Vapor phase growth of alumina whiskers by hydrolysis of aluminum fluoride

The vapor phase growth of alumina whiskers by the hydrolysis of aluminium flouride has been studied at an elevated temperature. The product was obtained in various forms: wool-like whiskers, needle-like whiskers, jointed needle-like crystals which consisted of linked small single crystals, tightly coagulated powder or as thin film covering the substrate. Aluminium oxi-fluoride was suggested as the intermediate gaseous species in the formation of alumina. The relation between the growth mechanism and crystal morphologies was studied.     

Growth and Morphology of Hollow Bi2Te3 Whiskers by Physical Vapour Deposition Method

Hollow crystals of bismuth telluride have been grown by the physical vapour deposition (PVD) method. Whisker crystals as long as 10 mm have been grown and were identified by X-ray analysis. The possible mechanism for the growth of hollow whiskers has also been suggested.     

Synthesis of bamboo‐like SiC whiskers from waste silica fume

A process for the utilization of wasted silica fume is proposed in this work. Silicon carbide (SiC) whiskers several tens of micrometers in length and with a bamboo‐like morphology have been successfully synthesized by a carbothermal reduction process using purified silica fume as the silicon source. The morphology and structure of SiC whiskers were investigated by X‐ray diffraction, Raman spectroscopy, scanning electron microscopy, and high‐resolution transmission electron microscopy. Studies found that the as‐synthesized whiskers were grown as single‐crystalline β‐SiC along the (111) growth direction. The whiskers consisted of hexagonal stems randomly decorated with larger‐diameter knots along their whole length. On the basis of the characterization results, a vapor–solid process was discussed as a possible growth mechanism of the β‐SiC whiskers.     

Study of the evaporation mechanism in silicon carbide crystals growth from vapour phase

Investigation of the thermal etching (evaporation) of the source material in the process of silicon carbide crystal growth from the vapour phase by the sublimation method has been carried out. It has been established that silicon carbide etching in the temperature interval (2200–2600) °C takes place with the formation of whiskers of evaporation. The mechanism of their formation has been examined and the character of the whisker distribution in the charge of the source silicon carbide has been studied.     

Catalytic epitaxy of ZnO whiskers via the vapor–crystal mechanism

A model of oriented growth of (0001) ZnO whiskers on sapphire substrates via the vapor–crystal mechanism using the catalytic properties of gold islands is proposed. The morphological transition from the primary pyramidal ZnO structures to hexagonal ZnO whiskers is described in terms of the minimization of the free energy density of three-dimensional heteroepitaxial islands.     

Sodium acetate tri-hydrate whiskers

A new kind of whisker, which has not been previously reported in the literature, was grown on membranes which were in contact with a saturated aqueous solution of sodium acetate, using several techniques. Cellulose acetate membranes were used in all the cases and growth was successful at 25 ± 2°C and 45–55% relative humidity. A dense colony of whiskers, sometimes stuck together in bundles, usually up to 5 cm in length and ranging in width from 0.3–100 μm, developed within 72 h of growth. The whiskers were identified as sodium acetate tri-hydrate by means of Debye-Scherrer X-ray powder method. Laue transmission photographs indicated the existence of twin crystals within the individual single crystal whiskers as proved by electron diffraction in TEM. Some whiskers included internal and external channels, and there were several secondary effects, such as thickening in the middle of a whisker, formation of arrow-heads or spirals at the tips and various modes of branching. The whisker morphology and the various growth phenomena may be explained as a whisker growth process from their bases, when we consider a continuous crystallization from material which is supplied through and over the membrane.     

Growth of tungsten whiskers oriented in <111> direction

The electron micro diffraction technique and pseudopotential ab initio calculations were implemented to study in details the formation and mechanism of growth of the tungsten whiskers during the reduction of nickel tungstate by CO gas. It has been shown that the W whiskers prefer to grow as crystals oriented in the <111> direction, and this process may be considered as the epitaxial growth on the hexagonal planes of Ni₄W particles. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of copper aluminum borate whiskers via flux method

Single‐crystal and uniform copper aluminum borate whiskers have been synthesized by heating a mixture of boric acid, copper sulfate and aluminum sulfate with potassium sulfate as flux at 870 °C for 4 h. The synthesized whiskers exhibit a well‐crystallized, one‐dimensional structure with diameters ranging from 100 nm to 5 μm, lengths from 5 to 100 μm. Heating temperature and flux addition affect the aspect ratio and morphology of the copper aluminum borate whiskers. A possible growth mechanism of the whiskers is proposed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Controlled growth of filamentary crystals and fabrication of single-crystal whisker probes

The growth of filamentary crystals (whiskers) on a single-crystal substrate through the vapour-liquid-solid mechanism is described. The possibility of fabricating oriented systems of whiskers on the basis of this mechanism of crystal growth is noted. A phenomenon that is important for nanotechnology is noted: the existence of a critical diameter of whiskers, below which they are not formed. The phenomenon of radial periodic instability, which is characteristic of nanowhiskers, is described and the ways of its elimination are shown. The possibility of transforming whiskers into single-crystal tips and the growth of crystalline diamond particles at their apices are noted as important for practice. Possible applications of systems of whiskers and tips are described briefly. Particular attention is paid to the latest direction in whisker technology—fabrication of single-crystal whisker probes for atomic force microscopy.     

