Akihito Imanishi

Platinum nanoparticle immobilization onto carbon nanotubes using Pt-sputtered room-temperature ionic liquid

Establishment of a facile Pt nanoparticle–SWCNT composite fabrication method that never requires a laborious pretreatment of SWCNTs or any chemical reagent was achieved by using Pt-sputtered RTILs.

Atomic-Scale Surface Local Structure of TiO2 and Its Influence on the Water Photooxidation Process.

The water photooxidation reaction on TiO2 and related metal oxides has been attracting strong attention from the point of view of solar water splitting. The water photooxidation reaction (i.e., oxygen evolution reaction) accompanies three other kinds of side reactions (photoluminescence (PL), surface roughening, and nonradiative recombination). These reactions are competitive with each other, and the ratio of their quantum efficiencies strongly depends on the atomic-scale surface local structure. This Perspective focuses on the atomic-scale surface local structure dependence of those four kinds of competitive reactions on a TiO2 (rutile) single-crystal electrode on which not only a terrace structure but also step structures were strictly controlled. The experimental results are discussed based on the reaction model of water photooxidation that we previously proposed. The photocatalytic activity of the TiO2 surface roughened by the photoinduced roughening process is also focused on.

Local analyses of ionic liquid/solid interfaces by frequency modulation atomic force microscopy and photoemission spectroscopy.

Local analyses of ionic liquid/solid electrode interfaces at a controlled electrode potential are of fundamental importance to understanding the origin and properties of the electric double layer at the interfaces, which is necessary for their application to electrochemical devices. This account summarizes our recent achievements of such analyses by using the novel analytical tools of electrochemical frequency modulation AFM (EC-FM-AFM) and electrochemical photoemission spectroscopy (EC-PES). Rather stable stepped structures composed of layers of ion pairs and softer solvation layers outside of the imaged layer were clearly visualized by FM-AFM depending on the substrates. An extremely extended diffusion layer was directly observed by EC-PES during the electrodeposition of metal ion solutes.

Si(111) Surface Modified with α,β-Unsaturated Carboxyl Groups Studied by MIR-FTIR

A Si(111) surface modified with alpha,beta-unsaturated carboxyl groups was fabricated using activated alkynes such as propiolic acid and propiolic acid methyl ester via hydrosilylation reaction. The obtained coverage of carboxyl groups was roughly estimated to be 55-60% in both cases from the Si-2p and C-1s X-ray photoelectron specroscopy (XPS) peak intensities. The detailed surface structures were investigated by multiple internal reflection Fourier transform infrared (MIR-FTIR) measurement. It was revealed that this reaction was promoted by visible light irradiation at room temperature. The Si surface modified with functional groups prepared under such a moderate condition is adaptable to functional devices which are easily damaged under UV irradiation or high temperature conditions.

Polymerization of room-temperature ionic liquid monomers by electron beam irradiation with the aim of fabricating three-dimensional micropolymer/nanopolymer structures.

A novel method for fabricating microsized and nanosized polymer structures from a room-temperature ionic liquid (RTIL) on a Si substrate was developed by the patterned irradiation of an electron beam (EB). An extremely low vapor pressure of the RTIL, 1-allyl-3-ethylimidazolium bis((trifluoromethane)sulfonyl)amide, allows it to be introduced into the high-vacuum chamber of an electron beam apparatus to conduct a radiation-induced polymerization in the nanoregion. We prepared various three-dimensional (3D) micro/nanopolymer structures having high aspect ratios of up to 5 with a resolution of sub-100 nm. In addition, the effects of the irradiation dose and beam current on the physicochemical properties of the deposited polymers were investigated by recording the FT-IR spectra and Youngs modulus. Interestingly, the overall shapes of the obtained structures were different from those prepared in our recent study using a focused ion beam (FIB) even if the samples were irradiated in a similar manner. This may be due to the different transmission between the two types of beams as discussed on the basis of the theoretical calculations of the quantum beam trajectories. Perceptions obtained in this study provide facile preparation procedures for the micro/nanostructures.

