Grain growth mechanism in heavily arsenic-doped polycrystalline silicon

The mechanism of grain growth in heavily arsenic-doped polycrystalline silicon has been investigated by developing a kinetic model. A computer simulation technique has been used to determine the grain boundary self-diffusion of the silicon atoms and hence the grain size for different arsenic concentrations, annealing times and temperatures has been estimated. The evaluated numerical values are compared with the available experimental values. Using this model the grain size distribution in arsenic-doped polysilicon for various values of arsenic concentration, annealing time and temperature has been determined. The results are discussed in detail.     

A study of the phosphorescence mechanism of polycrystalline diamond films

A study of the phosphorescence mechanisms in polycrystalline diamond films was carried out through their thermoluminescent (TL) vanishing glow response. The polycrystalline diamond films phosphoresced when kept at room or higher temperatures after being excited with a UV light source. The observed behaviour of shallow and deep traps during the phosphorescence process can be explained with a simple time-dependent model. The diamond film phosphorescence was induced by exciting with a UV light source of 4 W and 254 nm wavelength. The TL vanishing glow curves were integrated from room temperature to 350°C at a linear heating rate of 10°C s^-1 in a N₂ atmosphere. The optical response of the diamond films was studied by means of its luminescence spectra, showing a broad emission band centered around 500 nm.     

Bulk growth of polycrystalline indium phosphide

The growth of polycrystalline indium phosphide of different grain sizes varying from 15μm to 4000μm has been discussed. The materials have been characterized by a variety of methods including electrical and optical techniques. Device application of the InP prepared was demonstrated by the fabrication of Ag Schottky diodes andp ⁺-n junction using Zn diffusion. The variation of mobility with varying grain size has been determined experimentally and the results interpreted taking into account the effect of compensation.     

A general treatment of creep crack growth

A theoretical model for creep crack based on energy balance criterion in the fracture process region is proposed in the present paper. A concept based on the dissipation of thermoelastic-plastic-creep flux into the fracture process region is introduced from which a generalized power integral C_g^* was derived. This integral when is used in conjunction with the tearing modulus and other material parameters can characterize the crack growth behaviour in solids subject to general thermomechanical loadings. The analytical results computed by the proposed model have shown excellent agreement with some experimental results published by other prominent researchers.     

Heterogeneous nucleation and growth of polycrystalline silicon

The heterogeneous nucleation theory of silicon on SiO₂ and Si₃N₄ substrates has been developed using classical theory. It is shown that the experimental observations can be explained on the basis of the bond energies of O-H, N-H and Si-H. A reaction model is proposed for the growth of silicon on silicon from silane, using hydrogen as a carrier gas in the temperature region 600–900°C. The growth rate of silicon is shown to be equal toP _{SiH 4} P _{H 2} when the partial pressure of hydrogen is high, and is independent of the total pressure and the partial pressure of hydrogen in the lower region.     

The mechanism of sliding friction wear in polycrystalline solids

A new micromechanical model describing the sliding friction wear of polycrystalline solids is proposed. The model is consistent with a hypothesis suggested previously, according to which the transition from intensive to moderate wear (for the nonconforming bodies in sliding friction contact) is related to attaining a definite, sufficiently small shear strain rate at the friction surface, depending on the absolute value of the normal force applied to the friction contact. In addition, the model explains some well-known empirical relationships between the wear intensity and friction coefficient for steel on steel in a wide range of loads and pressures in the friction contact.     

Modeling and visualization of polycrystalline thin film growth

A novel polycrystalline thin film growth simulator, FACET, has been developed. FACET is a multi-scale model with two major components: an atomic level one-dimensional kinetic lattice Monte Carlo (1D KLMC) model and a real time feature scale two-dimensional facet nucleation and growth model.

The 1D KLMC model has been developed to calculate inter-facet diffusion rates. By inputting the diffusion activation energies, the model will calculate the inter-facet atomic flux between {1 0 0}, {1 1 0}, and {1 1 1} facets of FCC materials at any temperature. The results of the 1D KLMC model have been verified by comparison with a full three-dimensional kinetic lattice Monte Carlo (3D KLMC) model.

