UK scientists have pioneered a new way of manipulating several thousand atoms at a time, paving the way for building nanoscale electronic devices more quickly and easily at room temperature. Drawing with atoms In 1992 the very first man-made atomic structure was created by using a scanning tunnelling microscope (STM) to gently nudge individual atoms into a tiny nanometer scale logo for IBM. 
The team uses a Scanning Tunnelling Microscope (STM) to inject atoms onto a surface in a precise pattern, enabling them to build nanoscale devices more quickly and easily than before However, using this method atoms must be placed one-by-one, making the process very time-consuming, with even the most advanced microscopes taking many hours to position just a few atoms. In contrast, the new technique developed by the University of Bath in collaboration with the University of Birmingham, is able to move thousands of atoms simultaneously, but with similar precision. In their new method, the tip of the STM injects electrons onto a surface decorated with benzene molecules. The electrons can travel across the surface some tens of nanometers until they encounter one of the benzene molecules sitting on the surface, which causes the benzene to fly off into the gas phase. By carefully comparing the precise atomic position of the benzene molecules before and after the electron injections, the team was able to directly observe how high energy or “hot” electrons behave at room temperature for the first time. Hot electrons Hot electrons can leak out of silicon transistors and may limit the miniaturisation of computer circuits.They also play a critical role in transforming energy from light to electricity in photovoltaics. Their findings, published in the journal ("Atomically resolved real-space imaging of hot electron dynamics") show that instead of moving in straight lines as anticipated, they knock around like a ball in a pinball machine. Dr Peter Sloan from the University of Bath’s Department of Physics, explained: “Hot electrons are important in many processes but are really difficult to observe due to their short lifetimes, generally a millionth of a billionth of a second. “We were surprised to find that the hot electrons do not travel in straight lines, but instead behave as if they were a ball in a pin-ball machine, diffusing across the surface. “This confirms that Einstein’s theory of Brownian motion of electrons in semiconductors works even on the nanoscale. A finding that you just can’t observe with the “normal” low temperature experiments. 
The team's experiments show that high energy or "hot" electrons don't move in straight lines as anticipated. “Our findings help us understand the fundamental physics underlying the behaviour of hot electrons and will help pave the way for building new nanotechnology devices with atomic precision.” Professor Richard Palmer at the University of Birmingham commented: "The Birmingham-Bath program is providing us with new eyes to visualise very fast electronic processes and so is relevant not just to electronics and computing but also improving the performance of solar cells designed to capture renewable energy. “It's great to see British Universities collaborating so closely together." 91 per cent of our physics research was defined as ‘world-leading’ or ‘internationally excellent’ in the REF 2014 research assessment, placing our Department of Physics 13th amongst all UK departments for its research activities. The real-world impact of our research – its influence on the economy, society, quality of life etc. - was judged to be particularly strong with 100 per cent being world-leading or internationally excellent, ranking us fourth amongst all UK physics departments for the impact of our research.
read more "New method for building on an atomic scale"
The team uses a Scanning Tunnelling Microscope (STM) to inject atoms onto a surface in a precise pattern, enabling them to build nanoscale devices more quickly and easily than before However, using this method atoms must be placed one-by-one, making the process very time-consuming, with even the most advanced microscopes taking many hours to position just a few atoms. In contrast, the new technique developed by the University of Bath in collaboration with the University of Birmingham, is able to move thousands of atoms simultaneously, but with similar precision. In their new method, the tip of the STM injects electrons onto a surface decorated with benzene molecules. The electrons can travel across the surface some tens of nanometers until they encounter one of the benzene molecules sitting on the surface, which causes the benzene to fly off into the gas phase. By carefully comparing the precise atomic position of the benzene molecules before and after the electron injections, the team was able to directly observe how high energy or “hot” electrons behave at room temperature for the first time. Hot electrons Hot electrons can leak out of silicon transistors and may limit the miniaturisation of computer circuits.They also play a critical role in transforming energy from light to electricity in photovoltaics. Their findings, published in the journal ("Atomically resolved real-space imaging of hot electron dynamics") show that instead of moving in straight lines as anticipated, they knock around like a ball in a pinball machine. Dr Peter Sloan from the University of Bath’s Department of Physics, explained: “Hot electrons are important in many processes but are really difficult to observe due to their short lifetimes, generally a millionth of a billionth of a second. “We were surprised to find that the hot electrons do not travel in straight lines, but instead behave as if they were a ball in a pin-ball machine, diffusing across the surface. “This confirms that Einstein’s theory of Brownian motion of electrons in semiconductors works even on the nanoscale. A finding that you just can’t observe with the “normal” low temperature experiments. The team's experiments show that high energy or "hot" electrons don't move in straight lines as anticipated. “Our findings help us understand the fundamental physics underlying the behaviour of hot electrons and will help pave the way for building new nanotechnology devices with atomic precision.” Professor Richard Palmer at the University of Birmingham commented: "The Birmingham-Bath program is providing us with new eyes to visualise very fast electronic processes and so is relevant not just to electronics and computing but also improving the performance of solar cells designed to capture renewable energy. “It's great to see British Universities collaborating so closely together." 91 per cent of our physics research was defined as ‘world-leading’ or ‘internationally excellent’ in the REF 2014 research assessment, placing our Department of Physics 13th amongst all UK departments for its research activities. The real-world impact of our research – its influence on the economy, society, quality of life etc. - was judged to be particularly strong with 100 per cent being world-leading or internationally excellent, ranking us fourth amongst all UK physics departments for the impact of our research.
