Nonequilibrium statistical mechanical formulation for grain growth

A nonequilibrium statistical mechanical theory for grain growth is presented in this paper. The fluctuation of grain growth is determined from the self similarity of grain size distribution. The grain size distribution scaled by the averaged size is derived under the condition that the volume of specimen is strictly conserved. The growth law of grain is also derived. The scaled grain size distribution are compared with the associating lognormal distribution which is usually used in the analysis of the experimental results. It has been found that the theoretical results is in good agreement with experimental results.     

Ultra-large lateral grain growth by double laser recrystallization of a-Si films

A new double laser recrystallization technique that can produce ultra-large direction- and location-controlled lateral grains is presented. An excimer laser is combined with a pulse-modulated Ar⁺ laser to yield grains of tens of micrometers in size. The effect of different parameters on lateral grain growth is investigated. These parameters include the time delay between the two lasers, the excimer-laser fluence, the Ar⁺-laser power and the pulse duration. The process has a wide process window and is insensitive to both the excimer-laser fluence and the Ar⁺-laser power fluctuations. Preheating of the a-Si film with the Ar⁺ laser before firing the excimer laser is necessary for inducing lateral grain growth. The transient excimer-laser irradiation is believed to generate nucleation sites for initiating the subsequent lateral grain growth. The surface roughness of the recrystallized poly-Si is measured by atomic force microscopy. Received: 14 September 2000 / Accepted: 24 February 2001 / Published online: 27 June 2001     

Simulation of bimodal size distributions for coarsening

We introduce two very simple models to decribe coarsening. Both models possesses two characteristics: long range diffusive interaction and fluctuations. Computer simulations show that they lead to bimodal particle size distributions. The appearance of bimodal distribution can be related to a discontinuous particle growth rate.     

Carbon molecular sieves from PET for separations involving CH4, CO2, O2 and N2

Carbon molecular sieves (CMS) have been made for the first time from PET textile fibres by carbonisation and pore mouth narrowing using CVD of benzene. The diffusion of O₂, N₂, CO₂ and CH₄ in these materials, and also in the commercial CMS Takeda 3A, was studied. It was found that the best PET based CMS was obtained after 10 min CVD time and had adsorption capacities and rates of diffusion similar to those of the Takeda 3A.     

Recombination in steady supersonic flow in devices for laser isotope separation

We examine the kinetics of recombination in a weakly ionized, dilute, monatomic gas which is adiabatically expanding into vacuum. The hydrodynamic equations are solved exactly assuming; steady supersonic flow, maximal symmetry (isotropy), no heat conduction and no heating of the gas by the released recombination energy. This is applied to a problem which arises in the context of laser isotope separation.     

Enskog’s kinetic theory of dense gases for chemically reacting binary mixtures, II: Light scattering and sound propagation

Enskog’s kinetic theory for a symmetric moderately dense reaction A+A?B+B is used to determine Fick’s and Fourier’s law. The transport coefficients of diffusion, thermal-diffusion rate and thermal conductivity are represented graphically for endothermic and exothermic reactions and are analyzed as a function of the activation energy and of the density of the mixture. The Onsager reciprocity relations are numerically investigated and verified. The problems related to sound propagation and light scattering are investigated for such a mixture and it is shown that the influence of chemical reactions on phase velocity, attenuation coefficient and light scattering spectra is more pronounced for rarefied gases although there is a considerable change in these quantities as the mixture becomes denser.     

Conservative force fields in non-Gaussian statistics

In this Letter, we determine the κ-distribution function for a gas in the presence of an external field of force described by a potential U(r). In the case of a dilute gas, we show that the κ-power law distribution including the potential energy factor term can rigorously be deduced in the framework of kinetic theory with basis on the Vlasov equation. Such a result is significant as a preliminary to the discussion on the role of long range interactions in the Kaniadakis thermostatistics and the underlying kinetic theory.     

Preparation and microstructures of CoAg granular films with giant magnetoresistance

A series of Co _x Ag_1–x (0 x < 100 at.%) granular films were deposited onto glass substrates with the thickness on the order of 400 nm using the ion-beam cosputtering technique at different substrate temperatures. Systematical investigations were made on the Giant MagnetoResistance (GMR) effect and microstructures in these thin granular films. The magnetoresistance ratio strongly depends on cobalt concentration, substrate temperature, and the optimal value of GMR was observed in Co₂₂Ag₇₈ sample prepared at a temperature of 300 K. Microstructures of these films are closely related to the fabricating process, and thus influence the GMR.     

Fast solid-phase crystallization of amorphous silicon films on glass using low-temperature multi-step rapid thermal annealing

Effects of multi-step rapid thermal annealing of plasma-deposited amorphous silicon films on Corning 7059 glass are investigated. A three-step rapid thermal annealing for 10 s/step at 730° C after film deposition reduces the activation energy of electrical conductivity for silicon films from 0.64 to 0.51 eV and causes (111) grain growth with a size of 1500 Å, which is determined using scanning electron microscopy, Raman spectroscopy and X-ray diffractometry.     

