Skyrmion Generation by Current

Skyrmions, once a hypothesized field-theoretical object believed to describe the nature of elementary particles, became common sightings in recent years among several non-centrosymmetric metallic ferromagnets. For more practical applications of Skyrmionic matter as carriers of information, thus realizing the prospect of "Skyrmionics", it is necessary to have the means to create and manipulate Skyrmions individually. We show through extensive simulation of the Landau-Lifshitz-Gilbert equation that a circulating current imparted to the metallic chiral ferromagnetic system can create isolated Skyrmionic spin texture without the aid of external magnetic field.Comment: 8 pages, 5 figures, submitted to PR

Individually addressable and flexible pressure sensor matrixes with ZnO nanotube arrays on graphene

We report the fabrication of individually addressable, high-density, vertical zinc oxide (ZnO) nanotube pressure sensor arrays. High-sensitivity and flexible piezoelectric sensors were fabricated using dimension- and position-controlled, vertical, and free-standing ZnO nanotubes on a graphene substrate. Significant pressure/force responses were achieved from small devices composed of only single, 3 × 3, 5 × 5, and 250 × 250 ZnO nanotube arrays on graphene. An individually addressable pixel matrix was fabricated by arranging the top and bottom electrodes of the sensors in a crossbar configuration. We investigated the uniformity and robustness of pressure/force spatial mapping by considering the pixel size, the number of ZnO nanotubes in each pixel, and the lateral dimensions of individual ZnO nanotubes. A spatial resolution as high as 1058 dpi was achieved for a Schottky diode-based force/pressure sensor composed of ZnO nanotubes on a flexible substrate. Additionally, we confirmed the excellent flexibility and electrical robustness of the free-standing sensor arrays for high-resolution tactile imaging. We believe that this work opens important opportunities for 1D piezoelectric pressure/force sensor arrays with enormous applications in human-electronics interfaces, smart skin, and micro- and nanoelectromechanical systems

Ultra-Sharp Nanowire Arrays Natively Permeate, Record, and Stimulate Intracellular Activity in Neuronal and Cardiac Networks

Intracellular access with high spatiotemporal resolution can enhance our understanding of how neurons or cardiomyocytes regulate and orchestrate network activity, and how this activity can be affected with pharmacology or other interventional modalities. Nanoscale devices often employ electroporation to transiently permeate the cell membrane and record intracellular potentials, which tend to decrease rapidly to extracellular potential amplitudes with time. Here, we report innovative scalable, vertical, ultra-sharp nanowire arrays that are individually addressable to enable long-term, native recordings of intracellular potentials. We report large action potential amplitudes that are indicative of intracellular access from 3D tissue-like networks of neurons and cardiomyocytes across recording days and that do not decrease to extracellular amplitudes for the duration of the recording of several minutes. Our findings are validated with cross-sectional microscopy, pharmacology, and electrical interventions. Our experiments and simulations demonstrate that individual electrical addressability of nanowires is necessary for high-fidelity intracellular electrophysiological recordings. This study advances our understanding of and control over high-quality multi-channel intracellular recordings, and paves the way toward predictive, high-throughput, and low-cost electrophysiological drug screening platforms.Comment: Main manuscript: 33 pages, 4 figures, Supporting information: 43 pages, 27 figures, Submitted to Advanced Material

Scaling study of molecular beam epitaxy grown InAs/Al2O3 films using atomic force microscopy

Scaling study of polycrystalline InAs thin films grown by molecular beam epitaxy on c-plane sapphire (001) substrate has been presented using atomic force microscopy, corresponding height-height correlation function and two-dimensional fast Fourier transform profiles. Height-height correlation function profiles exhibit oscillations at larger lateral distances along with ring-like features in the respective two-dimensional fast Fourier transform scans and clearly indicate mound-like surface morphology. Scaling parameters, interface width and lateral correlation length were extracted and their dependence on the growth temperatures were investigated. The growth mechanism has been well explained in terms of diffusion effects and the obtained parameters qualitatively agrees with the parameters obtained for the growth of InAs films grown on Si(100) substrate under identical growth conditions. Our study suggests that molecular beam epitaxy grown InAs thin films on lattice mismatched substrates (c-plane sapphire(001) and Si(100) substrate) follows the same growth behavior under identical growth conditions