The feature scale polycrystalline thin film nucleation and growth model is based on describing grains in terms of two-dimensional faceted surfaces and grain boundaries. The profile of the nuclei are described by crystallographically appropriate facets. The position and orientation of the nuclei can be randomly selected or preferred textures can be created. Growth rates are determined from different deposition fluxes and surface diffusion effects. Quantitative microstructural characterization tools, including roughness analysis, average grain size analysis, and orientation distribution analysis, were incorporated into the model, which allows the users to design, conduct and analyze the virtual experiments within one integrated graphical user interface. Users can also visualize the nucleation and growth process of the film and obtain the final film microstructure. The effects of thickness, temperature, and deposition flux on thin film microstructures have been studied by FACET.     

Conduction mechanism in sputtered polycrystalline zinc oxide thin films

Conductivity and Hall effect data are reported for columnar polycrystalline zinc oxide films between 1 and 4 μm thick deposited onto insulating substrates by r.f. reactive sputtering. Crystallites are (00.1) oriented, typically a few hundred nanometers in diameter and 98%–99% packed. Resistivities between 10⁷ and 10¹¹ Ω cm at 300 K typically decrease by between one and three orders of magnitude for a 100 K temperature increase. The shallow oxygen vacancy donor is the only impurity level present in significant densities; IR absorption indicates densities greater than 10¹⁷ cm^-3, but Hall measurements show apparent carrier concentrations of between 10⁴ and 10⁸ cm^-3.This anomaly is resolved by invoking the Petritz diode model of conduction in discontinuous materials, modified to include the case of highly doped crystallites and applied to zinc oxide with deplectively chemisorbed intercrystalline states. Quantitative agreement is found for conductivity against temperature. The measurable Hall carrier concentration, deduced from the empirical intracrystallite carrier densities of between 1 × 10¹⁵ and 1 × 10¹⁹ cm^-3 and barrier heights of between 0.6 and 1.2 eV, agrees well with Hall effect measurements. Crystallite surface state densities of about 10¹³ cm^-2 are indicated as responsible for these effects.     

Probabilistic description of fatigue crack growth in polycrystalline solids

A stochastic model describing the crack evolution and scatter associated with the crack propagation process has been built on the basis of the discontinuous Markovian process. The evolution and scatter are identified in terms of constant probability curves whose equation is derived as In P_r(i) = B(e^KI₀ − e^Ki), i ≥ I₀, where i is the number of cycles, B and K are crack-length-dependent variables, P_r(i) is the probabiliity of the crack being at position r along the fracture surface after i cycles elapse and I₀ is the minimum number of cycles required for the crack to advance from one position on the fracture surface to the next. The validity of the model is established by comparing the crack growth curves generated for Al 2024-T3 at a specific loading condition with those experimentally obtained.     

Flaw growth in a polycrystalline lithium-aluminium-silicate glass ceramic

The growth of indentation-produced controlled flaws in a polycrystalline lithium-aluminium-silicate glass ceramic has been studied, over a wide range of temperatures and strain rates. Significant scatter in the fracture stress at elevated temperatures suggests that the extent of slow crack growth is highly sensitive to microstructural details. The initial flaw shape is important inK _IC determination. Up to 1000° C the fracture toughness,K _IC, is essentially strain-rate insensitive. The value ofK _IC decreases with temperature beyond 850° C. Intergranular cavity formation is suggested as the reason. Crack blunting by diffusive crack healing probably occurs at high temperatures. Also, intergranular slow crack growth occurs essentially under Mode I loading.     

