March 2015 in Kaprun, a small town in the alpine Pinzgau region of Austria. 
Graphene Study brings together research students working on graphene and related two-dimensional materials with experienced scientists and engineers from academia and industry. In addition to formal lectures and poster sessions, Graphene Week provides participants with opportunities for networking and community building.
These four subject areas will be led by four eminent research leaders. Professor Vladimir Falko (Lancaster) is responsible for fundamental science, high-frequency electronics will be covered by Dr Daniel Neumaier (AMO, Aachen), optoelectronics by Professor Andrea Ferrari (Cambridge), and spintronics by Professor Bart van Wees (Groningen). The subject leaders will in turn invite a number of specialist lecturers active in their respective research areas. We envisage around 80 student participants in the Graphene Study 2015 week. There will be 30 hours of lectures, two poster sessions, and three mini-workshops, including sessions on peer-review publication and research grant applications. The cultural programme will feature a welcome reception, slalom skiing competition, and a Pecha Kucha night. You can think of the latter as karaoke for geeks! A few months following the Graphene Study 2015 school, video recordings of its lectures, together with other relevant documents, will be made available to all free of charge via the flagship website. Registration opened on 15 December, and the early-bird concession extends to 18 January. The normal registration deadline is 8 February, but in extenuating circumstances we can extend this to 22 February at the very latest. Graphene Study 2015 kicks off at 17:00 on Monday 23 March with an introductory lecture by the most esteemed Nobel laureate, Professor Sir Kostya Novoselov. This will be followed by a drinks reception and dinner. The school ends at lunchtime on Saturday 28 March, with the farewell dinner and party taking place on the Friday evening. All Graphene Study participants will be accommodated under one roof – that of the 3* Jufa youth hotel. The nearest airport is Salzburg, which is around 100 kilometres by road from Kaprun. Travel by private car is possible, and there is a direct bus service between Salzburg airport and Zell am See.
Graphene Study brings together research students working on graphene and related two-dimensional materials with experienced scientists and engineers from academia and industry. In addition to formal lectures and poster sessions, Graphene Week provides participants with opportunities for networking and community building.
DSC_0096Graphene Study is the flagship’s principal contribution to fostering the next generation of researchers working at the forefront of nanomaterials science and technology. Whilst the school is commissioned and organised by the Graphene Flagship, it is open to the graphene community within and without the flagship consortium.
Graphene Study 2015 will focus on four closely related topics:
- – Fundamental science of 2D materials
- – High-frequency electronics
- – Optoelectronics
- – Spintronics
These four subject areas will be led by four eminent research leaders. Professor Vladimir Falko (Lancaster) is responsible for fundamental science, high-frequency electronics will be covered by Dr Daniel Neumaier (AMO, Aachen), optoelectronics by Professor Andrea Ferrari (Cambridge), and spintronics by Professor Bart van Wees (Groningen). The subject leaders will in turn invite a number of specialist lecturers active in their respective research areas. We envisage around 80 student participants in the Graphene Study 2015 week. There will be 30 hours of lectures, two poster sessions, and three mini-workshops, including sessions on peer-review publication and research grant applications. The cultural programme will feature a welcome reception, slalom skiing competition, and a Pecha Kucha night. You can think of the latter as karaoke for geeks! A few months following the Graphene Study 2015 school, video recordings of its lectures, together with other relevant documents, will be made available to all free of charge via the flagship website. Registration opened on 15 December, and the early-bird concession extends to 18 January. The normal registration deadline is 8 February, but in extenuating circumstances we can extend this to 22 February at the very latest. Graphene Study 2015 kicks off at 17:00 on Monday 23 March with an introductory lecture by the most esteemed Nobel laureate, Professor Sir Kostya Novoselov. This will be followed by a drinks reception and dinner. The school ends at lunchtime on Saturday 28 March, with the farewell dinner and party taking place on the Friday evening. All Graphene Study participants will be accommodated under one roof – that of the 3* Jufa youth hotel. The nearest airport is Salzburg, which is around 100 kilometres by road from Kaprun. Travel by private car is possible, and there is a direct bus service between Salzburg airport and Zell am See.
A qubit candidate shines brighter
In the race to design the world's first universal quantum computer, a special kind of diamond defect called a nitrogen vacancy (NV) center is playing a big role. NV centers consist of a nitrogen atom and a vacant site that together replace two adjacent carbon atoms in diamond crystal. The defects can record or store quantum information and transmit it in the form of light, but the weak signal is hard to identify, extract and transmit unless it is intensified. Now a team of researchers at Harvard, the University of California, Santa Barbara and the University of Chicago has taken a major step forward in effectively enhancing the fluorescent light emission of diamond nitrogen vacancy centers - a key step to using the atom-sized defects in future quantum computers. The technique, described in the journal ("Deterministic coupling of delta-doped nitrogen vacancy centers to a nanobeam photonic crystal cavity"), hinges on the very precise positioning of NV centers within a structure called a photonic cavity that can boost the light signal from the defect. 
A scanning electron microscope image of the diamond photonic cavity shows the nanoscale holes etched through the layer containing NV centers. The scale bar indicates 200 nanometers. (Image: Evelyn Hu/Harvard) A Potential Qubit Power Couple NV centers contain an unpaired electron that can store information in a property known as spin. Researchers can "read" the spin state of the electron by observing the intensity of particular frequencies of the light that the NV center emits when illuminated by a laser. At room temperatures, this pattern of light emission couples to multiple "sideband" frequencies, making it difficult to interpret. To amplify the most important element of the signal researchers can use a structure called a photonic cavity, which consists of a pattern of nanoscale holes that serve to enhance the NV center's light emission at its main frequency. "A photonic cavity that is properly matched to the NVs can substantially augment their capabilities," said Evelyn Hu, a researcher at Harvard whose group studies the optical and electronic behavior of materials that have been carefully sculpted at the nanoscale. NV centers whose signal is enhanced by photonic cavities could act as qubits, the fundamental units of quantum information in a quantum computer. Matchmaker, Matchmaker, Make Me a Match Photonic cavities best enhance the signal of NV centers located in a "hot spot" where the cavities' resonant fields are strongest, but making sure an atom-sized defect's location matches up with this spot is extremely tricky. "Strong spatial overlap is the hardest [task] to achieve in designing and fabricating a photonic cavity for NV centers," Hu said. She compared the task to turning on a fixed small light beam in a dark room containing ultra-small transmitters that send out information once they are illuminated by the 'right' beam. If the match is right, the signal from the transmitter is returned strongly, but the challenge is that the chances of the light hitting the transmitter are very small. Hu and her colleagues ultimately aim to make sure the beam (or field of the photonic cavity) will always hit the transmitter (or NV center), so that information will always be read out. They can do this by knowing the exact position of the tiny NV centers. The team took an important first step toward this goal by controlling the depth of the diamond defects using a technique called delta doping. "Integrating a plane of spins into these structures enables us to engineering the spin-photon interaction and exploit quantum effects for future technologies," said David Awschalom, a researcher at the University of Chicago whose group grows and characterizes these systems. The technique confines the possible location of NV centers to a layer approximately 6 nanometers thick sandwiched inside a diamond membrane approximately 200 nanometers thick. The researchers then etched holes into the membrane to create the photonic cavities. Using this method the researchers were able to increase the intensity of the light emitted by the NV centers by a factor of about 30 times. The team believes they can further enhance the emission by also controlling the position of the defects in the horizontal plane and are currently working on possible ways to achieve full 3-D control. Computers, Sensors and More Nitrogen vacancy centers aren't the only candidate for qubits, but they have attracted a lot of interest because their electrons have long spin lifetimes at room temperature, meaning they can maintain quantum information for a relatively long time. And the promise of NV centers doesn't stop at ultrafast computers. NV centers can also be used in non-computing applications, for examples as molecular-scale magnetic and temperature sensors that could measure the properties within single cells.
A scanning electron microscope image of the diamond photonic cavity shows the nanoscale holes etched through the layer containing NV centers. The scale bar indicates 200 nanometers. (Image: Evelyn Hu/Harvard) A Potential Qubit Power Couple NV centers contain an unpaired electron that can store information in a property known as spin. Researchers can "read" the spin state of the electron by observing the intensity of particular frequencies of the light that the NV center emits when illuminated by a laser. At room temperatures, this pattern of light emission couples to multiple "sideband" frequencies, making it difficult to interpret. To amplify the most important element of the signal researchers can use a structure called a photonic cavity, which consists of a pattern of nanoscale holes that serve to enhance the NV center's light emission at its main frequency. "A photonic cavity that is properly matched to the NVs can substantially augment their capabilities," said Evelyn Hu, a researcher at Harvard whose group studies the optical and electronic behavior of materials that have been carefully sculpted at the nanoscale. NV centers whose signal is enhanced by photonic cavities could act as qubits, the fundamental units of quantum information in a quantum computer. Matchmaker, Matchmaker, Make Me a Match Photonic cavities best enhance the signal of NV centers located in a "hot spot" where the cavities' resonant fields are strongest, but making sure an atom-sized defect's location matches up with this spot is extremely tricky. "Strong spatial overlap is the hardest [task] to achieve in designing and fabricating a photonic cavity for NV centers," Hu said. She compared the task to turning on a fixed small light beam in a dark room containing ultra-small transmitters that send out information once they are illuminated by the 'right' beam. If the match is right, the signal from the transmitter is returned strongly, but the challenge is that the chances of the light hitting the transmitter are very small. Hu and her colleagues ultimately aim to make sure the beam (or field of the photonic cavity) will always hit the transmitter (or NV center), so that information will always be read out. They can do this by knowing the exact position of the tiny NV centers. The team took an important first step toward this goal by controlling the depth of the diamond defects using a technique called delta doping. "Integrating a plane of spins into these structures enables us to engineering the spin-photon interaction and exploit quantum effects for future technologies," said David Awschalom, a researcher at the University of Chicago whose group grows and characterizes these systems. The technique confines the possible location of NV centers to a layer approximately 6 nanometers thick sandwiched inside a diamond membrane approximately 200 nanometers thick. The researchers then etched holes into the membrane to create the photonic cavities. Using this method the researchers were able to increase the intensity of the light emitted by the NV centers by a factor of about 30 times. The team believes they can further enhance the emission by also controlling the position of the defects in the horizontal plane and are currently working on possible ways to achieve full 3-D control. Computers, Sensors and More Nitrogen vacancy centers aren't the only candidate for qubits, but they have attracted a lot of interest because their electrons have long spin lifetimes at room temperature, meaning they can maintain quantum information for a relatively long time. And the promise of NV centers doesn't stop at ultrafast computers. NV centers can also be used in non-computing applications, for examples as molecular-scale magnetic and temperature sensors that could measure the properties within single cells.Study unveils new half-light half-matter quantum particles
Prospects of developing computing and communication technologies based on quantum properties of light and matter may have taken a major step forward thanks to research by City College of New York physicists led by Dr. Vinod Menon. In a pioneering study ("Strong light–matter coupling in two-dimensional atomic crystals"), Professor Menon and his team were able to discover half-light, half-matter particles in atomically thin semiconductors (thickness ∼ a millionth of a single sheet of paper) consisting of two-dimensional (2D) layer of molybdenum and sulfur atoms arranged similar to graphene. They sandwiched this 2D material in a light trapping structure to realize these composite quantum particles. "Besides being a fundamental breakthrough, this opens up the possibility of making devices which take the benefits of both light and matter," said Professor Menon. For example one can start envisioning logic gates and signal processors that take on best of light and matter. The discovery is also expected to contribute to developing practical platforms for quantum computing. Dr. Dirk Englund, a professor at MIT whose research focuses on quantum technologies based on semiconductor and optical systems, hailed the City College study. "What is so remarkable and exciting in the work by Vinod and his team is how readily this strong coupling regime could actually be achieved. They have shown convincingly that by coupling a rather standard dielectric cavity to exciton-polaritons in a monolayer of molybdenum disulphide, they could actually reach this strong coupling regime with a very large binding strength," he said. Professor Menon's research team included City College PhD students, Xiaoze Liu, Tal Galfsky and Zheng Sun, and scientists from Yale University, National Tsing Hua University (Taiwan) and Ecole Polytechnic -Montreal (Canada).
Gummy bears under antiparticle fire
Gelatin is used in the pharmaceutical industry to encapsulate active agents. It protects against oxidation and overly quick release. Nanopores in the material have a significant influence on this, yet they are difficult to investigate. In experiments on gummy bears, researchers at Technische Universität München (TUM) have now transferred a methodology to determine the free volume of gelatin preparations ("The Free Volume in Dried and H2O-Loaded Biopolymers Studied by Positron Lifetime Measurements"). 
Gummy bear on the experimental set-up. To prevent color influences, the researchers used red gummy bears only. Custom-tailored gelatin preparations are widely used in the pharmaceutical industry. Medications that do not taste good can be packed into gelatin capsules, making them easier to swallow. Gelatin also protects sensitive active agents from oxidation. Often the goal is to release the medication gradually. In these cases slowly dissolving gelatin is used. Nanopores in the material play a significant role in all of these applications. “The larger the free volume, the easier it is for oxygen to penetrate it and harm the medication, but also the less brittle the gelatin,” says PD Dr. Christoph Hugenschmidt, a physicist at TU München. However, characterizing the size and distribution of these free spaces in the unordered biopolymer is difficult. A methodology adapted by the Garching physicists Christoph Hugenschmidt and Hubert Ceeh provides relief. “Using positrons as highly mobile probes, the volume of the nanopores can be determined, especially also in unordered systems like netted gelatins,” says Christoph Hugenschmidt. Positrons are the antiparticles corresponding to electrons. They can be produced in the laboratory in small quantities, as in this experiment, or in large volumes at the Heinz Maier Leibnitz Research Neutron Source (FRM II) of the TU München. If a positron encounters an electron they briefly form an exotic particle, the so-called positronium. Shortly after it annihilates to a flash of light. To model gelatin capsules that slowly dissolve in the stomach, the scientists bombarded red gummy bears in various drying stages with positrons. Their measurements showed, that in dry gummy bears the positroniums survive only 1.2 nanoseconds on average while in soaked gummy bears it takes 1.9 nanoseconds before they are annihilated. From the lifetime of the positroniums the scientists can deduce the number and size of nanopores in the material.
