We have developed a continuous composition spread-pulsed laser deposition (CCS-PLD) system of scanning laser for exploring new functional complex metal oxides. Our new CCS-PLD system is based on a precisely controlled synchronization between the laser firing, target exchange, linear mask motion and mirror swinging, and provides more flexibility and control than earlier PLD-based approaches. Most importantly, the deposition energetics and the film thickness are kept constant across the entire composition range by using scanning laser. In this study, we fabricated binary composition-spread films composed of LaNiO3 and LaMnO3. Synchrotron radiation-photoemission spectroscopy of LaNiO3-LaMnO3 composition spread films was carried out to evaluate the valence band electronic structures. Here we report on the high-throughput fabrications and evaluations using the combination of composition spread thin film growth techniques and synchrotron radiation-photoelectron spectroscopy.
We developed a technique to prepare highly ordered thin films of organic molecular semiconductors. A quasi single crystalline monolayer of thin film phase pentacene was epitaxially grown on a substrate with a nm scale template prepared by step bunching of Si(111) surface. Band dispersion of the films was measured by angle resolved photoelectron spectroscopy at different temperatures and transfer integrals were derived from tight binding fit to the dispersion observed at 130 K. When the temperature was elevated to 300 K the second derivative plot of the photoelectron spectra became broader and the band dispersion was lost in two directions, whereas the dispersion was still observed in one direction. This finding suggests the anisotropy in phonon scattering, which determines the carrier mobility in the organic semiconductors at room temperature.
Development and potential applications of a three-dimensional X-ray absorption fine structure (XAFS) technique are described showing some preliminary data. By combining an X-ray microbeam with a depth-resolved XAFS technique, one can observe atomic, electronic and magnetic structures of thin film samples with a three-dimensional spatial resolution. A 3-5 μm beam size was achieved by adopting a two-step focusing mirror system, and two-dimensional magnetic images for a wedge-shaped Fe/Ni/Cu(100) thin film were obtained. On the other hand, the surface and interface components of XAFS spectra were extracted by applying the depth-resolved XAFS technique to a Ni/Cu(100) thin film. These results indicate that the three-dimensional XAFS measurements are now possible. Future prospects of this novel technique are also described.
We studied electronic structure and Rashba-type spin splitting in the (3×1) and (1×1) structures on Tl/Ge(111) using angle-resolved photoelectron spectroscopy (ARPES) and first-principles calculation incorporating the spin-orbit interaction. The calculations showed that Tl behaves as a monovalent ion and surface states involved with the Tl-Ge bond are formed mainly by the Tl 6p orbital and the Ge dangling bond. The surface states show k-dependent spin splitting up to ∼200 and ∼800 meV for the (3×1) and (1×1) structures, respectively. The occupied surface states were observed by ARPES. Their spin splittings were predicted to be 150−200 meV, while these were not resolved in the measurement. The largest splitting of ∼800 meV is calculated for the unoccupied states at K− on the (1×1) structure. The wavefunction is strongly localized in the Tl overlayer, indicating that the heavy core potential of Tl is essential for the large spin splitting.
Recently, the p-type doping by the adsorption of acceptor molecules on surfaces has been investigated in order to control the electronic properties of substrates. Valence and core-level photoelectron spectroscopy, X-ray absorption spectroscopy, scanning tunneling microscopy etc. have been utilized to elucidate the electronic structures and adsorbed states. In this article, recent studies on the adsorption of F4TCNQ on various surfaces are reviewed.
Photoelectron and Auger electron diffractions from a localized core level provide information on atomic configurations. Forward-focusing peaks indicate the directions of atoms surrounding the excited ones. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements by Auger electron yield detection, on the other hand, are powerful analysis tools for the electronic and magnetic structures of surfaces. However, all the information from atoms within the electron mean-free-path range is averaged into the obtained spectra. Here, we introduce a new method of disentangling spectra from different atomic layers by use of Auger electron diffraction. Taking an advantage of the forward-focusing peak as an excellent element- and site-selective probe, diffraction spectroscopy enables direct access to the electronic and magnetic structures at subsurface region. We have applied this method to the study of the electronic and magnetic structures of Ni thin film at atomic level.
We review some new developments in theory of photoemission from solids. In particular, multi-atom resonant photoemission (MARPE) and recoil processes in high-energy photoemission are discussed in detail. In the former and latter phenomena, radiation field screening and phonon excitation around an X-ray absorbing atom, respectively, play an important role.
Inorganic nanowires have diameters substantially below the wavelength of visible light and have electronic and optical properties that make them ideal for subwavelength laser and imaging technology. In this report, it will be presented that an electrode-free, continuously tunable coherent visible light source compatible with physiological environments has been developed from individual potassium niobate (KNbO3) nanowires. These wires exhibit efficient second harmonic generation, and act as frequency converters, allowing the local synthesis of a wide range of colours via sum and difference frequency generation. We use this tunable nanometric light source to implement a novel form of subwavelength microscopy, in which an infrared laser is used to optically trap and scan a nanowire over a sample, suggesting a wide range of potential applications in physics, chemistry, materials science and biology.