Hydrogen surface coverage of as-prepared nanocrystalline porous silicon

Abstract

Porous silicon (PoSi) surface coverage by hydrogen has been investigated by thermal desorption spectroscopy (TDS). The desorption rate of H 2 and SiH x ( x=1–4) molecules was monitored with a quadrupole mass spectrometer during linear heating of the samples in vacuum. The almost simultaneous desorption of several species containing hydrogen gives rise to complicated TD spectra. The full spectra can be understood as due to H-atom desorption from different bonding states at the PoSi surface, namely a SiH(a) surface monohydride, a SiH 2(a) dihydride and a SiH 3(a) trihydride. In order to obtain clean spectra for a kinetic analysis, as prepared samples were annealed at selected temperatures to isolate the contributions from the different bonding states. A detailed knowledge of the kinetic parameters for the desorption process has been obtained from these experiments. In this paper, the order of the reaction, activation energy and pre-exponential factor for desorption from each H bonding state will be presented.