Electronic Structure of the SrTiO3(001) Surfaces: Effects of the Oxygen Vacancy and Hydrogen Adsorption

K. Fukutania,S. Ogura,K. Fukada,M. Matsumoto 한국진공학회 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±0.8×1014 cm−2 with nuclear reaction analysis. From the IGS intensity and H coverage, we argue that H is positively charged as H~0:3+ 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.

ZVS-PWM Boost Chopper-Fed DC-DC Converter with Load-Side Auxiliary Edge Resonant Snubber

K.Ogura,S.Chandhaket,S.Nagai,T.Ahmed,M.Nakaoka 전력전자학회 2003 전력전자학술대회 논문집 Vol.2003 No.7(1)

This paper presents a high-frequency ZVS-PWM boost chopper-fed DC-DC converter with a single active auxiliary edge-resonant snubber which is used for power conditioner such as solar photovoltaic generation and fuel cell generation The experimental results of boost chopper fed ZVS-PWM DC-DC converter are evaluated in addition to Its switching voltage and current waveforms, and the switching V-I trajectory of the power devices are discussed and compared with the conventional hard switching DC-DC converter treated here The temperature performance of IGBT module, efficiency, and EMI noise characteristics of this ZVS-PWM DC-DC converter using IGBTs are measured and evaluated from an experimental point of view

The Probabilistic Characteristics of Fracture Toughness and Plane Strain Condition in SM41C Steel ( JAPAN )

K. Mogami,K. Ando,N. Ogura 대한기계학회 1990 KSME/JSME Joint Conference Fracture and Strength Vol.1 No.1

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.

Stellar contents and star formation in the young star cluster Be 59

Pandey, A. K.,Sharma, Saurabh,Ogura, K.,Ojha, D. K.,Chen, W. P.,Bhatt, B. C.,Ghosh, S. K. Blackwell Publishing Ltd 2008 Monthly notices of the Royal Astronomical Society Vol.383 No.3

<P>ABSTRACT</P><P>We present <I>UBV I</I><SUB><I>c</I></SUB> CCD photometry of the young open cluster Be 59 with the aim to study the star formation scenario in the cluster. The radial extent of the cluster is found to be ∼10 arcmin (2.9 pc). The interstellar extinction in the cluster region varies between <I>E</I>(<I>B</I>−<I>V</I>) ≃ 1.4 to 1.8 mag. The ratio of total-to-selective extinction in the cluster region is estimated as 3.7 ± 0.3. The distance of the cluster is found to be 1.00 ± 0.05 kpc. Using near-infrared (NIR) colours and slitless spectroscopy, we have identified young stellar objects (YSOs) in the open cluster Be 59 region. The ages of these YSOs range between <1 and ∼2 Myr, whereas the mean age of the massive stars in the cluster region is found to be ∼2 Myr. There is evidence for second-generation star formation outside the boundary of the cluster, which may be triggered by massive stars in the cluster. The slope of the initial mass function, Γ, in the mass range 2.5 < <I>M</I>/M<SUB>⊙</SUB>≤ 28 is found to be −1.01 ± 0.11 which is shallower than the Salpeter value (−1.35), whereas in the mass range 1.5 < <I>M</I>/M<SUB>⊙</SUB>≤ 2.5 the slope is almost flat. The slope of the <I>K</I>-band luminosity function is estimated as 0.27 ± 0.02, which is smaller than the average value (∼0.4) reported for young embedded clusters. Approximately 32 per cent of Hα emission stars of Be 59 exhibit NIR excess indicating that inner discs of the T Tauri star (TTS) population have not dissipated. The Midcourse Space Experiment (MSX) and <I>IRAS-HIRES</I> images around the cluster region are also used to study the emission from unidentified infrared bands and to estimate the spatial distribution of optical depth of warm and cold interstellar dust.</P>

ON THE REDDENING LAW AND DISTANCE OF THE GALACTIC GIANT HII REGION NGC 3603

PANDEY A. K.,OGURA K. The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1

The aim of the paper is to analyse the extinction law in the giant H II region NGC 3603. The ratio R is found to be greater than 5.0. In front of the cluster the reddening law is found to be normal. We have obtained a distance of $\~$5.3 Kpc which is significantly smaller than those adopted so far.

Effect of Abrasive and Fiber Component in Medium on Occlusal Wear of Antagonist and Porcelain

Kakuta K,Ogura H 대한치과재료학회 2011 대한치과기재학회 학술대회 Vol.2011 No.5

高分子 PVDF 振動子를 利用한 点集束超音波探觸子의 특성

韓應敎,黃汐泰,李範成,朴俊緖,小倉幸夫 한국비파괴검사학회 1992 한국비파괴검사학회지 Vol.12 No.2

In this study, we examine the characteristics of beam and the effect of these characteristics on the flaw detection by using different type of two transducers, which are PZT and PVDF film transducer. Consequently, the detection of infinitesimal flaw is more possible than PZT, since it has beam width at focus of 60%∼65% in contrast with PZT's. Moreover we can know PVDF transducer has superiority in detecting ability for sub-suface flaw detection in view of its acoustic impedance is near to water's and its focusing range is narrower than PZT's as 65%∼85% because it has spherical surface.

Sinewave-PWM ZVS Inverter using High-frequency Transformer for Utility AC Voltage Ink

S Chandhket,K Ogura,Y Konishi,M Nakaoka 전력전자학회 2003 전력전자학술대회 논문집 Vol.2003 No.7(2)

This paper presents a novel prototype of the utility-interfaced si- nusoidal pulse width modulated (SPWM) inverter using the high-frequency fiyback transformer for the small-scale solar photo- voltaic power conditioner (lkW - 4kW) The proposed SPWM power conditioner circuit with a high-frequency link has a function of electrical isolation, which is vital for solar photovoltaic power conditioner systems with the viewpoint of safety and convenience The discontinuous conduction mode (DCM) operation of the fly. back transformer is also maintained to simplify the topology of the inverter circuit and control scheme first, the operating principle of the proposed circuit is described for the understanding of the circuit parameters establishment. Then, the digitally constructed SPWM control scheme is presented The proposed circuit is verified by the computer Simulation and the prototype experiment<br/>

Utility-Interactive Modulated Sinewave Inverter with a High Frequency Flyback Transformer Link for Small-Scale Solar Photovoltaic Generator

Y.Konishi,S.Chandhaket,K.Ogura,M.Nakaoka 전력전자학회 2001 ICPE(ISPE)논문집 Vol.2001 No.10

This paper presents a novel prototype of the utility-interactive voltage source type sinewave pulse modulated power inverter using a high-frequency flyback transformer link The proposed power con­ditioner circuit for the solar photovoltaic generation and small scale fuel cell has an isolation function due to the safety of the power processing sys­tem, which is more cost effective and acceptable for the small-scale dis­tributed renewal energy conditioning and processing systems. The discon­tinuous current mode(DCM) of this power processing conversion circuit is applied to implement a simple circuit topology and pulse modulated con­trol scheme. Its operation principle is described on the basis of simulation evaluations and theoretical considerations. The simulation results obtained herein prove that the proposed inverter outputs with sinusoidal waveforms and unity power factor currents are synchronized to the main voltage in utility power source grid. In this paper, the soft switching topology of high-frequency linked sinewave pulse modulation inverter is proposed and dis­cussed.<br/> Index Terms -High frequency link, Flyback transformer link, Sinewave modulated inverter, Utility interactive power processing, Solar photovoltaic power conditioner, Renewal conversion energy and sustainable energy, Soft-switching topology.<br/>