Gummy bear on the experimental set-up. To prevent color influences, the researchers used red gummy bears only. Custom-tailored gelatin preparations are widely used in the pharmaceutical industry. Medications that do not taste good can be packed into gelatin capsules, making them easier to swallow. Gelatin also protects sensitive active agents from oxidation. Often the goal is to release the medication gradually. In these cases slowly dissolving gelatin is used. Nanopores in the material play a significant role in all of these applications. “The larger the free volume, the easier it is for oxygen to penetrate it and harm the medication, but also the less brittle the gelatin,” says PD Dr. Christoph Hugenschmidt, a physicist at TU München. However, characterizing the size and distribution of these free spaces in the unordered biopolymer is difficult. A methodology adapted by the Garching physicists Christoph Hugenschmidt and Hubert Ceeh provides relief. “Using positrons as highly mobile probes, the volume of the nanopores can be determined, especially also in unordered systems like netted gelatins,” says Christoph Hugenschmidt. Positrons are the antiparticles corresponding to electrons. They can be produced in the laboratory in small quantities, as in this experiment, or in large volumes at the Heinz Maier Leibnitz Research Neutron Source (FRM II) of the TU München. If a positron encounters an electron they briefly form an exotic particle, the so-called positronium. Shortly after it annihilates to a flash of light. To model gelatin capsules that slowly dissolve in the stomach, the scientists bombarded red gummy bears in various drying stages with positrons. Their measurements showed, that in dry gummy bears the positroniums survive only 1.2 nanoseconds on average while in soaked gummy bears it takes 1.9 nanoseconds before they are annihilated. From the lifetime of the positroniums the scientists can deduce the number and size of nanopores in the material.Magnetic vortices: Controlling core switching in Pac-man disks
Magnetic vortices in thin films can encode information in the perpendicular magnetization pointing up or down relative to the vortex core. These binary states could be useful for non-volatile data storage devices such as RAM memories, but the switching between them must be fast and energy-efficient. However, despite many efforts switching is still slow and requires very large currents. Pac-man disks, whose shape resembles the retro arcade game, seem to be a promising approach and Yoshinobu Nakatani and co-workers from the University of Electro-Communications now show a more efficient way of controlling switching in these devices ("Control of magnetic vortex core switching in a Pac-man disk using a single current pulse"). To better understand the mechanisms and the best switching conditions in the Pac-man disks, Nakatani's team used micro-magnetic simulations to investigate vortex core switching driven by an in-plane nanosecond current pulse. The simulations uncovered several interesting features. They found that the notch - Pac-man's mouth - plays the double role of annihilating and nucleating the vortex core. The kinetic field induced by the core motion gives the direction of nucleation. 
Prof. Nakatani team performed micro-magnetic simulations and took snapshots of the Pac-man disk (diameter = 200 nm, thickness = 40 nm) at different times (t = 0∼2.0 ns) .The rainbow images indicating the direction of the in-plane magnetization component, whereas the grayscale images show the out-of-plane magnetization (white,up; black,down). The vortex core switches from upward to downward. These results suggest that "by utilizing both the core switching at the notch edge and the direction of the core motion, the core polarity can be uniquely controlled by adjusting the direction of the current pulse". In this way the current density could be reduced by 75% compared with that of a circular disk of the same diameter and thickness. The insights provided by Nakatani's team could lead to an improved design of vortex core memory cells.
Prof. Nakatani team performed micro-magnetic simulations and took snapshots of the Pac-man disk (diameter = 200 nm, thickness = 40 nm) at different times (t = 0∼2.0 ns) .The rainbow images indicating the direction of the in-plane magnetization component, whereas the grayscale images show the out-of-plane magnetization (white,up; black,down). The vortex core switches from upward to downward. These results suggest that "by utilizing both the core switching at the notch edge and the direction of the core motion, the core polarity can be uniquely controlled by adjusting the direction of the current pulse". In this way the current density could be reduced by 75% compared with that of a circular disk of the same diameter and thickness. The insights provided by Nakatani's team could lead to an improved design of vortex core memory cells.Innovative nanophotonics: Integrating quantum light sources with nanofibers for quantum internet applications
"I had the idea for 'nanofiber quantum photonics' about 14 years ago," says Kohzo Hakuta, Director of the Center for Photonic Innovations at the University of Electro-Communications (UEC). "I want to integrate quantum light sources e.g. single quantum dot / single atom, into specially designed nanofibers. This 'fiber in-line technology' holds the potential to revolutionize distributed quantum networks for secure, ultra-high speed communication. Namely, the birth of the 'quantum internet. We are supported by Japan Science and Technology Agency through Strategic Innovation Program." Fiber in-line technology is advantageous for integrating these sources to the conventional fiber-based communication network. Now, Hakuta and his group at the Center for Photonic Innovations are addressing the following issues to develop fiber in-line technology to integrate quantum light sources into optical nanofibers. Fabrication of high efficiency tapered glass nanofibers; development of reproducible methods for integrating single quantum dots with nanofibers; integration of cavity structures with nanofibers; and experimental demonstration of cavity quantum electrodynamics (QED) with nanofibers. The work is carried out by an international group of researchers from countries including India, Vietnam, China and New Zealand. 
Composite photonic crystal cavity formed by combining an optical nanofiber and a nanofabricated grating. The PL intensity spectra of single quantum dots show strong enhancement at the cavity resonance demonstrating the cavity QED effect. "We have been working with our industrial partner Ishihara Sangyo Inc. to develop equipment for producing tapered nanofibers," explains Hakuta. "The resulting 400 nm diameter tapered fibers have 99% light transmission." A critical technology is to pick up single quantum dots from colloidal solution and deposit it on the nanofiber. This is accomplished using a computer controlled pico-liter liquid dispenser combined with an inverted microscope and precision translation stages. Photon counting experiments show the realization of single quantum dot deposition with spatial accuracy better than 3µm, and importantly, the maximum photon channelling efficiency is measured to be 22.0% as predicted from the theory. Furthermore, Hakuta and colleagues have developed a novel method to enhance this photon channelling efficiency by incorporating cavity structures. They are developing two methods. "On one hand, we can produce photonic crystal nanofibers with an array of thousands of highly ordered nano-craters using femto second lasers" explains Hakuta. "We were surprised to find highly periodic craters produced on the shadow sides of the nanofibers. Promptly we understood, it is due to the lensing effect of the nanofiber itself. On the other hand we are developing composite nanofiber cavities with external nano-grating structures". Using these composite nanofiber cavities they have demonstrated cavity QED with single quantum dots. This research has the potential of being a new paradigm in cavity QED, and forms the basis for quantum internet and other applications. Furthermore, femto-second laser fabricated photonic crystal nanofiber cavities coupled with cold atoms can realize various manipulation methods of single photons which offer the basic tools for the next generation of internet communications. References R. R. Yalla, M. Sadgrove, K. P. Nayak, and K. Hakuta. "Cavity quantum electrodynamics on a nanofiber using a composite photonic crystal cavity," . 113, 143601 (2014). K. P. Nayak, P. Zhang, and K. Hakuta, "Optical nanofiber based photonic crystal cavity," 39, 232 (2014). M. Sadgrove, R. R. Yalla, K. P. Nayak, and K. Hakuta. "Photonic crystal nanofiber using an external grating," 38, 2542 (2013). K. P. Nayak and K. Hakuta, "Photonic crystal formation on optical nanofibers using femtosecond laser ablation technique," 21, 2480 (2013). R. R. Yalla, Fam Le Kien, M. Morinaga, and K. Hakuta, "Efficient channeling of fluorescence photons from single quantum dots into guided modes of optical nanofiber," 109, 063602 (2012). R. R. Yalla, K. P. Nayak, and K. Hakuta, "Fluorescence photon measurements from single quantum dots on an optical nanofiber," 20, 2932 (2012).
Composite photonic crystal cavity formed by combining an optical nanofiber and a nanofabricated grating. The PL intensity spectra of single quantum dots show strong enhancement at the cavity resonance demonstrating the cavity QED effect. "We have been working with our industrial partner Ishihara Sangyo Inc. to develop equipment for producing tapered nanofibers," explains Hakuta. "The resulting 400 nm diameter tapered fibers have 99% light transmission." A critical technology is to pick up single quantum dots from colloidal solution and deposit it on the nanofiber. This is accomplished using a computer controlled pico-liter liquid dispenser combined with an inverted microscope and precision translation stages. Photon counting experiments show the realization of single quantum dot deposition with spatial accuracy better than 3µm, and importantly, the maximum photon channelling efficiency is measured to be 22.0% as predicted from the theory. Furthermore, Hakuta and colleagues have developed a novel method to enhance this photon channelling efficiency by incorporating cavity structures. They are developing two methods. "On one hand, we can produce photonic crystal nanofibers with an array of thousands of highly ordered nano-craters using femto second lasers" explains Hakuta. "We were surprised to find highly periodic craters produced on the shadow sides of the nanofibers. Promptly we understood, it is due to the lensing effect of the nanofiber itself. On the other hand we are developing composite nanofiber cavities with external nano-grating structures". Using these composite nanofiber cavities they have demonstrated cavity QED with single quantum dots. This research has the potential of being a new paradigm in cavity QED, and forms the basis for quantum internet and other applications. Furthermore, femto-second laser fabricated photonic crystal nanofiber cavities coupled with cold atoms can realize various manipulation methods of single photons which offer the basic tools for the next generation of internet communications. References R. R. Yalla, M. Sadgrove, K. P. Nayak, and K. Hakuta. "Cavity quantum electrodynamics on a nanofiber using a composite photonic crystal cavity," . 113, 143601 (2014). K. P. Nayak, P. Zhang, and K. Hakuta, "Optical nanofiber based photonic crystal cavity," 39, 232 (2014). M. Sadgrove, R. R. Yalla, K. P. Nayak, and K. Hakuta. "Photonic crystal nanofiber using an external grating," 38, 2542 (2013). K. P. Nayak and K. Hakuta, "Photonic crystal formation on optical nanofibers using femtosecond laser ablation technique," 21, 2480 (2013). R. R. Yalla, Fam Le Kien, M. Morinaga, and K. Hakuta, "Efficient channeling of fluorescence photons from single quantum dots into guided modes of optical nanofiber," 109, 063602 (2012). R. R. Yalla, K. P. Nayak, and K. Hakuta, "Fluorescence photon measurements from single quantum dots on an optical nanofiber," 20, 2932 (2012).Getting into your head: Gelatin nanoparticles could deliver drugs to the brain
Stroke victims could have more time to seek treatment that could reduce harmful effects on the brain, thanks to tiny blobs of gelatin that could deliver the medication to the brain noninvasively. University of Illinois researchers and colleagues in South Korea, led by U. of I. electrical and computer engineering senior research scientist Hyungsoo Choi and professor Kyekyoon “Kevin” Kim, published details about the gelatin nanoparticles in the journal ("Gelatin nanoparticles enhance the neuroprotective effects of intranasally administered osteopontin in rat ischemic stroke model"). 
Illinois professor Kyekyoon “Kevin” Kim, graduate student Elizabeth Joachim and research scientist Hyungsoo Choi developed tiny gelatin nanoparticles that can carry medication to the brain, which could lead to longer treatment windows for stroke patients. The researchers found that gelatin nanoparticles could be laced with medications for delivery to the brain, and that they could extend the treatment window for when a drug could be effective. Gelatin is biocompatible, biodegradable, and classified as “Generally Recognized as Safe” by the Food and Drug Administration. Once administered, the gelatin nanoparticles target damaged brain tissue thanks to an abundance of gelatin-munching enzymes produced in injured regions. The tiny gelatin particles have a huge benefit: They can be administered nasally, a noninvasive and direct route to the brain. This allows the drug to bypass the blood-brain barrier, a biological fence that prevents the vast majority of drugs from entering the brain through the bloodstream. “Overcoming the difficulty of delivering therapeutic agents to specific regions of the brain presents a major challenge to treatment of most neurological disorders,” said Choi. “However, if drug substances can be transferred along the olfactory nerve cells, they can bypass the blood-brain barrier and enter the brain directly.” To test gelatin nanoparticles as a drug-delivery system, the researchers used the drug osteopontin (OPN), which in rats can help to reduce inflammation and prevent brain cell death if administered immediately after a stroke. “It is crucial to treat ischemic strokes within three hours to improve the chances of recovery. However, a significant number of stroke victims don’t get to the hospital in time for the treatment,” Kim said. By lacing gelatin nanoparticles with OPN, the researchers found that they could extend the treatment window in rats, so much so that treating a rat with nanoparticles six hours after a stroke showed the same efficacy rate as giving them OPN alone after one hour – 70 percent recovery of dead volume in the brain. The researchers hope the gelatin nanoparticles, administered through the nasal cavity, can help deliver other drugs to more effectively treat a variety of brain injuries and neurological diseases. “Gelatin nanoparticles are a delivery vehicle that could be used to deliver many therapeutics to the brain,” Choi said. “They will be most effective in delivering drugs that cannot cross the blood-brain barrier. In addition, they can be used for drugs of high toxicity or a short half-life.“
Illinois professor Kyekyoon “Kevin” Kim, graduate student Elizabeth Joachim and research scientist Hyungsoo Choi developed tiny gelatin nanoparticles that can carry medication to the brain, which could lead to longer treatment windows for stroke patients. The researchers found that gelatin nanoparticles could be laced with medications for delivery to the brain, and that they could extend the treatment window for when a drug could be effective. Gelatin is biocompatible, biodegradable, and classified as “Generally Recognized as Safe” by the Food and Drug Administration. Once administered, the gelatin nanoparticles target damaged brain tissue thanks to an abundance of gelatin-munching enzymes produced in injured regions. The tiny gelatin particles have a huge benefit: They can be administered nasally, a noninvasive and direct route to the brain. This allows the drug to bypass the blood-brain barrier, a biological fence that prevents the vast majority of drugs from entering the brain through the bloodstream. “Overcoming the difficulty of delivering therapeutic agents to specific regions of the brain presents a major challenge to treatment of most neurological disorders,” said Choi. “However, if drug substances can be transferred along the olfactory nerve cells, they can bypass the blood-brain barrier and enter the brain directly.” To test gelatin nanoparticles as a drug-delivery system, the researchers used the drug osteopontin (OPN), which in rats can help to reduce inflammation and prevent brain cell death if administered immediately after a stroke. “It is crucial to treat ischemic strokes within three hours to improve the chances of recovery. However, a significant number of stroke victims don’t get to the hospital in time for the treatment,” Kim said. By lacing gelatin nanoparticles with OPN, the researchers found that they could extend the treatment window in rats, so much so that treating a rat with nanoparticles six hours after a stroke showed the same efficacy rate as giving them OPN alone after one hour – 70 percent recovery of dead volume in the brain. The researchers hope the gelatin nanoparticles, administered through the nasal cavity, can help deliver other drugs to more effectively treat a variety of brain injuries and neurological diseases. “Gelatin nanoparticles are a delivery vehicle that could be used to deliver many therapeutics to the brain,” Choi said. “They will be most effective in delivering drugs that cannot cross the blood-brain barrier. In addition, they can be used for drugs of high toxicity or a short half-life.“Graphene offers X-ray photoelectron spectroscopy a window of opportunity
X-ray photoelectron spectroscopy (XPS) is one of the most sensitive and informative surface analysis techniques available. However, XPS requires a high vacuum to operate, which makes analyzing materials in liquid and gaseous environments difficult. Now, researchers from the National Institute of Standards and Technology (NIST), ELETTRA (Italy) and Technical University of Munich (Germany) have found that graphene—a single-atom-thick sheet of carbon—could make using XPS to study materials in these environments much less expensive and complicated than the conventional approach. Their results were published in the journal ("Photoelectron spectroscopy of wet and gaseous samples through graphene membranes"). 
