Non-isothermal crystallization in amorphous selenium films

Abstract

The usual determination of kinetic parameters of crystallization of amorphous products is based on isothermal measurements. In general the crystallization of amorphous selenium thin films is studied by non-isothermal experiments (DTA). The adaptation to non-isothermal crystallization of the Avrami transformation rate equation allows us to determine different types of crystallization. These different regions enable one to determine the variations of the growth rate and of the nucleation rate versus temperature. The influence of the wavelength of illumination during the crystallization time on these parameters is also investigated.The last decades have seen a strong theoretical and experimental interest in the non-isothermal analysis techniques for the study of phase transformations. These non-isothermal techniques have several advantages: rapidity of experiment and facilities to extend the temperature range beyond that accessible to isothermal experiments. Also, many phase transformations depend on non-isothermal kinetics.Thus it is not surprising for the study of systems in which the temperature of the interface (amorphous-crystal for example) is well defined by the temperature of the system (i.e. the difference of temperature between the interface and the system is negligible), to see differential thermal analysis (DTA)and differential scanning calorimetry (DSC) as techniques which are applicable, in particular to the study of crystallization kinetics. Isothermal crystallization Avrami equationThe crystallized fraction x of the system at time t, is defined as follows:The volume V0 is the total volume of the sample and Ve(t) is the "extended crystallized volume", i.e. the volume which includes all the crystalline regions, assumed to be independent without taking into account possible overlapping, Vc(t ) is the real crystallized volume at time t. This notion of "extended crystallized volume" 20* J. Thermal Anal. 25 1982