Work Function Lowering of Graphite by Sequential Surface Modifications: Nitrogen and Hydrogen Plasma Treatment.

Graphite-related materials play an important role in various kinds of devices and catalysts. Controlling the properties of such materials is of great significance to widen the potential applications and improve the performance of such applications as field emission devices and catalyst for fuel cells. In particular, the work function strongly affects the performance, and thus development of methods to tune the work function widely is urgently required.

Tunable Chemical Coupling in Two-Dimensional van der Waals Electrostatic Heterostructures.

Heterostructures of two-dimensional (2D) atomic crystals provide fascinating molecular-scale design elements for emergent physical phenomena and functional materials, as integrating distinct monolayers into vertical heterostructures can afford coupling between disparate properties. However, the available examples have been limited to either van der Waals (vdW) or electrostatic (ES) heterostructures that are solely composed of noncharged and charged monolayers, respectively. Here, we propose a "vdW-ES heterostructure" chemical design in which charge-neutral and charged monolayer-building blocks with highly disparate chemical and physical properties are conjugated vertically through asymmetrically charged interfaces.

Growth temperature dependence of nitrogen doped graphene structure on Pt (111) and analysis of its reactivity with oxygen.

Nitrogen doping is an effective method for modulating the electronic states and properties of graphene. In particular, chemical vapor deposition using nitrogen-containing organic molecules such as pyridine has been expected to be a facile way to control the doping site and amount of nitrogen. However, the atomic structure of nitrogen-doped graphene (NG) synthesized from such molecules has not been investigated.

High degree reduction and restoration of graphene oxide on SiO at low temperature via remote Cu-assisted plasma treatment.

A high throughput synthesis method of graphene has been required for a long time to apply graphene to industrial applications. Of the various synthesis methods, the chemical exfoliation of graphite via graphene oxide (GO) is advantageous as far as productivity is concerned; however, the quality of the graphene produced by this method is far inferior to that synthesized by other methods, such as chemical vapor deposition on metals. Developing an effective reduction and restoration method for GO on dielectric substrates has been therefore a key issue.

Self-Aligned Growth of Organic Semiconductor Single Crystals by Electric Field.

We proposed a novel but facile method for growing organic semiconductor single-crystals via solvent vapor annealing (SVA) under electric field. In the conventional SVA growth process, nuclei of crystals appeared anywhere on the substrate and their crystallographic axes were randomly distributed. We applied electric field during the SVA growth of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) on the SiO2/Si substrate on which a pair of electrodes had been deposited beforehand.

The influence of source molecule structure on the low temperature growth of nitrogen-doped graphene.

Doping of heteroatoms such as nitrogen into the lattice structure of graphene can tune and tailor the overall electronic properties. N-doped graphene, depending on the nitrogen bonding mode and/or bonding configuration, displays subtly altered properties in comparison to pristine graphene. However, there remains a disappointing shortage of reliable methods for introducing dopants in a controlled and reproducible manner, preventing a thorough understanding of the relationship between structure and properties.

Radiation-mode optical microscopy on the growth of graphene.

Chemical vapour deposition (CVD) growth of graphene has attracted much attention, aiming at the mass production of large-area and high-quality specimens. To optimize the growth condition, CVD grown graphene is conventionally characterized after synthesis. Real-time observation during graphene growth enables us to understand the growth mechanism and control the growth more easily.

Modification of graphene/SiO2 interface by UV-irradiation: effect on electrical characteristics.

Graphene is a promising material for next-generation electronic devices. The effect of UV-irradiation on the graphene devices, however, has not been fully explored yet. Here we investigate the UV-induced change of the field effect transistor (FET) characteristics of graphene/SiO2.

Electric-field-assisted position and orientation control of organic single crystals.

We have investigated the motion of growing pentacene single crystals in solution under various electric fields. The pentacene single crystals in 1,2,4-trichlorobenzene responded to the electric field as if they were positively charged. By optimizing the strength and frequency of an alternating electric field, the pentacene crystals automatically bridged the electrodes on SiO2.

Modified bimodal growth mechanism of pentacene thin films at elevated substrate temperatures.

The growth of pentacene thin films at elevated temperatures was studied. We observed decreased grain size and crystallinity with increasing substrate temperature in 30 nm films, despite the increased grain size of the submonolayer films. These were attributed to a two-dimensional to three-dimensional growth transition and a pronounced desorption of the first monolayer molecules.

Real-time observation and control of pentacene film growth on an artificially structured substrate.

Suppression of nucleation around a gold electrode during pentacene growth on a SiO2 channel is found by photoemission electron microscopy. Mass flow is driven by the difference between the molecular orientations on SiO2 and gold. The poor connectivity at the channel/electrode boundary causes degradation in the performance of a field-effect transistor, which is found to be improved by self-assembled monolayer treatment on the electrode (see figure; thickness in monolayers (ML)).

Surface-mediated visible-light photo-oxidation on pure TiO(2)(001).

We used STM to observe visible light photo-oxidation reactions of formic acid on the ordered lattice-work structure of a TiO(2)(001) surface for the first time. The nanostructured surface makes the band gap significantly smaller than 3.0 eV only at the surface layer, and the surface state of the crystal enables a visible light response.

Alignment-induced epitaxial transition in organic-organic heteroepitaxy.

We report the epitaxial growth of thin films of a small organic molecule (pentacene) on polymer substrates with controllable photoalignment over a wide range. The pentacene molecular plane exhibited a distinct orientational change from parallel to perpendicular relative to the polymer chain with increasing substrate polymer alignment. Each orientation consists of twinlike domains.

Nanotransfer of the polythiophene molecular alignment onto the step-bunched vicinal Si(111) substrate.

A poly(3-dodecylthiophene-2,5-diyl) film having in-plane anisotropic molecular arrangement was successfully fabricated by transferring its Langmuir-Blodgett film onto a step-bunched Si(111) substrate. Polarized near-edge X-ray absorption fine structure measurements revealed that the polythiophene main chains are preferentially orientated along periodic facet/terrace nanostructures on the step-bunched substrate, whereas less anisotropy was found on a flat substrate. The step-bunched Si substrate has been proved to be effective for controlling the in-plane molecular arrangement in the polymer thin film.

Anisotropic polymerization of a long-chain diacetylene derivative Langmuir-Blodgett film on a step-bunched SiO2/Si surface.

Alternating facet/terrace nanostructures were fabricated on a SiO2 surface by step-bunching and thermal oxidation of a vicinal Si(111) substrate, and their influence upon the polymerization direction of a long-chain diacetylene derivative monolayer film was investigated by angle-dependent polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. It was found that the peak intensity of the C 1s-pi transition was stronger when the electric vector plane of the incident X-ray was parallel to the direction of the periodic facet/terrace structures rather than perpendicular to them. On the contrary, a polymer film fabricated on a flat SiO2 surface showed no in-plane anisotropy of the peak intensity.

Metal-induced gap states at well defined alkali-halide/metal interfaces.

In order to search for states specific to insulator/metal interfaces, we have studied epitaxially grown interfaces with element-selective near edge x-ray absorption fine structure. An extra peak is observed below the bulk edge onset for LiCl films on Cu and Ag substrates. The nature of chemical bonds as probed by x-ray photoemission spectroscopy and Auger electron spectroscopy remains unchanged, so we regard this as evidence for metal-induced gap states (MIGS) formed by the proximity to a metal, rather than local bonds at the interface.