Adsorption and photodissociation of 4-haloanilines on GaN(0001)

The adsorption of 4-chloro- and 4-iodoaniline on the GaN(0 0 0 1)-(1 x 1) surface, and the subsequent effects of exposure to near- or vacuum-ultraviolet radiation, have been studied. Both species adsorb via the molecular NH2 group, with the phenyl ring intact, as does aniline itself. Like aniline, both are very reactive with the clean surface, requiring only a small dose to reach saturation coverage. 4-Iodoaniline is photochemically active as an adsorbate on GaN. Ultraviolet radiation promotes dissociation of the molecular C-I bond, leading to the transfer of I to available Ga sites on the GaN surface. The process then terminates when all such sites are filled. Dissociation of the C-I bond does not appear to involve photoexcited carriers from the substrate and is, instead, suggested to occur through direct excitation of the adsorbate. The photochemical activity of 4-chloroaniline adsorbed on GaN is at present uncertain, but it appears to be relatively inert. (C) 2002 Elsevier Science B.V. All rights reserved.