SPECTROSCOPIC IDENTIFICATION OF THE REACTION INTERMEDIATES IN THE THERMAL-DECOMPOSITION OF TRIMETHYLINDIUM AT GAAS(100) SURFACES

High resolution electron energy loss spectroscopy (HREELS) has been us ed to study the adsorption and thermal decomposition of trimethylindiu m (TMIn) on Ga-terminated GaAs(100) surfaces. HREEL spectra recorded f or adsorption at room temperature are dominated by strong CH3 deformat ion and stretching modes and indicate that the surface species is base d on methyl groups, The intensities of these bands decrease with incre asing temperature consistent with a primary decomposition route involv ing the loss of CH3 groups from the surface. A small upward shift in t he frequency of the symmetric and asymmetric CH3 deformation modes is also observed with increasing temperature and indicates that decomposi tion takes place via an exchange reaction in which CH3 groups switch f rom In to Ga due to the stronger Ga-C bond. At temperatures greater th an 350 degrees C, the spectra are dominated by CH2 rocking, deformatio n and stretching vibrations. The presence of a surface methylene speci es at elevated temperatures suggests a second, minority decomposition pathway which involves dehydrogenation of surface CH3 groups to CH2.