PHONON-ASSISTED STICKING OF MOLECULAR-HYDROGEN ON SI(111)-(7X7)

The initial sticking probability for dissociative adsorption of molecular hydrogen on Si(111)- (7×7) was measured as a function of substrate temperature. By monitoring the hydrogen coverage of the surface in an H2 atmosphere with optical second-harmonic generation we find a sticking coefficient that increases from 2×10-9 at 580 K to 5×10-6 at 1050 K. An effective barrier to dissociative adsorption of 0.87±0.1 eV via a substrate-phonon-assisted process is deduced. The results reveal a new type of adsorption dynamics where the lattice distortions play a major role. © 1995 The American Physical Society.