Reaction of atomic hydrogen with hydrogenated porous silicon - Detection of precursor to silane formation

The reaction of electrochemically formed porous silicon with atomic hydrogen or atomic deuterium has been studied at cryogenic temperatures and at room temperature. Cryogenic temperatures were chosen in order to kinetically suppress silane formation (silicon etching) and to spectroscopically observe the surface precursor to SiH4 formation. By comparing developments in the Si-H and Si-D stretching mode regions of the infrared spectrum, it is demonstrated that SiH3 is stabilized at 133 K without formation of SiH4(g). Warming to near 200 K and above evolves SiH4(g) as SiH3 reacts with neighbor SiHx species. It is demonstrated that the reaction SiH3 + H-->SiH4(g) does not proceed rapidly at 133 K. This suggests that disproportionation of SiH3 and SiHx surface species to make SiH4(g) dominates in the etching process on porous silicon at lower temperatures.