A comparison of the stochastic theory of the crystal growth and the Stefan problem

The stochastic theory of the crystal growth is compared with the solution of the Stefan problem in the case of Sn solidification. It is shown that the stochastic theory gives the same results as the solution of the Stefan problem if kinetic processes at the solidification front are very rapid.     

Calculation of the activation energy from the tsee peaks of MgO

In this paper the analysis of the TSEE curves of MgO is presented and two methods of the calculations of the activation energy and the frequency factor of the TSEE peaks of MgO are compared. There is good agreement concerning the activation energy of the trapping centres between the least squares method for the fitting of experimental and theoretical curves and the universal calculation method developed by de Muer.     

Non-stationary crystallization in simple glass-forming materials

A crystal distribution function is established during the crystallization process of simple glass-forming melts on the basis of the numerical computation of the kinetic equation in a non-stationary regime for constant and non-constant temperature. Nucleation rate and time-temperature-transformation curves are determined from the calculations of the crystal distribution function at various constant temperatures for various parameters of the system (the dependence on the difference of the chemical potentials, the dependence on the surface energy etc.).     

Dynamics of solidification in binary melts during rapid cooling II. Analysis of basic equations

In the first part of our paper we have derived a set of stochastic differential equations which describe the solidification of binary melts. The equations have been derived within the framework of the model in which the mass and heat transport and the kinetics of the phase transition is considered. In the second part of our paper we present the analysis of the set of general equations. On the basis of this analysis it will be obvious which approximations can be used for the solution of the basic equations in a particular regime of solidification. The adiabatic approximation is one of them. Another situation occurs when the thermodynamic conditions of the phase transformation change fast with time. The system not only moves away from thermodynamic equilibrium but also we can observe inertia of the system, which results in a delay of the evolution of the system respecting the steady-state regime (e.g. the nucleation processes) and the adiabatic approximation cannot be assumed. Concluding this paper, the method used in paper [13] to describe the nucleation in binary systems is presented as an example of the solution of the set of general equations in the case where the adiabatic approximation cannot be adopted.     

Twodimensional stochastic theory of crystal growth

In the paper the twodimensional model of the stochastic theory of crystal growth is presented and used for the study of the morphology of the solidification front under different external conditions and for different rates of kinetic processes on the solidification front. The results show that the stability of the solidification front depends on the kinetic processes, which thus must be taken into account in the stability conditions.     

The temperature dependence of some thermodynamical quantities of ferromagnetic alloys in the region of magnetic phase transition

This paper deals with the behaviour of ferromagnetic alloys in the region of magnetic phase transition. The temperature dependences of spontaneous magnetization, magnetic susceptibility and specific heat are discused. The theoretical results are compared with experimental data.I wish to thank Professor L.Valenta for his kind guidance and advice given to me during my work on this paper.     

Diffusion of Au atoms and (5×2) phase formation on the Si(111) (7×7) surface

In this article we investigate the complex 1D mesoscopic model of adatom diffusion and the evolution of an ordered phase on the substrate surface. The analysis of the theoretical model is compared with the experimental results of the spreading of Au adatoms on Si(111)-(7×7) surface. The steady state solutions and their stability conditions are determined within the concept of the traveling-wave solution. It is shown that the formation of the ordered phase (5×2) and the difference in the diffusion of Au on (7×7) and on (5×2) structure results in a sharp edge of diffusion front which corresponds to the coverage of a saturated (5×2) phase. This edge moves linearly in time and α can be determined by experiment. The system of model equations enables the damped waves solution or temporary evolution of two steps.     

Monte carlo simulations of growth modes of Pb nanoislands on Si(111) surface

The growth of Pb islands on a Si(111) surface exhibits many interesting properties. For example, the self-assembled process results in a homogeneous distribution of Pb islands with uniform height. The dependence of this height on coverage and temperature can be expressed as a phase diagram [1]. In this paper we develop a model of the growth process that reflects the main features of the experimental observations and determines the key processes of quantum dot formation in a Pb/Si(111) system. The growth of islands is simulated by the Monte Carlo method. With suitably chosen parameters the model is able to reconstruct the phase diagram, via the dependence of the dynamics of Pb atoms on area and height. These dependencies are attributed to stress energy and quantum size effects.