数理物質系・物質工学域ナノ物質化学研究室 近藤研究室

Invited talkMaterials Science Seminar

Abstract

H-atom transfer and H-bond rearrangement are involved in many important physical, chemical, and biological processes such as proton conductor, acid?base reactions, and DNA [1]. However, an accurate and quantitative description of H-atom/bonding dynamics remains a very challenging topic and nuclear quantum effects (NQEs) and anharmonicity of the potential energy surface are outstanding problems in the field. In order to examine such dynamics, it is necessary to investigate model systems at the single-molecule level because NQEs and anharmonic nature are quite susceptive to a local environment of individual molecules and hidden by inhomogeneities of bulk samples. Low-temperature SPM has provided a new opportunity to study hydrogen-atom/bonding dynamics [2]. Single-molecule tautomerization serves as a fascinating model and I will discuss hydrogen-transfer reactions occurring through various external stimuli as well as quantum tunneling [3].

References

• Hydrogen-transfer reaction. J. T. Hynes, J. P. Klinman, H.-H. Limbach, R. L. Schowen, Weley-VCH, 2007.
• TK, Prog. Surf. Sci. 90, 239 (2015).
• TK et al. Phys. Rev. Lett. 111, 246101 (2013).; TK et al. Nature Chem. 6, 41 (2014).; J. Ladenthin et al. ACS Nano 9, 7287 (2015).; H. Bockmann et al. Nano Lett. 16, 1034 (2016).; J. Ladenthin et al. Nature Chem. 8, 935 (2016).; M. Koch et al. J. Am. Chem. Soc. 139, 12681 (2017).; TK, J. Chem. Phys. 148, 102330 (2018):; H. Bockmann et al. Nano Lett. 18, 152 (2018).

Invited talkセミナー

Abstract

シリコンはダイヤモンド型構造をとるため劈開面が無い。それ故、同族元素である黒鉛構造のカーボンのように剥離法によって二次元シートを取り出すことは困難である。本講演では、Zintl silicideの一つであるCaSi2から誘導される層状シリコン化合物に着目し、これらを単層剥離して得られる二次元シリコン物質群の合成と機能について紹介する。

Reference

R.Yaokawa, T. Ohsuna, T. Morishita, Y. Hayasaka, M. J. S. Spencer & H.i Nakano, Nature Communications 7, 10657 (2016)

Invited talkセミナー

Abstract

半導体光触媒は抗菌・抗ウイルス等の環境浄化や水素生成等のエネルギー製造技術として期待されている。本報告では、これまでの光触媒の研究開発の歴史を述べた上、界面の光励起プロセスを利用した新規な可視光応答型光触媒の開発について紹介する。更に、開発した光触媒のセルフクリーニング部材や抗菌・抗ウイルス用途への応用と、空港、病院などの施設における実証試験について報告する。

Invited talkセミナー

Abstract

Two-dimensional (2D) polymers are expected to have a great impact on many fundamental and applied aspects of science. Some recent demonstrations of covalent polymerization performed directly at surfaces have opened promising perspectives.[1] The polymer formation is usually obtained by deposition of the molecular precursors on the surface followed by thermal activation of the polymerization reaction. In particular, boronic acids can undergo a self-condensation (dehydration) reaction to create rigid boroxine rings and a planar polymer sheet. By using 1,4-benzenediboronic acid (BDBA) evaporated onto a well-defined metal surface, extended nanoporous 2D networks could grow. I will present recent scanning tunneling microscopy (STM) results in ultrahigh vacuum (UHV) reflecting various efforts to control the growth process of these two-dimensional covalent organic frameworks (influence of the deposition parameters, local activation of the reaction, coupling with an Ullmann reaction, nanopatterning).[2] In a second part I will show how the probe of an atomic force microscopy (AFM) can locally and selectively initiate a chemical reaction. Scanning probe lithography (SPL) is a highly promising tool for the creation of specific nanosized patterns on a surface with high spatial resolution. We reported a novel approach to chemically selective lithography using AFM probe with immobilized homogeneous catalyst, potentially opening an access to a diversity of nanoscale transformations of the surface-bound functional groups.[3] This new concept was proven for local epoxidation of alkene-terminated self-assembled monolayer on silicon using H₂O2 as an oxidant and a catalytic silicon AFM tip charged with manganese complexes with 1,3,7-triaza-cyclononane type ligand. By varying the reaction parameters (scanning speed, force applied), important insights into the reaction mechanism could be obtained.

