One-nanometer-thick nickel hydroxide nanosheets were prepared by exfoliation of layered nickel hydroxides intercalated with dodecyl sulfate (DS) ions. The shape of the nanosheets was hexagonal, as was that of the layered nickel hydroxides intercalated with DS ions. The nickel hydroxide nanosheets exhibited charge-discharge properties in strong alkaline electrolyte. The morphology of the nanosheet changed during the electrochemical reaction.

Semiconductor oxide nanosheets synthesized by exfoliation of layered oxides are two-dimensional crystals with a thickness of about 1 nm. [1][2][3][4] New layered materials and their films can be reassembled by electrostatic self-assembly deposition (ESD) [5] and by layer-by-layer (LBL) [6][7][8] techniques, respectively. Since the nanosheets have a negative charge in aqueous solution they can be used with various cationic species as the starting materials. Layered materials prepared from nanosheets and lanthanide (Ln) ions are promising as new functional materials because Ln ions have unique properties, such as luminescence and magnetic properties, that are attributable to the 4f electron orbital. For example, the titanate layered oxide intercalated with Eu 3+ ions prepared from titanate nanosheets and Eu 3+ ions has unique luminescence properties. [9][10][11] The layered oxide gives a red emission from the Eu 3+ ions which is induced by energy transfer through excitation of the bandgap of the titanate nanosheet, [9,10] and the emission from the Eu 3+ ions is promoted by intercalated water molecules.[10] Furthermore, spectral hole burning caused by the intercalated water molecules was observed in the excitation spectra at room temperature. [11] Nanosheets of TiO x , NbO x , and TaO x give a high photocurrent during the photoelectrochemical reaction under UV illumination with an energy higher than that of the bandgap. [12] This finding indicates that a large charge separation is produced between the holes in the valence band and the electrons in the conduction band during excitation of the bandgap. Consequently, layered oxide materials intercalated with Ln ions simultaneously exhibit both photoluminescence and a photoelectrochemical reaction during excitation of the bandgap on illumination with UV light. The study reported herein demonstrates a new form of dynamic control over the photoluminescence of Ln ions intercalated in self-assembled nanosheet films of TiO x and NbO x . The photoluminescence properties of Ln ions are changed by factors such as a change in the pH value and the addition of anionic species. [13][14][15][16][17] However, it is difficult to dynamically control the photoluminescence properties of Ln 3+ ions. In the present system, the emission intensities of the intercalated Eu 3+ and Tb 3+ ions can be readily controlled by varying the applied potential.The Figure S-1 in the Supporting Information). Figure 1 shows a schematic illustration of the system used for the measurement of the photoluminescence. The photoelectrochemical cell with three electrodes, with the nanosheet/Ln 3+ film acted as a working electrode, was placed in the sample chamber of a fluorescence spectrophotometer. A 0.1m K 2 SO 4 solution (pH 6.5) was used as the electrolyte solution. Figure 2 shows the emission intensities of the TiO/Eu and NbO/Tb films under illumination by UV light (wavelength: 260 nm) as a function of potential (sweep rate: 20 mV s À1 ). The red emission of the Eu 3+ ions (614 nm, 5 D 0 -7 F 2 ) appeared in...

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In order to study the origin of metallization of VO2 induced by electron injection, we deposit K atoms onto the surface of VO2 films grown on TiO2 (001) substrates, and we investigate the change in the electronic and crystal structures using in situ photoemission spectroscopy and x-ray absorption spectroscopy (XAS). The deposition of K atoms onto a surface of insulating monoclinic VO2 leads to a phase transition from insulator to metal. In this metallization state, the V-V dimerization characteristic to the monoclinic phase of VO2 still exists, as revealed by the polarization dependence of the XAS spectra. Furthermore, the monoclinic metal undergoes a transition to a monoclinic insulator with decrease in temperature, and to a rutile metal with increase in temperature. These results indicate the existence of a metallic monoclinic phase around the boundary between the insulating monoclinic and metallic rutile phases in the case of electron-doped VO2.

To investigate the relationship between the charge redistribution and ferromagnetism at the heterointerface between perovskite transition-metal oxides LaNiO 3 (LNO) and LaMnO 3 (LMO), we performed x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) measurements.In the LNO/LMO heterostructures with asymmetric charge redistribution, the electrons donated from Mn to Ni ions are confined within one monolayer (ML) of LNO at the interface, whereas holes are distributed over 3-4 ML on the LMO side. A detailed analysis of the Ni-L 2,3 and Mn-L 2,3 XMCD spectra reveals that Ni magnetization is induced only by the Ni 2+ ions in the 1 ML LNO adjacent to the interface, while the magnetization of Mn ions is increased in the 3-4 ML LMO of the interfacial region. The characteristic length scale of the emergent (increased) interfacial ferromagnetism of the LNO (LMO) layers is in good agreement with that of the charge distribution across the interface, indicating a close relationship between the charge redistribution due to the interfacial charge transfer and the ferromagnetism of the LNO/LMO interface. Furthermore, the XMCD spectra clearly demonstrate that the vectors of induced magnetization of both ions are aligned ferromagnetically, suggesting that the delicate balance between the exchange interactions occurring inside each layer and across the interface may induce the canted ferromagnetism of Ni 2+ ions, resulting in weak magnetization in the 1 ML LNO adjacent to the interface.3

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Through in situ photoemission spectroscopy, we investigated the change in the electronic and crystal structures of dimensionality-controlled VO2 films coherently grown on TiO2(001) substrates. In the nanostructured films, the balance between the instabilities of a bandlike Peierls transition and a Mott transition is controlled as a function of thickness. The characteristic spectral change associated with temperature-driven metal-insulator transition in VO2 thick films holds down to 1.5 nm (roughly corresponding to five V atoms along the [001] direction), whereas VO2 films of less than 1.0 nm exhibit insulating nature without V-V dimerization. These results suggest that the delicate balance between a Mott instability and a bandlike Peierls instability is modulated at a scale of a few nanometers by the dimensional crossover effects and confinement effects, which consequently induce the complicated electronic phase diagram of ultrathin VO2 films.

SrMoO3 is a promising material for its excellent electrical conductivity, but growing high-quality thin films remains a challenge. Here we synthesized epitaxial films of SrMoO3 using molecular beam epitaxy (MBE) technique under low oxygen-flow rate. Introduction of SrTiO3 buffer layers of 4-8 unit cells between the film and the (001)-oriented SrTiO3 or KTaO3 substrate was crucial to remove impurities and/or roughness of the film surface. The obtained film shows improved electrical conductivities as compared with films obtained by other techniques. The high quality of the SrMoO3 film is also verified by angle resolved photoemission spectroscopy (ARPES) measurements showing a clear Fermi surfaces.