Functionalizing the GaN(0 0 0 1)-(1×1) surface I. The chemisorption of aniline

Chemisorption of aniline (C6H5NH2) on the GaN(0 0 0 1)-(1×1) Ga-polar surface has been studied using mainly X-ray-excited Auger electron, electron energy loss and ultraviolet photoemission spectroscopies (XAES, ELS and UPS, respectively). The XAES data show adsorption near room temperature with a total sticking probability of ∼0.05 and a saturation coverage of ∼0.28 phenyl rings per surface lattice site. The ELS data show removal of the characteristic surface-state band centered at ∼3.4 eV and the appearance of a π→π∗ 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 (δχ≈−0.55 eV) due to a surface dipole layer, and measurement of δχ and of changes in band bending have been used to construct a partial energy level diagram for the aniline-covered surface.