Showing papers by "Susumu Saito published in 2013"

Intermolecular interactions and substrate effects for an adamantane monolayer on a Au(111) surface

Abstract: We study theoretically and experimentally the infrared (IR) spectrum of an adamantane monolayer on a Au(111) surface. Using a new STM-based IR spectroscopy technique (IRSTM) we are able to measure both the nanoscale structure of an adamantane monolayer on Au(111) as well as its infrared spectrum, while DFT-based ab initio calculations allow us to interpret the microscopic vibrational dynamics revealed by our measurements. We find that the IR spectrum of an adamantane monolayer on Au(111) is substantially modified with respect to the gas-phase IR spectrum. The first modification is caused by the adamantane–adamantane interaction due to monolayer packing and it reduces the IR intensity of the 2912 cm 1 peak (gas phase) by a factor of 3.5. The second modification originates from the adamantane–gold interaction and it increases the IR intensity of the 2938 cm 1 peak (gas phase) by a factor of 2.6, and reduces its frequency by 276 cm 1 . We expect that the techniques described here can be used for an independent estimate of substrate effects and intermolecular interactions in other diamondoid molecules, and for other

Energetics and electronic properties of heavily nitrogen-doped titanium dioxide

Abstract: We study nitrogen-doping effects on the energetics and electronic properties of titanium dioxide (TiO2) at high doping concentrations using the first-principles electronic-structure study. From the defect formation energies obtained, it is confirmed that nitrogen atoms should tend to be clustered in the heavily-doped system. This clustering should occur because dopants share the surrounding distorted region and then the lattice-distortion energy per dopant become smaller if dopants are located at shorter distances. We also find that the impurity-induced states seem to be sufficiently hybridized with the original valence band in all the cases studied. The system would show the photoabsorption spectrum expanding to the longer-wavelength region down to around 620nm in rutile and 730nm in anatase if nitrogen atoms are sufficiently doped.