VIBRATIONAL HREELS STUDY OF TRIS-NEOPENTYLGALLIUM ADSORBED ON GAAS(100) - IDENTIFICATION OF SURFACE SPECIES AND ELECTRON-EXCITATION MECHANISMS

High-resolution electron energy loss spectroscopy (HREELS) has been us ed to study the vibrational properties of trisneopentylgallium (Np3Ga) adsorbed on GaAs(100). Adsorption at room temperature leads to loss o f one Np group and subsequent formation of a Np2Ga surface species tha t is stable up to similar to 250 degrees C. For higher temperatures, d ecomposition leads to the formation of surface CH2 species either via a beta-Me elimination or a 1.5 H-atom abstraction mechanism. The CH2 s pecies is stable at high temperatures and is a possible cause ol the h igh carbon incorporation levels found in GaAs layers grown by atomic l ayer epitaxy using this precursor. Spectra recorded for room temperatu re adsorption of Np2Ga at different electron beam energies show that C -H and C-C vibrational modes of the molecule undergo strong resonant v ibrational excitation at 8 and 12 eV. No beam-induced dissociation was evident in spectra recorded at the resonant and higher electron beam energies, even after prolonged exposure to the incident HREELS beam. T his is in contrast to previous studies of Me3X (X = Ga, Al, In) metalo rganics which showed significant electron beam-induced conversion of C H3 to CH2. Dissociation does not occur with Np3Ga because the CH3 part of the neopentyl groups is not bonded directly to the surface, and an y CH2 groups that would be formed From beam-induced dissociation canno t be stabilised through interaction with the surface. (C) 1998 Publish ed by Elsevier Science B.V. All rights reserved.