Surface nano-processes induced by high-speed atomic and molecular beams

Teraoka, Yuden

Surface temperature and gas pressure are reaction controlling parameters of surface reactions. For instance, the following three reaction modes are selectable in the Si oxidation, "oxide film formation" in low temperature/high pressure conditions, "etching (SiO desorption)" in high temperature/low pressure conditions, and their coexistence depending on reaction conditions. Recently, it has been found that the oxidation reactions were also controllable by translational kinetic energy of O molecules. Although irradiation of high speed particles such as ion beams induces roughening of surface crystal structure and the beams reach into deep bulk, atomic and molecular beams with low incident energy restrict the reactions to be adsorption at the extreme surface. If the incident energy is larger than a potential energy barrier, a direct adsorption process may take place without trapping at physically-adsorbed states. Generally the barrier height is several eV so that surface-excited processes are available even by atomic and molecular beams with hyper-thermal incident energy. The atomic and molecular beams are very useful techniques for precise control of film formation and etching with sub-nano-meter scale. Furthermore, a research field of surface stereo-reaction dynamics may open by applying oriented-molecular-beam techniques. The molecular orientation may be effective 4th reaction controlling parameter in addition to surface temperature, gas pressure, and the 3rd parameter of incident energy. Atomic and molecular beam generation techniques, some practical applications of surface-excited reactions with low energy beams, and perspective of the surface-excited nano processes will be introduced in this review.