Layered lanthanide tantalates and their ion-exchanged phases (MLnTa 2 O 7 , M ~Cs, Rb, Na, and H; Ln ~La, Pr, Nd, and Sm) were prepared to evaluate their photocatalytic activity for water splitting under UV irradiation. The optical band gap energy was dependent on the lanthanide, Ln, but negligibly affected by the monovalent interlayer cations, M. By contrast, the photocatalytic activity was strongly affected by not only Ln but also M; the highest activity was attained by a series of M ~Rb with a sequence of Ln: Nd w Sm w La w Pr. The effect of Ln can be explained by the energy level and hybridization of the Ln 4f band, which was discussed based on the results of electronic structure calculations in our previous work. The ion exchanged phases (M ~Na and H) having deformed hydrous layer structure were less active compared to anhydrous Rb and Cs phases, whereas the NiO x loading of the Na phase greatly enhances the activity. It seems that the high mobility of water molecules between the layers allows the interlayer sites to behave as active sites for the photocatalytic reaction over NiO x -loaded catalysts.

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We propose a novel solar cell structure based on the concept of forming p or n window layers by the field effect instead of impurity doping, and we verify its performance experimentally. The device, a field-effect amorphous silicon solar cell (FESC), was designed with the aid of a device simulator and fabricated by a plasma chemical vapour deposition system. We have verified that the output current of the FESC was amplified by the field-effect bias application to the gate electrode. The fundamental properties of this new type of amorphous silicon solar cell are demonstrated for the first time.

Energy profiles have been evaluated by an ab initio molecular-orbital method for hydrogen-abstraction reactions from surface model compounds of growing hydrogenated amorphous silicon (a-Si:H) by a SiH3 radical, a presumed main precursor to a-Si:H, as well as by a hydrogen radical which should coexist in the silane plasma chemical vapor deposition. The activation energies calculated for these two reactions decrease as the cluster size of the film surface model SinH2n+2 increases from n=1 to n=4 to converge for n⩾4. This trend is in parallel with the variation of atomic charge delocalization. Both activation energies (0.22 and 0.28 eV, respectively) for the largest model, Si7H16, were low enough to induce the hydrogen abstractions from the surface to form dangling bonds, which spontaneously react with SiH3 radicals to form Si–Si bond. From thus produced H3Si–Si≡surface, hydrogen can be eliminated with SiH3 (or H) to reproduce a dangling bond. The initial step of the a-Si:H film growth is deduced by the calculation to proceed through sequential reactions of spontaneous addition of SiH3 to the dangling bonds, and the hydrogen abstraction to reproduce dangling bonds.