Nanowire electrodes for high-density stimulation and measurement of neural circuits

Brain-machine interfaces (BMIs) that can precisely monitor and control neural activity will likely require new hardware with improved resolution and specificity. New nanofabricated electrodes with feature sizes and densities comparable to neural circuits may lead to such improvements. In this perspective,we review the recent development of vertical nanowire (NW) electrodes that could provide highly parallel single-cell recording and stimulation fo rfuture BMIs. We compare the advantages of these devices and discuss some of the technical challenges that must be overcome for this technology to become a platform for next-generation closed-loop BMIs

Strong odd-frequency correlations in fully gapped Zeeman-split superconductors.

It is now well established that at a superconductor/ferromagnet (S/F) interface an unconventional superconducting state arises in which the pairing is odd-frequency. The hallmark signature of this superconducting state is generally understood to be an enhancement of the electronic density of states (DoS) at subgap energies close to the S/F interface. However, here we show that an odd frequency state can be present even if the DoS is fully gapped. As an example, we show that this is the case in the pioneering S/FI (where FI is a insulating ferromagnet) tunneling experiments of Meservey and Tedrow, and we derive a generalized analytical criterium to describe the effect of odd-frequency pairing on the DoS. Finally, we propose a simple experiment in which odd-frequency pairing in a Zeeman-split superconductor can be unambiguously detected via the application of an external magnetic field.J.L was supported by the Research Council of Norway, Grants No. 205591 and 216700 and the ”Outstanding Academic Fellows” programme at NTNU. J.W.A.R. acknowledges financial support from the Royal Society (”Superconducting Spintronics”) and through a Leverhulme Trust International Network Grant (grant IN-2013-033).This is the final version of the article. It first appeared from NPG via http://dx.doi.org/10.1038/srep1548

Two-Dimensional Layered Materials (Graphene-MoS2) Nanocatalysts for Hydrogen Production

Recent development of two-dimensional layered materials including graphene-family and related nanomaterials have arisen as potential game changer for energy, water and sensing applications. While graphene is a form of carbon arranged hexagonally within atomic thin sheet, MoS2 is becoming a popular, efficient, and cost-effective catalyst for electrochemical energy devices, in contrast to expensive platinum and palladium catalysts. In this work, we electrochemically desulfurize few-layer molybdenum disulfide (MoS2) and aerogels with reduced graphene oxide (rGO) prepared under hydrothermal conditions ((P\u3c 20 bar, T\u3c 200 oC), for improving hydrogen evolution reaction (HER) activity via point defects (S-vacancy). Moreover, the interactions between rGO and MoS2 components create emergent heterostructures with desirable physicochemical properties (specific surface area, mechanical strength, faster diffusion, facile electron and ion transport) enabled by chemically bridged (covalently) tailored interfaces. We demonstrate that with an optimized number defect density, particularly by exposing the edges of MoS2 layers and nanowalls in graphene-MoS2 ‘hybrid’ aerogels, interfacial processes during catalytic reactions are accelerated. To understand the effects of defects on HER activity, we varied the applied potential and operating duration for optimized defect density. This study offers a unique method for tuning the properties of layered MoS­2 and hybrids as promising, cost-effective and efficient nanocatalysts and establishes the structure–catalytic activity relationships via scanning electrochemical microscopy at electrode/electrolyte interface besides mapping electrochemical (re)activity and electro-active site distribution

Direction-dependent Optical Modes in Nanoscale Silicon Waveguides

On-chip photonic networks have the potential to transmit and route information more efficiently than electronic circuits. Recently, a number of silicon-based optical devices including modulators, buffers, and wavelength converts have been reported. However, a number of technical challenges need to be overcome before these devices can be combined into network-level architectures. In particular, due to the high refractive index contrast between the core and cladding of semiconductor waveguides, nanoscale defects along the waveguide often scatter light into the backward-propagating mode. These reflections could result in unwanted feedback to optical sources or crosstalk in bidirectional interconnects such as those employed in fiber-optic networks. It is often assumed that these reflected waves spatially overlap the forward-propagating waves making it difficult to implement optical circulators or isolators which separate or attenuate light based on its propagation direction. Here, we individually identify and map the near-field mode profiles of forward-propagating and reflected light in a single-mode silicon waveguide using Transmission-based near-field scanning optical microscopy (TraNSOM). We show that unlike fiber-optic waveguides, the high-index-contrast and nanoscale dimensions of semiconductor waveguides create counter propagating waves with distinct spatial near-field profiles. These near-field differences are a previously-unobserved consequence of nanoscale light confinement and could provide a basis for novel elements to filter forward-propagating from reflected light