PHOTOINDUCED DISSOCIATION OF H2S ON GAAS(100)

H2S adsorbed on GaAs(100) dissociates into H(ad) and HS(ad) under phot on irradiation in the range of lambda < 550 nm, resulting in enhanced H2S desorption peak at 340 K related to the recombination of H(ad) and HS(ad) as well as a larger H-2 desorption yield. The cross-section sh ows a declining feature with increasing wavelength and demonstrates a typical value of similar to 10(-20) cm(2) in the range between 250 and 450 nm. However, the photo-induced dissociation of HS(ad) was not obs erved under UV irradiation at 320 nm. The ratio between the remaining H2S coverage after UV irradiation and its initial value decreases expo nentially with irradiation time and light intensity. This result shows that the photo-induced dissociation of H2S(ad) is a single photon pro cess. H-2 ejecting from the surface during irradiation was also detect ed, which can be attributed to the direct reaction between the ''hot' H-atom formed from the H2S(ad) photodissociation and the neighbouring adsorbed H2S molecules or adsorbed H-atoms. (C) 1998 Elsevier Science B.V.