Real-Time Characterization Using in situ RHEED Transmission Mode and TEM for Investigation of the Growth Behaviour of Nanomaterials

Abstract A novel characterization technique using both in situ reflection high-energy electron diffraction (RHEED) transmission mode and transmission electron microscopy (TEM) has been developed to investigate the growth behaviour of semiconductor nanostructures. RHEED employed in transmission mode enables the acquisition of structural information during the growth of nanostructures such as nanorods. Such real-time observation allows the investigation of growth mechanisms of various nanomaterials that is not possible with conventional ex situ analytical methods. Additionally, real-time monitoring by RHEED transmission mode offers a complete range of information when coupled with TEM, providing structural and chemical information with excellent spatial resolution, leading to a better understanding of the growth behaviour of nanomaterials. Here, as a representative study using the combined technique, the nucleation and crystallization of InAs nanorods and the epitaxial growth of InxGa1−xAs(GaAs) shell layers on InAs nanorods are explored. The structural changes in the InAs nanorods at the early growth stage caused by the transition of the local growth conditions and the strain relaxation processes that occur during epitaxial coating of the shell layers are shown. This technique advances our understanding of the growth behaviour of various nanomaterials, which allows the realization of nanostructures with novel properties and their application in future electronics and optoelectronics

Qualitative analysis of growth mechanism of polycrystalline InAs thin films grown by molecular beam epitaxy

The mechanism of surfaces/interfaces and precise control of growth morphology is a key parameter for any specific device application. Herein, we report on a qualitative growth study of molecular beam epitaxy-grown polycrystalline InAs thin films on a lattice-mismatched Si(1 0 0) substrate using atomic force microscopy. The height-height correlation function (HHCF) and power spectral density function (PSDF) were employed to analyze the surface structures. Clear oscillatory behavior in the HHCF for sufficiently larger lateral distances suggests a mound-like morphology, which was confirmed by the existence of a characteristic frequency peak in the PSDF. The growth mechanism is described qualitatively by the Schwoebel barrier (roughening) effect coupled with the Mullins diffusion model (smoothing effect)

Variable-Color Light-Emitting Diodes Using GaN Microdonut arrays

Microdonut-shaped GaN/InxGa1-xN light-emitting diode (LED) microarrays are fabricated for variable-color emitters. The figure shows clearly donut-shaped light emission from all the individual microdonut LEDs. Furthermore, microdonut LEDs exhibit spatially-resolved blue and green EL colors, which can be tuned by either controlling the external bias voltage or changing the size of the microdonut LED

Growth and characterizations of GaN micro-rods on graphene films for flexible light emitting diodes

We report the growth of GaN micro-rods and coaxial quantum-well heterostructures on graphene films, together with structural and optical characterization, for applications in flexible optical devices. Graphene films were grown on Cu foil by means of chemical vapor deposition, and used as the substrates for the growth of the GaN micro-rods, which were subsequently transferred onto Si02/Si substrates. Highly Si-doped, n-type GaN micro-rods were grown on the graphene films using metalorganic chemical vapor deposition. The growth and vertical alignment of the GaN micro-rods, which is a critical factor for the fabrication of high-performance lightemitting diodes (LEDs), were characterized using electron microscopy and X-ray diffraction. The GaN micro-rods exhibited promising photoluminescence characteristics for optoelectronic device applications, including room-temperature stimulated emission. To fabricate flexible LEDs, InxGai,N/GaN multiple quantum wells and a p-type GaN layer were deposited coaxially on the GaN micro-rods, and transferred onto Ag-coated polymer substrates using lift-off. Ti/Au and Ni/Au metal layers were formed to provide electrical contacts to the n-type and p-type GaN regions, respectively. The micro-rod LEDs exhibited intense emission of visible light, even after transfer onto the flexible polymer substrate, and reliable operation was achieved following numerous cycles of mechanical deformation. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License