Researchers at Okayama University have created a new IR spectroscopic technique utilizing the properties of a metamaterial-based absorber to enhance spectral output. Trials on a self-assembling monolayer of 16-MHDA acid showed distinct peaks corresponding to carbon-hydrogen stretching in the monolayer. The researchers carefully designed their absorber to maximise the IR signal and minimise background noise. The metamaterial consists of 50 nm gold ribbons on a thick gold film, separated by a layer of magnesium fluorine (see image). The wavelength of IR is longer and has less energy than visible light, meaning that it is not strong enough to excite electrons, unlike other types of spectroscopy. IR absorption spectroscopy therefore exploits the ability of IR to induce vibrations in bonded atoms. Organic compounds will absorb IR radiation corresponding to the different types of molecular vibrations present; the resulting absorption spectra tell scientists about the unique chemical structure of the compounds. To test the capabilities of the new metamaterial, the team decided to identify the stretching vibrational modes of carbon-hydrogen bonds in 16-Mercaptohexadecanoic (16-MHDA) acid. They dipped the absorber in 16-MHDA ethanol solution to encourage a self-assembling monolayer of the acid molecules to develop. Under IR radiation at different incident angles, the metamaterial-monolayer spectral output displayed distinct peaks corresponding to carbon-hydrogen stretching, with the most pronounced peaks under IR at an angle of 40°. The new metamaterial approach gave highly-detailed measurements pertaining to tiny molecular details (at the attamole level) in the 16-MHDA monolayer. The researchers hope their new technique will open doors to the development of ultrasensitive IR inspection technologies for material science and security applications. Background Metamaterials The ability to manipulate the light absorption of materials could revolutionize many technologies, such as photovoltaic cells and thermal devices. Research into the design and development of plasmonic metamaterials is still relatively new. These materials are synthetic, and scientists can design their surface structures to exploit the behavior of surface plasmons – quasiparticles that exist on metal surfaces and interact with light – to achieve tuneable optical properties. Infrared absorption spectroscopy could be dramatically enhanced by the introduction of tuneable metamaterial-based absorbers designed to enable high-resolution detection of tiny molecular details. Methodology The metamaterial absorber built by the team comprised gold nano-ribbons (measuring 50 nm thick) on a gold film base, with a thin layer of magnesium fluorine separating the two gold layers. As molecular monolayers self-assemble on noble metal surfaces, they hypothesized that the gold-based metamaterial would prove a strong candidate for enabling the high-resolution measurement of IR-induced vibrational modes in self-assembling monolayers. Their approach involved covering their metamaterial absorber with an ultrathin self-assembling monolayer of 16-MDHA acid molecules. They also covered a bare gold film sample with the same monolayer for comparison. The researchers subjected the two monolayers to IR radiation at different incident angles. The monolayer on bare gold exhibited a low signal-noise ratio, and it was very difficult to see the absorption dips on the spectral output corresponding to the IR-induced carbon-hydrogen stretching in the monolayer. In contrast, the absorption dips were very well-pronounced in the spectral read-out for the metamaterial-monolayer, because the vibrational modes of the 16-MHDA molecules resonated with the plasmonic modes of the metamaterial. This so-called ‘resonant coupling’ produced distinct peaks corresponding to IR-induced carbon-hydrogen stretching in the 16-MHDA molecular structure. The resonant coupling was dependent on the angle of the incident light, with the clearest, strongest signal at an angle of 40°. Future work The researchers believe their absorber may open doors to new ultra-sensitive IR detection technologies. Further, their technique could be exploited in other ways – by optimizing the surface structure of other metamaterials, they could enhance resonant coupling still further and enable sensitivities down to the zeptomole level.
