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Nano Letters

Alan Cervantes Farrell, Pradeep Nuwan Senanayake, Xiao Meng, Nick Y Hsieh, Diana L Huffaker
We present the electrical properties of p-n junction photodetectors comprised of vertically oriented p-GaAs nanowire arrays on n-GaAs substrate. We measure an ideality factor as low as n = 1.0 and a rectification ratio > 10(8) across all devices, with some > 10(9), comparable to the best GaAs thin film photodetectors. Analysis of the Arrhenius plot of the saturation current yields an activation energy of 690 meV - approximately half the bandgap of GaAs - indicating generation-recombination current from mid-gap states is the primary contributor to the leakage current at low bias...
March 23, 2017: Nano Letters
Renjie Chen, Katherine L Jungjohann, William M Mook, John Nogan, Shadi A Dayeh
Alloyed and compound contacts between metal and semiconductor transistor channels enable self-aligned gate processes which play a significant role in transistor scaling. At nanoscale dimensions and for nanowire channels, prior experiments focused on reactions along the channel length, but the early stage of reaction in their cross-sections remains unknown. Here, we report on the dynamics of the solid-state reaction between metal (Ni) and semiconductor (In0.53Ga0.47As), along the cross-section of nanowires that are 15 nm in width...
March 23, 2017: Nano Letters
Sarwat A Baig, Jessica L Boland, Djamshid A Damry, Hark Hoe Tan, Chennupati Jagadish, Hannah J Joyce, Michael B Johnston
Progress in the terahertz (THz) region of the electromagnetic spectrum is undergoing major advances, with advanced THz sources and detectors being developed at a rapid pace. Yet, ultrafast THz communication is still to be realised, owing to the lack of practical and effective THz modulators. Here, we present a novel ultrafast active THz polarization modulator based on GaAs semiconductor nanowires arranged in a wire-grid configuration. We utilise an optical pump--terahertz probe spectroscopy system and vary the polarization of the optical pump beam to demonstrate ultrafast THz modulation with a switching time of less than 5\,ps and a modulation depth of -8dB...
March 23, 2017: Nano Letters
Jin-Woo Han, Dong-Il Moon, M Meyyappan
Vacuum tubes that sparked the electronics era had given way to semiconductor transistors. Despite their faster operation and better immunity to noise and radiation compared to the transistors, the vacuum device technology has become extinct due to the high power consumption, integration difficulties and short lifetime of the vacuum tubes. We combine the best of vacuum tubes and modern silicon nanofabrication technology here. The surround gate nanoscale vacuum channel transistor consists of sharp source and drain electrodes separated by sub-50 nm vacuum channel with a source to gate distance of 10 nm...
March 23, 2017: Nano Letters
Mingyang Li, Yi Yang, Yichuan Ling, Weitao Qiu, Fuxin Wang, Tianyu Liu, Yu Song, Xiao-Xia Liu, Ping-Ping Fang, Yexiang Tong, Yat Li
High temperature activation has been commonly used to boost the photoelectrochemical (PEC) performance of hematite nanowires for water oxidation, by inducing Sn diffusion from fluorine-doped tin oxide (FTO) substrate into hematite. Yet, hematite nanowires thermally annealed at high temperature suffer from two major drawbacks that negatively affect their performance. First, the structural deformation reduces light absorption capability of nanowire. Second, this "passive" doping method leads to non-uniform distribution of Sn dopant in nanowire and limits the Sn doping concentration...
March 23, 2017: Nano Letters
Johannes Gooth, Mattias Borg, Heinz Schmid, Vanessa Schaller, Stephan Wirths, Kirsten E Moselund, Mathieu Luisier, Siegfried Karg, Heike Riel
Coherent interconnection of quantum bits remains an ongoing challenge in quantum information technology. Envisioned hardware to achieve this goal is based on semiconductor nanowire (NW) circuits, comprising individual NW devices that are linked through ballistic interconnects. However, maintaining the sensitive ballistic conduction and confinement conditions across NW intersections is a non-trivial problem. Here, we go beyond the characterization of a single NW device and demonstrate ballistic 1D quantum transport in InAs NW cross-junctions, monolithically integrated on Si...
March 23, 2017: Nano Letters
Fabian Schuster, Jonas Kapraun, Gilliard N Malheiros-Silveira, Saniya Deshpande, Connie J Chang-Hasnain
In this Letter, we report the site-controlled growth of InP nanolasers on a silicon substrate with patterned SiO2 nanomasks by low-temperature metal-organic chemical vapor deposition, compatible with silicon complementary metal-oxide-semiconductor (CMOS) post-processing. A two-step growth procedure is presented to achieve smooth wurtzite faceting of vertical nanopillars. By incorporating InGaAs multiquantum wells, the nanopillar emission can be tuned over a wide spectral range. Enhanced quality factors of the intrinsic InP nanopillar cavities promote lasing at 0...
