We developed a full-field X-ray diffraction (FFXRD) imaging method using a straight polycapillary realized in the laboratory that can obtain X-ray diffraction (XRD) images with a large area in a short time throughout the simple process without the synchrotron radiation facility. The FFXRD imaging instrument can obtain the XRD images of several millimeter sizes in several hundreds of seconds at each lattice plane. The positional resolution and the spatial resolution was improved by using a straight polycapillary with long type. The FFXRD imaging instrument was attached to the heat treatment system and Cu plate was heat-treated at 300°C. As an example of in situ monitoring of the change in the crystal structure distribution, a high-temperature oxidation process of Cu was observed. The XRD images of Cu, Cu2O, and CuO at each lattice plane were obtained every hour. While the crystal structure distribution of Cu was reduced, the crystal structure distribution of Cu2O and CuO were increased with the oxidation process of Cu by the heat treatment. The change of the crystal structure distribution near the surface by the oxidation process of Cu was confirmed. The XRD image obtained by the FFXRD imaging instrument was analyzed by micro-XRD measurements and confirmed that the FFXRD imaging instrument can accurately obtain the crystal structure distribution. In order to obtain the XRD image with a large area, the FFXRD imaging instrument that can be realized in the laboratory has advantages regarding the exposure time of X-rays and in situ analysis.
Direct Ga-doping into ZnO nanoparticles (NPs) were tried by thermal treatment mixed with Ga2O3 particles. Residual Ga2O3 particles were completely removed by appropriate centrifugation process. To confirm the Ga-doping, variations of sheet resistances for sprayed NP-layers on glass substrates were investigated, showing successful and dramatic reduction from GΩ sq−1-order to sub-kΩ sq−1. The minimum sheet resistance reached to 225 Ωsq−1. From X-ray diffraction and X-ray photoelectron spectroscopy analyses, it can be concluded that Ga atoms diffused from Ga2O3 into ZnO-NPs in the thermal treatment process, and some of them substituted for Zn atoms and were activated as donors. These results can contribute to continuous advance of ZnO-NP-based thin-film-transistor fabrication technique.
Peter Varga has passed on October 27, 2018. His pioneering discoveries of chemical resolution at the atomic scale on surface alloys, atomic resolution of ultrathin alkali halides, nucleation of bcc iron in ultrathin films, and the microscopic structure of ultrathin alumina films stimulated worldwide research. In recognition of his outstanding scientific contributions, in December 2017 the Japanese Society for the Promotion of Science (JSPS) awarded him a prize for his distinguished contribution on the clarification of surface phenomena by atomic level investigations and the development of novel functional materials. This contribution highlights the life of Peter Varga as a scientist and as a person. With his elegance, his energy, his wit, and his generosity he was a close friend and role model to many of us, and showed us how to combine scientific curiosity and creativity with the lightness of being.
Peter Varga at the 13th International Workshop on Inelastic Ion—Surface Collisions
Two-dimensional angle-resolved photoelectron spectroscopy is a powerful method to study the electronic structure of a crystal surface. The latest version of the angle-resolved photoelectron spectroscopy analyzer was installed at the BL6U of the UVSOR-III Synchrotron. This spectrometer consists of a hemispherical electron analyzer equipped with a mechanical deflector and a mesh electrostatic lens close to the sample to make the size of acceptance cone tunable. A constant-energy photoelectron angular distribution of the valence band dispersion cross section in the large wave number region can be efficiently obtained by applying a negative bias voltage to the sample and using a mechanical deflector. Here, the three-dimensional bulk band and the surface state dispersion mappings of Au(111) surface are presented to show the performance of the current photoelectron spectroscopy experimental station. We revisited the dual observation of bulk and surface electronic structures at this kinetic energy regime.
SiO2-supported NiP binary catalysts show high activity for the non-oxidative coupling of methane (NOCM) reactions, one of the most difficult but important catalytic reactions. We have studied the SiO2-supported NiP binary catalysts by extended X-ray absorption fine structure (EXAFS) with different Ni : P ratios. NiP binary catalyst with the composition of Ni : P = 1 : 1 was the most active among the three different compositions. EXAFS showed that the NiP catalyst with Ni : P = 1 : 1 had a Ni2P structure. The structure was stable after the high temperature (1173 K) NOCM reaction conditions for 12 h. It is interesting that Ni2P shows high catalytic activities in many other reactions such as hydrodesulfurization, hydrogen evolution reaction, and so on. It may be due to the appropriate electronic and geometrical modification of a Ni active site by P.