Applications of real time ellipsometry in elucidating the nucleation, growth, microstructural evolution, and surface modification of thin film hydrogenated amorphous silicon (a-Si:H)-based materials will be discussed. The reactive, high pressure environment of rf plasma-enhanced chemical vapor deposition (PECVD) and the disordered structure of a-Si:H preclude characterization by most conventional surface analytical techniques. Yet detailed information on the bonding and structure of surfaces, interfaces, and very thin films is crucial for multilayer photoelectronic device fabrication.