March 23, 2017: Nano Letters
Federico Giberti, Márton Vörös, Giulia Galli
Heterogeneous nanostructures, such as quantum dots (QDs) embedded in solid matrices or core-shell nanoparticles, are promising platforms for a wide variety of applications, including phosphors with increased quantum yield, photocatalysis, and solar energy conversion. However, characterizing and controlling their interfacial morphology and defects, which greatly influence their electronic properties, have proven difficult in numerous cases. Here we carried out atomistic calculations on chalcogenide nanostructured materials, i...
March 23, 2017: Nano Letters
Kevin Chang, Alexander Eichler, Jan Rhensius, Luca Lorenzelli, Christian L Degen
Charge transport in nanostructures and thin films is fundamental to many phenomena and processes in science and technology, ranging from quantum effects and electronic correlations in mesoscopic physics, to integrated charge- or spin-based electronic circuits, to photoactive layers in energy research. Direct visualization of the charge flow in such structures is challenging due to their nanometer size and the itinerant nature of currents. In this work, we demonstrate non-invasive magnetic imaging of current density in two-dimensional conductor networks including metallic nanowires and carbon nanotubes...
March 22, 2017: Nano Letters
Jonas Christopher Rose, Maria Camara Torres, Khosrow Rahimi, Jens Köhler, Martin Moeller, Laura De Laporte
Injectable biomaterials provide the advantage of a minimally invasive application but mostly lack the required structural complexity to regenerate aligned tissues. Here, we report a new class of tissue regenerative materials that can be injected and form an anisotropic matrix with controlled dimensions using rod-shaped, magnetoceptive microgel objects. Microgels are doped with small quantities of superparamagnetic iron oxide nanoparticles (0.0046 vol%), allowing alignment by external magnetic fields in the millitesla order...
March 22, 2017: Nano Letters
Yue Lu, Yiliang Lin, Zhaowei Chen, Quanyin Hu, Yang Liu, Shuangjiang Yu, Wei Gao, Michael D Dickey, Zhen Gu
Effective endosomal escape remains as the "holy grail" for endocytosis-based intracellular drug delivery. To date, most of the endosomal escape strategies rely on small molecules, cationic polymers, or pore-forming proteins, which are often limited by the systemic toxicity and lack of specificity. We describe here a light-fueled liquid-metal transformer for effective endosomal escape-facilitated cargo delivery via a chemical-mechanical process. The nanoscale transformer can be prepared by a simple approach of sonicating a low-toxicity liquid-metal...
March 22, 2017: Nano Letters
Chen Yan, Xiaolong Wang, T V Raziman, Olivier J F Martin
Plasmonic antennas and planar structures have been undergoing intensive developments in order to control the scattering and absorption of light. One specific class, extrinsic chiral surfaces, that does not possess 2-fold rotational symmetry exhibits strong asymmetric transmission for different circular polarizations under obliquely incident illumination. In this work, we show that the design of those surfaces can be optimized with complex multipolar resonances in order to twist the fluorescence emission from nearby molecules...
March 22, 2017: Nano Letters
Patryk Kusch, Stefan Mastel, Niclas Sven Mueller, Nieves Morquillas, Sebastian Heeg, Roman Gorbachev, Fredrik Schedin, Uwe Huebner, Jose Ignacio Pascual, Stephanie Reich, Rainer Hillenbrand
Surface-enhanced Raman spectroscopy (SERS) enables sensitive chemical studies and materials identification, relying on electromagnetic (EM) and chemical-enhancement mechanisms. Here we introduce a tool for the correlative nanoimaging of EM and SERS hotspots - areas of strongly enhanced EM fields and Raman scattering, respectively. To that end, we implemented a grating spectrometer into a scattering-type scanning near-field optical microscope (s-SNOM) for mapping of both the elastically and inelastically (Raman) scattered light from the near-field probe - a sharp silicon tip...
