Maoqi He

Growth of large-scale GaN nanowires and tubes by direct reaction of Ga with NH3

Large-scale wurtzite GaN nanowires and nanotubes were grown by direct reaction of metal gallium vapor with flowing ammonia in an 850–900 °C horizontal oven. The cylindrical structures were as long as 500 μm with diameters between 26 and ∼100 nm. Transmission electron microscopy, scanning electron microscopy, and x-ray diffraction were used to measure the size and structures of the samples. Preliminary results show that the size of the nanowires depends on the temperature and the NH3 flow rate. The growth mechanism is discussed briefly. The simple method presented here demonstrates that GaN nanowires can be grown without the use of a template or catalyst, as reported elsewhere.

Growth of GaN nanowires by direct reaction of Ga with NH3

Semiconducting, single crystal wurtzite GaN nanowires have been grown by direct reaction of metal Ga with NH3 in a tube furnace. This paper discusses the growth mechanism. Nanowires grow only between 8251C and 925 o C. Their diameters vary between 20 and 150 nm and depend directly on temperature and NH3 flow rate. Wires as long as 500mm have been fabricated; once wires have formed, their length increases directly with time in the reactor. There are three different stages in the process, each of which has its own mechanism. First, a nearly amorphous GaN matrix forms, followed by growth of hillocks of thin GaN platelets. Finally, nanowires emerge from the edges of the platelets in characteristic directions. This analysis can be used as a guide for controlling GaN wire diameters and lengths. Strategies for growth of thinner and thicker nanowires are suggested. Thicker cylindrical structures denoted as rods grow from the face of the platelets. Description of their growth mechanism requires further study. r 2001 Elsevier Science B.V. All rights reserved.

InAs nanowires and whiskers grown by reaction of indium with GaAs

Free-standing InAs nanowires and whiskers were grown employing reaction of indium (In) liquid and vapor with GaAs substrate. The arsenic (As) atoms resulting from this reaction were transported by a flow of N2 or NH3 to the growth location where they reacted with In to produce InAs nanowires and whiskers. Scanning electron microscopy, energy dispersive x-ray spectroscopy, and transmission electron microscopy of the products indicate that the diameter of the nanowires and whiskers ranges from 15 nm to 2 μm depending on the growth temperature, the composition is InAs, and the structure is zinc-blende crystal with [110] or [100] growth direction. The As source and growth mechanism were discussed. The method for synthesis involved no any template, catalyst, toxic As source, nor even lattice matched substrate.

Electronic and Structural Characteristics of Zinc-Blende Wurtzite Biphasic Homostructure GaN Nanowires

We report a new biphasic crystalline wurtzite/zinc-blende homostructure in gallium nitride nanowires. Cathodoluminescence was used to quantitatively measure the wurtzite and zinc-blende band gaps. High-resolution transmission electron microscopy was used to identify distinct wurtzite and zinc-blende crystalline phases within single nanowires through the use of selected area electron diffraction, electron dispersive spectroscopy, electron energy loss spectroscopy, and fast Fourier transform techniques. A mechanism for growth is identified.

Novel chemical-vapor deposition technique for the synthesis of high-quality single-crystal nanowires and nanotubes.

The strength and versatility of a chemical-vapor deposition technique for thin, long, uniform, single-crystal, good-quality nanowire growth, without the use of template, have been described. Remarkably, while the full width at half maximum of a high-quality GaN thin film is 4 meV, that of a GaN whisker is 9 meV, which confirms high quality of the grown whiskers and nanowires. The versatility of the method is reflected by its ability to produce II-VI and III-V binary, ternary, and even, for the first time, quaternary nanowires in a controlled manner. The same versatility enables the realization of both cubic and hexagonal phases of nanowires and nanotubes. Chemical-vapor deposition technique generally makes use of highly poisonous arsine and phosphine for the synthesis of As- and P-based films. The present one is free from this shortcoming; it can produce As- and P-based nanowires without the use of these poisonous gases. A notable feature of the method is that properties of nanowires thus synthesized depend strongly on their shape, size, and geometry, and that certain growth conditions can only lead to such shapes and sizes.

Reaction rates of the CN radical with diacetylene and dicyanoacetylene

Abstract Rates of CN reactions with diacetylene (DA) and dicyanoacetylene (DCA) have been measured at room temperature from the decay of the CN radical at various sample pressures by laser induced fluorescence. The rate constants are (4.2 ± 0.2) × 10 −10 and (5.4 ± 0.2) × 10 −13 in units of cm 3 molec −1 s −1 for DA and DCA, respectively, which follow the general pattern of CN reactions with hydrocarbons and nitriles. In the lower temperature circumstellar envelopes and Titans atmosphere, the CN reaction with C 4 H 2 may be more important, while the reaction with C 4 N 2 may become less important.

365nm operation of n-nanowire/p-gallium nitride homojunction light emitting diodes

The authors report gallium nitride (GaN) nanoscale light emitting diodes utilizing n-GaN nanowire/p-GaN substrate homojunctions. Utilizing electric field assisted alignment, n-type gallium nitride nanowires were placed on the surface of a p-doped GaN thin film. Electroluminescence with 365nm peak wavelength and 25nm full width half maximum was observed from these p-n junctions. These nanowire/epilayer p-n junction diodes were passivated with a thin layer of SiO2 and did not exhibit any parasitic emission related to the bulk or surface defects. The present fabrication scheme, utilizing only batch fabrication techniques, yields reliable, electrically injected nanoscale ultraviolet light sources.

Novelty and versatility of self-catalytic nanowire growth: A case study with InN nanowires

Various novel features have been discussed of the self-catalytic nanowire growth technique with application to InN nanowire growths. It is hard to grow InN nanowires due to the very low dissociation temperature (500–600°C) of InN and the very low dissociation rate of NH3 at this low temperature. However, scanning electron microscopy images show that the self-catalytic technique very efficiently produced long, uniform, single-crystal InN nanowires. Unlike most other methods, the technique is also versatile enough to produce a wide variety of nanowires standing and lying on the substrates. It is also useful to grow nanowires by the conventional vapor-liquid-solid formalism. Energy-dispersive spectroscopy showed that the composition of the nanowires is that of InN. X-ray diffraction patterns indicated that these nanowires had a pure hexagonal wurtzite structure.

Biphasic GaN nanowires: Growth mechanism and properties

Catalyst-free vapor-solid nanowire growth has been used to produce novel multiphase zinc-blende/wurtzite gallium nitride nanowires. Multiphase nanowire growth occurred at nanoscale nucleation sites on platelets of gallium nitride. Growth temperature has been shown to exert a strong influence on nucleation site formation. Scanning electron microscopy (SEM) was used to characterize the matrix from which the nanowires grew. Nanowires were characterized with transmission electron microscopy (TEM).

Phase separations of single-crystal nanowires grown by self-catalytic chemical vapor deposition method

The fundamentals of phase separations of single-crystal III-V nitride nanowires grown by self-catalytic chemical vapor deposition method have been studied. Experimental tools, such as high resolution transmission electron microscopy and scanning electron microscopy, have been used to characterize the nanowires. The study indicates that nanowires with diameters exceeding about 100 nm undergo phase transitions and/or crystal structure deterioration. The study highlights a relationship between the crystal structure and the kinetics of growth of nanowires.