Drawing shows the set-up for an X-ray photoelectron spectroscopy instrument incorporating suspended, electron-transparent graphene membranes - or windows - that separate the sample from the high-vacuum detection system. (Image: NIST) Researchers have analyzed cells and microorganisms using visible light, which, while informative and gentle, cannot be used to probe objects much smaller than about 500 nanometers. But many of life’s most important processes and interactions take place at much smaller length scales. The same is true with batteries: everything that can go wrong with them takes place at the tiny interfaces between the electrodes and the electrolyte—far beyond the reach of optical microscopes. Many researchers would like to use X rays or electrons to look deeper into these materials, but few labs have the sophisticated equipment necessary to do so, and those labs that are so outfitted are often too pricey for today’s budget-conscious scientists. XPS works by bombarding the surface under study with X rays. The atoms on the surface of the material absorb the X-ray energy and re-emit that energy as photoelectrons. Scientists study the kinetic energy and number of the emitted electrons for clues about the sample’s composition and electronic state. Because X rays and photoelectrons interact with the air, XPS has to be performed under high vacuum, which makes it hard to study materials that have to be in a pressurized environment. What researchers needed was a window material that was nearly transparent to X rays and photoelectrons, but impermeable to gases and liquids and strong enough to withstand the mechanical stress of one atmosphere’s worth of pressure. Knowing that graphene, the wonder material of the 21st century, has these properties, the group explored using it as a window to separate their sample stage’s atmospheric pressure liquid compartment from the high-vacuum conditions inside the electron spectrometer. According to NIST researcher Andrei Kolmakov, their results demonstrate that more than enough X rays—and resultant photoelectrons—are able to pass through the graphene window to produce good quality XPS data from liquids and gases. As an added bonus, the group was also able to measure the intensity of radiation needed to create bubbles in water, a frequently unwanted occurrence that happens when the X rays split water into oxygen and hydrogen. Knowing the point at which bubbles form, they were able to define an upper limit on the intensities of the X rays (or electrons) that can be used in this approach. “We think our work could fill a much-needed gap,” says Kolmakov. “There are many scientists whose work would benefit from using XPS at ambient pressure, but there are not enough instruments that are equipped to analyze the samples under these conditions, and the ones out there are often too costly to use. Our design is far simpler and has the potential to reduce costs to the level that this type of measurement could be afforded by many more labs. With this imaging capability, other researchers could, for example, learn much more about how to create longer- lasting batteries and develop safer and more effective drugs.” Of course, as often happens with new technologies, the approach has a few challenges and limitations. Kolmakov says that the adhesion of the graphene to the surface surrounding the opening needs to be improved. Moreover, the barrage of X rays degrades atomically thin graphene over time, so the team is planning to look for ways to mitigate that, if possible.
Drawing shows the set-up for an X-ray photoelectron spectroscopy instrument incorporating suspended, electron-transparent graphene membranes - or windows - that separate the sample from the high-vacuum detection system. (Image: NIST) Researchers have analyzed cells and microorganisms using visible light, which, while informative and gentle, cannot be used to probe objects much smaller than about 500 nanometers. But many of life’s most important processes and interactions take place at much smaller length scales. The same is true with batteries: everything that can go wrong with them takes place at the tiny interfaces between the electrodes and the electrolyte—far beyond the reach of optical microscopes. Many researchers would like to use X rays or electrons to look deeper into these materials, but few labs have the sophisticated equipment necessary to do so, and those labs that are so outfitted are often too pricey for today’s budget-conscious scientists. XPS works by bombarding the surface under study with X rays. The atoms on the surface of the material absorb the X-ray energy and re-emit that energy as photoelectrons. Scientists study the kinetic energy and number of the emitted electrons for clues about the sample’s composition and electronic state. Because X rays and photoelectrons interact with the air, XPS has to be performed under high vacuum, which makes it hard to study materials that have to be in a pressurized environment. What researchers needed was a window material that was nearly transparent to X rays and photoelectrons, but impermeable to gases and liquids and strong enough to withstand the mechanical stress of one atmosphere’s worth of pressure. Knowing that graphene, the wonder material of the 21st century, has these properties, the group explored using it as a window to separate their sample stage’s atmospheric pressure liquid compartment from the high-vacuum conditions inside the electron spectrometer. According to NIST researcher Andrei Kolmakov, their results demonstrate that more than enough X rays—and resultant photoelectrons—are able to pass through the graphene window to produce good quality XPS data from liquids and gases. As an added bonus, the group was also able to measure the intensity of radiation needed to create bubbles in water, a frequently unwanted occurrence that happens when the X rays split water into oxygen and hydrogen. Knowing the point at which bubbles form, they were able to define an upper limit on the intensities of the X rays (or electrons) that can be used in this approach. “We think our work could fill a much-needed gap,” says Kolmakov. “There are many scientists whose work would benefit from using XPS at ambient pressure, but there are not enough instruments that are equipped to analyze the samples under these conditions, and the ones out there are often too costly to use. Our design is far simpler and has the potential to reduce costs to the level that this type of measurement could be afforded by many more labs. With this imaging capability, other researchers could, for example, learn much more about how to create longer- lasting batteries and develop safer and more effective drugs.” Of course, as often happens with new technologies, the approach has a few challenges and limitations. Kolmakov says that the adhesion of the graphene to the surface surrounding the opening needs to be improved. Moreover, the barrage of X rays degrades atomically thin graphene over time, so the team is planning to look for ways to mitigate that, if possible.Crafting ultrathin color coatings
In a sub-basement deep below the Laboratory for Integrated Science and Engineering at Harvard University, Mikhail Kats gets dressed. Mesh shoe covers, a face mask, a hair net, a pale gray jumpsuit, knee-high fabric boots, vinyl gloves, safety goggles, and a hood with clasps at the collar—these are not to protect him, Kats explains, but to protect the delicate equipment and materials inside the cleanroom. While earning his Ph.D. in applied physics at the Harvard School of Engineering and Applied Sciences, Kats has spent countless hours in this cutting-edge facility. With his adviser, Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, Kats has contributed to some stunning advances. One is a metamaterial that absorbs 99.75 percent of infrared light—very useful for thermal imaging devices. Another is an ultrathin, flat lens that focuses light without imparting the distortions of conventional lenses. And the team has produced vortex beams, light beams that resemble a corkscrew, that could help communications companies transmit more data over limited bandwidth. Certainly the most colorful advance to emerge from the Capasso lab, however, is a technique that coats a metallic object with an extremely thin layer of semiconductor, just a few nanometers thick. Although the semiconductor is a steely gray color, the object ends up shining in vibrant hues. That's because the coating exploits interference effects in the thin films; Kats compares it to the iridescent rainbows that are visible when oil floats on water. Carefully tuned in the laboratory, these coatings can produce a bright, solid pink—or, say, a vivid blue—using the same two metals, applied with only a few atoms' difference in thickness. Capasso's research group announced the finding in 2012, but at that time, they had only demonstrated the coating on relatively smooth, flat surfaces like silicon. This fall, the group published a second paper, in the journal , taking the work much further ("Ultra-thin optical interference coatings on rough and flexible substrates"). 
Behind the scenes in the Center for Nanoscale Systems, Mikhail Kats (Ph.D. '14) demonstrates the fabrication process for ultrathin coatings that shine in vivid colors. Kats and Prof. Federico Capasso have shown that these interference effects work on rough materials like paper. "I cut a piece of paper out of my notebook and deposited gold and germanium on it," Kats says, "and it worked just the same." That finding, deceptively simple given the physics involved, now suggests that the ultrathin coatings could be applied to essentially any rough or flexible material, from wearable fabrics to stretchable electronics. "This can be viewed as a way of coloring almost any object while using just a tiny amount of material," Capasso says. It was not obvious that the same color effects would be visible on rough substrates, because interference effects are usually highly sensitive to the angle of light. And on a sheet of paper, Kats explains, "There are hills and valleys and fibers and little things sticking out—that's why you can't see your reflection in it. The light scatters." On the other hand, the applied films are so extremely thin that they interact with light almost instantaneously, so looking at the coating straight on or from the side—or, as it turns out, looking at those rough imperfections in the paper—doesn't make much difference to the color. And the paper remains flexible, as usual. Demonstrating the technique in the cleanroom at the Center for Nanoscale Systems, a National Science Foundation–supported research facility at Harvard, Kats uses a machine called an electron beam evaporator to apply the gold and germanium coating. He seals the paper sample inside the machine's chamber, and a pump sucks out the air until the pressure drops to a staggering 10^-6 Torr (a billionth of an atmosphere). A stream of electrons strikes a piece of gold held in a carbon crucible, and the metal vaporizes, traveling upward through the vacuum until it hits the paper. Repeating the process, Kats adds the second layer. A little more or a little less germanium makes the difference between indigo and crimson. This particular lab technique, Kats points out, is unidirectional, so to the naked eye very subtle differences in the color are visible at different angles, where slightly less of the metal has landed on the sides of the paper’s ridges and valleys. "You can imagine decorative applications where you might want something that has a little bit of this pearlescent look, where you look from different angles and see a different shade," he notes. "But if we were to go next door and use a reactive sputterer instead of this e-beam evaporator, we could easily get a coating that conforms to the surface, and you wouldn't see any differences." Many different pairings of metal are possible, too. "Germanium's cheap. Gold is more expensive, of course, but in practice we're not using much of it," Kats explains. Capasso’s team has also demonstrated the technique using aluminum. "This is a way of coloring something with a very thin layer of material, so in principle, if it's a metal to begin with, you can just use 10 nanometers to color it, and if it's not, you can deposit a metal that's 30 nm thick and then another 10 nm. That's a lot thinner than a conventional paint coating that might be between a micron and 10 microns thick.” In those occasional situations where the weight of the paint matters, this could be very significant. Capasso remembers, for example, that the external fuel tank of NASA’s space shuttle used to be painted white. After the first two missions, engineers stopped painting it and saved 600 pounds of weight. Because the metal coatings absorb a lot of light, reflecting only a narrow set of wavelengths, Capasso suggests that they could also be incorporated into optoelectronic devices like photodetectors and solar cells. “The fact that these can be deposited on flexible substrates has implications for flexible and maybe even stretchable optoelectronics that could be part of your clothing or could be rolled up or folded,” Capasso says. Harvard's Office of Technology Development continues to pursue commercial opportunities for the new color coating technology and welcomes contact from interested parties. Kats, who concludes his year-long postdoctoral research position at SEAS this month, will become an assistant professor at the University of Wisconsin, Madison, in January. He credits those many hours spent in Harvard’s state-of-the-art laboratory facilities for much of his success in applied physics. "You learn so much while you're doing it," Kats says. "You can be creative, discover something along the way, apply something new to your research. It’s marvelous that we have students and postdocs down here making things."
Behind the scenes in the Center for Nanoscale Systems, Mikhail Kats (Ph.D. '14) demonstrates the fabrication process for ultrathin coatings that shine in vivid colors. Kats and Prof. Federico Capasso have shown that these interference effects work on rough materials like paper. "I cut a piece of paper out of my notebook and deposited gold and germanium on it," Kats says, "and it worked just the same." That finding, deceptively simple given the physics involved, now suggests that the ultrathin coatings could be applied to essentially any rough or flexible material, from wearable fabrics to stretchable electronics. "This can be viewed as a way of coloring almost any object while using just a tiny amount of material," Capasso says. It was not obvious that the same color effects would be visible on rough substrates, because interference effects are usually highly sensitive to the angle of light. And on a sheet of paper, Kats explains, "There are hills and valleys and fibers and little things sticking out—that's why you can't see your reflection in it. The light scatters." On the other hand, the applied films are so extremely thin that they interact with light almost instantaneously, so looking at the coating straight on or from the side—or, as it turns out, looking at those rough imperfections in the paper—doesn't make much difference to the color. And the paper remains flexible, as usual. Demonstrating the technique in the cleanroom at the Center for Nanoscale Systems, a National Science Foundation–supported research facility at Harvard, Kats uses a machine called an electron beam evaporator to apply the gold and germanium coating. He seals the paper sample inside the machine's chamber, and a pump sucks out the air until the pressure drops to a staggering 10^-6 Torr (a billionth of an atmosphere). A stream of electrons strikes a piece of gold held in a carbon crucible, and the metal vaporizes, traveling upward through the vacuum until it hits the paper. Repeating the process, Kats adds the second layer. A little more or a little less germanium makes the difference between indigo and crimson. This particular lab technique, Kats points out, is unidirectional, so to the naked eye very subtle differences in the color are visible at different angles, where slightly less of the metal has landed on the sides of the paper’s ridges and valleys. "You can imagine decorative applications where you might want something that has a little bit of this pearlescent look, where you look from different angles and see a different shade," he notes. "But if we were to go next door and use a reactive sputterer instead of this e-beam evaporator, we could easily get a coating that conforms to the surface, and you wouldn't see any differences." Many different pairings of metal are possible, too. "Germanium's cheap. Gold is more expensive, of course, but in practice we're not using much of it," Kats explains. Capasso’s team has also demonstrated the technique using aluminum. "This is a way of coloring something with a very thin layer of material, so in principle, if it's a metal to begin with, you can just use 10 nanometers to color it, and if it's not, you can deposit a metal that's 30 nm thick and then another 10 nm. That's a lot thinner than a conventional paint coating that might be between a micron and 10 microns thick.” In those occasional situations where the weight of the paint matters, this could be very significant. Capasso remembers, for example, that the external fuel tank of NASA’s space shuttle used to be painted white. After the first two missions, engineers stopped painting it and saved 600 pounds of weight. Because the metal coatings absorb a lot of light, reflecting only a narrow set of wavelengths, Capasso suggests that they could also be incorporated into optoelectronic devices like photodetectors and solar cells. “The fact that these can be deposited on flexible substrates has implications for flexible and maybe even stretchable optoelectronics that could be part of your clothing or could be rolled up or folded,” Capasso says. Harvard's Office of Technology Development continues to pursue commercial opportunities for the new color coating technology and welcomes contact from interested parties. Kats, who concludes his year-long postdoctoral research position at SEAS this month, will become an assistant professor at the University of Wisconsin, Madison, in January. He credits those many hours spent in Harvard’s state-of-the-art laboratory facilities for much of his success in applied physics. "You learn so much while you're doing it," Kats says. "You can be creative, discover something along the way, apply something new to your research. It’s marvelous that we have students and postdocs down here making things."Trapping light with a twister
Researchers at MIT who succeeded last year in creating a material that could trap light and stop it in its tracks have now developed a more fundamental understanding of the process. The new work — which could help explain some basic physical mechanisms — reveals that this behavior is connected to a wide range of other seemingly unrelated phenomena. The findings are reported in a paper in the journal ("Topological Nature of Optical Bound States in the Continuum"), co-authored by MIT physics professor Marin Soljacic; postdocs Bo Zhen, Chia Wei Hsu, and Ling Lu; and Douglas Stone, a professor of applied physics at Yale University. 
