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."
Researchers create 'green' process to reduce molecular switching waste
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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.
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