Structural Characterization of Organothiolate Adlayers on Gold:  The Case of Rigid, Aromatic Backbones

Abstract

Here, we present the results of a detailed characterization of rigid-rod thiolate adlayers on Au(111) made by self-assembly of organothiols containing a terphenyl backbone, namely, p-terphenylthiol (TPT, C6H5-(C6H4)2-SH) and p-terphenylmethanethiol (TPMT, C6H5-(C6H4)2-CH2-SH) on Au(111). The results of low energy electron diffraction measurements reveal the presence of long-range order for adlayers prepared from both molecules. From the body of data obtained by X-ray photoelectron spectroscopy, infrared reflectionabsorption spectroscopy, near-edge X-ray absorption fine structure measurements, and scanning tunneling microscopy, a structure model for adlayers of TPT and TPMT on Au(111) is proposed.

Electronic structure and polymerization of a self-assembled monolayer with multiple arene rings

“…In some aromatic thiol SAM overlayers, [69][70][71] with very high molecular coverages, a lattice constant of 5 Å is reported and this can be reconciled with the critical points of our observed band dispersion under some conditions. A reciprocal lattice vector of 1.25 Å −1 , if the adlayer lattice is a rectangular lattice, would provide a 5.1± 0.2 Å lattice spacing in one direction.…”

“…Still this lattice constant is consistent with a 2 ϫ 2 hexagonal structure. If only the sulfur is considered, this band dispersion provides a lattice constant that is close to one of lattice spacing of the herringbone structure proposed for terphenylmethylthiol and related molecules, [69][70][71] although not the other. The rectangular lattice, such as is observed with 4Јmethylbiphenyl-4-yl-ethyl thiol and 4Јmethylbiphenyl-4yl-buthyl thiol, 70,71 is more of a hexagonal packing consistent with a 6 Å spacing, if super periodicities are NOT considered.…”

“…The fact that the second Brillouin zone point is not well defined as ⌫ , in the band structure, is certainly consistent with data obtained from superposition of several TPDMT domains of different orientations. Combinations of 5 Å and 6 Å lattice spacing with a roughly hexagonal packing have been seen in the LEED and molecular resolution STM results from some aromatic SAM layers, [53][54][55][69][70][71] and cannot be excluded by our data either.…”

“…For SAMs formed from ͓1,1Ј;4Ј, 1Љ-terphenyl͔-4-methanethiol, a commensurate ͱ 3 ϫ 2 ͱ 3 structure, with an intermolecular spacing of about 5 Å, was observed by LEED and molecular resolution STM, 69 while a ͱ 3 ϫ ͱ 3R30°, with an intermolecular spacing again of about 5 Å, has been observed in other molecular resolution STM studies. 72,73 The band structure critical points might be reconciled to such a ͱ 3 ϫ ͱ 3 R30°hexagonal packing, if the band mapping is taken along the T line of the surface hexagonal Brillouin zone, toward the Brillouin zone edge ͑K ͒, but the second Brillouin center should not be observed in this case, so this structure remains difficult to reconcile with our data.…”

Conformations and charge transport characteristics of biphenyldithiol self-assembled-monolayer molecular electronic devices: A multiscale computational study

“…For example, superlattice diffraction spots that are expected for a herringbone-type arrangement of the biphenyl backbones were not observed in a low-energy He atom diffraction experiment 26 because of the small coherence length. 30 We suspect that the existence of two competing packing structures might contribute to such structural indeterminacy of ͑methyl-͒mercaptobiphenyl SAMs. Indeed, in addition to the hexagonal phase of the ͑ ͱ 3 ϫ ͱ 3͒R30°surface lattice, a stripe phase with commensurate rectangular ͑8 ϫ 2 ͱ 3͒R30°s urface lattice, which might be related to our less-stable parallel packing configuration, was observed.…”