The left structure is showing the natural tooth in its gypsum mold, the middle structure is the artificial tooth (sintered but not yet polymer infiltrated). The model on the right has been sintered and polymer infiltrated. It is embedded in a "puck" to enable polishing and coated with platinum to prevent charging in the electron microscope. (Photo: Tobias Niebel/ETH Zurich) It is a procedure the ETH researchers call magnetically assisted slip casting (MASC). "The wonderful thing about our new procedure is that it builds on a 100-year-old technique and combines it with modern material research," says Studart's doctoral student Tobias Niebel, co-author of a study just published in the specialist journal ("Magnetically assisted slip casting of bioinspired heterogeneous composites"). Revival of a 100-year-old technique This is how MASC works: the researchers first create a plaster cast to serve as a mould. Into this mould, they pour a suspension containing magnetised ceramic platelets, such as aluminium oxide platelets. The pores of the plaster mould slowly absorb the liquid from the suspension, which causes the material to solidify and to harden from the outside in. The scientists create a layer-like structure by applying a magnetic field during the casting process, changing its orientation at regular intervals. As long as the material remains liquid, the ceramic platelets align to the magnetic field. In the solidified material, the platelets retain their orientation. Through the composition of the suspension and the direction of the platelets, a continuous process can be used to produce multiple layers with differing material properties in a single object. This creates complex materials that are almost perfect imitations of their natural models, such as nacre or tooth enamel. "Our technique is similar to 3D printing, only 10 times faster and much more cost-effective," says Florian Bouville, a post-doc with Studart and co-lead author of the study. Artificial teeth from casting moulds To demonstrate the potential of the MASC technique, Studart's research group produced an artificial tooth with a microstructure that mimics that of a real tooth. The surface of the artificial tooth is as hard and structurally complex as a real tooth, while the layer beneath is softer, just like the dentine of the natural model. The co-lead author of the study, doctoral student Hortense Le Ferrand, and her colleagues began by creating a plaster cast of a human wisdom tooth. They then filled this mould with a suspension containing aluminium oxide platelets and glass nanoparticles as mortar. Using a magnet, they aligned the platelets perpendicular to the surface of the object. Once the first layer was dry, the scientists poured a second suspension into the same mould. This suspension, however, did not contain glass particles. The aluminium oxide platelets in the second layer were aligned horizontally to the surface of the tooth using the magnet. This double-layered structure was then 'fired' at 1,600 degrees to compress and harden the material: the term sintering is used for this process. Finally, the researchers filled the pores that remained after the sintering with a synthetic monomer used in dentistry, which subsequently polymerised. Artificial teeth behave just like real teeth The researchers are very happy with the result. "The profile of hardness and toughness obtained from the artificial tooth corresponds exactly with that of a natural tooth," says a pleased Studart. The procedure and the resulting material lend themselves for applications in dentistry. However, as Studart points out, the current study is just an initial proof-of-concept, which shows that the natural fine structure of a tooth can be reproduced in the laboratory. "The appearance of the material has to be significantly improved before it can be used for dental prostheses." Nonetheless, as Studart explains, the artificial tooth clearly shows that a degree of control over the microstructure of a composite material can be achieved, previously the sole preserve of living organisms. One part of the MASC process, the magnetisation and orientation of the ceramic platelets, has already been patented. However, the new production process for such complex biomimetic materials also has other potential applications. For instance, copper platelets could be used in place of aluminium oxide platelets, which would allow the use of such materials in electronics. "The base substances and the orientation of the platelets can be combined as required, which rapidly and easily makes a wide range of different material types with varying properties feasible," says Studart.