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08:06 EDT 28th May 2015 | BioPortfolio

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Showing PubMed Articles 1–25 of 2,400+ from Nano letters


A Bamboo-Inspired Nanostructure Design for Flexible, Foldable, and Twistable Energy Storage Devices.

Flexible energy storage devices are critical components for emerging flexible electronics. Electrode design is key in the development of all-solid-state supercapacitors with superior electrochemical performances and mechanical durability. Herein, we propose a bamboo-like graphitic carbon nanofiber with a well-balanced macro-, meso-, and microporosity, enabling excellent mechanical flexibility, foldability, and electrochemical performances. Our design is inspired by the structure of bamboos, where a periodic...


Assessment of strain-generated oxygen vacancies using SrTiO3 bicrystals.

Atomic-scale defects strongly influence the electrical and optical properties of materials, and their impact can be more pronounced in localized dimensions. Here we directly demonstrate that strain triggers the formation of oxygen vacancies in complex oxides by examining the tilt boundary of SrTiO3 bicrystals. Through transmission electron microscopy and electron energy loss spectroscopy, we identify the strains along the tilt boundary and oxygen vacancies in the strain-imposed regions between dislocation c...


Epitaxial growth of GaN nanowires with high structural perfection on a metallic TiN film.

Vertical GaN nanowires are grown in a self-induced way on a sputtered Ti film by plasma-assisted molecular beam epitaxy. Both in-situ electron diffraction and ex-situ ellipsometry show that Ti is converted to TiN upon exposure of the surface to the N plasma. The ellipsometric data, in addition, demonstrate this TiN film to be metallic. The diffraction data evidence that the GaN nanowires have a strict epitaxial relationship to this film. Photoluminescence spectroscopy of the GaN nanowires shows excitonic tr...


Impact of Surface-Bound Small Molecules on the Thermoelectric Property of Self-Assembled Ag2Te Nanocrystal Thin Films.

Small molecules with functional groups can show different electron affinity and binding behavior on nanocrystal surface, which, in principle, could be used to alternate the electrical transport in self-assembled nanocrystal thin films. These small molecules can also serve for scattering the phonons to reduce the thermal conductivity. Here, we present our research on the thermoelectric characteristic of self-assembled silver telluride (Ag2Te) nanocrystal thin films which are fabricated by a layer-by-layer (L...


Core-Shell CdS-Cu2S Nanorod Array Solar Cells.

As an earth-abundant p-type semiconductor, copper sulfide (Cu2S) is an attractive material for application in photovoltaic devices. However, it suffers from a minority carrier diffusion length that is less than the length required for complete light absorption. Core-shell nanowires and nanorods have the potential to alleviate this difficulty because they decouple the length scales of light absorption and charge collection. To achieve this geometry using Cu2S, cation exchange was applied to an array of CdS n...


Ultrafast Lateral Photo-Dember Effect in Graphene Induced by Nonequilibrium Hot Carrier Dynamics.

The photo-Dember effect arises from the asymmetric diffusivity of photoexcited electrons and holes, which creates a transient spatial charge distribution and hence the build up of a voltage. Conventionally, a strong photo-Dember effect is only observed in semiconductors with a large asymmetry between the electron and hole mobilities, such as in GaAs or InAs, and is considered negligible in graphene due to its electron-hole symmetry. Here we report the observation of a strong lateral photo-Dember effect indu...


Indirect Band Gap Emission by Hot Electron Injection in Metal/MoS2 and Metal/WSe2 Heterojunctions.

Transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, are free of dangling bonds, and therefore make more 'ideal' Schottky junctions than bulk semiconductors, which produce Fermi energy pinning and recombination centers at the interface with bulk metals, inhibiting charge transfer. Here, we observe a more than 10X enhancement in the indirect band gap photoluminescence of transition metal dichalcogenides (TMDCs) deposited on various metals (e.g., Cu, Au, Ag), while the direct band gap emission rem...


Phonon Engineering in Isotopically Disordered Silicon Nanowires.

The introduction of stable isotopes in the fabrication of semiconductor nanowires provides an additional degree of freedom to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. With this perspective, we report on phonon engineering in metal catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors 28SiH4, 29SiH4, and 30SiH4 with purity better than 99.9%. M...


A skyrmion-based dynamic magnonic crystal.

