Work function lowering of LaB by monolayer hexagonal boron nitride coating for improved photo- and thermionic-cathodes

Yamaguchi, Hisato*; Yusa, Ryunosuke*; Wang, G.*; Pettes, M. T.*; Liu, F.*; Tsuda, Yasutaka; Yoshigoe, Akitaka; Abukawa, Tadashi*; Moody, N. A.*; Ogawa, Shuichi*

Applied Physics Letters, 122(14), p.141901_1 - 141901_7, 2023/04

https://doi.org/10.1063/5.0142591

A lowering of work function for LaB by monolayer hexagonal BN coating is reported. Photoemission electron microcopy (PEEM) and thermionic emission electron microscopy (TEEM) both revealed that the hBN coated region of a LaB(100) single crystal has lower work function compared to the bare (i.e., non-coated) and graphene coated regions. A larger decrease of work function for the hBN coated LaB(100) compared to graphene coated LaB(100) was qualitatively supported by our density functional theory (DFT) calculations. Adding an oxide layer in the calculations improved consistency between the calculation and experimental results. We followed up our calculations with synchrotron-radiation X-ray photoelectron spectroscopy (SR-XPS) and confirmed the presence of an oxide layer on our LaB.

Gas barrier properties of chemical vapor-deposited graphene to oxygen imparted with sub-electronvolt kinetic energy

Ogawa, Shuichi*; Yamaguchi, Hisato*; Holby, E. F.*; Yamada, Takatoshi*; Yoshigoe, Akitaka; Takakuwa, Yuji*

Journal of Physical Chemistry Letters (Internet), 11(21), p.9159 - 9164, 2020/11

https://doi.org/10.1021/acs.jpclett.0c02112

Atomically thin layers of graphene have been proposed to protect surfaces through the direct blocking of corrosion reactants such as oxygen with low added weight. The long term efficacy of such an approach, however, is unclear due to the long-term desired protection of decades and the presence of defects in as-synthesized materials. Here, we demonstrate catalytic permeation of oxygen molecules through previously-described impermeable graphene by imparting sub-eV kinetic energy to molecules. These molecules represent a small fraction of a thermal distribution thus this exposure serves as an accelerated stress test for understanding decades-long exposures. The permeation rate of the energized molecules increased 2 orders of magnitude compared to their non-energized counterpart. Graphene maintained its relative impermeability to non-energized oxygen molecules even after the permeation of energized molecules indicating that the process is non-destructive and a fundamental property of the exposed material.

The H-Invitational Database (H-InvDB); A Comprehensive annotation resource for human genes and transcripts

Yamasaki, Chisato*; Murakami, Katsuhiko*; Fujii, Yasuyuki*; Sato, Yoshiharu*; Harada, Erimi*; Takeda, Junichi*; Taniya, Takayuki*; Sakate, Ryuichi*; Kikugawa, Shingo*; Shimada, Makoto*; et al.

Nucleic Acids Research, 36(Database), p.D793 - D799, 2008/01

https://doi.org/10.1093/nar/gkm999

Here we report the new features and improvements in our latest release of the H-Invitational Database, a comprehensive annotation resource for human genes and transcripts. H-InvDB, originally developed as an integrated database of the human transcriptome based on extensive annotation of large sets of fulllength cDNA (FLcDNA) clones, now provides annotation for 120 558 human mRNAs extracted from the International Nucleotide Sequence Databases (INSD), in addition to 54 978 human FLcDNAs, in the latest release H-InvDB. We mapped those human transcripts onto the human genome sequences (NCBI build 36.1) and determined 34 699 human gene clusters, which could define 34 057 protein-coding and 642 non-protein-coding loci; 858 transcribed loci overlapped with predicted pseudogenes.

Impurity release and deuterium retention properties of a ferritic steel wall in JFT-2M

Ogawa, Hiroaki; Yamauchi, Yuji*; Tsuzuki, Kazuhiro; Kawashima, Hisato; Sato, Masayasu; Shinohara, Koji; Kamiya, Kensaku; Kasai, Satoshi; Kusama, Yoshinori; Yamaguchi, Kaoru*; et al.

