Masaru Shimomura

Poly(acrylonitrile)/activated carbon composite polymer gel electrolyte for high efficiency dye sensitized solar cells

In this article, we prepared poly(acrylonitrile)(PAN)/LiI/activated carbon (Ac. carbon) composite gel polymer electrolyte (GPE) and investigated its working mechanism in dye-sensitized solar cells (DSSCs) for the first time. The gel electrolyte, formed by a hot pressing method, is composed of poly(acrylonitrile) (PAN) as a gelling agent, ethylene carbonate (EC), propylene carbonate (PC), I2, 4-tert-butyl pyridine and 1-N-butyl-3-hexyl imidazolium iodide. We synthesised GPEs with the addition of different concentrations of Ac. carbon instead of the ceramic filler for application in DSSCs. The TiO2 photoelectrode films with 20 μm thicknesses were prepared by the hand spray technique. In addition, we also prepared PAN/SiO2 (∼20 nm) based gel electrolytes using the same procedure without Ac. carbon, and compared them to the optimal results. The GPEs were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the cells and the electrical conductivities of the GPEs were measured from the complex impedance plots. We found that the PAN/Ac. carbon GPE shows the best electrical conductivity of about 8.67 × 10−3 S cm−1. Cyclic voltammograms reveal that the PAN/Ac. carbon gel electrolyte itself has some catalytic behaviour, which may enhance its photovoltaic performance. Finally, we fabricated a DSSC based on this GPE and it exhibited the best solar cell efficiency of 8.42%, which is only 1% lower than that of a DSSC based on the conventional liquid electrolyte (9.5%).

Surface structures and electronic states of H2S‐treated InP(001)

We find two different surface structures, (1×2) and (1×1), for H2S‐treated InP(001). They depend upon exposure of H2S at about 350 °C. The coverage of sulfur is estimated to be about a half monolayer and one full monolayer for the (1×2) and (1×1) structures, respectively. The (1×1) structure is reconstructed to the (1×2) structure upon annealing at about 550 °C. It is suggested that sulfur is bonded to only In atoms and substitutes some of the phosphorus atoms below the first layer. Inverse photoemission spectra show strong reduction in intensity of 1.2 eV peak above the Fermi level for a clean InP(001)‐(4×2) surface upon adsorption of H2S. This reduction implies a decrease in unoccupied surface states due to dangling bonds of indium dimers on the clean surface. The result of adsorption of oxygen on the (1×2) and (1×1) surfaces indicates significant passivation to oxidation of the surfaces.

Clean GaP(001)‐(4×2) and H2S‐treated (1×2)S surface structures studied by scanning tunneling microscopy

Clean GaP(001)‐(4×2) and H2S‐treated (1×2) surfaces are studied by scanning tunneling microscopy (STM). We have observed a (4×2)/c(8×2) STM image for the cation‐stabilized GaP(001) surface. The result suggests that the unit cell of the (4×2) structure consists of two Ga dimers with two missing Ga dimers. For the (1×2)S surface, the previous model that sulfur atoms are adsorbed on the Ga dimer and that a missing row of sulfur is formed along the [110] direction is supported by the STM result.

Surface reconstruction of InP(001) upon adsorption of H2S studied by low-energy electron diffraction, scanning tunneling microscopy, high-resolution electron energy loss, and x-ray photoelectron spectroscopies

Reconstruction of an InP(001) surface structure upon H2S adsorption has been studied by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), high-resolution electron energy loss (HREELS), and x-ray photoelectron spectroscopies (XPS). The HREELS result indicates that H2S is dissociated on the surface even at RT, leading to evolution of hydrogen from the surface. LEED patterns show (2×4) and (2×1) structures for the surface with sulfur coverages, 0 and 0.5–1 ML, respectively. A complex pattern appears at 0.25 ML. We find in STM images that the (2×1) structure starts to form even at 0.1 ML sulfur coverage at 350 °C. The (2×1) structure is almost established at 0.5 ML although the protrusions of about two atoms in size exist on the surface. The new (2×1) structure begins to grow from protrusions above 0.5 ML on the (2×1) surface found at 0.5 ML and it is established at about 1 ML where the c(2×2) structure with small domain is found. XPS result shows one chemical state of sulfur at 0.5...