Fundamental aspects of VLS growth

The kinetics and the mechanism of the vapor-liquid-solid (VLS) growth are discussed. Emphasis is placed on the dependence of the growth rate on the whisker diameter. It is found that the rate decreases abruptly for submicron diameters and vanishes at some critical diameter d_c ? 0,1 μm according to the Gibbs-Thomson effect. A new method for simultaneous determination of kinetic coefficients and of supersaturations has been developed. The method can be used to measure the coefficients of some materials as well as the temperature dependence of the coefficient for silicon and the activation energy of the process. From the dependence of supersaturation on the diameter we conclude that whiskers grow by a poly-nuclear mechanism. The periodic instability of the diameter is discussed and the rate-determining step is analysed. We conclude that phenomena on the liquid-solid interface are the decisive ones. In determining the role of liquid phase in vapor growth we measured the “liquid phase effectivity coefficient” as a function of crystallization condition; the coefficient typically was about 10²?10³. It is stressed that the liquid phase reduces the activation energy both on vapor-liquid interfaces (for chemical reactions) and on liquid-solid interfaces (for nucleation). The liquid phase ensures growth rates as high as 1 cm/sec, provided there are no barriers between the interfaces. The growth mechanism of the side faces was studied, and it was observed that the faces grow mainly by a chain mechanism rather than by two-dimensional nucleation. In work on surface diffusion in the VLS whiskers growth by CVD, we found that the whiskers grow mainly by direct deposition rather than by diffusion on the side faces. It is concluded that the VLS mechanism is important also for the vapor growth of platelets, films, and bulk crystals.     

Growth Mechanism in Atomic Layer Epitaxy (I) Re-evaporation of Cd and Te from CdTe(111) Surfaces Monitored by Auger Electron Spectroscopy

The mechanism of atomic layer epitaxy (ALE) of cadmium telluride has been studied. Auger electron spectroscopy is used to measure the isothermal re-evaporation rates of elemental Cd and Te deposits on the (111)A and (111)B surfaces of CdTe substrates. The results include an observation that the sticking coefficients of Cd and Te are smaller than unity at the growth temperatures typical of CdTe ALE. After desorption the substrates are left partially covered: 35% by a Cd overlayer on the (111)B surface and 72% by Te on the (111)A surface. The re-evaporation rates of Cd and Te experience a drastic change near the substrate-deposit interface. These rates appear two orders of magnitude smaller than those of bulk-like amorphous Cd and Te solids. The activation energies for reevaporation of the near-interface layer region are estimated to be: 1.5 eV for Te on the (111)A face, 1.0 eV for Te on (111)B and 0.5 eV for Cd on (111)B. It has also been shown that AES can be used to identify the polarity of the CdTe(111) surfaces. The relative difference in peak-to-peak intensity ratios of Cd MNN to Te MNN for (111)A and (111)B is (11 ± 2)%.     

Über das Wachstum von Silberamalgamwhiskern

The growth of whiskers from silver amalgam is investigated; The whiskers grew in aqueous solution on mercury surface by means of one kind of internal electrolysis. They possess the shape of hexagonal capillary tubes filled with mercury. A potentiostatic method has been developed for measuring supersaturation, resp. overvoltage during the whisker growth. The same method permitted the experimentator lightly to rule the whisker growth process.     

Growth mechanism of copper whiskers by the hydrogen reduction of cuprous iodide

A small quantity of cuprous iodide (less than 30 mg) was reduced by hydrogen at 650 or 700°C for various periods of time (15 sec to 4 min) and quenched to interrupt whisker growth. This was done in order to examine the nature of the growth of copper whiskers. Scanning electron microscopic observation and X-ray microanalysis revealed that almost all the whiskers quenched after the growth for 30 sec or less had cuprous iodide droplets at their tips and also the lateral surfaces were covered by thin cuprous iodide layers. The manner in which the copper crystals grow is similar to growth by the droplet mechanism or by the VLS mechanism in that the nutrient is supplied by a liquid drop on the tip of the whisker. Whiskers thicken during and after the growth in length. The whiskers quenched after the growth for 1 min or more had well-developed lateral surfaces and did not have the droplets at the tips. Preferential condensation and reduction were found to occur at the whisker edges. Based on the observed facts, a growth mechanism is presented. Secondary whisker growth on the whisker tips was also investigated.     

六钛酸钾晶须的制备及生长机理的研究

通过KDC方法成功制备了六钛酸钾(K2Ti6O13)晶须,并进行了热重分析和差热分析,研究烧结时间和烧结温度对K2Ti6O13晶须结晶过程的影响,通过X射线衍射分析了K2Ti6O13晶须的相组成和晶体指数.此外,通过扫描电子显微镜和透射电子显微镜研究晶须的微观结构,揭示了K2Ti6O13晶须的生长机理.     

