Chemical Reaction between Single Hydrogen Atom and Graphene

We study chemical reaction between a single hydrogen atom and a graphene, which is the elemental reaction between hydrogen and graphitic carbon materials. In the present work, classical molecular dynamics simulation is used with modified Brenner's empirical bond order potential. The three reactions, that is, absorption reaction, reflection reaction and penetration reaction, are observed in our simulation. Reaction rates depend on the incident energy of the hydrogen atom and the graphene temperature. The dependence can be explained by the following mechanisms: (1) The hydrogen atom receives repulsive force by pi-electrons in addition to nuclear repulsion. (2) Absorbing the hydrogen atom, the graphene transforms its structure to the ``overhang'' configuration such as sp-3 state. (3) The hexagonal hole of the graphene is expanded during the penetration of the hydrogen atom.Comment: 10 pages, 9 figures. This paper was submitted to PR

Hybrid Simulation between Molecular Dynamics and Binary Collision Approximation Codes for Hydrogen injection onto Carbon Materials

Molecular dynamics (MD) simulation with modified Brenner's reactive empirical bond order (REBO) potential is a powerful tool to investigate plasma wall interaction on divertor plates in a nuclear fusion device. However, MD simulation box's size is less than several nm for the performance of a computer. To extend the size of the MD simulation, we develop a hybrid simulation code between MD code using REBO potential and binary collision approximation (BCA) code. Using the BCA code instead of computing all particles with a high kinetic energy for every step in the MD simulation, considerable computation time is saved. By demonstrating a hydrogen atom injection on a graphite by the hybrid simulation code, it is found that the hybrid simulation code works efficiently in a large simulation box.Comment: 5 pages, 5 figure

Molecular Dynamics Simulation of Chemical Vapor Deposition of Amorphous Carbon: Dependence on H/C Ratio of Source Gas

By molecular dynamics simulation, the chemical vapor deposition of amorphous carbon onto graphite and diamond surfaces was studied. In particular, we investigated the effect of source H/C ratio, which is the ratio of the number of hydrogen atoms to the number of carbon atoms in a source gas, on the deposition process. In the present simulation, the following two source gas conditions were tested: one was that the source gas was injected as isolated carbon and hydrogen atoms, and the other was that the source gas was injected as hydrocarbon molecules. Under the former condition, we found that as the source H/C ratio increases, the deposition rate of carbon atoms decreases exponentially. This exponential decrease in the deposition rate with increasing source H/C ratio agrees with experimental data. However, under the latter molecular source condition, the deposition rate did not decrease exponentially because of a chemical reaction peculiar to the type of hydrocarbon in the source gas.Comment: accepted by Jpn. J. Appl. Phys. (2008

多要素認証の認証コード通知を偽ったSMSの調査と対応

核融合科学研究所ではMicrosoft 365 for Education A3を契約し，認証方式にSMSなどを用いた多要素認証を必須としている．2021年12月に利用者からNIFS-CSIRTに対し中国語の意図せぬマイクロソフトの認証コード通知のSMSが着信したとの報告があり，研究所全域に情報提供を呼びかけた結果，認証方式にSMSを設定している利用者の2割以上が意図せぬSMSを受信していたことが判明した．その後，Azure ADログの確認とマイクロソフト社へ問合せの結果，利用者情報の漏洩はないことを確認した．同社からはあわせて，長期的にはSMSなど公衆交換電話網を介在させる認証方式は避けた方がよい旨の助言があった．未だに根本的な原因は不明であるが，本稿では本事案の調査と対応について考察する

Triple Hybrid Simulation Method for Tungsten Fuzzy Nanostructure Formation

To represent the formation of fuzzy nanostructures produced on a tungsten surface by exposure to a helium plasma, we have developed a hybrid simulation method that combines the binary collision approximation, molecular dynamics, and kinetic Monte Carlo calculations (BCA-MD-KMC). Since the MD code has been parallelized using the domain decomposition method (DDM) for execution in a multi-CPU environment, we developed the BCA code from scratch to mesh it efficiently with the DDM. The BCA-MD-KMC hybrid simulation code achieved a helium irradiation time of 0.1 seconds or longer, in spite of functioning at the level of atomic-scale models. In consequence, we have been able to observe the formation of concave and convex structures on a tungsten surface in the simulation