Spectroscopic evidence for reduction of unoccupied states in the band gap of GaP(001) by H2S passivation

Clean and H2S‐adsorbed GaP(001) surfaces have been studied by inverse and ultraviolet photoemission spectroscopy (IPES) and (UPS) and by high‐resolution electron energy loss spectroscopy. H2S is found to be dissociated on the surface, leaving only sulfur on it, which is consistent with UPS results. IPES spectra show strong reduction in intensity at 1.5 and 4.5 eV above the Fermi level upon sulfur adsorption. The reduction in the former indicates tremendous decrease of unoccupied states, which correspond to dangling bonds of surface gallium atoms, in the band gap by H2S passivation.

Nonpolar (1120) p-Type Nitrogen-Doped ZnO by Remote-Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Nonpolar crystal orientation showed a positive effect on the chemical bonding states of nitrogen-doped ZnO (ZnO:N) for attaining p-type conductivity. Remote-plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD) was used to grow nonpolar- and polar-orientated films on R-plane and a-plane sapphires, respectively. Non-polar orientation permitted nitrogen doping as the acceptor mode with lesser donor complexes giving p-type conductivity in both as-grown and annealed conditions. Carbon complexes (C with O) were observed in both orientations with lower binding energy in the nonpolar orientation showing weak complexes in the nonpolar mode. The difference in the mechanism of nitrogen incorporation depending on nonpolar- and polar-oriented growths was explained.

The structure of the InP(001)-(4 × 2) surface studied by scanning tunneling microscopy

Abstract The structure of an InP(001)-(4 × 2) surface, prepared by ion bombardment and annealing, has been studied by scanning tunneling microscopy. In the occupied states (sample bias V s = −1.5 V) image three protrusions arranged in a triangular shape are seen in the (4 × 2) surface unit cell. Three kinds of combination of the triangle, α, β and γ, are found in the [110] direction. Conversely, one protrusion in the unoccupied states ( V s = +1.5 V) image is seen in the unit cell. A structure model of the (4 × 2) surface is proposed.

Improved performance of dye-sensitized solar cells using a diethyldithiocarbamate-modified TiO 2 surface

The surface modification of a TiO2 electrode with diethyldithiocarbamate (DEDTC) in dye-sensitized solar cells (DSSCs) was studied. Results fromX-ray photoelectron spectroscopy (XPS) indicate that over half of the sulfur atoms become positively charged after the DEDTC treatment of the TiO2 surface. DSSCs were fabricated with TiO2 electrodes modified by adsorbing DEDTC using a simple dip-coating process. The conversion efficiency of the DSSCs has been optimized to 6.6% through the enhancement of the short-circuit current density (JSC = 12.74 mA/cm2). This is substantially higher compared to the efficiency of 5.9% (JSC = 11.26 mA/cm2) for the DSSCs made with untreated TiO2 electrodes.

Electronic states and superconducting properties of Bi2Sr2(Ca, Gd)Cu2Oy studied by X-ray photoelectron and inverse-photoemission spectroscopy

Abstract Measurements of superconducting properties, X-ray photoelectron and inverse-photoemission spectroscopy have been performed on Bi 2 Sr 2 Ca 1− x Gd x Cu 2 O y (0 ≤ x ≤ 1.0) ceramics, where the metal-insulator transition is observed at x ∼ 0.6. The density of states at the Fermi level is reduced with increasing Gd ion contents at Ca sites. Annealing the samples in vacuo increases the critical temperature even at optimum hole concentration ( x = 0.1). Changes in the electronic states are discussed in terms of the hole concentration.

Highly site-selective adsorption of trimethylphosphine on a Si(111)-(7 × 7) surface studied by a scanning tunneling microscope (STM)

Abstract Adsorption of trimethylphosphine (TMP) on a Si(111)-(7 × 7) surface has been studied using a scanning tunneling microscope (STM). We find that most of the TMP molecules are adsorbed preferably on center adatom sites at the surface. It is observed that the TMP molecule on a corner adatom is moved to a center adatom site at RT. TMP is more stable on the center adatom sites than on the corner adatom sites.