Plot of radiative quality factor as a function of wave vector for a photonic crystal slab. At five positions, this factor diverges to infinity, corresponding to special solutions of Maxwell equations called bound states in the continuum. These states have enough energy to escape to infinity but remain spatially localized. (Image: Courtesy of the researchers) Light can usually be confined only with mirrors, or with specialized materials such as photonic crystals. Both of these approaches block light beams; last year’s finding demonstrated a new method in which the waves cancel out their own radiation fields. The new work shows that this light-trapping process, which involves twisting the polarization direction of the light, is based on a kind of vortex — the same phenomenon behind everything from tornadoes to water swirling down a drain. In addition to revealing the mechanism responsible for trapping the light, the new analysis shows that this trapped state is much more stable than had been thought, making it easier to produce and harder to disturb. “People think of this [trapped state] as very delicate,” Zhen says, “and almost impossible to realize. But it turns out it can exist in a robust way.” In most natural light, the direction of polarization — which can be thought of as the direction in which the light waves vibrate — remains fixed. That’s the principle that allows polarizing sunglasses to work: Light reflected from a surface is selectively polarized in one direction; that reflected light can then be blocked by polarizing filters oriented at right angles to it. But in the case of these light-trapping crystals, light that enters the material becomes polarized in a way that forms a vortex, Zhen says, with the direction of polarization changing depending on the beam’s direction. Because the polarization is different at every point in this vortex, it produces a singularity — also called a topological defect, Zhen says — at its center, trapping the light at that point. 
Vortices of bound states in the continuum. The left panel shows five bound states in the continuum in a photonic crystal slab as bright spots. The right panel shows the polarization vector field in the same region as the left panel, revealing five vortices at the locations of the bound states in the continuum. These vortices are characterized with topological charges +1 or -1. (Image: Courtesy of the researchers) Hsu says the phenomenon makes it possible to produce something called a vector beam, a special kind of laser beam that could potentially create small-scale particle accelerators. Such devices could use these vector beams to accelerate particles and smash them into each other — perhaps allowing future tabletop devices to carry out the kinds of high-energy experiments that today require miles-wide circular tunnels. The finding, Soljacic says, could also enable easy implementation of super-resolution imaging (using a method called stimulated emission depletion microscopy) and could allow the sending of far more channels of data through a single optical fiber. “This work is a great example of how supposedly well-studied physical systems can contain rich and undiscovered phenomena, which can be unearthed if you dig in the right spot,” says Yidong Chong, an assistant professor of physics and applied physics at Nanyang Technological University in Singapore who was not involved in this research. Chong says it is remarkable that such surprising findings have come from relatively well-studied materials. “It deals with photonic crystal slabs of the sort that have been extensively analyzed, both theoretically and experimentally, since the 1990s,” he says. “The fact that the system is so unexotic, together with the robustness associated with topological phenomena, should give us confidence that these modes will not simply be theoretical curiosities, but can be exploited in technologies such as microlasers.”
Plot of radiative quality factor as a function of wave vector for a photonic crystal slab. At five positions, this factor diverges to infinity, corresponding to special solutions of Maxwell equations called bound states in the continuum. These states have enough energy to escape to infinity but remain spatially localized. (Image: Courtesy of the researchers) Light can usually be confined only with mirrors, or with specialized materials such as photonic crystals. Both of these approaches block light beams; last year’s finding demonstrated a new method in which the waves cancel out their own radiation fields. The new work shows that this light-trapping process, which involves twisting the polarization direction of the light, is based on a kind of vortex — the same phenomenon behind everything from tornadoes to water swirling down a drain. In addition to revealing the mechanism responsible for trapping the light, the new analysis shows that this trapped state is much more stable than had been thought, making it easier to produce and harder to disturb. “People think of this [trapped state] as very delicate,” Zhen says, “and almost impossible to realize. But it turns out it can exist in a robust way.” In most natural light, the direction of polarization — which can be thought of as the direction in which the light waves vibrate — remains fixed. That’s the principle that allows polarizing sunglasses to work: Light reflected from a surface is selectively polarized in one direction; that reflected light can then be blocked by polarizing filters oriented at right angles to it. But in the case of these light-trapping crystals, light that enters the material becomes polarized in a way that forms a vortex, Zhen says, with the direction of polarization changing depending on the beam’s direction. Because the polarization is different at every point in this vortex, it produces a singularity — also called a topological defect, Zhen says — at its center, trapping the light at that point. Vortices of bound states in the continuum. The left panel shows five bound states in the continuum in a photonic crystal slab as bright spots. The right panel shows the polarization vector field in the same region as the left panel, revealing five vortices at the locations of the bound states in the continuum. These vortices are characterized with topological charges +1 or -1. (Image: Courtesy of the researchers) Hsu says the phenomenon makes it possible to produce something called a vector beam, a special kind of laser beam that could potentially create small-scale particle accelerators. Such devices could use these vector beams to accelerate particles and smash them into each other — perhaps allowing future tabletop devices to carry out the kinds of high-energy experiments that today require miles-wide circular tunnels. The finding, Soljacic says, could also enable easy implementation of super-resolution imaging (using a method called stimulated emission depletion microscopy) and could allow the sending of far more channels of data through a single optical fiber. “This work is a great example of how supposedly well-studied physical systems can contain rich and undiscovered phenomena, which can be unearthed if you dig in the right spot,” says Yidong Chong, an assistant professor of physics and applied physics at Nanyang Technological University in Singapore who was not involved in this research. Chong says it is remarkable that such surprising findings have come from relatively well-studied materials. “It deals with photonic crystal slabs of the sort that have been extensively analyzed, both theoretically and experimentally, since the 1990s,” he says. “The fact that the system is so unexotic, together with the robustness associated with topological phenomena, should give us confidence that these modes will not simply be theoretical curiosities, but can be exploited in technologies such as microlasers.”Iridium nanoparticles resist deactivation in biofuel production
Steam reforming turns methane from biomass into a mixture that can be further converted into transportation fuels. By combining experimental and theoretical approaches, researchers at the Pacific Northwest National Laboratory (PNNL) Institute for Integrated Catalysis determined key properties of potentially more durable rhodium and iridium catalysts, which drive the reactions ("Highly active and stable MgAl2O4-supported Rh and Ir catalysts for methane steam reforming: A combined experimental and theoretical study"). Catalysts that quickly fail because of high temperatures and tar buildup are not practical for large-scale steam reforming production. Small iridium particles proved fast and stable. Why It Matters By providing an enhanced understanding of the performance of rhodium- and iridium-based steam methane reforming (SMR) catalysts, this study paves the way for better characterizing and optimally screening potential catalysts for steam reforming methane and other hydrocarbons. Ultimately, findings will lead to selecting and developing high-performing SMR catalysts. Methods The researchers investigated the performance of a series of noble metal SMR catalysts supported on spinel magnesium aluminum oxide, a specific support in catalytic reactions for steam reforming. The team found that rhodium and iridium catalysts displayed the best combination of high SMR activity and favorable stability in the presence of simulated biomass -- derived syngas-a fuel gas mixture primarily of hydrogen and carbon monoxide -- which can be further converted to transportation fuels and other useful chemicals. Scanning transmission electron microscopy images showed rhodium and iridium nanoclusters formed and stabilized on the support at high temperatures and in the presence of steam. These highly dispersed nanoparticles showed excellent activity for methane steam reforming in the presence of tars. Moreover, theoretical modeling revealed the small rhodium and iridium particles bind strongly to the support surface and activate both water and methane more effectively than larger particles. These catalysts resisted deactivation through sintering -- the process by which particles segregate into larger inactive particles, especially at high temperatures. In addition, the iridium catalyst resisted deactivation through carbon deposition and was more active than the counterpart rhodium catalyst for SMR. Taken together, the findings suggest the supported iridium SMR catalysts could potentially replace nickel-based catalysts, which are highly susceptible to deactivation from carbon deposition and sintering. The research was conducted in Process Development Laboratory East at PNNL and Quiet Wing at EMSL, Environmental Molecular Sciences Laboratory, a U.S. Department of Energy (DOE) national scientific user facility at PNNL. Computations were done in EMSL and at the National Energy Research Scientific Computing Center. What's Next? The researchers are continuing to delve into the properties and behaviors of catalysts for SMR and other reactions that can change our nation's energy landscape.
Rätsel des platinarmen Nanokatalysators geklärt
Neuartige Nanopartikel-Katalysatoren könnten die Kosten für Brennstoffzellen dramatisch reduzieren. Ein von Berliner und Jülicher Forschern entwickelter Katalysator kommt mit einem Zehntel der üblichen Platinmenge aus. Doch wie die oktaedrische Form der Partikel und die besondere Verteilung der Elemente zustande kommen, war bisher unklar. Mithilfe ultrahochauflösender Elektronenmikroskopie konnten die Wissenschaftler nun erstmals zeigen, dass das kristalline Wachstum in unterschiedlichen Stufen verläuft. Die Erkenntnisse könnten helfen, die bislang noch kurze Lebensdauer zu verbessern ("Element-specific anisotropic growth of shaped platinum alloy nanocrystals"). 
Berliner und Jülicher Forscher konnten mithilfe ultrahochauflösender Elektronenmikroskopie zeigen, dass das kristalline Wachstum von neuartigen Katalysatorpartikeln für Brennstoffzellen in mehreren Stufen verläuft. Zunächst bildet sich ein kugelförmiges Gebilde (links), daraus wächst ein so genannter „Hexapod“ (Mitte), der vorwiegend aus Platinatomen (rot) besteht, und in der letzten Phase des Wachstums lagern sich bevorzugt Nickelatome (grün) in den Hohlräumen zwischen den sechs Armen an und komplettieren die Oktaederform (rechts). Am Ende sind die Nickel- und Platinatome nicht gleichmäßig im Katalysatorpartikel verteilt. (Bild: Forschungszentrum Jülich/TU Berlin) Mit einer Grösse von zehn Nanometern sind die Teilchen des hocheffizienten Katalysatormaterials ungefähr zehntausendmal kleiner als der Durchmesser eines menschlichen Haares. Charakteristisch ist ihre Form, die einem Oktaeder – zwei an den Grundflächen aneinandergesetzten Pyramiden – entspricht. Auf welche Weise sich die Oktaederform während des Wachstums ausbildet und wie sich dabei die Elemente der Platin-Nickel- oder auch Platin-Kobalt-Legierung verteilen, war bislang völlig unbekannt. Diese Informationen sind jedoch entscheidend um Katalysator-Nanopartikel mit optimaler Leistungsfähigkeit und Haltbarkeit herzustellen. „Aktivität und Stabilität der Partikel hängen entscheidend davon ab, wie die Elemente im Katalysatormaterial verteilt sind. Hierbei kann schon eine einzelne atomare Lage einen grossen Unterschied bewirken“, erläutert Dr. Marc Heggen vom Ernst Ruska-Centrum (ER-C) und vom Jülicher Peter Grünberg Institut. Wie die Forscher des Forschungszentrums Jülich, der Technischen Universität Berlin und der Tsinghua Universität in China herausfanden, wachsen die kristallinen Katalysatorteilchen nicht gleichmässig, sondern in mehreren Stufen. Zunächst bildet sich, ausgehend von einem kugelförmigen Keim, innerhalb weniger Stunden ein kreuzförmiges Grundgerüst mit sechs Spitzen, das nahezu ausschliesslich aus Platinatomen entsteht. Anschliessend lagern sich in einem sehr viel langsameren Wachstumsschritt vorwiegend Nickel- oder Kobaltatome in den entstandenen Mulden an. Wenn die Oberflächen des Oktaeders glatt aufgefüllt sind, stoppt das Wachstum. Die Form gilt für diese Art Katalysatoren als ideal, weil die chemischen Reaktionen an den Oberflächen besonders effektiv ablaufen. Die Ungleichverteilung der Elemente während des Wachstums bleibt im Oktaeder erhalten und hat entscheidenden Einfluss auf sein katalytisches Verhalten. „Dass wir nun genauer verstehen, wie solche binären Partikel bei der Herstellung wachsen, wird dabei helfen, die Effizienz und Stabilität schon bald weiter zu verbessern“, ist sich Heggen sicher. Um mit atomarer Genauigkeit zu erkennen, wo sich welches Element befindet, nutzten die Forscher eines der weltweit höchstauflösenden Elektronenmikroskope am ER-C, einer Einrichtung der Jülich Aachen Research Alliance. Dabei wird der Elektronenstrahl fein gebündelt durch die Probe geschickt. Durch die Wechselwirkungen mit der Probe verliert er einen Teil seiner Energie, wodurch jedes Element in der Probe wie mit einem Fingerabdruck eine charakteristische Spur hinterlässt. Herkömmliche Elektronenmikroskope können solche chemischen Signaturen nicht mit atomarer Auflösung erkennen.
