Phase Transitions in Layered Film Systems

In addition to measuring the crystallization temperatures of supercooled melts, supercooling studies suppose obtaining information on the kinetics of phase transitions and the effect of successive heating and cooling series on the behavior of melts. Nanocomposite systems, in particular, structures of the “small particles in a more refractory matrix” type, are currently attracting special interest. The study of such objects requires the development of special methods that provide data on the kinetics of phase transitions and allow the carrying out of multiple thermal cycling of nanocomposite samples. Effective techniques to investigate these aspects and systems are based on observing the resistance of the films or the resonant frequency of the piezoelectric crystal on which the films are deposited. In the first case, the criterion for melting and crystallization of the layer is a jump in the electrical resistance of the film. In the second case, it is a jump in the quartz resonator’s quality factor. Using these techniques, studies of supercooling during crystallization of the fusible component in multilayer films have been carried out. It is shown that for contact pairs containing bismuth, the temperature and kinetics of crystallization depend on the condensation mechanism of the fusible metal. The observed differences are explained by the different morphology of samples obtained by condensation of bismuth into liquid and solid phases. Bismuth layers deposited into the solid phase form a connected system of inclusions, which is preserved even during thermal cycling. Such a system crystallizes as a single unit, and its formation is provided by grain boundaries of the more refractory layer.