Stoichiometric GaAs(100) surfaces were functionalized with monolayers of an aromatic compound, 1,1‘-biphenyl-4-thiol (BPT), and the engineered surfaces were studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy. BPT molecules were found to form a well-ordered and densely packed self-assembled monolayer on these substrates. The attachment to the substrate occurs over the thiolate headgroup while the intact biphenyl moieties have an upright orientation with an average tilt angle of 31.5° ± 5°. The functionalization of GaAs by BPT was found to prevent an oxidation and contamination of the substrate, keeping the GaAs surface in a pristine state. The surface engineering of GaAs with functionalized aromatic monolayers can provide a crucial link for combining GaAs-based semiconductor nanostructures with bio-organic molecular assemblies.

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High-resolution X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy were applied to characterize GaAs(100) surface engineered by self-assembled monolayers (SAMs) of 4′-substituted aromatic molecules: 4′-methyl-4-mercaptobiphenyl (CH 3 -BPT) and 4′-hydroxy-4-mercaptobiphenyl (OH-BPT). Both of these molecules formed ordered and densely packed SAMs on GaAs, which were able to protect the substrate from degradation under ambient conditions. The molecular attachment in the SAMs is mediated by As-thiolate bond while the intact aromatic backbones have an upright orientation with average tilt angles of 31.0°and 37.2°for CH 3 -BPT and OH-BPT films, respectively. The difference in the tilt angle is attributed to a higher (by 7-10%) packing density of the former SAM, suggesting that the character of 4′-substitution affects the quality of the resulting SAM on the GaAs substrate.