Berliner und Jülicher Forscher konnten mithilfe ultrahochauflösender Elektronenmikroskopie zeigen, dass das kristalline Wachstum von neuartigen Katalysatorpartikeln für Brennstoffzellen in mehreren Stufen verläuft. Zunächst bildet sich ein kugelförmiges Gebilde (links), daraus wächst ein so genannter „Hexapod“ (Mitte), der vorwiegend aus Platinatomen (rot) besteht, und in der letzten Phase des Wachstums lagern sich bevorzugt Nickelatome (grün) in den Hohlräumen zwischen den sechs Armen an und komplettieren die Oktaederform (rechts). Am Ende sind die Nickel- und Platinatome nicht gleichmäßig im Katalysatorpartikel verteilt. (Bild: Forschungszentrum Jülich/TU Berlin) Mit einer Grösse von zehn Nanometern sind die Teilchen des hocheffizienten Katalysatormaterials ungefähr zehntausendmal kleiner als der Durchmesser eines menschlichen Haares. Charakteristisch ist ihre Form, die einem Oktaeder – zwei an den Grundflächen aneinandergesetzten Pyramiden – entspricht. Auf welche Weise sich die Oktaederform während des Wachstums ausbildet und wie sich dabei die Elemente der Platin-Nickel- oder auch Platin-Kobalt-Legierung verteilen, war bislang völlig unbekannt. Diese Informationen sind jedoch entscheidend um Katalysator-Nanopartikel mit optimaler Leistungsfähigkeit und Haltbarkeit herzustellen. „Aktivität und Stabilität der Partikel hängen entscheidend davon ab, wie die Elemente im Katalysatormaterial verteilt sind. Hierbei kann schon eine einzelne atomare Lage einen grossen Unterschied bewirken“, erläutert Dr. Marc Heggen vom Ernst Ruska-Centrum (ER-C) und vom Jülicher Peter Grünberg Institut. Wie die Forscher des Forschungszentrums Jülich, der Technischen Universität Berlin und der Tsinghua Universität in China herausfanden, wachsen die kristallinen Katalysatorteilchen nicht gleichmässig, sondern in mehreren Stufen. Zunächst bildet sich, ausgehend von einem kugelförmigen Keim, innerhalb weniger Stunden ein kreuzförmiges Grundgerüst mit sechs Spitzen, das nahezu ausschliesslich aus Platinatomen entsteht. Anschliessend lagern sich in einem sehr viel langsameren Wachstumsschritt vorwiegend Nickel- oder Kobaltatome in den entstandenen Mulden an. Wenn die Oberflächen des Oktaeders glatt aufgefüllt sind, stoppt das Wachstum. Die Form gilt für diese Art Katalysatoren als ideal, weil die chemischen Reaktionen an den Oberflächen besonders effektiv ablaufen. Die Ungleichverteilung der Elemente während des Wachstums bleibt im Oktaeder erhalten und hat entscheidenden Einfluss auf sein katalytisches Verhalten. „Dass wir nun genauer verstehen, wie solche binären Partikel bei der Herstellung wachsen, wird dabei helfen, die Effizienz und Stabilität schon bald weiter zu verbessern“, ist sich Heggen sicher. Um mit atomarer Genauigkeit zu erkennen, wo sich welches Element befindet, nutzten die Forscher eines der weltweit höchstauflösenden Elektronenmikroskope am ER-C, einer Einrichtung der Jülich Aachen Research Alliance. Dabei wird der Elektronenstrahl fein gebündelt durch die Probe geschickt. Durch die Wechselwirkungen mit der Probe verliert er einen Teil seiner Energie, wodurch jedes Element in der Probe wie mit einem Fingerabdruck eine charakteristische Spur hinterlässt. Herkömmliche Elektronenmikroskope können solche chemischen Signaturen nicht mit atomarer Auflösung erkennen.Van der Waals epitaxy and photoresponse of hexagonal tellurium nanoplates on flexible mica sheets
Van der Waals epitaxy (vdWE) has recently been identified as a facile synthesis technique in the growth of ultrathin two dimensional (2D) layered materials and their vertical heterostructures. Unlike conventional heteroepitaxy, vdWE utilizes substrates whose surface is chemically inert because of the absence of surface dangling bonds such as fluorophlogopite mica. In the vdWE growth, the overlayer and substrate are mainly connected by weak van der Waals interaction instead of strong chemical bonding. Therefore, vdWE can circumvent strict requirement of lattice matching, enabling the growth of defect-free overlayer with different crystalline symmetry to that of substrate. In addition, vdWE allows overlayer to be perfectly relaxed without excessive strain in the heterointerface. These superior properties of vdWE make it a powerful technique to grow various 2D layered materials with highly single crystalline. As mentioned initially, vdWE has been successfully applied to prepare layered topological insulator Bi2X3 (X=Se or Te) nanoplates on mica, graphene flakes on h-BN or mica, atomically thin III-VI semiconductor flakes on mica and transition-metal dichalcogenide nanoplates on graphene or mica. However, the utilization and characteristics of vdWE on 2D nanoarchitectures for many important non-layered materials are still not very well documented. Furthermore, 2D nanoarchitectures are of great importance in fabricating electronic and optoelectronic device due to their compatibility with traditional microfabrication techniques. A fundamental research of vdWE effects on the growth of planar/lamellar nanoarchitectures of non-layered materials could enable the development of various functional devices such as flexible photodetector. In new work coming out of the Jun He group at the National Center for Nanoscience and Technology, the researchers have successfully realized 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. 
Researchers successfully realize 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. Chemically inert mica surface is found to be crucial for the lateral growth of hexagonal tellurium nanoplates since it (1) facilitates the migration of tellurium adatoms along mica surface and (2) allows a large lattice mismatch. Furthermore, 2D tellurium hexagonal nanoplates-based photodetectors are in situ fabricated on flexible mica sheets. Efficient photoresponse is obtained even after bending the device for 100 times, indicating 2D tellurium hexagonal nanoplates-based photodetectors on mica sheets have a great application potential in flexible and wearable optoelectronic devices. (© ACS) The results have been published in the July 2, 2014 online edition of ("Van der Waals epitaxy and photoresponse of hexagonal tellurium nanoplates on flexible mica sheets"). The obtained 2D hexagonal Te nanoplate shows highly single crystalline, large lateral dimensions (6-10 µm) and thin thickness (30-80 nm). Due to the absence of surface dangling bond on mica substrate, Te adatoms have a high migration rate along the mica surface and thus promptly move towards growth sites, which results in a fast lateral growth of 2D Te hexagonal Te nanoplate without strict lattice match. Unique 2D geometry of regular Te hexagonal nanoplates facilitates their fabrications into functional electronic and optoelectronic device. In this work, they have fabricated single 2D Te hexagonal nanoplate photodetector directly on flexible mica growth substrate. High photoresponse is observed in two-terminal 2D Te hexagonal nanoplate device even after bending the flexible mica sheet for 100 times. Their work extends the research area of 2D materials from layered materials to nonlayered materials which will bring out intriguing electronic properties.
Researchers successfully realize 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. Chemically inert mica surface is found to be crucial for the lateral growth of hexagonal tellurium nanoplates since it (1) facilitates the migration of tellurium adatoms along mica surface and (2) allows a large lattice mismatch. Furthermore, 2D tellurium hexagonal nanoplates-based photodetectors are in situ fabricated on flexible mica sheets. Efficient photoresponse is obtained even after bending the device for 100 times, indicating 2D tellurium hexagonal nanoplates-based photodetectors on mica sheets have a great application potential in flexible and wearable optoelectronic devices. (© ACS) The results have been published in the July 2, 2014 online edition of ("Van der Waals epitaxy and photoresponse of hexagonal tellurium nanoplates on flexible mica sheets"). The obtained 2D hexagonal Te nanoplate shows highly single crystalline, large lateral dimensions (6-10 µm) and thin thickness (30-80 nm). Due to the absence of surface dangling bond on mica substrate, Te adatoms have a high migration rate along the mica surface and thus promptly move towards growth sites, which results in a fast lateral growth of 2D Te hexagonal Te nanoplate without strict lattice match. Unique 2D geometry of regular Te hexagonal nanoplates facilitates their fabrications into functional electronic and optoelectronic device. In this work, they have fabricated single 2D Te hexagonal nanoplate photodetector directly on flexible mica growth substrate. High photoresponse is observed in two-terminal 2D Te hexagonal nanoplate device even after bending the flexible mica sheet for 100 times. Their work extends the research area of 2D materials from layered materials to nonlayered materials which will bring out intriguing electronic properties.Nanosensoren für Herz und Hirn
16 Arbeitsgruppen der Christian-Albrechts-Universität zu Kiel (CAU), des Universitätsklinikums Schleswig-Holstein (UKSH) und des Fraunhofer Instituts für Siliziumtechnik (ISIT) erforschen zukünftig gemeinsam neuartige Sensoren für die medizinische Diagnostik. Damit sollen über winzigste Magnetfelder Gehirn- und Herzfunktionen aufgezeichnet werden. Die Geräte sollen es auch möglich machen, Prothesen mit Gedanken zu steuern und das Lernen zu optimieren. Mehr als 2 Millionen Euro für zunächst zwei Jahre gibt die Deutsche Forschungsgemeinschaft (DFG) für die zehn Teilprojekte. 
Im Reinraum des Kieler Nanolabors. Sensoren, die ohne Kühlung und Abschirmung auskommen und kaum detektierbare Magnetfelder aufspüren können, sind das ehrgeizige Ziel der Forschenden. Das würde die Magnetoenzephalographie (MEG) und die Magnetokardiographie (MKG) weiterentwickeln. "Neue visionäre medizinische Anwendungen sind denkbar, die mit bisherigen Sensoren nicht zu verwirklichen sind, zum Beispiel neue Körperüberwachungssysteme“, erklärt Professor Eckhard Quandt vom Kieler Institut für Materialwissenschaft, der die Projektanträge federführend begleitete. "Meine herzlichsten Glückwünsche gehen an alle beteiligten Kolleginnen und Kollegen“, freute sich CAU-Präsident Professor Lutz Kipp über den Förderbescheid. "Die DFG hat die Innovationskraft und grosse gesellschaftliche Bedeutung der Nano- und Oberflächenforschung an der Universität Kiel erkannt. Wir hoffen sehr, dass auch das Land durch Erfolge wie diese anerkennt, welche Bedeutung die Spitzenforschung für die Reputation Schleswig-Holsteins und die Versorgung der Bevölkerung mit Zukunftstherapien hat.“ Vielversprechende Vorarbeiten haben die Wissenschaftlerinnen und Wissenschaftler bereits im Sonderforschungsbereich "Magnetoelektrische Verbundwerkstoffe – biomagnetische Schnittstelle der Zukunft“ geleistet. Ergebnis dieses Projektes waren Werkstoffe, die aus sogenannten magnetostriktiven und piezoelektrischen Materialien bestehen. Werden diese verformt, entsteht eine elektrische Spannung. Umgekehrt verformen sie sich, wenn eine Spannung angelegt wird. Damit war es den Kieler Forschenden bereits gelungen, kaum vorhandene Magnetfelder zu messen. In den kommenden zwei Jahren wollen sie die Messgrenze weiter nach unten verschieben, aus den Sensoren Systeme entwickeln und diese in der Kardiologie und Enzelphalographie einsetzen. Optimistisch stimmt Quandt dabei die etablierte und enge Zusammenarbeit in Kiel zwischen Materialwissenschaft, Physik, Elektrotechnik und Medizin.
Im Reinraum des Kieler Nanolabors. Sensoren, die ohne Kühlung und Abschirmung auskommen und kaum detektierbare Magnetfelder aufspüren können, sind das ehrgeizige Ziel der Forschenden. Das würde die Magnetoenzephalographie (MEG) und die Magnetokardiographie (MKG) weiterentwickeln. "Neue visionäre medizinische Anwendungen sind denkbar, die mit bisherigen Sensoren nicht zu verwirklichen sind, zum Beispiel neue Körperüberwachungssysteme“, erklärt Professor Eckhard Quandt vom Kieler Institut für Materialwissenschaft, der die Projektanträge federführend begleitete. "Meine herzlichsten Glückwünsche gehen an alle beteiligten Kolleginnen und Kollegen“, freute sich CAU-Präsident Professor Lutz Kipp über den Förderbescheid. "Die DFG hat die Innovationskraft und grosse gesellschaftliche Bedeutung der Nano- und Oberflächenforschung an der Universität Kiel erkannt. Wir hoffen sehr, dass auch das Land durch Erfolge wie diese anerkennt, welche Bedeutung die Spitzenforschung für die Reputation Schleswig-Holsteins und die Versorgung der Bevölkerung mit Zukunftstherapien hat.“ Vielversprechende Vorarbeiten haben die Wissenschaftlerinnen und Wissenschaftler bereits im Sonderforschungsbereich "Magnetoelektrische Verbundwerkstoffe – biomagnetische Schnittstelle der Zukunft“ geleistet. Ergebnis dieses Projektes waren Werkstoffe, die aus sogenannten magnetostriktiven und piezoelektrischen Materialien bestehen. Werden diese verformt, entsteht eine elektrische Spannung. Umgekehrt verformen sie sich, wenn eine Spannung angelegt wird. Damit war es den Kieler Forschenden bereits gelungen, kaum vorhandene Magnetfelder zu messen. In den kommenden zwei Jahren wollen sie die Messgrenze weiter nach unten verschieben, aus den Sensoren Systeme entwickeln und diese in der Kardiologie und Enzelphalographie einsetzen. Optimistisch stimmt Quandt dabei die etablierte und enge Zusammenarbeit in Kiel zwischen Materialwissenschaft, Physik, Elektrotechnik und Medizin.Quantum world without queues could lead to better solar cells
In a recent study ("Coherent two-dimensional photocurrent spectroscopy in a PbS quantum dot photocell") from Lund University in Sweden, researchers have used new technology to study extremely fast processes in solar cells. The research results form a concrete step towards more efficient solar cells. The upper limit for the efficiency of normal solar cells is around 33 per cent. However, researchers now see a possibility to raise that limit to over 40 per cent, thereby significantly improving the potential of this energy source. The experiments in the present study involved ‘juggling’ on quantum level with photons, i.e. light particles, and electrons. Quantum level refers to the microcosm of the world formed by individual atoms and their building blocks. In juggling the particles, the researchers took advantage of the fact that the laws of nature work slightly differently on quantum level than what we are used to in our world. “We were actually a bit surprised that it worked”, said Tönu Pullerits, Professor of Chemical Physics at Lund University. In the study, Tönu Pullerits and his colleagues studied solar cells containing nanometre-sized balls of material known as quantum dots. These quantum dots can be likened to individual artificial atoms of semiconductor materials. When sunlight hits the quantum dots, two electrons can be extracted from one photon, which can increase the efficiency of the solar cells. “This would mean a radical improvement to solar cells”, said Professor Pullerits. The explanation for this effect lies in the laws of quantum mechanics that control particles on the quantum scale. The phenomenon is called quantum coherence and can lead to a type of energy transfer that produces an almost perfect flow of energy without any obstacles. Coherence opens up a possibility that the flow of energy can find the shortest route by taking all the possible routes at the same time and then selecting the best. To stretch a metaphor, you could compare it to avoiding choosing a queue in the supermarket – instead you can stand in all the queues and see which moves the fastest. Although in reality, the process is extremely fast: it takes a matter of billionths of a second in the quantum world. There are ongoing discussions between researchers on whether the phenomenon might be used by certain photosynthetic organisms to capture sunlight. Over recent years, Tönu Pullerits and his colleagues have conducted research to try to understand and control the coherence phenomenon in order to make use of it in more efficient solar cells, but the results can also be used in other contexts where the transport and interaction of electrons and photons is decisive, such as in future high-speed quantum electronics.
