Molecular Self-Assembly at Bare Semiconductor Surfaces: Cooperative Substrate−Molecule Effects in Octadecanethiolate Monolayer Assemblies on GaAs(111), (110), and (100)

Abstract

The structures of self-assembled monolayers formed by chemisorption of octadecanethiol onto the surfaces of GaAs(001), (110), (111-A)-Ga, and (111-B)-As have been characterized in detail by a combination of X-ray photoelectron, near-edge X-ray absorption fine structure, and infrared spectroscopies and grazing incidence X-ray diffraction. In all cases, the molecular lattices are ordered with hexagonal symmetry, even for the square and rectangular intrinsic substrate (001) and (110) lattices, and the adsorbate lattice spacings are all incommensurate with their respective intrinsic substrate lattices. These results definitively show that the monolayer organization is driven by intermolecular packing forces to assemble in a hexagonal motif, such as would occur in the approach to a limit for an energetically featureless surface. The accompanying introduction of strain into the soft substrate surface lattice via strong S substrate bonds forces the soft substrate lattice to compliantly respond, introducing quasi-2D strain. A notably poorer organization for the (111-A)-Ga case compared to the (111-B)-As and other faces indicates that that the Ga-terminated surface lattice is more resistant to adsorbate packing-induced stress. Overall, the results show that surface molecular self-assembly must be considered as a strongly cooperative process between the substrate surface and the adsorbate and that inorganic substrate surfaces should not be considered as necessarily rigid when strong intermolecular adsorbate packing forces are operative.

Thiolate versus Selenolate: Structure, Stability, and Charge Transfer Properties

“…The spectra in Figure resonances and an increase in the relative intensity of the major benzonitrile-related feature (5). These changes can be tentatively explained by the conjugation between the π* systems of the nitrile moiety and naphthalene backbone, resulting in a redistribution of the electron density and, subsequently, in changes in the oscillator strengths of the involved electronic transitions.…”

Field - dipole interactions in L-cysteine-thiolate self assembled at p- and n-GaAs(100) electrodes

“…Analysis of the S-2p core-level region ( Fig. 3a) proved that L-cysteine is bound to the GaAs surface through the thiol head-group, the doublet with binding energies of 162.20/163.38 AE 0.2 eV being characteristic for thiolate species [18][19][20]. No evidence was found for the presence of cystine and/or a second L-cysteine layer having its amino and carboxyl groups electrostatically bound with the first layer and hence a free thiol group.…”

Structure-Building Forces in Biphenyl-Substituted Alkanethiolate Self-Assembled Monolayers on GaAs(001): The Effect of the Bending Potential

“…The assignments were made in accordance with refs 29, 38, 40, 41, and 44. The Journal of Physical Chemistry C Article on the Ga-terminated GaAs(111) substrate, even though their quality was inferior to that of the analogous monolayer prepared on the As-terminated GaAs(111) surface. 28 In addition to the characteristic features discussed above, broad shoulders related to oxide species were always perceptible at the high BE side of the major emissions; they could be related to oxide residuals surviving the etching procedure and subsequent self-assembly, 29 but, most likely, resulted from postoxidation during the storage and handling of the samples before the spectroscopic experiments. Despite the passivation by the BPn SAMs, penetration of airborne oxidative species into the underlying GaAs was still possible, mediated, in particular, by defects in the monomolecular films.…”