RESONANT VIBRATIONAL-EXCITATION AND ELECTRON-INDUCED DISSOCIATION PROCESSES IN HREELS STUDIES OF TRIMETHYLINDIUM CHEMISORBED ON GAAS(100)

Vibrational high resolution electron energy loss spectroscopy (HREELS) has been used to monitor the wide variety of electron induced process es involving excited electronic states for trimethylindium ((CH3)(3)In ) chemisorbed on GaAs(100). The vibrational modes of the adsorbed CH3 groups undergo strong resonant vibrational excitation at 10 eV. HREEL spectra of the adsorbed layer, recorded with beam energies greater tha n 8 eV, indicate the formation of a surface CH, species characterised by a single deformation mode (delta(CH2)) at 1340 cm(-1). The conversi on of CH3 to CH2 rises dramatically at the resonance energy of 10 eV a nd reaches a broad maximum between 20 and 30 eV. The implication is th at the incident HREELS beam leads to decomposition of adsorbed CH3 gro ups. It is suggested that resonant dissociative electron attachment an d dipolar dissociation processes are responsible for the conversion of CH3 to CH2 at the surface.