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].