Thermodynamics (with an emphasis on surface problems)

Abstract

An elementary presentation of basic thermodynamic notions is given. It is followed by a discussion of the second virial coefficient. This coefficient, although assigned here to gases and vapours in their adsorbed state, receives a much wider significance than the one based on the non-ideality of these gases and vapours. Thus it is shown that space charge effects can be described by means of second virial coefficients. A brief survey of statistical thermodynamics serves to contribute to the solution of such problems as that of the efficiency of lasers and of the temperature dependence (and of the non-additivity) of London-Van der Waals forces. Again the second virial coefficient is made use of, and its relation to the mean field approximation is pointed out. After a concise discussion of the mean field approximation, the problem of the (2 × 1) → (7 × 7) transition of the silicon (111) surface is dealt with, and considerable attention is given to various aspects of surface segregation. These include the segregation at the surface of an alloy A 1+ s B 1− s , in which an order-disorder transition is allowed to take place and in which s is a variable composition parameter. Another aspect is that of the kinetics of the segregation. Starting from irreversible thermodynamics, a simple equation is derived for the diffusion, which is consistent with the mean field approximation. An outline of the thermodynamics of strained solids is given, resulting in a discussion of the physical meaning of the product of the heat of vaporization per unit volume, and the compressibility of cubic crystals. This product, a dimensionless number, varies from 0.1 (rare gas crystals) to 0.6 (alkali metals). As an application, the deformation of the surface region of the (111) surface of silicon crystals obtained by cleavage, is discussed and a reasonable insight is obtained on the basis of the thermodynamics of strained solids.