Real Time Studies of the Evolution of Structural, Optical, and Electronic Properties in Thin Films

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w:\awards\awards96\*.doc 9622774 Collins Real time spectroscopic ellipsometry (SE) and polarimetry, combined with microstructural analysis by direct techniques will be applied to characterize the nucleation, coalescence, and growth processes as well as the optical properties of thin films. The SE techniques applied here are unique in their ability to determine the optical properties and electronic structure with monolayer sensitivity as a continuous function of thickness for films fabricated by methods employed widely in industry, for example, plasma-enhanced chemical vapor deposition and magnetron sputtering. The research is divided into two projects: (I) the preparation of semiconductor films and the study of size effects in these films as they evolve from clusters through the coalescence stage to continuous growth, and (ii) the role of gas composition, substrate material, and substrate temperature on the evolution of bonding and structure in diamond films. The materials systems studied have a wide range of applications in thin film photovoltaic devices, photon and electron emission devices, and optical and mechanical coatings. As a result, synergistic relationships will be established between this program and other programs with industry for the transfer of new instrument designs, materials technologies, and human resources. %%% The growth of thin films under vacuum from vapor sources will be studied as they are formed, atomic layer-by-layer. Such studies will make use of novel, high-speed measurement techniques that involve directing a polarized white light beam into the reactor, reflecting it from the surface of the growing film, and detecting the change in polarization upon reflection. These techniques provide the thickness of the film with atomic layer sensitivity, the growth rate of the film, and its optical properties, t he latter including the index of refraction and absorption coefficient. The films to be studied include amorphous and crystalline semiconductors, with applications in optical and electronic devices such as solar cells and light-emitting diodes, and diamond with applications as optical, mechanical, and electron-emitting coatings. The program has four goals: (i) developing high sensitivity optical instrumentation, (ii) obtaining a better understanding of how thin films grow, (iii) optimizing thin films for specific applications based on this understanding, and (iv) establishing synergistic relationships between this program and other programs with industry for the transfer of new instrument designs, materials technologies, and human resources. ***