We have recently developed processes to grow ultrathin amorphous silicon oxide and amorphous silicon nitride layers on clean Si (111) and Si (100) surfaces exploring the self-limiting nature of the direct oxidation of Si with O-2, and the self-limiting nature of the direct nitridation of Si with atomic N produced by microwave dissociation of N-2, at processing temperatures around 500 degrees C. In some of today's microprocessor devices mixed dielectric systems are used as complementary metal oxide semiconductor gate dielectrics. We demonstrate the use of our processes to produce such systems in various structures, and with maximum control, by exposing oxide to N, or nitride to O-2 at 500 degrees C. In addition we produce a stacked layer, consisting of 7-8 angstrom of SiO2 on top of Si (100), with a layer of varying thickness of Si3N4 grown on top of this structure. The growth of Si3N4 occurs at room temperature in this process. Such structures or thermally postprocessed structures thereof should be further examined as potential stacked gate dielectrics in the next generation of Si-based microelectronics. (c) 2006 American Vacuum Society.