A New Conception of Evaporation and Condensation: Atomic Energies and the Impact on Thin Film Structure

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How fast do atoms fly away from a surface as they evaporate? Do they accelerate as they approach a surface when they condense? Remarkably these questions have not yet been answered by science. Given the importance of evaporation and condensation phenomena in fields ranging from atmospheric science to petrochemical synthesis to thin film coating manufacturing it is clear that answering these questions will be of foremost scientific significance. This proposed research will experimentally investigate these questions and will, for the first time, provide definitive answers. Utilizing mechanical velocity selectors in vacuum we will measure the distribution of velocities of atoms ejected from hot liquid and solid surfaces. In addition we will condense thin film coatings with beams of velocity-filtered vapour and investigate the effect of kinetic energy on the structure and properties of these thin films. Following the development of thermodynamics and the kinetic theory of matter in the 19th century a series of experiments were conducted to verify that the atoms and molecules of gases do indeed exhibit the velocities predicted by the Maxwell-Boltzmann (MB) distribution. First Stern in 1920, then Eldridge in 1927, and Zartman in 1931, employed rotating velocity filters to measure the distribution of velocities of atoms emitted from small apertures in ovens, all confirming the expected MB distribution. The veracity of the kinetic theory was confirmed, and in fact similar apparatus have been employed since for the study of chemical reaction dynamics in the field of molecular beams, and have become a core modern materials technology, e.g. molecular beam epitaxy. What they have all missed, however, is that effusion from an oven is not at all the same as direct ballistic evaporation from a solid or liquid surface. This proposed research will examine the energies of atoms involved in ballistic evaporation and condensation utilizing modern experimental techniques. It will provide answers to several important current questions, e.g. are atoms deflected from ballistic trajectories as they approach a growing thin film surface? ("steering"). We will also develop technologies for manufacturing nanostructured thin films with velocity-filtered vapour.