Abstract: Decomposition of ozone in a microwave discharge cavity leads to formation of highly energetic excited states of atomic oxygen which can efficiently oxidize materials at a temperature far less than that needed for purely thermal oxidation. This technique can be applied to formation of films of silica at the surface of silicon and silicon carbide while maintaining quite moderate surface temperatures, often under 100.degree. C. The technique can be used generally in a process to oxidize materials whose oxidation requires a standard free energy change of less than about +636 kJ/mol.