Growth Of Filamentary Crystals Research Articles

Kinetics of the growth of filamentary KH2PO4 crystals on a seed crystal

At oversaturations exceeding the inert range end for face {101} due to the presence of admixture Al(NO3)3 · 9H2O, a new phase is observed during the growth of this face in the form of filamentary crystals. Some experimental dependences of the growth rate of filamentary potassium dihydrophosphate (KH2PO4) crystals on the oversaturation have been obtained at different admixture concentrations. The growth of filamentary crystals occurs by the mechanism of two-dimensional nucleation. Their formation is governed by the effect of [AlHPO4]+ complexes in the form of Cabrera and Vermilyea stoppers.

Kinetics of formation of filamentary crystals at electrodeposition

Initial stages of nucleation and growth of filamentary crystals at the electrodeposition is considered. Time dependences of overpotential and the number and the size of filamentary crystals are simulated. The effect of current and electrolyte concentration on the kinetics of nucleation and growth of crystals is studied.

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.

Growth of filamentary KDP crystals from solution with the addition of Al(NO3)3 · 9H2O

To elucidate the mechanism of nucleation and growth of filamentary crystals on the bipyramid faces of KH2PO4 (KDP) crystals from solution with the addition of Al(NO3)3 · 9H2O, the growth rates and transverse dimensions of the crystals were measured at various supersaturations, temperatures, and impurity concentrations. The dependences obtained can be interpreted with due regard for the competition between the intrinsic and impurity particles in the presence of Cabrera-Vermilyea stoppers.

Torsion of prismatic elastic bodies containing screw dislocations

The problem of the stressed state of a prismatic anisotropic rod containing screw dislocations, the axes of which are parallel to the rod axis, is considered. Such defects may arise during the growth of filamentary crystals (metal “whiskers”), and may also exist in multiply connected cylindrical structures. The torsion of an anisotropic elastic bar with a multiply connected cross-section is investigated initially, assuming that the stresses and strains are single-valued but dispensing with the requirement that the warping function should be single-valued. The boundary-value problem is formulated in terms of the Prandtl stress function, which, unlike the warping function, is single-valued in a multiply connected region. A variational formulation of the boundary-value problem for the stress function is given. From the variational principle obtained a torsion boundary-value problem is formulated when there are lumped or continuously distributed dislocations. A modification of the membrane analogy for the torsion problem is proposed which takes into account the presence of dislocations. General theorems of the theory of the torsion of a rod containing dislocations are formulated. An effective formula is derived for the angle of torsion of a bar due to a specified dislocation distribution. Problems on dislocations in a thin-walled rod and a rectangular anisotropic bar are solved.

A quantitative study on the growth of silicon whiskers from silane and germanium whiskers from germane

The impurity-induced nucleation and the kinetics of the growth of filamentary crystals of silicon and germanium from silane and germane respectively have been studied in a closed system. Silicon whiskers were grown on heated substrates at temperatures between 550 and 900 °C, germanium whiskers at temperatures between 300 and 500 °C, both at hydride pressures between 5 and 100 Torr, and with Au as impurity. Whisker growth was also obtained with Ag, Cu, Ni and Pd, but not with In, Sn and Bi. The rates of growth of the whiskers in the length direction increase with increasing substrate temperature and hydride pressure, and are of the order of a hundred times higher than the rates of thickness growth of whiskers and substrate. As compared with the non-impurity aided deposition of Si and Ge from the hydrides, where there is an exponential relation between deposition rate and reciprocal temperature, the effect of the growth stimulus at the tip is reflected in a decrease of the activation energy and an increase in the pre-exponential factor. In terms of the VLS mechanism the catalyzed decomposition reaction at the V-L interface is the rate-controlling step.

Filamentary Crystal Growth Associated with Impact Craters from Hypervelocity Microparticles

A filamentary crystal growth is associated with impacts of hypervelocity microparticles upon copper foil. They are copper whiskers formed by the condensation of the target material vaporzied by the impact.

A Diffusion Model for Filamentary Crystal Growth

A surface diffusion model for filamentary crystal growth from the vapor phase is presented which accounts for extensive growth normal to the surface. The model is based on the mechanism by which adsorbed atoms are incorporated into surface steps and the anisotropy associated with the capture process. It is shown that filamentary crystals may be initiated at a variety of surface structures including dislocations or impurities but that neither of these is prerequisite. Rather, filamentary crystal growth depends on mobility differences of atoms adsorbed on various crystal planes and the mechanism of capture at surface steps. Results of computer calculations simulating filamentary crystal growth are presented.

Study of the Filamentary Growth of Silicon Crystals from the Vapor

The preparation from vapor and the structure of filamentary crystals of silicon have been studied in detail. It was found by chemical etching, by examination for a twist associated with a screw dislocation, and by observations in the electron microscope, that both ribbons and needles of small dimensions are free of dislocations and imperfections. Certain impurities such as gold, nickel, or platinum, however, are essential for the growth of filamentary crystals. The growth of micron size and larger whisker crystals from the vapor takes place in two stages. The first is a rapid extension in length of a leader-like crystal of small cross section; the second, a slow thickening of the leader through deposition on lateral faces. Initial growth is associated with impurities and does not require an axial screw dislocation. Subsequent growth may be explained by classical nucleation at a step and lateral translation of the step.