Brattkus 9705089 The goal of the proposed research is to develop and analyze asymptotic models which describe the spreading of thin solid films on solid substrates. Models are based upon a slender-body approximation that is valid for rapidly spreading films which nearly wet the underlying substrate. The asymptotic technique has been tested on a simple model of liquid phase epitaxy where the dominant mechanism of film growth is solidification. Approximate solutions representing steady planar spreading have been compared to numerical solutions of the exact problem. We find that the boundary conditions at a contact line may be applied directly to the asymptotic equations describing the spreading film even though the slender-body approximation is not valid there (this is due to the presence of a weak gradient singularity). For steadily spreading films these contact angle conditions select the spreading rate. The asymptotic equations are used to test the linear stability of a planar film and it is found to be stable. The technology behind thin film deposition is of principal importance to the development of new and more compact semiconductor devices. Moreover, this technology is unusual in that it is extremely sensitive to frontier research in materials science. We propose to examine the conditions that are applied at a tri-junction between a solid film, its nutrient phase, and its substrate, and determine the role that these contact conditions play in influencing the rate of growth and the morphology of spreading solid films. Our preliminary results suggest that contact conditions significantly influence both. A basic knowledge of the connection between the contact conditions and the growth and morphology of thin solid films will aid in controlling the deposition process.