Skyrmions like it hot
A simulation study by researchers from the RIKEN Center for Emergent Matter Science has demonstrated the feasibility of using lasers to create and manipulate nanoscale magnetic vortices ("Creation of skyrmions and antiskyrmions by local heating"). The ability to create and control these ‘skyrmions’ could lead to the development of skyrmion-based information storage devices. The information we consume and work with is encoded in binary form (as ‘1’s or ‘0’s) by switching the characteristics of memory media between two states. As we approach the performance and capacity limits of conventional memory media, researchers are looking toward exotic physics to develop the next generation of magnetic memories. 
Schematic representation of skyrmion creation by local heating using a laser. (Image: Mari Ishida, RIKEN Center for Emergent Matter Science) One such exotic phenomenon is the skyrmion—a stable, nanoscale whirlpool-like magnetic feature characterized by a constantly rotating magnetic moment. Theoretically, the presence or absence of a skyrmion at any location in a magnetic medium could be used to represent the binary states needed for information storage. However, researchers have found it challenging to reliably create and annihilate skyrmions experimentally due to the difficulty in probing the mechanics of these processes in any detail. The challenge lies in the incredibly short timescale of these processes, which at just a tenth of a nanosecond is up to billion times shorter than the timescale observable under the Lorentz microscope used to measure magnetic properties. The study authors, Wataru Koshibae and Naoto Nagaosa, sought a solution to this problem by constructing a computational model that simulates the heating of a ferromagnetic material with pinpoint lasers (Fig. 1). This localized heating creates both skyrmions and ‘antiskyrmions’. The simulations, based on known physics for these systems, showed that the characteristics of skyrmions are heavily dependent on the intensity and spot size of the laser. Further, by manipulating these two parameters, it is possible to control skyrmion characteristics such as creation time and size. “Heat leads to random motion of magnetic spins,” explains Nagaosa. “We therefore found it surprising that local heating created a topologically nontrivial ordered object, let alone composite structures of skyrmions and antiskyrmions” The issue of control is what differentiates these structures. Nagaosa believes that as skyrmions are quite stable, these nanoscale features could conceivably be used as an information carrier if a reliable means of creating them at will can be achieved. Koshibae and Nagaosa’s work could therefore form the basis of the development of state-of-the-art memory devices. The work also provides valuable information on the creation of topological particles, which is crucial for advancing knowledge in many other areas of physics.
Schematic representation of skyrmion creation by local heating using a laser. (Image: Mari Ishida, RIKEN Center for Emergent Matter Science) One such exotic phenomenon is the skyrmion—a stable, nanoscale whirlpool-like magnetic feature characterized by a constantly rotating magnetic moment. Theoretically, the presence or absence of a skyrmion at any location in a magnetic medium could be used to represent the binary states needed for information storage. However, researchers have found it challenging to reliably create and annihilate skyrmions experimentally due to the difficulty in probing the mechanics of these processes in any detail. The challenge lies in the incredibly short timescale of these processes, which at just a tenth of a nanosecond is up to billion times shorter than the timescale observable under the Lorentz microscope used to measure magnetic properties. The study authors, Wataru Koshibae and Naoto Nagaosa, sought a solution to this problem by constructing a computational model that simulates the heating of a ferromagnetic material with pinpoint lasers (Fig. 1). This localized heating creates both skyrmions and ‘antiskyrmions’. The simulations, based on known physics for these systems, showed that the characteristics of skyrmions are heavily dependent on the intensity and spot size of the laser. Further, by manipulating these two parameters, it is possible to control skyrmion characteristics such as creation time and size. “Heat leads to random motion of magnetic spins,” explains Nagaosa. “We therefore found it surprising that local heating created a topologically nontrivial ordered object, let alone composite structures of skyrmions and antiskyrmions” The issue of control is what differentiates these structures. Nagaosa believes that as skyrmions are quite stable, these nanoscale features could conceivably be used as an information carrier if a reliable means of creating them at will can be achieved. Koshibae and Nagaosa’s work could therefore form the basis of the development of state-of-the-art memory devices. The work also provides valuable information on the creation of topological particles, which is crucial for advancing knowledge in many other areas of physics.Gold nanorods target cancer cells
Using tiny gold nanorods, researchers at Swinburne University of Technology have demonstrated a potential breakthrough in cancer therapy. They have shown for the first time that gold nanorods can be used to inhibit cancer cell growth in cervical cancer. 
Laser confocal scattering image of a HeLa cells cultured with EGF-Nanospheres for 30 mins (in green) together with a lipophilic tracer (DiD, in red). Dr Chiara Paviolo from Swinburne’s Centre for Micro-Photonics attached tiny particles to the cell receptors in HeLa cells from the first human cell line to be cloned to stop cancer cell proliferation. “Cell receptors send growth signals to the cell by binding with an external molecule called a growth factor and then clustering together,” Dr Paviolo said. Growth factors are normally used to stimulate the growth of cells and are involved in 20 per cent of cancers. “By placing growth factors at the ends of 100nm gold nanorods we could prevent the clustering of the receptors at a defined distance and thereby shut off the growth signal,” she said. “The simple explanation is that receptors need to cluster together to send a signal but if you keep them apart, it stops them from signalling.” Dr Paviolo said more research into the use of nanoparticles as blocking agents should be undertaken. This work was undertaken by Dr Paviolo under the direction of Associate Professor Andrew Clayton and Associate Professor James Chon. It combines expertise in receptor biophysics and nanotechnology and highlights the multidisciplinary nature of the activities of the Centre for Micro-Photonics. The research was funded by an ARC Discovery Grant and has been published in the prestigious nanotechnology journal ("Inhibiting EGFR Clustering and Cell Proliferation with Gold Nanoparticles"). Dr Paviolo presented her work at the Australian Institute of Physics conference in Canberra last week.
Laser confocal scattering image of a HeLa cells cultured with EGF-Nanospheres for 30 mins (in green) together with a lipophilic tracer (DiD, in red). Dr Chiara Paviolo from Swinburne’s Centre for Micro-Photonics attached tiny particles to the cell receptors in HeLa cells from the first human cell line to be cloned to stop cancer cell proliferation. “Cell receptors send growth signals to the cell by binding with an external molecule called a growth factor and then clustering together,” Dr Paviolo said. Growth factors are normally used to stimulate the growth of cells and are involved in 20 per cent of cancers. “By placing growth factors at the ends of 100nm gold nanorods we could prevent the clustering of the receptors at a defined distance and thereby shut off the growth signal,” she said. “The simple explanation is that receptors need to cluster together to send a signal but if you keep them apart, it stops them from signalling.” Dr Paviolo said more research into the use of nanoparticles as blocking agents should be undertaken. This work was undertaken by Dr Paviolo under the direction of Associate Professor Andrew Clayton and Associate Professor James Chon. It combines expertise in receptor biophysics and nanotechnology and highlights the multidisciplinary nature of the activities of the Centre for Micro-Photonics. The research was funded by an ARC Discovery Grant and has been published in the prestigious nanotechnology journal ("Inhibiting EGFR Clustering and Cell Proliferation with Gold Nanoparticles"). Dr Paviolo presented her work at the Australian Institute of Physics conference in Canberra last week.New sensor could improve one of nanotechnology's most useful microscopes
Spotting molecule-sized features—common in computer circuits and nanoscale devices—may become both easier and more accurate with a sensor developed at the National Institute of Standards and Technology (NIST). With their new design, NIST scientists may have found a way to sidestep some of the problems in calibrating atomic force microscopes (AFMs). 
Self-calibrating AFM probe: Light travels down the optical fiber on the left, striking the top edge of the gold-plated segment lodged in the sensor’s tip. The light pressure sets the sensor vibrating. The long fiber on the right connects to an interferometer (not shown), which measures the tip’s movement, giving a value for the probe's stiffness. The sensor is attached to the wall at left in two places; darker sections of the image are empty space. (Image: Melcher/NIST) The AFM is one of the main scientific workhorses of the nano age. It can resolve features as small as individual atoms. Instead of magnifying with a lens, AFMs “feel” a surface, using a flexible cantilever with a tiny, sharp tip. As the tip passes near a nanoscale feature on a surface, interactions between the atoms on the tip and on the object’s surface cause the cantilever to bend, revealing the finest of details. Because the forces that cause the tip to bend are fairly weak, scientists have increased AFM sensitivity by making the tip vibrate at a particular frequency as it passes over the surface and measuring how much the frequency changes. Frequency can be measured more precisely than almost anything else in the physical sciences. The trouble comes in calibrating the tip’s sensitivity. AFMs operate well in a near vacuum at temperatures around minus 268 degrees Celsius. This means the tip and specimen interact in a tight space behind several walls—hardly an easy spot to cram calibration equipment. As a result, calibration entails removing the tip and checking it at room temperature, a process that not only can skew AFM results but requires calibration equipment that few people outside national metrology institutes possess. “With our sensor, that problem could disappear,” says NIST’s Gordon Shaw. “The tools you need to calibrate the tip are built right into the sensor, so it would not need to be removed from the AFM.” The NIST team’s sensor is a redesign of the device that makes the tip vibrate ("A self-calibrating optomechanical force sensor with femtonewton resolution"). Made of a silicate material akin to the quartz used in some wristwatches, the cantilever is a roughly three-millimeter-long rectangle that looks a bit like a hollow diving board. At the end where the diver would bounce is a mirror that reflects light shining from an LED. The LED can be adjusted to deliver a specific amount of energy. When the photons strike the mirror, they exert enough pressure to set the cantilever vibrating. The distance the tip travels upwards and downwards—measured by an interferometer—reveals how stiff the diving board is at that temperature. This is the critical figure needed to equate a change in the tip’s frequency to a change in atomic force. “The sensor is capable of resolving forces as small as femtonewtons, about 1,000 times less than the force necessary to stretch out a single DNA molecule,” Shaw says. “It gives us a useful reference, which is hard to come by when you’re working with such tiny forces.” It is the first of a class of self-calibrating NIST-on-a-chip embedded standards that merges laser power, force and mass calibrations in a portable package that can be used in tight spaces, like the AFM.
Self-calibrating AFM probe: Light travels down the optical fiber on the left, striking the top edge of the gold-plated segment lodged in the sensor’s tip. The light pressure sets the sensor vibrating. The long fiber on the right connects to an interferometer (not shown), which measures the tip’s movement, giving a value for the probe's stiffness. The sensor is attached to the wall at left in two places; darker sections of the image are empty space. (Image: Melcher/NIST) The AFM is one of the main scientific workhorses of the nano age. It can resolve features as small as individual atoms. Instead of magnifying with a lens, AFMs “feel” a surface, using a flexible cantilever with a tiny, sharp tip. As the tip passes near a nanoscale feature on a surface, interactions between the atoms on the tip and on the object’s surface cause the cantilever to bend, revealing the finest of details. Because the forces that cause the tip to bend are fairly weak, scientists have increased AFM sensitivity by making the tip vibrate at a particular frequency as it passes over the surface and measuring how much the frequency changes. Frequency can be measured more precisely than almost anything else in the physical sciences. The trouble comes in calibrating the tip’s sensitivity. AFMs operate well in a near vacuum at temperatures around minus 268 degrees Celsius. This means the tip and specimen interact in a tight space behind several walls—hardly an easy spot to cram calibration equipment. As a result, calibration entails removing the tip and checking it at room temperature, a process that not only can skew AFM results but requires calibration equipment that few people outside national metrology institutes possess. “With our sensor, that problem could disappear,” says NIST’s Gordon Shaw. “The tools you need to calibrate the tip are built right into the sensor, so it would not need to be removed from the AFM.” The NIST team’s sensor is a redesign of the device that makes the tip vibrate ("A self-calibrating optomechanical force sensor with femtonewton resolution"). Made of a silicate material akin to the quartz used in some wristwatches, the cantilever is a roughly three-millimeter-long rectangle that looks a bit like a hollow diving board. At the end where the diver would bounce is a mirror that reflects light shining from an LED. The LED can be adjusted to deliver a specific amount of energy. When the photons strike the mirror, they exert enough pressure to set the cantilever vibrating. The distance the tip travels upwards and downwards—measured by an interferometer—reveals how stiff the diving board is at that temperature. This is the critical figure needed to equate a change in the tip’s frequency to a change in atomic force. “The sensor is capable of resolving forces as small as femtonewtons, about 1,000 times less than the force necessary to stretch out a single DNA molecule,” Shaw says. “It gives us a useful reference, which is hard to come by when you’re working with such tiny forces.” It is the first of a class of self-calibrating NIST-on-a-chip embedded standards that merges laser power, force and mass calibrations in a portable package that can be used in tight spaces, like the AFM.EU publishes nanomaterial guidance for employers and workers
This Guidance document offers an overview of the issues surrounding the safe use of manufactured nanomaterials in the workplace, sets out the broad outlines of preventive action and provides a practical tool for complying with specific aspects of ensuring workers’ safety, such as risk assessment and risk management. This may be of particular value to those who may not have an in-depth technical understanding of the issues involved, and may assist in ensuring compliance with the Occupational Safety and Health (OSH) legislation when dealing with manufactured nanomaterials. Download guidance for workers (pdf). Download guidance for employers and health and safety practitioners (pdf).