Ti-Al-Nb2O5系原位合成Al2O3晶须的形成机理分析

本文研究了以粉埋法原位合成的Al2O3晶须的形态和反应过程以及晶须的生长机理.通过物相测试表明产物由Al2O3、TiAl3、NbAl3和少量的AlN相组成,SEM结合EDS分析表明原位合成了直径小于100nm的Al2O3晶须,晶须呈棉絮状分布于基体交界处.基于铝的过剩,TiAl3相是Ti-Al界面的唯一产物.Ti与O2以反应时间短的动力学势优先形成的TinOm中间产物是Al2O3晶须生成的控制步骤.Nb2O5与铝液的双效复合催化作用,提高了晶须的生成速率;同时Al的用量因AlN的生成而减小,导致生成晶须的催化活性点减小,而扩散到每个活性点周围的TinOm及Nb2O5浓度增加,导致晶须分布密而均匀.Al2O3晶核在催化剂的作用下以螺旋位错生长形成长径比较为理想的Al2O3晶须.     

Microstructure and optical properties of phase-change Ge–Sb–Te nanoparticles grown by pulsed-laser ablation

Phase-change Ge–Sb–Te (GST) nanoparticles have been in-situ synthesized by a pulsed-laser ablation method. During the ablation process, growth parameters including temperature of heat treatment, pressure, and laser fluence are extensively explored. Scanning and transmission electron microscopy are used to study microstructure and phase formation of the nanoparticles. Fourier transform analysis of electron micrographs exhibits an evidence of existence of the stoichiometric single GST-225 phase. We have measured micro-Raman scattering spectra of commercially available GST-124, -147, and -225 bulk and GST nanoparticles. Lack of the amorphous Te–Te stretching mode near 150 cm⁻¹ from the Raman spectra of the bulk samples indicates that the samples are well-crystallized. From the measurements of GST nanoparticles with different growth conditions, we could get information towards the optimal growth conditions for better crystalline quality of the GST nanoparticles. Our results suggest that micro-Raman scattering spectroscopy can be used to study phases and phase changes in the GST bulk crystals and nanoparticles through local structural information, which is being developed for low-power non-volatile memory applications.     

Oriented growth of whiskers of AIIIBV compounds by VLS-mechanism

The oriented growth of GaAs, GaP, InAs and GaInAs whiskers on the same (GaAs, GaP) or different (InAs/GaAs, GaInAs/GaAs) substrates was studied. A detailed morphological study of GaAs whiskers on polar A(III), B(111 ) and non-polar (001), (011) substrates was performed. The growth conditions for ordered (perpendicular to substrate) growth on the A(111) and B(111 ) faces were determined. There were found discrete spectra of whisker systems on all substrates with the preferential growth of “arsenic” B{111 } faces. The dependence of the growth rate on the whisker diameter is typical for the vapour-liquid-solid (VLS) mechanism and is used for the determination of kinetic coefficients for polar faces. There was observed a periodic instability in growth of InAs and GaInAs whiskers.     

Vapor-phase growth of CdF<Subscript>2</Subscript> whiskers in the CdF<Subscript>2</Subscript>-GaF<Subscript>3</Subscript> system

Insulating CdF₂ whiskers of helical shape with a diameter from 10 to 30 μm and a length exceeding 7 mm have been grown for the first time. The conditions of their growth suggest that they grow through the classical vapor-liquid-solid mechanism.     

H2SO4-H2O中硝酸铜对脱硫石膏晶须生长的影响

以处理后的脱硫石膏为原料,在H₂SO₄-H₂O体系中以Cu(NO₃)₂为晶形控制剂采用水热法制备脱硫石膏晶须,探讨了Cu(NO₃)₂对脱硫石膏晶须生长的影响机理。结果表明:Cu(NO₃)₂对脱硫石膏有明显促溶作用,其中Cu²⁺可减小溶液中各离子的活度系数,使溶液中的Ca²⁺浓度增大。NO^-₃通过静电作用在Ca²⁺周围聚集并对SO^2-₄产生屏蔽作用,导致脱硫石膏继续溶解并使Ca²⁺和SO^2-₄的浓度处于相对稳定状态,有利于半水脱硫石膏晶体的形核与生长。此外,Cu²⁺还可在晶须的生长过程中选择性吸附在晶须表面,生成CuSO₄,促进了脱硫石膏的结晶生长,最终在Cu(NO₃)₂用量为2.0%(质量分数)时制备的脱硫石膏晶须长径比约为73。     

Growth and characterization of SSD InP crystals used as substrates for infra-red LED's

Bulk indium phosphide crystals have been grown by the synthesis, solute diffusion (SSD) method. Various growth temperatures and temperature gradients in the indium melt were investigated. The growth temperature of about 850–900°C and the temperature gradient of about 10–15°C cm⁻¹ were found as the most suitable growth conditions. All grown crystals were of the n-type either undoped or doped with Te or Sn. Infrared light-emitting junctions were grown by single LPE process. Characteristic surface structures of InP epitaxial layers as a function of the growth temperature and cooling rate were observed. Efficiencies of LED's have been typically 0.8%. Single LPE process on LEC InP substrates has given LED's with substantially lower efficiencies.