We have used high-resolution X-ray photoelectron spectroscopy (XPS) to investigate the molecular dependence on sulfur chemical states of organosulfur monolayers of alkanethiol, dialkyl disulfide, monosulfide, thiophene, and aromatic thiols on a Au(111) surface. When monosulfides or thiophenes adsorbed on the Au surface, the S(2p) peaks appeared between 161 and 164 eV, and peak fitting revealed that these organosulfurs exhibited almost the same peaks as those of alkanethiol and dialklyl disulfide monolayers. The monolayer made from monosulfide with shorter alkyl chains exhibited almost the same S(2p) XPS spectrum as the typical alkanethiol or dialkyl disulfide monolayers. Another S(2p3/2) peak appeared for aromatic derivatized thiol SAMs at around 161 eV, in addition to strong doublet S(2p) peak observed at 162.0 and 163.3 eV in the S(2p) spectra. The 161 eV peak was observed even in the S(2p) XPS spectra of alkanethiol or dialkyl disulfide monolayers, at the initial stage of monolayer growth or after low-temperature (∼ 100 °C) annealing of low molecular density alkanethiol SAMs. We consider that this 161 eV peak can be formed without molecular decomposition as well as due to the atomic sulfur produced by C-S cleavage.

Following the proposal of a new structural model by Fenter et al. (Science 1994, 266, 1216, several reports have indicated the existence of dimers in a self-assembled monolayer (SAM) film on Au (111). We synthesized an asymmetric disulfide with hydrocarbon and fluorocarbon chains, and observed phaseseparated domains in the SAM film with force microscopy after annealing at 100 °C for 8 h. The phase separation clearly shows the cleavage of the S-S bond of the disulfide in the film. Although it cannot be confirmed whether the phase-separated domains consist of exchanged dimers or monomers (thiolates), we obtained new insights into the stability and diffusion of molecules in SAM films.

We investigated the adsorption processes of terphenyl (TP) derivatized thiols, [1,1‘:4‘,1‘ ‘-terphenyl]-4-thiol (TP0), which form self-assembled monolayers (SAMs) on Au(111). Scanning tunneling microscopy observation revealed that the adsorption process is dependent on the solvent in which the TP0 molecules can dissolve. When methylene chloride was used as a solvent, the TP0 molecules nucleate anisotropically along 〈112〉 directions with a 3-fold symmetry at the initial stage. At 1 min of immersion, a phase-separated image was taken. In the topographically lower region, molecular lattices (a = 0.65 ± 0.05 nm, b = 1.3 ± 0.05 nm) appeared, where the TP0 molecules were arranged parallel to the Au surface. After more than 5 min of immersion, the molecular lattices disappeared and larger striped patterns with a spacing of ca. 8 nm were observed. On the other hand, when ethanol was used as a solvent, the adsorption process of the TP0 molecules completely changed, and such larger striped patterns were not observed after 1 day of immersion. Our data demonstrate that ethanol facilitated the formation of the more densely packed TP0 SAMs than methylene chloride solvent.

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We construct a kink solution on a non-BPS D-brane using Berkovits' formulation of superstring field theory in the level truncation scheme. The tension of the kink reproduces 95% of the expected BPS D-brane tension. We also find a lump-like solution which is interpreted as a kink-antikink pair, and investigate some of its properties. These results may be considered as successful tests of Berkovits' superstring field theory combined with the modified level truncation scheme.

The electrical conduction of self-assembled monolayers (SAMs) made from conjugated molecules was measured using conductive probe atomic force microscopy (CP-AFM), with a focus on the molecular structural effect on conduction. First, the electrical conduction of SAMs made from phenylene oligomer SAMs was measured. The resistances through the monolayers increased exponentially with an increase in molecular length and the decay constants of transconductance beta were about 0.45 to 0.61 A(-1) measured at lower bias region. We further investigated the influence of applied load on the resistances. The resistances through terphenyl SAMs increased with an increase in the applied load up to 14 nN. Second, using an insertion technique into insulating alkanethiol SAMs, the electrical conduction of single conjugated terphenyl methanethiol and oligo(para-phenylenevinylene) (OPV) molecules embedded into insulating alkanethiol SAMs were measured. Electrical currents through these single molecules of OPVs were estimated to be larger than those through single terphenyl molecules, suggesting that the OPV structure can increase the electrical conduction of single molecules. Third, apparent negative differential resistance (NDR) was observed at higher bias measurements of SAMs. The appearance of NDR might be related to roughness of SAM surface, because apparent NDR was often observed on rough surfaces. In any case, the tip-molecule contact condition strongly affected carrier transport through metal tip/SAM/metal junction.

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Hexa-peptide nanotubes ͑cyclo͓-͑L-Gln-D-Ala) 3 ]) and octa-peptide nanotubes ͑cyclo͓-͑L-Gln-D-Ala͒ 4 ]) were synthesized by a solid-phase method using Fmoc chemistry. We investigated their morphology by atomic force microscopy ͑AFM͒ and observed the single straight nanotube forms. We also obtained AFM images of the nano-order and/or micro-order assemblies on the same substrates. The assembled forms were rather different between the hexa-peptide nanotubes and the octa-peptide nanotubes. While the former produce nanobundles or microbundles, the latter form micro-order aggregated bundles.