Preparation of gold nanoparticles using reactive species produced in room-temperature ionic liquids by accelerated electron beam irradiation

Au nanoparticles that are expected to be a key material for supporting future technologies were produced with brief accelerated electron beam irradiation to various 1-alkyl-3-methylimidazolium cation ([R1MeIm]+)-based room-temperature ionic liquids (RTILs) with aurate. The resulting Au nanoparticles were able to remain in a nearly-monodispersed state in the RTILs for several weeks at least although the surface was not covered with a stabilizing agent, which is usually employed so as to prevent aggregation behaviour. The particle size increased with increasing the irradiation dose as well as decreasing the alkyl chain length of the [R1MeIm]+ if the RTIL consisted of the same anion species. The shapes of the Au nanoparticles obviously altered with the anionic species in the RTILs used for the preparation.

Three-dimensional micro/nano-scale structure fabricated by combination of non-volatile polymerizable RTIL and FIB irradiation

Room-temperature ionic liquid (RTIL) has been widely investigated as a nonvolatile solvent as well as a unique liquid material because of its interesting features, e.g., negligible vapor pressure and high thermal stability. Here we report that a non-volatile polymerizable RTIL is a useful starting material for the fabrication of micro/nano-scale polymer structures with a focused-ion-beam (FIB) system operated under high-vacuum condition. Gallium-ion beam irradiation to the polymerizable 1-allyl-3-ethylimidazolium bis((trifluoromethane)sulfonyl)amide RTIL layer spread on a Si wafer induced a polymerization reaction without difficulty. What is interesting to note is that we have succeeded in provoking the polymerization reaction anywhere on the Si wafer substrate by using FIB irradiation with a raster scanning mode. By this finding, two- and three-dimensional micro/nano-scale polymer structure fabrications were possible at the resolution of 500,000 dpi. Even intricate three-dimensional micro/nano-figures with overhang and hollow moieties could be constructed at the resolution of approximately 100 nm.

Reactions of SiH to SiX (X=halogen) bonds at H-terminated Si(111) surfaces in hydrogen halide solutions in the presence of oxidants

Abstract The chemical reactivity of SiH (and SiH2) bonds at H-terminated Si(111) surfaces immersed in hydrogen halide (HX; X=Cl, Br, and I) solutions has been investigated by measurements of FTIR and XPS spectra and flat-band potentials. The decreases in the intensity of FTIR bands, together with the increases in the surface atomic (X/Si) ratios obtained from XPS spectra, clearly showed that SiH bonds in the HX solutions changed to SiX in the presence of oxidants such as dissolved oxygen and I2. The conclusion was supported by large positive shifts in the flat-band potential of Si(111). The extent of the changes depended on the concentration and oxidizing power of oxidant and the immersion time. On the other hand, the SiH (and SiH2) bonds were fairly stable in the HX solutions, which contain no oxidant, showing only slight decreases in amount, less than about 6% after immersion for 10 min. It is discussed that the formation of SiX bonds occurs through hole injection by an oxidant, followed by nucleophillic attack of halide ions. Spectral changes observed for the SiH vibration bands are also discussed on the basis of the formation of SiX bonds.

Gradual improvements of charge carrier mobility at ionic liquid/rubrene single crystal interfaces

We report evolution of electric characteristics of an electric double layer field-effect transistor based on the ionic liquid/rubrene single crystal interfaces. In contrast to usual devices, the field effect mobility was found to gradually increase with time for a day, followed by minor long-term fluctuations. Although the details of the evolution were somewhat device dependent, the final values of the mobility turned out to be 3–4 times larger irrespective of the initial values. These observations are explained by the evolution of the flat interface by defect-induced spontaneous dissolution of rubrene molecules at the ionic liquid/rubrene single crystal interfaces, revealed by frequency modulation atomic force microscopy.

Structures and Chemical Reactions of So2 Adsorbates Studied By Surface Xafs

Adsorption and surface chemical reactions of SO2 on Ni, Cu and Pd metal surfaces are studied by using surface XAFS, as well as XPS and STM. It has turned out that SO2 lies flat on the Ni(100), Ni(110) and Ni(111) surfaces, while it stands on Pd(100) and Pd(111). By raising the temperature, surface reactions occur on these metal surfaces. Typical reactions on Ni and Cu are 3SO2 → S+2SO3, while those on Pd are 2SO2 → S+SO4. The structures of the adsorbate species are elucidated.