Functionalizing the GaN(0001)-(1x1) surface I. The chemisorption of aniline

Chemisorption of aniline (C6H5NH2) on the GaN(0 0 0 1)-(1 x 1) Ga-polar surface has been studied using mainly Xray-excited Auger electron, electron energy loss and ultraviolet photoemission spectroscopics (XAES, ELS and UPS, respectively). The XAES data show adsorption near room temperature with a total sticking probability of similar to0.05 and a saturation coverage of similar to0.28 phenyl rings per surface lattice site. The ELS data show removal of the characteristic surface-state band centered at similar to3.4 eV and the appearance of a pi - pi* loss at 6.5 eV due to C=C bonds. In contrast, benzene (C6H6) does not chemisorb under these conditions. The UPS data, which have been analyzed with the aid of density functional theory molecular orbital calculations, indicate that adsorption occurs with a phenyl-NH group forming a Ga-N-Ga bridge. Adsorption causes a decrease in electron affinity (deltachi approximate to -0.55 eV) due to a surface dipole layer, and measurement of deltachi and of changes in band bending have been used to construct a partial energy level diagram for the aniline-covered surface. (C) 2002 Elsevier Science B.V. All rights reserved.