Discovery opens door for radical reduction in energy consumed by digital devices
An article in ("Negative capacitance in a ferroelectric capacitor") describes the first direct observation of a long-hypothesized but elusive phenomenon called “negative capacitance.” The work describes a unique reaction of electrical charge to applied voltage in a ferroelectric material that could open the door to a radical reduction in the power consumed by transistors and the devices containing them. Capacitance is the ability of a material to store an electrical charge. Ordinary capacitors—found in virtually all electronic devices—store charge as a voltage is applied to them. The new phenomenon has a paradoxical response: when the applied voltage is increased, the charge goes down. Hence its name, negative capacitance. “This property, if successfully integrated into transistors, could reduce the amount of power they consume by at least an order of magnitude, and perhaps much more,” says the paper’s lead author Asif Khan. That would lead to longer-lasting cell phone batteries, less energy-consumptive computers of all types, and, perhaps even more importantly, could extend by decades the trend toward faster, smaller processors that has defined the digital revolution since its birth. 
The atomic structure of a ferroelectric material exhibits the so-called “negative capacitance” effect. If successfully built into transistors, it could drastically reduce the electricity needed to run computer processors and other transistor-dependent devices. (Illustration: Suraj S. Cheema) Without a major breakthrough of this sort, the trend toward miniaturization and increased function is threatened by the physical demands of transistors operating at a nano scale. Even though the tiny switches can be made ever smaller, the amount of power they need to be turned on and off can be reduced only so much. That limit is defined by what is known as the Boltzmann distribution of electrons—often called the Boltzmann Tyranny. Because they must be fed an irreducible amount of electricity, ultra-small transistors that are packed too tightly cannot dissipate the heat they generate to avoid self-immolation. In another decade or so, engineers will exhaust options for packing more computing power into ever tinier spaces, a consequence viewed with dread by device manufacturers, sensor developers, and a public addicted to ever smaller and more powerful devices. The new research, conducted at UC Berkeley under the leadership of CITRIS researcher and associate professor of electrical engineering and computer sciences Sayeef Salahuddin, provides a possible way to overcome the Boltzmann Tyranny. It relies on the ability of certain materials to store energy intrinsically and then exploit it to amplify the input voltage. This could, in effect, potentially “trick” a transistor into thinking that it has received the minimum amount of voltage necessary to operate. The result: less electricity is needed to turn a transistor on or off, which is the universal operation at the core of all computer processing. The material used to achieve negative capacitance falls in a class of crystalline materials called ferroelectrics, which was first described in the 1940s. These materials have long been researched for memory applications and commercial storage technologies. Ferroelectrics are also popular materials for frequency control circuits and many microelectromechanical systems (MEMS) applications. However, the possibility of using these materials for energy efficient transistors was first proposed by Salahuddin in 2008, right before he joined Berkeley as an assistant professor. Over the past six years, Khan—one of Salahuddin’s first graduate students at Berkeley—has used pulse lasers to grow many kinds of ferroelectric materials and has devised and revised ingenious ways to test for their negative capacitance. In addition to transforming the way transistors work, negative capacitance could also potentially be used to develop high-density memory storage devices, super capacitors, coil-free oscillators and resonators, and for harvesting energy from the environment. Exploiting the negative capacitance of ferroelectrics is one in a list of strategies for reducing the per-joule cost of storing a single bit of information, says UC Berkeley professor of materials science, engineering, and physics Ramamoorthy Ramesh, another of the paper’s authors. Ramesh’s decades of seminal work on ferroelectric materials and device structures for manipulating them underlies the group’s findings. “We have just launched a program called the attojoule-per-bit program. It is an effort to reduce the total energy consumed for manipulating a bit to one attojoule (10-18),” says Ramesh. To achieve that kind of per-bit energy consumption, we need to take advantage of all possible pathways. The negative capacitance of ferroelectrics is going to be a very important one,” he says. This work was enabled by access to CITRIS’s Marvell Nanofabrication Laboratory, a research facility on the UC Berkeley campus that specifically encourages the exploration of new materials and processes. One of the most advanced academic nanofabrication labs of its type in the world, the NanoLab is the birthplace of other game-changing technologies, such as the three-dimensional FinFET transistor that has led the way to scaling far beyond the limits of ordinary transistors. “Today,” says professor Ming Wu, Marvell NanoLab Faculty Director, “every single transistor built for next-generation microprocessors or computers is FinFET.” “CITRIS’s Marvell NanoLab has state-of-the-art equipment for making semiconductor devices and integrated circuits,” says Wu. “But we take these tools and capabilities and apply them to materials that are so new that industry fabrication labs would not touch them. New materials like these negative capacitance ferroelectrics are not only welcome here, they are actively encouraged.” “The next step,” says Salahuddin, “is to try to make actual transistors such that they can exploit the new phenomenon, We need to make sure they are compatible with silicon processing, that they are manufacturable, and that the measurement techniques we’ve now proven in principle are practical and scalable.”
The atomic structure of a ferroelectric material exhibits the so-called “negative capacitance” effect. If successfully built into transistors, it could drastically reduce the electricity needed to run computer processors and other transistor-dependent devices. (Illustration: Suraj S. Cheema) Without a major breakthrough of this sort, the trend toward miniaturization and increased function is threatened by the physical demands of transistors operating at a nano scale. Even though the tiny switches can be made ever smaller, the amount of power they need to be turned on and off can be reduced only so much. That limit is defined by what is known as the Boltzmann distribution of electrons—often called the Boltzmann Tyranny. Because they must be fed an irreducible amount of electricity, ultra-small transistors that are packed too tightly cannot dissipate the heat they generate to avoid self-immolation. In another decade or so, engineers will exhaust options for packing more computing power into ever tinier spaces, a consequence viewed with dread by device manufacturers, sensor developers, and a public addicted to ever smaller and more powerful devices. The new research, conducted at UC Berkeley under the leadership of CITRIS researcher and associate professor of electrical engineering and computer sciences Sayeef Salahuddin, provides a possible way to overcome the Boltzmann Tyranny. It relies on the ability of certain materials to store energy intrinsically and then exploit it to amplify the input voltage. This could, in effect, potentially “trick” a transistor into thinking that it has received the minimum amount of voltage necessary to operate. The result: less electricity is needed to turn a transistor on or off, which is the universal operation at the core of all computer processing. The material used to achieve negative capacitance falls in a class of crystalline materials called ferroelectrics, which was first described in the 1940s. These materials have long been researched for memory applications and commercial storage technologies. Ferroelectrics are also popular materials for frequency control circuits and many microelectromechanical systems (MEMS) applications. However, the possibility of using these materials for energy efficient transistors was first proposed by Salahuddin in 2008, right before he joined Berkeley as an assistant professor. Over the past six years, Khan—one of Salahuddin’s first graduate students at Berkeley—has used pulse lasers to grow many kinds of ferroelectric materials and has devised and revised ingenious ways to test for their negative capacitance. In addition to transforming the way transistors work, negative capacitance could also potentially be used to develop high-density memory storage devices, super capacitors, coil-free oscillators and resonators, and for harvesting energy from the environment. Exploiting the negative capacitance of ferroelectrics is one in a list of strategies for reducing the per-joule cost of storing a single bit of information, says UC Berkeley professor of materials science, engineering, and physics Ramamoorthy Ramesh, another of the paper’s authors. Ramesh’s decades of seminal work on ferroelectric materials and device structures for manipulating them underlies the group’s findings. “We have just launched a program called the attojoule-per-bit program. It is an effort to reduce the total energy consumed for manipulating a bit to one attojoule (10-18),” says Ramesh. To achieve that kind of per-bit energy consumption, we need to take advantage of all possible pathways. The negative capacitance of ferroelectrics is going to be a very important one,” he says. This work was enabled by access to CITRIS’s Marvell Nanofabrication Laboratory, a research facility on the UC Berkeley campus that specifically encourages the exploration of new materials and processes. One of the most advanced academic nanofabrication labs of its type in the world, the NanoLab is the birthplace of other game-changing technologies, such as the three-dimensional FinFET transistor that has led the way to scaling far beyond the limits of ordinary transistors. “Today,” says professor Ming Wu, Marvell NanoLab Faculty Director, “every single transistor built for next-generation microprocessors or computers is FinFET.” “CITRIS’s Marvell NanoLab has state-of-the-art equipment for making semiconductor devices and integrated circuits,” says Wu. “But we take these tools and capabilities and apply them to materials that are so new that industry fabrication labs would not touch them. New materials like these negative capacitance ferroelectrics are not only welcome here, they are actively encouraged.” “The next step,” says Salahuddin, “is to try to make actual transistors such that they can exploit the new phenomenon, We need to make sure they are compatible with silicon processing, that they are manufacturable, and that the measurement techniques we’ve now proven in principle are practical and scalable.”A gold nanocatalyst for clear water
A new catalyst could have dramatic environmental benefits if it can live up to its potential, suggests research from Singapore. A*STAR researchers have produced a catalyst with gold-nanoparticle antennas that can improve water quality in daylight and also generate hydrogen as a green energy source ("Novel Au/La-SrTiO3 microspheres: Superimposed Effect of Gold Nanoparticles and Lanthanum Doping in Photocatalysis"). This water purification technology was developed by He-Kuan Luo, Andy Hor and colleagues from the A*STAR Institute of Materials Research and Engineering (IMRE). “Any innovative and benign technology that can remove or destroy organic pollutants from water under ambient conditions is highly welcome,” explains Hor, who is executive director of the IMRE and also affiliated with the National University of Singapore. 
Improved photocatalyst microparticles containing gold nanoparticles can be used to purify water. (Image: A*STAR Institute of Materials Research and Engineering) Photocatalytic materials harness sunlight to create electrical charges, which provide the energy needed to drive chemical reactions in molecules attached to the catalyst’s surface. In addition to decomposing harmful molecules in water, photocatalysts are used to split water into its components of oxygen and hydrogen; hydrogen can then be employed as a green energy source. Hor and his team set out to improve an existing catalyst. Oxygen-based compounds such as strontium titanate (SrTiO3) look promising, as they are robust and stable materials and are suitable for use in water. One of the team’s innovations was to enhance its catalytic activity by adding small quantities of the metal lanthanum, which provides additional usable electrical charges. Catalysts also need to capture a sufficient amount of sunlight to catalyze chemical reactions. So to enable the photocatalyst to harvest more light, the scientists attached gold nanoparticles to the lanthanum-doped SrTiO3 microspheres (see image). These gold nanoparticles are enriched with electrons and hence act as antennas, concentrating light to accelerate the catalytic reaction. The porous structure of the microspheres results in a large surface area, as it provides more binding space for organic molecules to dock to. A single gram of the material has a surface area of about 100 square meters. “The large surface area plays a critical role in achieving a good photocatalytic activity,” comments Luo. To demonstrate the efficiency of these catalysts, the researchers studied how they decomposed the dye rhodamine B in water. Within four hours of exposure to visible light 92 per cent of the dye was gone, which is much faster than conventional catalysts that lack gold nanoparticles. These microparticles can also be used for water splitting, says Luo. The team showed that the microparticles with gold nanoparticles performed better in water-splitting experiments than those without, further highlighting the versatility and effectiveness of these microspheres.
Improved photocatalyst microparticles containing gold nanoparticles can be used to purify water. (Image: A*STAR Institute of Materials Research and Engineering) Photocatalytic materials harness sunlight to create electrical charges, which provide the energy needed to drive chemical reactions in molecules attached to the catalyst’s surface. In addition to decomposing harmful molecules in water, photocatalysts are used to split water into its components of oxygen and hydrogen; hydrogen can then be employed as a green energy source. Hor and his team set out to improve an existing catalyst. Oxygen-based compounds such as strontium titanate (SrTiO3) look promising, as they are robust and stable materials and are suitable for use in water. One of the team’s innovations was to enhance its catalytic activity by adding small quantities of the metal lanthanum, which provides additional usable electrical charges. Catalysts also need to capture a sufficient amount of sunlight to catalyze chemical reactions. So to enable the photocatalyst to harvest more light, the scientists attached gold nanoparticles to the lanthanum-doped SrTiO3 microspheres (see image). These gold nanoparticles are enriched with electrons and hence act as antennas, concentrating light to accelerate the catalytic reaction. The porous structure of the microspheres results in a large surface area, as it provides more binding space for organic molecules to dock to. A single gram of the material has a surface area of about 100 square meters. “The large surface area plays a critical role in achieving a good photocatalytic activity,” comments Luo. To demonstrate the efficiency of these catalysts, the researchers studied how they decomposed the dye rhodamine B in water. Within four hours of exposure to visible light 92 per cent of the dye was gone, which is much faster than conventional catalysts that lack gold nanoparticles. These microparticles can also be used for water splitting, says Luo. The team showed that the microparticles with gold nanoparticles performed better in water-splitting experiments than those without, further highlighting the versatility and effectiveness of these microspheres.Pyramid nanoscale antennas beam light up and down
Researchers from FOM Institute AMOLF and Philips Research have designed and fabricated a new type of nanoscale antenna. The new antennas look like pyramids, rather than the more commonly used straight pillars. The pyramid shape enhances the interference between the magnetic and electric fields of light. This makes the pyramid-shaped antenna capable of enhancing light emission and beaming different colours of light towards opposite directions. This finding could lead to more efficient light emitting devices (LEDs). The researchers publish their results online on 12 December 2014 in ("Breaking the Symmetry of Forward-Backward Light Emission with Localized and Collective Magnetoelectric Resonances in Arrays of Pyramid-Shaped Aluminum Nanoparticles"). 
