His thesis research focused on the metastable atom electron spectroscopy of clean and adsorbate-covered silicon surfaces. In 1991, he joined the Solid State Chemistry Laboratory, Nagoya University, Nagoya, Japan, where he is currently working as a research associate. His current research interests include electron spectroscopy of functional organic materials, electronic structure of organic/ inorganic interfaces, and molecular orientation of thin organic films. From 1995 to 1997, he was on leave at the Institute for Molecular Science, Okazaki, Japan, to investigate the electronic structure of organic/metal interfaces with synchrotron radiation.

The function of electronically functional organic materials often originates at an interface, one example being organic electroluminescent devices (the Figure shows a typical energy diagram). Therefore, elucidation of the electronic structure at interfaces will lead to a better understanding of these devices, enabling their performance to be improved. Basic concepts are reexamined and recent progress in the area is reviewed.

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The effect of the method used to clean indium–tin–oxide (ITO) on its work function was investigated by ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy. With only ultrasonic cleaning in the organic solvent, considerable carbon contamination remained on the ITO surface and the work function was low (4.5 eV). In contrast, ultraviolet (UV)–ozone treatment removed significant carbon contamination, with an increase in the work function to 4.75 eV, which improves the hole-injection efficiency into the organic hole-transport layer in organic electroluminescent devices. Although carbon contamination on the ITO surface was also removed by Ar+ sputtering, it was accompanied by the removal of oxygen from ITO, and the work function was reduced (4.3 eV). Three factors, i.e.,: (i) C-containing contaminants, (ii) the O/In ratio, and (iii) the In/Sn ratio on the ITO surface affect the work function. The present results and those of other workers suggest that these three factors affect the work function in the order: (ii)>(i)>(iii), and (i) is the main cause of the increase in the work function in the UV–ozone or O2 plasma treatments.

Development of sunlight-driven water splitting systems with high efficiency, scalability, and cost-competitiveness is a central issue for mass production of solar hydrogen as a renewable and storable energy carrier. Photocatalyst sheets comprising a particulate hydrogen evolution photocatalyst (HEP) and an oxygen evolution photocatalyst (OEP) embedded in a conductive thin film can realize efficient and scalable solar hydrogen production using Z-scheme water splitting. However, the use of expensive precious metal thin films that also promote reverse reactions is a major obstacle to developing a cost-effective process at ambient pressure. In this study, we present a standalone particulate photocatalyst sheet based on an earth-abundant, relatively inert, and conductive carbon film for efficient Z-scheme water splitting at ambient pressure. A SrTiO:La,Rh/C/BiVO:Mo sheet is shown to achieve unassisted pure-water (pH 6.8) splitting with a solar-to-hydrogen energy conversion efficiency (STH) of 1.2% at 331 K and 10 kPa, while retaining 80% of this efficiency at 91 kPa. The STH value of 1.0% is the highest among Z-scheme pure water splitting operating at ambient pressure. The working mechanism of the photocatalyst sheet is discussed on the basis of band diagram simulation. In addition, the photocatalyst sheet split pure water more efficiently than conventional powder suspension systems and photoelectrochemical parallel cells because H and OH concentration overpotentials and an IR drop between the HEP and OEP were effectively suppressed. The proposed carbon-based photocatalyst sheet, which can be used at ambient pressure, is an important alternative to (photo)electrochemical systems for practical solar hydrogen production.

The polarization energies of 44 organic solids were determined by ultraviolet photoelectron spectroscopy in the gaseous and solid states. Condensed polycyclic aromatic hydrocarbons with planar molecular structures were found to have a common value, 1.7 eV, independent of their molecular sizes and also their crystal structures. The common value is approximately interpreted by the first-order expression for the polarization energy. A large variation of values in the range 0.9-3.0 eV was obtained for several compounds. Among them, molecules with intricate structures have smaller values and those with large molecular polarizabilities have larger values than the common value. These results indicate that the polarization energy of an organic solid is mainly determined by two factors: the molecular polarizability and the molecular packing in the solid. Intermolecular interactions in the solid, other than the van der Waals force, also contribute to the value.

We observed high and persistent spontaneous buildup of the surface potential ͑SP͒ upon vacuum deposition of tris͑8-hydroxyquinolinato͒ aluminum͑III͒ (Alq 3) on an Au substrate under dark conditions. SP determined by the Kelvin probe method reached 28 V at a thickness of 560 nm and the surface of the Alq 3 film was positively charged. We propose a model in which preferential orientation of the dipole moments of Alq 3 molecules is the origin of this buildup of the SP. The intensity of second-harmonic generation was also dramatically increased by the deposition of Alq 3 under dark conditions, which supports the notion of a buildup of dipole layers. This giant surface potential was almost completely removed by irradiation of Alq 3 molecules with visible light, and irradiation during deposition also prevented the buildup of SP.

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