HF CVD diamond nucleation and growth on polycrystalline copper: A kinetic study

This paper reports on the kinetics of diamond nucleation and growth on polycrystalline copper investigated by in situ Auger Electron Spectroscopy and Scanning Electron Microscopy. Copper is a reference substrate to study the diamond nucleation from graphite. The substrate is first treated with diamond paste. However the diamond seeds let on the surface by the pre-treatment are almost completely transformed into graphite. The nucleation of CVD diamond can be well described in the framework of carbon phase transformations. Diamond seeds deposited on the substrate are first transformed into graphitic layers. A process occurring on the edges site of graphite is subsequently postulated, in agreement with the Lambrecht model.     

Cavity growth and grain boundary sliding in polycrystalline solids

A basic method is presented for the estimate of the overall mechanical response of solids which contain periodically distributed defects (inhomogeneities, regions undergoing inelastic flow, voids, and inclusions). This method is then applied to estimate the shape and growth pattern of voids that are periodically distributed over the grain boundaries in a viscous matrix. The interaction effects are fully accounted for, and the results are compared with calculations for a single void in an infinitely extended viscous solid, by Budiansky, Hutchinson, and Slutsky. Then, for a polycrystalline solid that undergoes relaxation by grain boundary sliding, the relaxed moduli are obtained, again fully accounting for the interaction effects. Finally, the overall inelastic nonlinear response at elevated temperatures is discussed in terms of a model which considers nonlinear power law creep within the grains, and linear viscous flow in the grain boundaries.     

Computer simulation of normal grain growth in polycrystalline thin films

A modified Monte Carlo method is proposed to simulate the two-dimensional normal grain growth in polycrystalline thin films. With the newly modified method, not only the simulation efficiency is improved but also the simulated time exponent of grain growth attained n = 0.49 ± 0.01, which is very close to the theoretical value for steady grain growth n = 0.5. Simulation of the complete process of normal grain growth including the steady state is made possible by means of the present method. The grain size distribution in the simulated thin films was found to vary continuously and slowly with time, the gamma and the Hillert functions may be two of the expression forms during its transition, and the latter corresponds to quasi steady grain growth. The so called self-similarity of the grain size distribution during the normal grain growth in two-dimensions is also discussed according to the simulation results.     

Grain growth and mechanical properties in bulk polycrystalline silicon

The grain structure of bulk polycrystalline silicon has been examined as a function of annealing temperatures and times between 1000 and 1400°C and 6 to 24 hours, respectively. The initial high aspect grain structure decomposes into roughly equiaxed grains at 1000°C over the course of 24 hours. The grains proceed to grow via Oswald ripening with an activation energy for grain growth of 1.49 eV. The hardness increases slightly during annealing and the subsequent transformation to an equiaxed grain structure, from a Vickers hardness of 964 to 1160 kg/mm². The fracture toughness is 0.8 MPa(m)^1/2in the as grown structure, and increases to 1 MPa(m)^1/2in annealed samples. The hardness and fracture toughness are independent of grain size for grain diameters between 2.7 and 4 m.     

The mechanism of plastic deformation of polycrystalline alloys in the initial micro-yield range

This article describes the results of a study of laws governing the distribution of strains in a possibly smallest region (a portion of a grain) of a polycrystalline alloy under stresses lower than the macroscopic yield point. Tensometric strain measurements were carried out on loaded specimens and their structure studied. The laws of micro-plastic strains in the latter deformation stages (i.e., under stresses higher than the yield point) were also investigated. It was postulated that the most effective strengthening of an alloy will be produced by treatments inhibiting the flow of the material in grain-boundary regions.     

A study of the growth mechanism of CVD-grown ZnO nanowires

ZnO nanowires were grown by CVD process using both pure Zn powder and a mixture of ZnO and graphite powders as the Zn source, and the key factors controlling nanowire growth were identified. In both processes, the partial pressure of zinc vapor determines the prevailing growth morphology and is sensitive to the growth conditions. In the case of Zn powder as the source, the predominant growth mechanism is driven by self-catalyzed growth on the Si substrate, and in the case of a mixture of ZnO and graphite used as the source, the formation of ZnO nanowires is controlled by the vapor–liquid-solid mechanism, where the gold particles serve as catalyst.