March 21, 2017: Nano Letters
Gene Siegel, Cristian V Ciobanu, Badri Narayanan, Michael Snure, Stefan C Badescu
Growth of hBN on metal substrates is often performed via chemical vapor deposition from a single precursor (e.g., borazine) and results in hBN monolayers limited by the substrates catalyzing effect. Departing from this paradigm, we demonstrate close control over the growth of mono-, bi-, and trilayers of hBN on copper using triethylborane and ammonia as independent sources of boron and nitrogen. Using density functional theory (DFT) calculations and reactive force field molecular dynamics, we show that the key factor enabling the growth beyond the first layer is the activation of ammonia through heterogeneous pyrolysis with boron-based radicals at the surface...
March 21, 2017: Nano Letters
Haldun Sevincli
The critical points and the corresponding singularities in the density of states of crystals were first classified by Van Hove with respect to their dimensionality and energy-momentum dispersions. Here, different from saddle-point Van Hove singularities, the occurrence of a continuum of critical points, which give rise to strong singularities in two-dimensional elemental hexagonal lattices, is shown using a minimal tight-binding formalism. The model predicts quartic energy-momentum dispersions in spite of quadratic or linear ones, which is also the origin of the strong singularity...
March 20, 2017: Nano Letters
Zheng Xi, Daniel P Erdosy, Adriana Mendoza-Garcia, Paul N Duchesne, Junrui Li, Michelle Muzzio, Qing Li, Peng Zhang, Shouheng Sun
We synthesize a new type of hybrid Pd/WO2.72 structure with 5 nm Pd nanoparticles (NPs) anchored on 50 x 5 nm WO2.72 nanorods (NRs). The strong Pd-WO2.72 coupling results in the lattice expansion of Pd from 0.23 nm to 0.27 nm and the decrease of Pd surface electron density. As a result, the Pd/WO2.72 shows much enhanced catalysis towards electrochemical oxidation of formic acid in 0.1 M HClO4 - it has a mass activity of ~1600 mA/mgPd in a broad potential range of 0.4-0.85 V (vs. RHE) and shows no obvious activity loss after a 12 h chronoamperometry test at 0...
March 20, 2017: Nano Letters
Toan Trong Tran, Danqing Wang, Zaiquan Xu, Ankun Yang, Milos Toth, Teri W Odom, Igor Aharonovich
Quantum emitters in two dimensional materials are promising candidates for studies of light-matter interaction and next generation, integrated on-chip quantum nanophotonics. However, realization of integrated nanophotonic systems requires coupling of emitters to optical cavities and resonators. In this work, we demonstrate hybrid systems in which quantum emitters in 2D hexagonal boron nitride (hBN) are deterministically coupled to high quality plasmonic nanocavity arrays. The plasmonic nanoparticle arrays offer a high quality, low loss cavity in the same spectral range as the quantum emitters in hBN...
March 20, 2017: Nano Letters
Dao Xiang, Jian Wu, Reuven Gordon
Tunnel resistance can be modulated with bias via the Coulomb blockade effect, which gives a highly nonlinear response current. Here we investigate the optical response of a metal-insulator-nanoparticle-insulator-metal structure and show switching of a plasmonic gap from insulator to conductor via Coulomb blockade. By introducing a sufficiently large charging energy in the tunnelling gap, the Coulomb blockade allows for a conductor (tunneling) to insulator (capacitor) transition. The tunnelling electrons can be delocalized over the nanocapacitor again when a high energy penalty is added with bias...
March 20, 2017: Nano Letters
F Hartmann, P Maier, M Rebello Sousa Dias, S Göpfert, L K Castelano, M Emmerling, C Schneider, S Höfling, M Kamp, Y V Pershin, G E Marques, V Lopez-Richard, L Worschech
Electronic circuits composed of one or more elements with inherent memory, that is, memristors, memcapacitors, and meminductors, offer lower circuit complexity and enhanced functionality for certain computational tasks. Networks of these elements are proposed for novel computational paradigms that rely on information processing and storage on the same physical platform. We show a nanoscaled memdevice able to act as an electronic analogue of tipping buckets that allows reducing the dimensionality and complexity of a sensing problem by transforming it into a counting problem...
March 20, 2017: Nano Letters
Lauren E Marbella, Xing Yee Gan, Derrick C Kaseman, Jill E Millstone
Recently, a wide variety of new nanoparticle compositions have been identified as potential plasmonic materials including earth-abundant metals such as aluminum, highly doped semiconductors, as well as metal pnictides. For semiconductor compositions, plasmonic properties may be tuned not only by nanoparticle size and shape, but also by charge carrier density which can be controlled via a variety of intrinsic and extrinsic doping strategies. Current methods to quantitatively determine charge carrier density primarily rely on interpretation of the nanoparticle extinction spectrum...
March 17, 2017: Nano Letters
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