Phase Transformation Dynamics, Melting and Stress Evolution in Dielectric Films and at Surfaces

Abstract

Thin films exhibit contrasting physical properties to related bulk single crystals as a result of the deposition method used and the concomitant two-dimensional nature of the film. Such behavior results from the presence of mixed crystalline and/or amorphous phases, film residual stress resulting in part from disparities in film–substrate thermal properties, crystallite grain size, crystallite orientation and non-stoichiometry. While all of these film characteristics can be studied using numerous methods (SEM, TEM, XRD, EXAFS, XPS), the availability of new laser sources and sensitive area detectors make Raman spectroscopy the method of choice.In situand both spatially and temporally resolved measurements on films and surfaces are described, suggesting the superiority of Raman methods for film and materials surface characterization in ambient environments. Phase transformation dynamics in sputtered and sol–gel-derived films subjected to an externally applied stress (temperature, pressure, high incident laser fluence) were studied in real time. Transient Raman measurements which follow the temperature-induced crystallization of amorphous sol–gel-deposited oxide films allow rate constants and evolving stress heterogeneity to be determined. In regimes where structural phase transformations do not occur, the response of phonon frequencies to pressure or temperature is a manifestation of anharmonicity in the vibrational potential energy. Perturbations to the molecular structure of the film or surface layer also can be inferred from measured spectra and are demonstrated here from Raman measurements of molten glass surfaces.