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Electronic Structure of the SrTiO₃(001) Surfaces
K. Takeyasua,K. Fukada,S. Ogura,M. Matsumoto,K. Fukutani 한국진공학회(ASCT) 2014 Applied Science and Convergence Technology Vol.23 No.5
The influence of electron irradiation and hydrogen adsorption on the electronic structure of the SrTiO3 (001) surface was investigated by ultraviolet photoemission spectroscopy (UPS). Upon electron irradiation of the surface, UPS revealed an electronic state within the band gap (in-gap state: IGS) with the surface kept at 1×1. This is considered to originate from oxygen vacancies at the topmost surface formed by electron-stimulated desorption of oxygen. Electron irradiation also caused a downward shift of the valence band maximum indicating downward band-bending and formation of a conductive layer on the surface. With oxygen dosage on the electron-irradiated surface, on the other hand, the IGS intensity was decreased along with upward band-bending, which points to disappearance of the conductive layer. The results indicate that electron irradiation and oxygen dosage allow us to control the surface electronic structure between semiconducting (nearly-vacancy free: NVF) and metallic (oxygen de cient: OD) regimes by changing the density of the oxygen vacancy. When the NVF surface was exposed to atomic hydrogen, in-gap states were induced along with downward band bending. The hydrogen saturation coverage was evaluated to be 3.1±0.8×10<SUP>14</SUP> cm<SUP>?2</SUP> with nuclear reaction analysis. From the IGS intensity and H coverage, we argue that H is positively charged as H<SUP>~0:3+</SUP> on the NVF surface. On the OD surface, on the other hand, the IGS intensity due to oxygen vacancies was found to decrease to half the initial value with molecular hydrogen dosage. H is expected to be negatively charged as H? on the OD surface by occupying the oxygen vacancy site.
Measurements of Neutron-Capture Cross Sections of ^(244)Cm and ^(246)Cm at J-PARC/MLF/ANNRI
A. Kimura,K. Furutaka,S. Goko,H. Harada,T. Kin,F. Kitatani,M. Koizumi,S. Nakamura,M. Ohta,M. Oshima,Y. Toh,T. Fujii,S. Fukutani,J. Hori,K. Takamiya,M. Igashira,T. Katabuchi,M. Mizumoto,T. Kamiyama,K. 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
For developments of innovative nuclear reactors, strong demands exist for the improvement of the accuracy of the neutroncapture cross sections of minor actinides (MAs) and long-lived fission products. We have constructed a Ge-spectrometer using the Accurate Neutron-Nucleus Reaction measurement Instrument (ANNRI) in the J-PARC materials and life science experimental facility (MLF). Preliminary neutroncapture cross sections of ^(244)Cm and ^(246)Cm were obtained in the neutron energy range from 1.0 eV up to 300 eV.
Measurements of Neutron-Capture Cross Sections of Palladium Isotopes at the J-PARC/MLF/ANNRI
S. Nakamura,K. Furutaka,S. Goko,H. Harada,A. Kimura,T. Kin,F. Kitatani,M. Koizumi,M. Ohta,M. Oshima,Y. Toh,J. Hori,T. Fujii,S. Fukutani,K. Takamiya,M. Igashira,T. Katabuchi,M. Mizumoto,T. Kamiyama,K. 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
The operation of a new experimental apparatus called ``Accurate Neutron-Nucleus Reaction measurement Instrument (ANNRI)''in the Material and Life science experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC) has been started for neutroncapture crosssection measurements of minor actinides and long-lived fission products. As a part of the measurements, we have measured the time-of-flight spectra of palladium-105, 106, 107 and 108 with a ``4π Ge spectrometer'' installed at the ANNRI. We obtained preliminary results of the cross sections for palladium-107 and 105 in neutron energies ranging from 0.1 eV to 300 eV.