Search

We synthesized soluble rod-like silylthiophene, silylbithiophene, and silylquaterthiophene derivatives with various functional groups. Their self-assembled monolayer films on silicon oxide were evaluated by atomic force microscopy, X-ray photoelectron spectroscopy, water contact angle measurements, and fourier transform infrared-reflection absorption spectroscopy. We found that the molecular density (molecules/area) of the resultant films increased with thiophene moiety. This is probably due to the effective π-stacking of aromatic rings between molecules.

We have succeeded in the formation of one-dimensional wire-like structure in the self-assembled monolayers (SAMs) made from the mixture of an unsymmetric disulfide consisting of hydrocarbon and fluorocarbon chains and a symmetric disulfide of hydrocarbon chains on Au(111). By focusing on co-adsorption process of the above two disulfide molecules onto the Au surface, it is found that an exchange reaction should take place and a part of the symmetric disulfide molecules was replaced by the unsymmetric disulfides during immersion in the solution. The molecules having fluorocarbons were also found to replace hydrocarbons on Au surface.

The formation process of an alkylsiloxane self-assembled monolayer (SAM) on silicon oxide produced under various conditions was investigated. The growth rate of octadecyltrichlorosilane (OTS) SAM was dependent on the moisture level in the oxidation system. Area-selective oxidation of a silicon substrate with a native oxide layer was carried out under controlled humidity conditions by the field induced oxidation (FIO) technique using an atomic force microscope with a conductive cantilever. The silicon substrate partly FIO oxidized under dry nitrogen was immersed into the OTS solution, and the contact angle and topographic image showed that the OTS layer was formed only on the native oxide. In contrast, when the FIO was performed under a humidity of 88%, OTS SAM was formed both on FIO and native oxides. These results indicate that SAM formation on silicon oxides can be locally suppressed by FIO in a dry environment. Using this technique, we could fabricate an OTS SAM line structure as narrow as 22 nm.

We have studied phase-separation and patterning of self-assembled monolayers (SAMs) on Au(111). In this study, we used an ethanol solution of mixed unsymmetric disulfide with hydrocarbon and fluorocarbon chains [CF3(CF2)5(CH2)2S–S(CH2)7CH3], and a symmetric disulfide of hydrocarbon chains [CH3(CH2)7S–S(CH2)7CH3], to derive the SAMs. Then we obtained a wire-like structure with a width of 5 nm extending to about 100 nm in these SAMs after they were annealed at 100°C for 8 h. The formation of nanowires indicated that anisotropic nucleation of hydrocarbon parts along the [112] direction of the Au surface occurred.

Phase-separation of self-assembled monolayer (SAM) made from binary components is studied. The interaction between the molecules in the SAM films was estimated by a simple Monte Carlo simulation. The molecules are arranged on the two-dimensional triangular lattice sites and exchange their position with the probability determined from the molecular interaction energy calculated over the fifth nearest neighbors. One-to-one mixture with lattice sizes of 128×128, 256×256, and 512×512 was calculated, and the threshold energy for the domain formation was independent of the size. On the other hand, the domain shape and size depended on the calculation method and the lattice size. The threshold energy at 300 K corresponds to the estimated interaction between the hydrocarbon chains of 7–8 carbon atoms.