A linear array of periodically spaced and individually controllable skyrmions is introduced as a magnonic crystal. It is numerically demonstrated that skyrmion nucleation and annihilation can be accurately controlled by a nanosecond spin polarized current pulse through a nanocontact. Arranged in a periodic array, such nanocontacts allow the creation of a skyrmion lattice that causes a periodic modulation of the waveguide's magnetization, which can be dynamically controlled by changing either the strength of...


Electrical and Surface Properties of InAs/InSb Nanowires Cleaned by Atomic Hydrogen.

We present a study of InAs/InSb heterostructured nanowires by x-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM) and in-vacuum electrical measurements. Starting with pristine nanowires covered only by the native oxide formed through exposure to ambient air, we investigate the effect of atomic hydrogen cleaning on the surface chemistry and electrical performance. We find that clean and unreconstructed nanowire surfaces can be obtained simultaneously for both InSb and InAs by heating ...


Enhanced Amplified Spontaneous Emission in Perovskites using a Flexible Cholesteric Liquid Crystal Reflector.

Organic-inorganic perovskites are highly promising solar cell materials, with laboratory-based power conversion efficiencies already matching those of established thin film technologies. Their exceptional photovoltaic performance is in part attributed to the presence of efficient radiative recombination pathways, thereby opening up the possibility of efficient light-emitting devices. Here, we demonstrate optically-pumped amplified spontaneous emission (ASE) at 780 nm from a 50-nm-thick film of CH3NH3PbI3 pe...


In situ investigation of Li and Na ion transport with single nanowire electrochemical devices.

In the last decade, Li ion batteries are widely considered to be the most promising rechargeable batteries for the rapid development of mobile devices and electric vehicles. There is also much interest in Na ion batteries, especially in the field of static grid storage due to their much lower production cost compared with Li ion batteries. However, the fundamental mechanism of Li and Na ion transport in nanoscale electrodes of batteries has been rarely experimentally explored. This insight can guide the dev...

Friday 29th November 1241

Sn-seeded GaAs nanowires as self-assembled radial p-n junctions.

The widespread use of Au as a seed particle in the fabrication of semiconductor nanowires presents a fundamental limitation to the potential incorporation of such nanostructures into electronic devices. Although several other growth techniques have been demonstrated, the use of alternative seed particle metals remains an underexplored but potentially very promising way to influence the properties of the resulting nanowires while simultaneously avoiding gold. In this letter we demonstrate the use of Sn as a ...


Near-field imaging of phased array metasurfaces.

Phased-antenna metasurfaces can impart abrupt, spatially-dependent changes to the amplitude, phase, and polarization of light and thus mold wavefronts in a desired fashion. Here we present an experimental and computational near-field study of metasurfaces based on near-resonant V-shaped antennas, and connect their near- and far-field optical responses. We show that far-fields can be obtained from limited, experimentally-obtained knowledge of the near-fields, paving the way for experimental near-field charac...


Metallic properties of the Si(111)-5×2-Au surface from infrared plasmon polaritons and ab initio theory.

The metal-atom chains on the Si(111)-5×2-Au surface represent an exceedingly interesting system for the understanding of one-dimensional electrical interconnects. While other metal-atom chain structures on silicon suffer from metal-to-insulator transitions, Si(111)-5×2-Au stays metallic at least down to 20 K as we have proven by the anisotropic absorption from localized plasmon polaritons in the infrared. A quantitative analysis of the infrared plasmonic signal done here for the first time yields valuable...


Coupling mediated coherent control of localized surface plasmon polaritons.

We investigate the phase-dependent excitation of localized surface plasmon polaritons in coupled nanorods by using nonlinear spectroscopy. Our design of a coupled three-nanorod structure allows independent excitation with cross-polarized light. Here, we show that the excitation of a particular plasmon mode can be coherently controlled by changing the relative phase of two orthogonally polarized light fields. Furthermore, we observe a phase relation for the excitation that is dominantly caused by damping eff...

Tuesday 8th November 1239

Compressible Viscoelastic Liquid Effects Generated by the Breathing Modes of Isolated Metal Nanowires.

Transient absorption microscopy is used to examine the breathing modes of single gold nanowires in highly viscous liquids. By performing measurements on the same wire in air and liquid, the damping contribution from the liquid can be separated from the intrinsic damping of the nanowire. The results show that viscous liquids strongly reduce the vibrational lifetimes, but not to the extent predicted by standard models for nanomaterial-liquid interactions. To explain these results a general theory for compress...