The figure shows how much light (PLE, photoluminescence excitation) the individual pyramid-shaped antenna emits at various wavelengths (colours) of light in comparison to the antennas in the array. The individual antenna peaks at a wavelength of about 650 nanometer, whereas the antennas in the array peak at about 580 nanometer. The micrograph (top right corner) was made with an electron microscope. The colour of the arrow corresponds to the colour used in the other figure. Individual antennas A straight nanoscale antenna will mainly respond to the electric field of light. This means that the effects of the magnetic field of light, which holds half of the energy of light, are disregarded. For a long time this was not considered as an issue that could be solved, because most of the metals used to fabricate antennas do not respond to the magnetic field of light anyway. This changed recently, due to the rapid developments in metamaterial research. What seemed to be impossible in the past – making antennas that respond strongly to the magnetic field of light — can now be done by structuring metals on the nanoscale. With these ideas in mind, the AMOLF and Philips researchers built the pyramid shaped antenna. By carefully designing the height and inclination of the antenna’s side walls, the researchers found that the response to the magnetic field of light is almost as strong as the response to the electric field of light. Antennas in an array After witnessing the described effects in individual nanoscale antennas, the researchers took it one step further and placed multiple pyramid-shaped antennas in an array. The effect that the antennas have on each other turns out to be quite striking. At certain wavelengths (colours) of light, the antennas can couple to each other via the light that is scattered on the surface of the array. This makes the group of antennas more effective in beaming light than the sum of the individual antennas. In addition, the antenna array may operate collectively at one wavelength, while at the same time the antennas operate individually at a different wavelength. Thus, the same array of pyramid-shaped antennas may beam light of a certain colour upward, and of a different colour downward. Applications The array of nanoscale pyramid-shaped antennas has great potential for the improvement of LEDs. Currently, many LEDs are designed to emit light in one direction, for instance only ‘upward’. Such LEDs are used for example in automotive lighting or spotlight illumination. Unfortunately, the light emitting material inside a LED emits light with equal intensities both upward and downward. Since only the ‘upward’ emission is useful, the downward moving light needs to be recycled by adding several optical elements, such as mirrors, to the LED. These elements make the LED bulky and less efficient, since some light is inevitably lost during the recycling process. Integrating the pyramid shaped antennas in the LED has great potential for overcoming these disadvantages. The pyramid-shaped antennas are able to selectively beam one colour of light upward. If an undesired colour is present, this can be beamed downward. This development could greatly enhance the efficiency of single LEDs and improve the integration of LEDs in combined light systems.
The figure shows how much light (PLE, photoluminescence excitation) the individual pyramid-shaped antenna emits at various wavelengths (colours) of light in comparison to the antennas in the array. The individual antenna peaks at a wavelength of about 650 nanometer, whereas the antennas in the array peak at about 580 nanometer. The micrograph (top right corner) was made with an electron microscope. The colour of the arrow corresponds to the colour used in the other figure. Individual antennas A straight nanoscale antenna will mainly respond to the electric field of light. This means that the effects of the magnetic field of light, which holds half of the energy of light, are disregarded. For a long time this was not considered as an issue that could be solved, because most of the metals used to fabricate antennas do not respond to the magnetic field of light anyway. This changed recently, due to the rapid developments in metamaterial research. What seemed to be impossible in the past – making antennas that respond strongly to the magnetic field of light — can now be done by structuring metals on the nanoscale. With these ideas in mind, the AMOLF and Philips researchers built the pyramid shaped antenna. By carefully designing the height and inclination of the antenna’s side walls, the researchers found that the response to the magnetic field of light is almost as strong as the response to the electric field of light. Antennas in an array After witnessing the described effects in individual nanoscale antennas, the researchers took it one step further and placed multiple pyramid-shaped antennas in an array. The effect that the antennas have on each other turns out to be quite striking. At certain wavelengths (colours) of light, the antennas can couple to each other via the light that is scattered on the surface of the array. This makes the group of antennas more effective in beaming light than the sum of the individual antennas. In addition, the antenna array may operate collectively at one wavelength, while at the same time the antennas operate individually at a different wavelength. Thus, the same array of pyramid-shaped antennas may beam light of a certain colour upward, and of a different colour downward. Applications The array of nanoscale pyramid-shaped antennas has great potential for the improvement of LEDs. Currently, many LEDs are designed to emit light in one direction, for instance only ‘upward’. Such LEDs are used for example in automotive lighting or spotlight illumination. Unfortunately, the light emitting material inside a LED emits light with equal intensities both upward and downward. Since only the ‘upward’ emission is useful, the downward moving light needs to be recycled by adding several optical elements, such as mirrors, to the LED. These elements make the LED bulky and less efficient, since some light is inevitably lost during the recycling process. Integrating the pyramid shaped antennas in the LED has great potential for overcoming these disadvantages. The pyramid-shaped antennas are able to selectively beam one colour of light upward. If an undesired colour is present, this can be beamed downward. This development could greatly enhance the efficiency of single LEDs and improve the integration of LEDs in combined light systems.Researchers create 'green' process to reduce molecular switching waste
Dartmouth researchers have found a solution using visible light to reduce waste produced in chemically activated molecular switches, opening the way for industrial applications of nanotechnology ranging from anti-cancer drug delivery to LCD displays and molecular motors. The study appears in the ("Waste Management of Chemically Activated Switches: Using a Photoacid To Eliminate Accumulation of Side Products"). Chemically activated molecular switches are molecules that can shift controllably between two stable states and that can be reversibly switched -- like a light switch -- to turn different functions "on" and "off." For example, light-activated switches can fine-tune anti-cancer drugs, so they target only cancer cells and not healthy ones, thereby eliminating the side effects of chemotherapy. But such switches typically generate waste and side products that are problematic. One way of making these processes cleaner is by using light energy, similar to how photosynthesis operates in nature. In their experiments, the researchers show that a merocyanine-based photoacid derivative can effectively be used in a switching process that is fast, efficient and forms no wastes. "We address a bottleneck that's been hampering the field for decades -- what to do with the accumulated salts and side products when activating such switches," says co-author Ivan Aprahamian, an associate professor of chemistry. "Acids, bases and other compounds need to be constantly added to the mix to make sure the system can be switched, but within a few cycles there is so much waste that it interferes with the switching process. We found a neat solution by coupling an efficient photoacid to our chemically activated hydrazone switch. We showed the system can be efficiently modulated more than 100 times with no accumulation of waste or degradation. We are using visible light to accomplish this, so in reality we are converting light energy into a chemical output, similar to what happens in photosynthesis. You can look at this as a 'green' process that closes the loop in a nanotech-related process, and it will reduce waste in future industrial applications of molecular switches."
Self-repairing subsea material
Embryonic faults in subsea high voltage installations are difficult to detect and very expensive to repair. Researchers believe that self-repairing materials could be the answer. The vital insulating material which encloses sensitive high voltage equipment may now be getting some 'first aid'. "We have preliminary results indicating that this is a promising concept, but we need to do more research to check out other solutions and try the technique out under different conditions". So says SINTEF researcher Cédric Lesaint, who is hoping that the industry will soon wake up to the idea. The technology used involves so-called 'microcapsules', which are added to traditional insulation materials and have the ability to 'sniff out' material fatigue and then release repairing molecules. The team working on this project is made up of chemists, physicists and electrical engineers. If they succeed, they may have discovered the next generation of insulating materials which can be applied in costly electrical installations. 
Subsea installations can get longer life-time with self-repairing materials. (Illustration: SINTEF Energy ) Electrical trees So-called electrical trees develop in electrical insulation materials that are approaching the end of their useful lives. Electrical stress fields exploit small weaknesses in the insulation material and generate hair-thin channels that spread through the material like the branches of a tree. When the channels finally reach the surface of the insulation material, the damage is done and short-circuiting will occur. "Short-circuiting is almost always linked to an electrical tree", explains Lesaint's colleague, Øystein Hestad. Faults of this kind are extremely expensive to repair, especially if they occur in a device installed on an offshore wind farm or a subsea oil production installation – perhaps even under inhospitable Arctic conditions. Under such conditions, say researchers, self-repairing insulation materials represent a cost-effective alternative to traditional repair methods. Microcapsules SINTEF researchers have based their work on an established idea developed to repair mechanical damage and cracks in composite materials. The composites are mixed with microcapsules filled with a liquid monomer – single molecules which have the property to join with each other (polymerise) to form long-chain molecules. If cracks or other forms of damage encroach on the capsules, the monomer is released and fills the cracks. "As far as we know, we're the first to have tested this technique on damage resulting from electrical stress fields", says Lesaint. The microcapsules they incorporated into the insulation materials burst when they encounter one of the branches of an electrical tree. The liquid monomer then invades the thin channels forming the 'tree' and polymerises. The channels are filled in and the electrical degradation of the insulation material is halted. In this way the 'immune defences' of the insulation material are strengthened, and the lifetime of the installation extended. Looking for partners This summer, the SINTEF research team presented the concept at a conference in Philadelphia, USA. "Many people were surprised, especially when they realised that we had chosen to share the concept with others", says Lesaint. "Taking the chance that other researchers might steal such a good idea is a risk we have to take", he says. The industry has also expressed some interest, but so far not enough to consider funding further research. "We're being met with curious interest, but have been told to come back when we have more test results", says Lesaint. "The problem is that at present we have insufficient funds to conduct the research needed to carry the project forward", he says. Next year will thus decide as to whether this self-repairing project will take the step from being a promising concept to becoming the next generation of insulation materials.
Subsea installations can get longer life-time with self-repairing materials. (Illustration: SINTEF Energy ) Electrical trees So-called electrical trees develop in electrical insulation materials that are approaching the end of their useful lives. Electrical stress fields exploit small weaknesses in the insulation material and generate hair-thin channels that spread through the material like the branches of a tree. When the channels finally reach the surface of the insulation material, the damage is done and short-circuiting will occur. "Short-circuiting is almost always linked to an electrical tree", explains Lesaint's colleague, Øystein Hestad. Faults of this kind are extremely expensive to repair, especially if they occur in a device installed on an offshore wind farm or a subsea oil production installation – perhaps even under inhospitable Arctic conditions. Under such conditions, say researchers, self-repairing insulation materials represent a cost-effective alternative to traditional repair methods. Microcapsules SINTEF researchers have based their work on an established idea developed to repair mechanical damage and cracks in composite materials. The composites are mixed with microcapsules filled with a liquid monomer – single molecules which have the property to join with each other (polymerise) to form long-chain molecules. If cracks or other forms of damage encroach on the capsules, the monomer is released and fills the cracks. "As far as we know, we're the first to have tested this technique on damage resulting from electrical stress fields", says Lesaint. The microcapsules they incorporated into the insulation materials burst when they encounter one of the branches of an electrical tree. The liquid monomer then invades the thin channels forming the 'tree' and polymerises. The channels are filled in and the electrical degradation of the insulation material is halted. In this way the 'immune defences' of the insulation material are strengthened, and the lifetime of the installation extended. Looking for partners This summer, the SINTEF research team presented the concept at a conference in Philadelphia, USA. "Many people were surprised, especially when they realised that we had chosen to share the concept with others", says Lesaint. "Taking the chance that other researchers might steal such a good idea is a risk we have to take", he says. The industry has also expressed some interest, but so far not enough to consider funding further research. "We're being met with curious interest, but have been told to come back when we have more test results", says Lesaint. "The problem is that at present we have insufficient funds to conduct the research needed to carry the project forward", he says. Next year will thus decide as to whether this self-repairing project will take the step from being a promising concept to becoming the next generation of insulation materials.Broadband graphene optical modulator on silicon
At this week’s IEEE International Electron Devices Meeting (IEDM 2014), nanoelectronics research center imec and its associated lab at Ghent University have demonstrated the industry’s first integrated graphene optical electro-absorption modulator (EAM) capable of 10Gb/s modulation speed. Combining low insertion loss, low drive voltage, high thermal stability, broadband operation and compact footprint, the device marks an important milestone in the realization of next-generation, high-density low-power integrated optical interconnects. Integrated optical modulators with high modulation speed, small footprint and broadband athermal operation are highly desired for future chip-level optical interconnects. Graphene is a promising material to achieve this, owing to its fast tunable absorption over a wide spectral range. Imec’s graphene-silicon EAM consists of a 50µm long graphene-oxide-silicon capacitor structure implemented on top of a planarized silicon-on-insulator (SOI) rib waveguide. For the first time, high-quality optical modulation was demonstrated in a hybrid graphene-silicon modulator, at bit rates up to 10Gb/s. A competitive optical insertion loss below 4dB and extinction ratio of 2.5dB were obtained over a broad wavelength range of 80nm around 1550nm center wavelength. Moreover, no significant changes in performance were observed for temperatures in the range of 20-49°C, implying a robust athermal operation. As such, imec’s graphene-silicon EAM outperforms state-of-the-art SiGe EAMs on thermal robustness and optical bandwidth specifications. “With this breakthrough result, imec has illustrated the huge potential of graphene optical EA modulators with respect to thermal, bandwidth, and footprint benefits,” said Philippe Absil, 3D and Optical Technologies department director at imec. “This achievement underscores our dedicated work and industry leadership in R&D on high bandwidth chip-level optical input/output. Future work will focus on further improving the modulation speed of our graphene EAM, similar to the speed obtained in highly optimized Si(Ge) modulators (30-50 Gb/s).” Imec’s research on high-bandwidth optical input/output (I/O) explores optical solutions for realizing high-bandwidth chip-level I/O. With support by its associated lab at Ghent University it aims at developing a scalable, manufacturable silicon-based optical interconnect technology for the telecom and datacom industry. Imec’s portfolio includes low-loss strip waveguides, highly efficient grating couplers, 25Gb/s Mach-Zehnder modulators, 25Gb/s Ge photodetectors and more. Imec’s R&D on high bandwidth chip-level input/output is performed in cooperation with imec’s key partners in its core CMOS programs including Intel, Samsung, TSMC, Globalfoundries, Micron, Sony, SK Hynix, Huawei. Imec recently joined the Graphene Flagship, Europe’s 1 billion EUR Programme covering the whole value chain from materials production to components and system. This will further strengthen imec’s strategic position in exploiting Graphene’s unique properties for optical interconnect applications.
Subscribe to:
Posts (Atom)