Strong Explosive Interaction of Hydrogenated Porous Silicon with Oxygen at Cryogenic Temperatures

We report new types of heterogeneous hydrogen-oxygen and silicon-oxygen branched chain reactions which have been found to proceed explosively after the filling of pores of hydrogen-terminated porous silicon (Si) by condensed or liquid oxygen in the temperature range of 4.2–90 K. Infrared vibrational absorption spectroscopy shows that, while initially Si nanocrystals assembling the layers have hydrogen-terminated surfaces, the final products of the reaction are SiO₂ and H₂O. Time-resolved optical experiments show that the explosive reaction develops in a time scale of 10^-6 s. We emphasize the remarkable structural properties of porous Si layers which are crucial for the strong explosive interaction.