Structure of quasi-free-standing graphene on the SiC (0001) surface prepared by the rapid cooling method

Sumi, Tatsuya*; Nagai, Kazuki*; Bao, J.*; Terasawa, Tomoo; Norimatsu, Wataru*; Kusunoki, Michiko*; Wakabayashi, Yusuke*

Applied Physics Letters, 117(14), p.143102_1 - 143102_5, 2020/10

https://doi.org/10.1063/5.0021071

A systematic structural study of epitaxial graphene samples on the SiC (0001) surface has been performed by the surface X-ray diffraction method, which is a non-contact technique. For samples with only a buffer layer, one layer graphene, and multilayer graphene, the distances between the buffer layer and the surface Si atoms were found to be 0.23 nm. This value is the same as reported values. For quasi-free-standing graphene samples prepared by the rapid cooling method, there was no buffer layer and the distance between the quasi-free-standing graphene and the surface Si atoms was 0.35 nm, which is significantly shorter than the value in hydrogen-intercalated graphene and slightly longer than the interplane distance in graphite. The Si occupancy deviated from unity within 1 nm of the SiC surface. The depth profile of the Si occupancy showed little sample dependence, and it was reproduced by a simple atomistic model based on random hopping of Si atoms.

Direct observation of symmetrization of hydrogen bond in -AlOOH under mantle conditions using neutron diffraction

Sano, Asami; Hattori, Takanori; Komatsu, Kazuki*; Kagi, Hiroyuki*; Nagai, Takaya*; Molaison, J. J.*; Dos Santos, A. M.*; Tulk, C. A.*

Scientific Reports (Internet), 8(1), p.15520_1 - 15520_9, 2018/10

https://doi.org/10.1038/s41598-018-33598-2

The pressure response of hydrogen bond in aluminous hydroxide -AlOOH, which is an important candidate for water carrier to the deep Earth in a subducting slab, was investigated using neutron diffraction under high pressure. The symmetrization of hydrogen bond in which hydrogen locates at the center between two oxygen atoms was observed directly for the first time. The present result indicates that the changes of mineral properties such as increase in bulk modulus and sound velocities, which were previously found, were induced by the symmetrization and disorder state that was also found at just below the symmetrization pressure. Even the symmetrization is a small change in the hydrogen location but it is playing an important role in determining the physical properties of minerals.

Design and performance of high-pressure PLANET beamline at pulsed neutron source at J-PARC

Hattori, Takanori; Sano, Asami; Arima, Hiroshi*; Komatsu, Kazuki*; Yamada, Akihiro*; Inamura, Yasuhiro; Nakatani, Takeshi; Seto, Yusuke*; Nagai, Takaya*; Utsumi, Wataru; et al.

Nuclear Instruments and Methods in Physics Research A, 780, p.55 - 67, 2015/04

https://doi.org/10.1016/j.nima.2015.01.059

PLANET is a time-of-flight (ToF) neutron beamline dedicated to high-pressure and high-temperature experiments. The large six-axis multi-anvil high-pressure press designed for ToF neutron diffraction experiments enables routine data collection at high pressures and high temperatures up to 10 GPa and 2000 K, respectively. To obtain clean data, the beamline is equipped with the incident slits and receiving collimators to eliminate parasitic scattering from the high-pressure cell assembly. The high performance of the diffractometer for the resolution ( / 0.6%) and the accessible -spacing range (0.2-8.4 ) together with low-parasitic scattering characteristics enables precise structure determination of crystals and liquids under high pressure and temperature conditions.

Pressure responses of portlandite and H-D isotope effects on pressure-induced phase transitions

Iizuka, Riko*; Kagi, Hiroyuki*; Komatsu, Kazuki*; Ushijima, Daichi*; Nakano, Satoshi*; Sano, Asami; Nagai, Takaya*; Yagi, Takehiko*

Physics and Chemistry of Minerals, 38(10), p.777 - 785, 2011/12

https://doi.org/10.1007/s00269-011-0450-3

The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening observed from the Raman and IR spectra of Ca(OH) occurred at lower pressures than those of Ca(OD). In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns. X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization in a helium pressure medium within the examined pressure region. These results suggest that the H-D isotope effect is engendered in the local environment surrounding H(D) atoms.

