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.

The effect of capillary force due to surface water on friction force microscopy (FFM) was examined by comparing FFM images on oxidized Si surfaces partially covered with chemically bound hydrocarbon (HC) monolayers in vacuo and in an ambient atmosphere. It was found also from force-distance curves and FFM under various relative humidities that adhesive and friction forces observed on the hydrophobic HC covered surface were almost independent of the humidity, while those on the hydrophilic bare oxidized Si surface increased with an increase in the humidity. The higher friction observed on the oxidized Si in the higher humidity was interpreted by the higher effective normal load due to the higher capillary force which originated from a surface water film formed by adsorption of water vapor in the humid air. The results suggest a novel scanning hydrophilicity microscope under a controlled humidity which can be used to map local hydrophilicities of a sample surface in a x-y plane.

No abstract

A cyclic carbazole oligomer for organic light-emitting diodes is described. This cyclic oligomer has a high glass transition temperature (105 °C ), and high quality amorphous film can be prepared by the conventional spin-coating technique. We examined the characteristics of this cyclic oligomer for electron transport layer applications. The device structure of indium tin oxide/hole transport layer/electron transport layer/Al was used. The EL device exhibited green light with a luminance of 60 cd m−2 at 15 V and the external quantum efficiency was 0.44%. tuted carbazole main-chain17 and hyperbranched polymers18