Abstract :
Ultra-thin layers of silicon dioxide (< 1 nm) can be applied via the UVO3CVD method whereby a gas mixture of O3O2 and TMOSN2 (TMOS = tetramethyl orthosilicate) is decomposed with UV light (254 nm) to form silicon dioxide at room temperature and atmospheric pressure. A reaction chamber is designed and the parameters that influence the deposition rate are optimized. The deposition rate is independent of the TMOS concentration, but depends on the ozone concentration. Probably, the reaction kinetics is pseudo-first-order in the ozone concentration. With increased distance between the UV lamp and the substrate the deposited silicon dioxide contains more organic groups.
Silicon dioxide layers deposited on metal substrates are analyzed with static-SIMS, XPS, RBS, SEM, and glancing incidence asymmetric Bragg diffraction (GIABD). Both with XPS and with RBS the maximum deposition rate of the present equipment is determined to be 1 Å/min. According to the XPS measurements the OSi ratio in the deposit is 2.2 and the carbon content is near zero. With static-SIMS characteristic fragment ions of silicon dioxide and the metal substrate are detected. The relative peak intensities of these fragments linearly relate with the silicon dioxide layer thickness when the layer thickness is smaller than 2 nm. With SEm ultra-thin silicon-dioxide layers can be visualized, because the secondary electron emission of a coated and an uncoated metal surface is different. This is probably attributable to a difference in surface potential. With GIABD a 29 nm thick layer was found to be crystalline, but no known diffraction pattern of SiOx fitted the measured pattern.
Metals can be coated with ultra-thin silicon dioxide. It was found that these ultra-thin layers inhibit metal corrosion. A metal surface coated with ultra-thin silicon dioxide can be further modified with known coupling agents, such as silanes, as if the metal was silicon dioxide.