Journal of Nuclear Materials, 329-333(Part1), p.678 - 682, 2004/08

https://doi.org/10.1016/j.jnucmat.2004.04.192

no abstracts in English

Real-time synchrotron radiation photoelectron spectroscopic observation of high temperature thermal anneal processes of oxidized graphene

Hozumi, Hideaki*; Yamaguchi, Hisato*; Kaga, Toshihide*; Eda, Goki*; Mattevi, C.*; Ogawa, Shuichi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Teraoka, Yuden; Yamada, Takatoshi*; et al.

no journal, , 

In order to clarify the time evolution of the chemical bonding state during thermal reduction of graphene oxide (GO), real-time photoelectron spectroscopy was employed for observing the thermal reduction kinetics of GO. The GO was prepared by the modified Hummer method. The experiments were performed using the surface reaction analysis apparatus placed at the BL23SU of SPring-8. The XPS measurements were performed simultaneously during the annealing at 473 K, 673 K, 873 K, and 1073 K. The C1s photoelectron spectra are decomposed by 8 components. The - transition loss peak intensity is propotional to the intensity of sp graphene components with temperature elevation. In addition, defect intensity increased in proportion with the sp graphene intensity. These facts indicate that defects were formed on the graphene during reduction and these defects cause the recovery of electric conductivity, that is, the appearance of Fermi edge.

Real-time XPS study of reduction of graphene oxide; Effect of hydrazine treatment

Watanabe, Daiki*; Ogawa, Shuichi*; Yamaguchi, Hisato*; Hozumi, Hideaki*; Eda, Goki*; Mattevi, C.*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Teraoka, Yuden; Yamada, Takatoshi*; et al.

no journal, , 

no abstracts in English

Chemical bonding states and electronic states of reduced graphene oxides studied by real-time photoelectron spectroscopy

Watanabe, Daiki*; Ogawa, Shuichi*; Yamaguchi, Hisato*; Hozumi, Hideaki*; Eda, Goki*; Mattevi, C.*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Teraoka, Yuden; Yamada, Takatoshi*; et al.

no journal, , 

Effects of hydrazine processing in reduction of oxidized graphene

Watanabe, Daiki*; Ogawa, Shuichi*; Yamaguchi, Hisato*; Hozumi, Hideaki*; Eda, Goki*; Mattevi, C.*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Teraoka, Yuden; Yamada, Takatoshi*; et al.

no journal, , 

no abstracts in English

Real-time XPS study of reduction of graphene oxide; Effect of hydrazine treatment

Watanabe, Daiki*; Ogawa, Shuichi*; Yamaguchi, Hisato*; Hozumi, Hideaki*; Mattevi, C.*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Teraoka, Yuden; Yamada, Takatoshi*; Chhowalla, M.*; et al.

no journal, , 

Modification of graphene by treatment of photoemission-assisted plasma

Takabayashi, Susumu*; Fukuda, Akito*; Tsukazaki, Ryuta*; Koga, Hisashi*; Yamaguchi, Hisato*; Ogawa, Shuichi*; Takakuwa, Yuji*; Tsuda, Yasutaka; Yoshigoe, Akitaka

no journal, , 

Graphene has a wide variety of potential applications, including as a channel material in field-effect transistors and as a gas barrier film. The chemical modification and reformation of graphene was studied using photoemission-assisted plasma. In the C 1s photoelectron spectra of graphene/Cu substrates treated under Townsend discharge conditions, which prevent ion damage, both sp2 carbon (sp2 C-C, sp2 C-H) of graphene and a sp3 carbon (sp3 C-H) were observed by synchrotron radiation XPS, indicating that the six-membered ring structure of graphene was cleaved and hydrogen was bonded to it. On the other hand, annealing in a hydrogen-reducing atmosphere resulted in the disappearance of the sp3 C-H and sp2 C-H peaks and the appearance of the sp3 C-C peak, corresponding to hydrogen desorption.