The current peak that appears on a linear-scan voltammogram for the reductive desorption of alkanethiol self-assembled monolayers (SAMs) from a gold surface in an aqueous alkaline solution exhibits intriguing features:  the narrow full width at half-maximum (fwhm) of the peak, e.g., 20 mV for dodecanethiol SAMs, the saturation of fwhm in the SAM composed of long-chain alkanethiols, an asymmetric shape, the shift of the peak potential with increasing the alkyl chain length, and the peak area that is greater than what is expected from the (√3 × √3)R30° structure of adsorbed alkanethiols on Au(111). A Padé approximant expression for the adsorption isotherm proposed by Blum and Huckaby based on the two-dimensional Ising model, in combination with the semi-infinite linear diffusion of desorbed species, well explains these salient features of the reductive desorption behavior. The double-layer charging current can amount to one-third of the charge calculated from the area of the peak of the reductive desorption, explaining the discrepancy between the adsorbed amount of an alkanethiol calculated from the peak area and that expected from the (√3 × √3)R30° structure.

The structure of the self-assembled monolayers (SAMs) of n-alkanethiols [CH3(CH2)nSH, n=3–11, 13–15, 17] on Au(111) has been studied using broad-bandwidth sum frequency generation spectroscopy. Sum-frequency vibrational spectra show three pronounced CH3 vibrational modes for all alkanethiol investigated, indicating that the commonly accepted picture that the alkyl chain for the long-chain alkanethiol SAMs has the all-trans conformation applies even to the short chain SAMs. The chain-length dependence of the ratio of the intensity for the CH3 symmetric vibrational mode to that for the CH3 asymmetric mode clearly shows the odd–even effect due to the difference in the direction of methyl group for SAMs with odd and even n, also supporting that the alkyl chain of SAMs has the all-trans conformation. An analysis of the vibrational intensities with respect to the angle between the main axis of the methyl group and the surface normal reveals that the structure of the alkanethiol SAMs gradually changes with n.

The charge-ordering states with lattice distortions of a halogen-bridged binuclear-metal mixed-valence complex (called MMX chain), Pt2(dta)4I (dta = CH3CS2 -), have been investigated by transport, magnetic, and optical measurements. This complex is a binuclear unit-assembled conductor containing metal−metal bonds. It exhibits metallic conduction above room temperature, representing the first example of a metallic halogen-bridged one-dimensional transition-metal complex. Below 300 K it shows semiconducting behavior, which is considered to be of the Mott−Hubbard type due to electron correlation. The metal−semiconductor transition at 300 K (= T M - S) is derived from a valence transition of Pt from an averaged-valence state of 2.5+ to a trapped-valence state of 2+ and 3+. The charge-ordering modes are considered to be −IPt2+−Pt3+−IPt2+−Pt3+−IPt2+−Pt3+−IPt2+−Pt3+−I for the semiconducting phase below T M - S and −I−Pt2.5+−Pt2.5+−I−Pt2.5+−Pt2.5+−I−Pt2.5+−Pt2.5+−I−Pt2.5+−Pt2.5+−I− for the metallic phase above T M - S. 129I Mössbauer spectroscopic study is reported for a low-temperature insulating phase below 80 K. The low-temperature electronic structure is considered to be an alternate charge-ordering state with lattice distortions of IPt2+−Pt3+−I−Pt3+−Pt2+IPt2+−Pt3+−I−Pt3+−Pt2+I. The present binuclear platinum complex inherently possesses valence instability of the intermediate valence 2.5+. X-ray photoelectron spectroscopy and polarized reflection measurements are also reported.

Widely accommodating: Novel TiO2/Nb nanotube layers (see picture, right) are grown on a titanium–niobium alloy. Niobium doping of TiO2 enlarges the cell parameters of the anatase lattice (left; Nb green, Ti gray, O red), facilitating the intercalation of H+ and Li+ ions, and even larger Na+ ions (blue) into the lattice.