Atomic sheets or layers on surfaces have been significant playgrounds for low-dimensional physics and also promising elements for future technology. There are varieties of such two-dimensional crystal sheets that show rich functionalities. In this special issue, we present selected research topics on various types of atomic sheets.
We present a review on the electronic applications of compound materials nanosheets as semiconductor channel materials. Also, we report our results about the device fabrication and characterization of high-k/metal gate MoS2 metal-oxide-semiconductor field-effect transistors (MOSFETs). To investigate the scattering mechanism to be responsible for the mobility of MoS2 MOSFETs, the effective mobility has been estimated from the capacitance-voltage and current-voltage characteristics of top-gated MoS2 MOSFET with HfO2/TaN gate. Phonon-limited carrier transport probably limited the mobility of the MoS2 device exhibiting the better mobility. In contrast, the transport characteristics of the MoS2 device exhibiting the lower mobility was dominated by charged impurity scattering in MoS2.
The topological aspects in the physics of atomic layers, particularly the valley physics, are briefly reviewed. First, the Berry curvature of band structure is introduced as a basic concept for the k-space topology. The stability of Dirac cones and the valley splitting of Landau levels in gapped graphene are explained topologically. The valley Hall effect in gapped graphene is discussed as a remarkable topological transport phenomenon. The spin-valley correspondence is also mentioned in 2H-MoS2 monolayer with no inversion symmetry.
Electric double layer transistor (EDLT) has attracted attentions over the decade as a useful tool to induce and control fascinating many physical properties at two dimensional (2D) materials surface based on its giant capacitance. This paper highlights another aspect of EDLT: electrochemical reaction as a method to achieve ultrathin films. Precise tuning of reactivity of electrochemical etching between ionic liquid and solid surface makes it possible to peel off 2D materials layer-by-layer. This technique was applied to an iron-based superconductor FeSe in EDLT towards the observation of high temperature superconductivity in ultra-thin film form.
We report on structure determinations of graphene and silicene on metal substrates using total-reflection high-energy positron diffraction (TRHEPD) technique. The magnitude of buckling in graphene (silicene) and the spacing between graphene and substrate are crucial to elucidate the origin of the electronic property of graphene adsorbed on a substrate. In this study, these structure parameters for graphene/Co(0001), graphene/Cu(111), and silicene/Ag(111) were determined with the aid of surface sensitivity of the TRHEPD. The experimental verification of these parameters will promote a better understanding of the properties of graphene and silicene.
The role of promoting materials for the preferential oxidation (PROX) reaction of CO in H2 on Pt-catalysts was elucidated by using the Pt-catalyst supported on a CNT with Ni-MgO at its terminal end and the CNT-p with no Ni-MgO. The role of Ni-MgO is not the synergy effect on the Pt but set up a new catalytic oxidation reaction cycle of CO in the presence of H2O. The dynamic In-situ IR spectroscopy suggested the rate determining slow step of HCOO + OH → CO2 + H2O, where H2O molecule plays like a molecular catalyst in cooperation of Pt and promoting materials. The contribution of H2O is expressed by n(CO + 1/2O2) + H2O → n CO2 + H2O, where n is CO2 molecules by one H2O molecule staying on the surface. According to this new concept, the selectivity is given by n/(n+1), which takes 50%∼100% depending on the staying time of H2O on the catalyst. The mysterious high selectivity reported on the Pt-nano rods in SiO2-nano-tube and the curious selectivity on Au/CeO2 depending on the crystal shape of CeO2 are well rationalized by this new mechanism.
科学警察研究所は,警察庁付属の国立研究機関で,犯罪科学に関する総合的な研究を行っている。筆者の所属する犯罪行動科学部では,心理学,社会学などの「行動科学」に基づき,少年の非行防止,犯罪被害の予防,捜査の支援などに資する研究を進めている。筆者自身は,これまで,主に少年の非行防止や犯罪予防に関する研究を行ってきた。その過程で,犯罪の被害にあわれた方々の多くが,ほとんど異口同音にこう語られることに,強い衝撃を受けた。「こんな思いをするのは私たちだけでたくさんです。二度とこんな事が起きないようにしてください。」この痛切な言葉に,自分は,研究活動を通じてどのように応えることができるのか。それが,常に頭のなかにあった。本稿では,科学が支える子どもの被害防止の実現のために,「危険なできごとカルテ」や「聞き取りマップ」,そして「予防犯罪学」の構想を紹介する。