Theoretical modeling of the benzoic acid adsorption on the GaAs (001)-β2(2 × 4) oxidized surface

We describe a computational model of benzoic acid adsorbed on the most abundant and technologically important GaAs surface. The performances of many electronic devices based on organic layers deposited on semiconductor surfaces, critically depend on the quality of the layer, and thus on the features of the organic/inorganic bonds. Since very few is known about the atomic structure of such interfaces, theoretical modeling plays a central role in understanding these systems at the microscopic scale. We have optimized the structures of several clusters mimicking the unoxidized and oxidized GaAs (001) surface, using them to study the preferred arrangements of adsorbed benzoic acid molecules. The largest clusters were also used to investigate the cooperative effects between two adsorbed molecules, obtaining the most likely structure for a perfectly packed layer. Finally, we show the correlation of a microscopic observable, namely the energy of the lowest lying empty orbital concentrated on the organic moiety, with the electron affinity measured for para-substituted benzoic acids adsorbed on GaAs.