Investigations of evanescent heat transfer and measurements of the acoustic reflection coefficient for thin metal films

Evanescent waves are always present near the surfaces of materials and are generated by the random thermal motion of charges, which produce fluctuating electromagnetic fields that extend approximately a thermal wavelength, {dollar}hbar c/Ksb{lcub}B{rcub}T{dollar} beyond the surfaces of the materials. Evanescent waves can transfer energy from one material to another if the second material extends into the region where the evanescent waves have appreciable amplitude. In the first part of this thesis, we present a macroscopic, phenomenological theory for the heat flow mediated by evanescent waves between two material half-spaces of differing temperatures whose surfaces are separated by a vacuum gap of width l. For separations much larger than the thermal wavelength, our result reduces to the Stefan-Boltzmann law and for separations much less than the thermal wavelength, the thermal flux due to evanescent waves is orders of magnitude larger than blackbody radiation. For l sufficiently small, the heat transfer varies as {dollar}lsp{lcub}-2{rcub}{dollar}. As a special case, we explore the behavior of the heat flux between Drude materials and found that heat flow exhibits a wide range of behavior for different gap widths and electrical conductivities.; In the second part of this thesis, we present a picosecond ultrasonic method for studying the interfacial bonding between a thin metal film and a substrate. In this method, a subpicosecond laser pulse produces a rapid heating of the film. Relaxation of the thermal stress created by the heating sets the film into vibration. The rate at which the film vibrations damp out via sound transmission into the substrate depends on both the interfacial bonding and the acoustic properties of the film and substrate. Measurements of the damping rate thus provide a means of assessing interfacial bond strength. As a demonstration, we modified the interfacial bonding by irradiating small areas of some samples with 2.5 He{dollar}sp+{dollar} MeV ions, a procedure which is known to improve bonding. Measurements of the damping rate in the ion irradiated areas were significantly higher than in the "as deposited" regions of the samples. The increase in the damping rate induced any ion irradiation indicates an improved interfacial bonding.