Horizontal Nanowires Research Articles

A Method to Determine the Strain and Nucleation Sites of Stacked Nano-Objects

We determine the compositional distribution with atomic column resolution in a horizontal nanowire from the analysis of aberration-corrected high resolution Z-contrast images. The strain field in a layer capping the analysed nanowire is determined by anisotropic elastic theory from the resulting compositional map. The reported method allows preferential nucleation sites for epitaxial nanowires to be predicted with high spatial resolution, as required for accurate tuning of desired optical properties. The application of this method has been exemplified in this work for stacked InAs(P) horizontal nanowires grown on InP separated by 3 nm thick InP layers, but we propose it as a general method to be applied to other stacked nano-objects.

The growth of ultralong and highly blue luminescent gallium oxide nanowires andnanobelts, and direct horizontal nanowire growth on substrates

We report the growth of ultralongβ-Ga2O3 nanowires and nanobelts on silicon substrates using a vapor phase transport method. Thegrowth was carried out in a tube furnace, with gallium metal serving as the gallium source.The nanowires and nanobelts can grow to lengths of hundreds of nanometers and evenmillimeters. Their full lengths have been captured by both scanning electronmicroscope (SEM) and optical images. X-ray diffraction (XRD) patterns andtransmission electron microscope (TEM) images have been used to study the crystalstructures of these nanowires and nanobelts. Strong blue emission from these ultralongnanostructures can be readily observed by irradiation with an ultraviolet (UV)lamp. Diffuse reflectance spectroscopy measurements gave a band gap of 4.56 eVfor these nanostructures. The blue emission shows a band maximum at 470 nm.Interestingly, by annealing the silicon substrates in an oxygen atmosphere to form a thickSiO2 film, andgrowing Ga2O3 nanowires over the sputtered gold patterned regions, horizontalGa2O3 nanowiregrowth in the non-gold-coated regions can be observed. These horizontal nanowires can grow to as longas over 10 µm in length. Their composition has been confirmed by TEM characterization. This representsone of the first examples of direct horizontal growth of oxide nanowires on substrates.

Synthesis and Properties of High-Quality InN Nanowires and Nanonetworks

We report on the growth of high-quality InN nanowires by the vapor–liquid–solid mechanism at rates of up to 30 μm/h. Smooth and horizontal nanowire growth has been achieved only with nanoscale catalyst patterns, while large-area catalyst coverage resulted in uncontrolled and three-dimensional growth. The InN nanowires grow along the [110] direction with diameters of 20 to 60 nm and lengths of 5 to 15 μm. The nanowires bend spontaneously or get deflected from other nanowires at angles that are multiples of 30°, forming nanonetworks. The gate-bias-dependent mobility of the charge carriers ranges from 55 cm2/V s to 220 cm2/V s, and their concentration is ∼1018 cm−3.

Self-organized ZnAl2O4 nanostructures grown on -sapphire

Abstract Self-organized ZnAl2O4 nanostructures with the appearance (in SEM) of high aspect ratio horizontal nanowires are grown on uncatalysed c -sapphire by vapour phase transport. The nanostructures grow as three equivalent crystallographic variants on c -sapphire. Raman and cathodoluminescence spectroscopy confirm that the nanostructures are not ZnO and TEM shows that they are the cubic spinel, zinc aluminate, ZnAl2O4, formed by the reaction of Zn and O with the sapphire substrate.

Epitaxial growth of aligned GaN nanowires and nanobridges

AbstractHomo‐epitaxialy grown aligned GaN nanowires were prepared on crystalline GaN mesas. The GaN nanowires showed preferential growth along the 〈10$ \bar 1 $0〉 direction (m‐axis direction). By using selectively positioned and crystallographically well defined GaN epitaxial lateral overgrowth (ELO) mesas as substrate, we obtained horizontally aligned GaN nanowires, in comb‐like arrays and hexagonal network interconnecting the ELO mesas. Preliminary testing of the nanomechanical behavior of horizontal nanowires is reported. Combination of ELO with nanowire synthesis is expected to provide a new paradigm for nano‐electronic and electromechanical devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and Characterization of High Quality InN Nanowires and Nano-networks

ABSTRACTHigh quality InN nanowires have been synthesized in a horizontal quartz-tube furnace through direct reaction between metallic Indium and Ammonia using Nitrogen as the carrier gas. Thin film of Au on SiO2/Si substrate has been used as the catalyst layer, facilitating vapor-liquid-solid growth of the nanostructures. The nanowires were grown at a very fast rate of up to 30 μm/hr. Smooth and horizontal nanowire growth was achieved only with nanoscale catalyst patterns, while large area catalyst coverage resulted in uncontrolled and three-dimensional growth. The InN nanowires, which were usually covered with a thin shell layer of In2O3, grew along [110] direction, with overall diameters 20 - 60 nm and lengths 5 - 15 μm. The synthesized nanowires bent spontaneously or got deflected from other nanowires at multiples of 30 degrees forming nano-networks. The catalyst particles for the NWs were found mostly at the sides of the NW apex which helped them to bend spontaneously or get deflected from other NWs at angles which were multiples of 30 degrees. The NW based FETs with a back-gated configuration have already been investigated. The gate-bias dependent mobility of the NWs ranged from 55 cm2/Vs to 220 cm2/Vs, and their carrier concentration was ∼1018 cm−3.

Directed growth of horizontal silicon nanowires by laser induced decomposition of silane

We present an original method to force the horizontal growth of silicon nanowires by laser assisted chemical vapor deposition of silane. The Ar+ laser beam, tightly focused on the absorbing sample, induces a local thermal horizontal gradient over the laser spot area, which determines the growth direction of the nanowires (NWs). The reaction of formation of Si NWs occurs via the vapor-liquid-solid process, when gold particles are spread on the surface to catalyze the reaction. The effect of laser power (i.e., of laser induced local temperature) and silane pressure on the morphology of the nanowires is presented.

Silicon Vertically Integrated Nanowire Field Effect Transistors

Silicon nanowires have received considerable attention as transistor components because they represent a facile route toward sub-100-nm single-crystalline Si features. Herein we demonstrate the direct vertical integration of Si nanowire arrays into surrounding gate field effect transistors without the need for postgrowth nanowire assembly processes. The device fabrication allows Si nanowire channel diameters to be readily reduced to the 5-nm regime. These first-generation vertically integrated nanowire field effect transistors (VINFETs) exhibit electronic properties that are comparable to other horizontal nanowire field effect transistors (FETs) and may, with further optimization, compete with advanced solid-state nanoelectronic devices.

Growth habits and defects in ZnO nanowires grown on GaN/sapphire substrates

Growth habits and defects in epitaxial ZnO nanowires grown from Au catalyst on (00.1) GaN/sapphire substrate using the vapor-liquid-solid (VLS) technique were studied using electron microscopy and x-ray diffraction. The results revealed presence of both horizontal (crawling-like) and vertical nanowires having similar orientation relationship to the substrate (00.1)ZnO‖(00.1)GaN, [11.0]ZnO‖[11.0]GaN. The crawling-like growth precedes the vertical growth, and the coalescence and overgrowth of the crawling nanowires produce a highly defective layer which separates the substrate and vertical nanorods. Transmission electron microscopy revealed a high density of planar defects in this interfacial layer. A significant density of stacking faults residing on the (0001) planes was also observed in the shorter vertical nanorods. The crawling nanowires are under residual compressive strain, whereas the vertical nanorods grow strain-free.