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Research Review: Feb. 12

By Caroline Hayes, Senior Editor

Paper brain is not for lightweights; piezo-elements recreate fingerprints ; super graphene can be super-conductor; germanium nanowire-based anode gives Li-Ion batteries new lease of life.

Naning-photo credit Dream Designs

Researchers at the School of Electronic Science and Engineering, Nanjing University, China have produces a paper-based device that mimics a human brain’s electrochemical signalling.
It holds promise for developing inexpensive, artificial neural networks in robotics as well as in computer processing.
The premise is an IZO (indium zinc oxide) TFT (thin film transistor) replicates the junction between two neurons, in a brain (the biological synapse). In humans, the synapse is the channel for chemical and electrical signals between neurons to pass messages. To simulate a spike, caused when neuron voltages change dramatically, releasing neurotransmitters to send message to the next neuron. The researchers reproduced this spike by applying a small voltage to the first electrode in their device which caused protons—acting as a neurotransmitter—from the silicon dioxide films to migrate towards the IZO channel opposite it.
This caused negatively charged electrons, and a current to flow through the IZO channel, mimicking a signal in a normal neuron.
The researchers found that as more neurotransmitters passed across a synapse, the connection became stronger – this synaptic plasticity is how humans learn and memorize things.
Corresponding author of the study, Qing Wan, said: ‘A paper-based synapse could be used to build lightweight and biologically friendly artificial neural networks, and, at the same time, with the advantages of flexibility and biocompatibility, could be used to create the perfect organism–machine interface for many biological applications.’
The TFT will be presented Thursday February 13, in IOP Publishing’s journal Nanotechnology.

Partners from France, Germany, Ireland, Lithuania and Hungary, are involved in a project to develop fingerprint sensors with resolutions beyond 500dpi, which is the minimum resolution required by the US Federal Bureau of Investigation for automated fingerprint identification.
The PiezoMat research project is funded by the European Commission and will aim to develop robust fingerprint sensors by integrating and interconnecting large numbers of piezoelectric elements on a chip. These elements are made of vertical zinc oxide (ZnO) nanowires grown directly onto a network of interconnected electrodes manufactured via microelectronics processing. It is also distinctive for using what are described as innovative manufacturing processes, for the nanowire patterning, growth and encapsulation. It also used multi-physics-model-supported design, dedicated characterization and test infrastructures.
The three-year, €2.9million (approximately $4million) project is part of the EC’s Seventh Framework Program (FP7) for research and technological development. Particpants include CEA-Leti (France) the microelectronics, microtechnology and nanotechnology center, Fraunhofer IAF (Germany) which develops electronic and optical devices based on modern micro- and nanostructures, the Research Centre for Natural Sciences, Hungarian Academy of Science, which conducts research on functional materials and nanometer-scale structures, Specific Polymer (France) a company which will act as an R&D service provider and Tyndall National Institute (Ireland) R&D facility.

Researchers at the University of Vienna have shed light on more qualities of graphene. Using a photoemission method, they demonstrated the superconducting pairing mechanism in calcium-doped graphene, using an angle-resolved photoemission spectroscopy.
Nikolay Verbitskiy and Alexander Grüneis from the University of Vienna, Alexander Fedorov and Denis Vyalikh from IFW-Dresden and TU-Dresden and Danny Haberer from the University of California at Berkeley found that calcium induces superconductivity in graphene at a critical temperature of only 1.5K.
The results, published in the journal Nature Communications.
Picture caption: ARPES measurements of calcium-doped graphene. Left: the Fermi surface of graphene (top) and the Dirac cone (bottom). Right: The kink in the spectral function in the two crystallographic main directions. Image: A. Grüneis and A.V. Fedorov

More than doubling the capacity of lithium-ion battery anodes, research published by the journal Nano Letters reports a new germanium nanowire-based anode that increases the capacity and lifetimes of lithium-ion batteries.
The research was supported by Science Foundation Ireland (SFI) under the Principal Investigator Program to Dr Kevin Ryan and by EU.
Ryan says: “The typical lithium-ion battery today is based on graphite and has a relatively low capacity…we used an alternative element, germanium, which is of a higher capacity. The challenge has been that the material expands quite dramatically during charging and falls apart after a relatively small number of cycles. By using nanotechnology, we have found a way to restructure germanium, in the form of nanowires, into a stable porous material that is an ideal battery material as it remains stable over very long time scales during continued operation.”
The research team have also ensured that their nanotechnology solution was scalable, low-cost and low-energy making the technology both greener and commercially viable, which is promising for electric vehicles as well as computing and communications which demand longer battery life with each generation.

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