POSSIBLE INTERMEDIATE IN H2S DISSOCIATION ON GAAS(100)

The adsorption and dissociation of H2S on GaAs(100) has been studied u sing high-resolution electron energy loss spectroscopy, thermal desorp tion spectroscopy, and isotope exchange techniques. The dissociative a dsorption of H2S at 100 K produces only H-As species with a vibrationa l frequency of 2072 cm(-1). Upon warming to 200 K, the vibration of H- As clearly shifts to 2105 cm(-1), corresponding to a free H-As species . In addition, the formation of H- Ga (1887 cm(-1)) is also observed u pon thermal annealing. In coadsorption studies of H2S and D atoms, thr ee main desorption features of H2S were observed at 135, 200, and 375 K, respectively. The peaks at 135 and 375 K can be attributed to the d esorption of molecularly adsorbed H2S and the recombinative desorption of adsorbed H and HS, respectively. In addition to the 375 K peak, th e desorption feature at 200 K also undergoes isotope exchange between coadsorbed D atoms and H2S . These observations strongly suggest that the dissociative adsorption of H2S on GaAs (100) involves an intermedi ate of Ga-HS-H-As. (C) 1998 American Institute of Physics. [S0003-6951 (98)03845-5].