A silicon precursor composition is described, including a silylene compound selected from among: silylene compounds of the formula: wherein each of R and R1 is independently selected from organo substituents; amidinate silylenes; and bis(amidinate) silylenes. The silylene compounds are usefully employed to form high purity, conformal silicon-containing films of SiO2, Si3N4, SiC and doped silicates in the manufacture of microelectronic device products, by vapor deposition processes such as CVD, pulsed CVD, ALD and pulsed plasma processes. In one implementation, such silicon precursors can be utilized in the presence of oxidant, to seal porosity in a substrate comprising porous silicon oxide by depositing silicon oxide in the porosity at low temperature, e.g., temperature in a range of from 50° C. to 200° C.