PHASE-TRANSFORMATION DYNAMICS, MELTING AND STRESS EVOLUTION IN DIELECTRIC FILMS AND AT SURFACES

Thin films exhibit contrasting physical properties to related bulk sin gle crystals as a result of the deposition method used and the concomi tant two-dimensional nature of the film. Such behavior results from th e presence of mixed crystalline and/or amorphous phases, film residual stress resulting in part from disparities in film-substrate thermal p roperties, crystallite grain size, crystallite orientation and non-sto ichiometry. While all of these film characteristics can be studied usi ng numerous methods (SEM, TEM, XRD, EXAFS, XPS), the availability of n ew laser sources and sensitive area detectors make Raman spectroscopy the method of choice. In situ and both spatially and temporally resolv ed measurements on films and surfaces are described, suggesting the su periority of Raman methods for film and materials surface characteriza tion in ambient environments. Phase transformation dynamics in sputter ed 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-i nduced crystallization of amorphous sol-gel-deposited oxide films allo w rate constants and evolving stress heterogeneity to be determined. I n regimes where structural phase transformations do not occur, the res ponse of phonon frequencies to pressure or temperature is a manifestat ion of anharmonicity in the vibrational potential energy. Perturbation s to the molecular structure of the film or surface layer also can be inferred from measured spectra and are demonstrated here from Raman me asurements of molten glass surfaces.