Simulation of long time averaged concentration under actual meteorological conditions

Hara, Tomohiro*; Oba, Ryoji*; Okabayashi, Kazuki*; Yoneda, Jiro*; Nagai, Haruyasu; Hayashi, Takashi*

Proceedings of International Workshop on Physical Modelling of Flow and Dispersion Phenomena (PHYSMOD 2007), p.167 - 174, 2007/08

We simulated a meandering effect of wind direction fluctuation on horizontal gas diffusion over Mt. Tsukuba, using a rotating turntable in the wind tunnel experiment. Experimental results were validated with field data observed by Japan Atomic Energy Research Institute (JAERI), 1989 and 1990. We also simulated actual unsteady phenomena of airflow and gas diffusion over Mt. Tsukuba, and compared the calculated results with field data. Both data agreed well under neutral, stable and unstable atmospheric stabilities.

User operation at J-PARC and strategy of high pressure research with neutron

Utsumi, Wataru; Abe, Jun; Hattori, Takanori; Fukazawa, Hiroshi; Yamauchi, Hiroki; Igawa, Naoki; Kagi, Hiroyuki; Arima, Hiroshi*; Arakawa, Masashi; Komatsu, Kazuki*; et al.

no journal, , 

no abstracts in English

Change in compressibility of MOOH oxyhydroxide at high pressure

Sano, Asami; Yagi, Takehiko*; Kagi, Hiroyuki*; Nagai, Takaya*; Komatsu, Kazuki*

no journal, , 

High-pressure neutron diffraction experiment at SNAP, SNS

Sano, Asami; Hattori, Takanori; Utsumi, Wataru; Komatsu, Kazuki*; Kagi, Hiroyuki*; Nagai, Takaya*

no journal, , 

-AlOOH, distorted rutile type oxyhydroxide, is an important hydrous mineral in the deep earth that has the ability to transport hydrogen into the lower mantle. Theoretical studies have pointed out that hydrogen would locate at the center between two oxygen atoms at high pressure, which is so called symmetrization of the hydrogen bond. To investigate the pressure response of strong hydrogen bond -AlOOH, we conduct neutron diffraction experiment at SNAP in SNS. Neutron diffraction patterns of -AlOOH was measured on SNAP to 7 GPa. The intensity of the peak that is only observed in the space group P2nm become weak at high pressure suggesting the transition to H-disordered or symmetric hydrogen bond model with Pnnm.

Neutron diffraction study on -AlOOH at high pressure

Sano, Asami; Komatsu, Kazuki*; Hattori, Takanori; Nagai, Takaya*; Kagi, Hiroyuki*; Molaison, J.*; Moreira Dos Santos, A.*; Tulk, C.*

no journal, , 

-AlOOH is a high pressure polymorph of diaspore. Previous theoretical studies predict that hydrogen bond become symmetric at high pressure. Neutron diffraction experiment at high pressure found that O-D bond is elongated at high pressure, in support these predictions. Powder X-ray diffraction studies also found that the change in compressibility occurs at high pressure. To investigate the sequence to the symmetrization and its relation with the change in compressibility, we conducted neutron diffraction experiments on -AlOOH was conducted at SNAP, SNS. The results suggest the transition from hydrogen ordered structure to disordered structure at 6.7 GPa. Strong DH isotope effect was also found in the hydrogen bond geometry at high pressure.

Performance and the current status of the high-pressure neutron diffractometer PLANET

Hattori, Takanori; Sano, Asami; Arima, Hiroshi*; Komatsu, Kazuki*; Yamada, Akihiro*; Nagai, Takaya*; Katayama, Yoshinori; Inoue, Toru*; Utsumi, Wataru; Kagi, Hiroyuki*; et al.

no journal, , 

The PLANET is the world's first neutron beamline specialized for high-pressure and high-temperature experiments. The most characteristic feature is the capability to investigate the state of the matter at high-pressure and high-temperatures up to 20 GPa and 2000 K with the multi-anvil high-pressure apparatus. The construction was started in 2008. The beamline was commissioned in the first half year of JFY 2012 and the new data is being taken by project members. This year, the beamline is reborn to a public beamline of J-PARC. In this talk, the performance of the PLANET and the typical results are introduced. The resolution of the diffraction pattern (d/d=c.a 0.6%) was found to be almost equal to the designed value (0.5%). The elimination of the background from the sample surrounding materials, which is the most important feature of the high-pressure experiments, was found to be accomplished with the use of the severe incident collimator and radial receiving collimator system. The beamline is opened for general users since the last half year of JFY2013 (from Feb.).