Thursday 27th May 1238

3D Imaging of Twin Domain Defects in Gold Nanoparticles.

Topological defects are ubiquitous in physics and include crystallographic imperfections such as defects in condensed matter systems. Defects can determine many of the material's properties thus providing novel opportunities for defect engineering. However, it is difficult to track buried defects in three dimensions with nanoscale resolution. Here we report three-dimensional visualization of gold nanocrystal twin domains using Bragg Coherent X-ray Diffractive Imaging in an aqueous environment. We capture th...


Effect of elastic strain fluctuation on atomic layer growth of epitaxial silicide in Si nanowires by point contact reactions.

Effects of strain impact a range of applications involving mobility change in field-effect-transistors. We report the effect of strain fluctuation on epitaxial growth of NiSi2 in a Si nanowire via point contact and atomic layer reactions, and we discuss the thermodynamic, kinetic, and mechanical implications. The generation and relaxation of strain shown by in situ TEM is periodic and in synchronization with the atomic layer reaction. The Si lattice at the epitaxial interface is under tensile strain, which ...


Strain hardening and size effect in five-fold twinned Ag nanowires.

Metallic nanowires usually exhibit ultra-high strength, but low tensile ductility owing to their limited strain hardening capability. Here we study the unique strain hardening behavior of the five-fold twinned Ag nanowires by nanomechanical testing and atomistic modeling. In situ tensile tests within a scanning electron microscope (SEM) revealed strong strain hardening behavior of the five-fold twinned Ag nanowires. Molecular dynamics simulations showed that such strain hardening was critically controlled b...


High-power genuine ultraviolet light-emitting diodes based on colloidal nanocrystal quantum dots.

Thin-film ultraviolet (UV) light-emitting diodes (LEDs) with emission wavelengths below 400 nm are emerging as promising light sources for various purposes, from our daily lives to industrial applications. However, current thin-film UV-emitting devices radiate not only UV light but also visible light. Here, we introduce genuine UV-emitting colloidal nanocrystal quantum dot (NQD) LEDs (QLEDs) using precisely controlled NQDs consisting of a 2.5-nm-sized CdZnS ternary core and a ZnS shell. The core size is fur...


Germanium Silicon Alloy Anode Material Capable of Tunable Overpotential by Nanoscale Si Segregation.

We developed the novel electrode which enables fine control of overpotential by exploiting surface segregation that is the enrichment of one component at the surface of binary alloy. To realize this approach, we controlled the proportion of Si with low Li diffusivity at the surface by annealing the SiGe nanowire in H2 environment at various temperatures. The resulting SiGe nanowires annealed at 850 °C exhibited high reversible capacity (> 1031 mA·h·g-1), and long cycle life (400 cycles) with high capacit...


Understanding the Anchoring Effect of Two-dimensional Layered Materials for Lithium-sulfur Batteries.

Although the rechargeable lithium-sulfur battery system has attracted significant attention due to its high theoretical specific energy, its implementation has been impeded by multiple challenges, especially the dissolution of intermediate lithium polysulfide (Li2Sn) species into the electrolyte. Introducing anchoring materials, which can induce strong binding interaction with Li2Sn species, has been demonstrated as an effective way to overcome this problem and achieve long-term cycling stability and high-r...


Low-frequency Interlayer Breathing Modes in Few-layer Black Phosphorus.

As a new two-dimensional layered material, black phosphorus (BP) is a very promising material for nanoelectronics and optoelectronics. We use Raman spectroscopy and first-principles theory to characterize and understand the low-frequency (LF) interlayer breathing modes (


Tunable Dirac electron and hole self-doping of topological insulators induced by stacking defects.

Self-doping of Dirac cones in Bi2X3 (X=Se, Te) topological insulators can be tuned by controlling the sequence of stacking defects in the crystal. Twin boundaries inside Bi2X3 drive n- or p-type doping of the surface states, originated by the defect induced spontaneous polarization. Doping up to 10(12)-10(13) e/cm(2) may be achieved depending on the defect distribution. Our findings open the route to fabrication of Bi2X3 surfaces with tailored intrinsic charge and spin densities.

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