Nanocrystalline-grained Bi-Sr-Ca-Cu-O and its superconducting property

Received: 5 August 1997/Accepted: 2 October 1997     

Beyond the Navier–Stokes equations: Burnett hydrodynamics

This work is mainly concerned with the extension of hydrodynamics beyond the Navier–Stokes equations, a regime known as Burnett hydrodynamics. The derivation of the Burnett equations is considered from several theoretical approaches. In particular we discuss the Chapman–Enskog, Grad’s method, and Truesdell’s approach for solving the Boltzmann equation. Also, their derivation using the macroscopic approach given by extended thermodynamics is mentioned. The problems and successes of these equations are discussed and some alternatives proposed to improve them are mentioned. Comparisons of the predictions coming from the Burnett equations with experiments and/or simulations are given in order to have the necessary elements to give a critical assessment of their validity and usefulness.     

Implementation of diffuse reflection boundary conditions in a thermal lattice Boltzmann model with flux limiters

We discuss three new implementation versions of diffuse reflection boundary conditions in a thermal lattice Boltzmann model. Their accuracy is investigated in the case of Couette flow by considering the slip regime. The best results are recovered with versions 2 and 3, which rely on outgoing fluxes to express the particle distribution functions in the ghost nodes outside the flow domain. Version 2 is found to be more economical since it involves no interpolation procedure. This version was thereafter used to investigate the temperature profile in Couette flow for various values of Prandtl number, as well as the capability of the thermal LB model to capture the Knudsen minimum in Poiseuille flow.     

Spontaneous growth of arsenic oxide micro-crystals on chemically etched MnAs surfaces

Micrometer-size crystals are observed to grow spontaneously on chemically etched MnAs surfaces. The wet chemical etching leaves a nearly exclusive pile of amorphous arsenic on the surface when the MnAs layer is etched incompletely. Using Raman spectroscopy, we identify that these micro-crystals are the arsenolite crystal of arsenic oxides. The manganese in the MnAs layer is oxidized by the hydrogen peroxide in the etch solution to MnO₂, which then works as the catalyst for the rapid oxidation and crystallization of the amorphous arsenic. Received: 14 November 2002 / Accepted: 18 November 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-30/20377-515, E-mail: takagaki@pdi-berlin.de     

Three related proposals for a theoretical definition of turbulence

We pull together some developments in turbulence research to make three propositions: (1) when the steady-state solution of any transport equation produces multi-valued velocity fields, the system described is turbulent, (2) turbulent-laminar transitions are marked by the occurrence of a singularity in the derivative of velocity with respect to time, (3) the onset of turbulence in noble gases may be described quantum mechanically using the cell model of a gas, producing two testable laws describing the critical pressure of a turbulent gas.     

Study of phase separation in Ti-Co-N thin films on silicon substrate

73 Co₂₇ and Ti₇₃Co₂₇- N during thermal annealing has been studied by SIMS, AES and XRD methods. It has been shown that in case of Ti₇₃Co₂₇ the CoSi₂ layer was not formed and the formation of ternary silicide compounds CoTiSi and Co₃Ti₂Si took place. At the same time in case of Ti₇₃Co₂₇- N the bottom layer CoSi₂ and the upper layer based on TiN were formed. The interaction behaviour has been found to depend on nitrogen concentration in initial film. For high amount of nitrogen the diffusion of Si atoms into upper layer and Si₃N₄ phase formation were observed. The possible variants of solid-phase interaction between silicon and the alloys containing intermetallic compounds and influence of nitrogen on this process are discussed. Received: 25 September 1996 / Accepted: 11 October 1996     

Crystal growth and dielectric, piezoelectric and elastic properties of Ca3TaGa3Si2O14 single crystal

Single crystals of Ca₃TaGa₃Si₂O₁₄ (CTGS) were successfully grown from stoichiometric melts by the conventional Czochralski technique. The relative dielectric constants, the piezoelectric strain constants and the elastic compliance constants of CTGS single crystal have been determined by an electric bridge and resonance-antiresonance method. At room temperature, the two piezoelectric strain constants d₁₁ and d₁₄ are −4.58×10⁻¹² coulombs per newton (C/N) and 10.43×10⁻¹² coulombs per newton (C/N), respectively. The velocities of the bulk acoustic wave are also calculated.     

Concerning bounds on the transport and mechanical properties of multicomponent composite materials

The Hashin-Shtrikman and Walpole bounds for the transport properties and bulk modulus of multicomponent composite materials are shown to be attained in a wide range of cases. Thus in these cases the bounds are the best possible bounds that can be given in terms of the properties of the components and the volume fractions. For three-component materials new bounds are conjectured. The conjectured bounds are presumed to apply in the cases where the Hashin-Shtrikman and Walpole bounds are not attained.     

Electrical resistivity and magnetostriction of nanocrystalline Fe-N-B ribbon

Because of the high saturation magnetization of nanocrystalline Fe_84.6N_7.8B_7.4 ribbon with α″-Fe₁₆N₂ nanocrystallites embedded in an amorphous matrix, its electrical resistivity and magnetostriction were studied to improve its soft magnetic properties. The prepared sample exhibits a higher electrical resistivity of 246 μΩ cm and a smaller saturation magnetostriction of 2.52 ppm. The present results indicate that nanocrystalline Fe_84.6N_7.8B_7.4 ribbon with α″-Fe₁₆N₂ phase is a good candidate for soft magnetic materials.