References

• J. Bjork, F. Hanke, Chemistry-a European Journal 20, 928 (2014)
• S. Clair, M. Abel, L. Porte, Chemical Communications 50, 9627 (2014)
• D. Valyaev et al., Chemical Science 4, 2815 (2013)

Invited talkセミナー

Abstract

Recent years have witnessed an ever growing interest in carbon based materials, especially after the experimental observation of graphene. In this context, adsorption of hydrogen atoms on graphene and nanoribbons can be used to tailor their electronic and magnetic properties, as already suggested for other“defects,” with the advantage of being easier to realize than, e.g. C vacancies. In addition, interaction of hydrogen atoms with graphitic compounds has been playing an important role in a number of fields as diverse as coatings for nuclear fusion reactors, hydrogen storage, and interstellar chemistry. Hydrogen atoms are known to chemisorb onto graphitic surfaces to form dimers, that can react forming H₂ molecules. Here we review the mechanism of chemisorption and dimers formation in graphene bulk and edges, that is governed by the peculiar aromatic electronic structure. Then we show recent dynamical simulations of H₂ recombination through the Eley-Rideal mechanism, with both accurate quantum wave packet calculations on model potential energy surfaces and ab initio molecular dynamics. We show that steering of the projectile atom gives an important contribution to the reaction at low collision energies and prevents dimers formation. At higher energies, on the other hand, the so-called ortho and para dimers form abundantly, in agreement with recent STM and molecular beams experiments. As well, we show preliminary calculations about the mechanism of H adsorption on single carbon vacancies and nanoribbon edges, stressing their possible applications in understanding carbon magnetism and catalytic activity.

Invited talk物質科学セミナー

Abstract

近年、有機EL素子、有機FET、単一分子素子など、機能性分子を用いたデバイスの研究が盛んに行われている。それらの機能は、分子自体の電子状態はもちろん、分子のコンフォメーションや配列状態、基板表面との相互作用などによって大きく変わる。そこで我々は、走査型トンネル顕微鏡(STM)を用いた高分解能実空間観察技術を駆使し、金属表面に吸着した機能性ナノ分子のさまざまな性質を明らかにしようとしている[1]。本講演では、金属表面に吸着したオリゴチオフェン、ポルフィリン、イリジウム錯体などのナノサイズ分子について、STM 観察やトンネル電子分光による直接観察によって明らかになった結果を報告する。特に、内容を（1）吸着分子のコンフォメーション解析や異性体識別、電子状態計測などを中心にした単一分子観察[2]、（2）表面拡散や分子間相互作用[3]、（3）分子を表面で組み上げる超分子自己組織化に分けて概説する予定である。

References

• 日本物理学会誌(2011)
• JCP(2001), JPC B(2006), JPC B(2008), JCP(2008)
• PRL(2007), PRB(2010)
• Nature(2001), JACS(2002), JCP(2004), APL(2006+2010), AdvMater(2007), JPC C(2008+2009)

Invited talk

Abstract

A major goal of research in heterogeneous catalysis is to determine the mechanisms by which chemical reactions take place on transition metal surfaces. In pursuit of this goal, surface spectroscopic methods are often used to identify stable molecular species that form in the course of surface chemical reactions. The technique of reflection absorption infrared spectroscopy (RAIRS) has the sensitivity and resolution to measure the vibrational spectra of a large variety of molecular species present on surfaces at submonolayer coverages, including novel intermediates that are structurally distinct from species that are stable in the gas phase. As each molecule has a unique vibrational spectrum, RAIRS can be used to definitively identify particular chemical species. On the other hand, the technique is not quantitative and therefore does not readily yield the coverages of various species that might coexist on a surface. In contrast, with low temperature scanning tunneling microscopy (LT-STM) individual atoms and molecules can be observed and their absolute coverages readily determined. The LT-STM, however, generally lacks chemical specificity. By combining RAIRS data obtained at the University of Illinois at Chicago with LT-STM images obtained at the Institute of Chemical and Physical Research in Wakoshi, Japan, of the same surface chemical systems, a great deal of new and unique information on surface intermediates can be obtained. This will be illustrated with several adsorbates and their reactions on the Pt(111) surface. The methyl isocyanide molecule (CH₃NC) forms coordination complexes with a variety of transition metals and undergoes several characteristic reactions, such as protonation at the N atom. This latter reaction is readily revealed to occur on Pt(111) with RAIRS. With the LT-STM, individual molecules of CH₃NC are observed to be transformed into a new form through reaction with hydrogen, and based on the RAIRS results, this new form is inferred to be methylaminocarbyne, CH3HNC. The LT-STM can be further used to manipulate individual CH₃NC and CH3HNC molecules, and to remove an H atom from CH3HNC to form CH₃NC, a reaction that does not occur thermally. A similar correlation of RAIRS and LT-STM results has been obtained for various C₂Hx species that form through the adsorption and reaction of acetylene and ethylene on Pt(111). Some of the C₂Hx species that have been identified and characterized in this way include vinyl (CHCH₂), vinylidene (CCH₂), ethylidyne (C₂H₃), and ethynyl (CCH).

Invited talk

Abstract

Interfacial water is of importance for a variety of disciplines including electrochemistry, (photo-) catalysis and biology. Water interfaces are characterized by the interruption of the bulk hydrogen bonded network, which gives interfacial water its unique properties (e.g. high surface tension). Using surface-specific Vibrational Sum-Frequency Generation (VSFG) Spectroscopy, we investigate the vibrational spectrum of the outermost monolayer of interfacial water molecules. The O-H stretch vibration ofinterfacial water provides a sensitive marker of the local environment of interfacial water molecules. In time-resolved measurements, the vibrational lifetime of hydrogen-bonded interfacial water is determined using a novel, surface-specific 4th-order VSFG spectroscopy. The O-H stretch vibration of interfacial water is resonantly excited with an intense, 100 fs infrared pulse; the vibrational relaxation dynamics are followed with femtosecond, time-resolved VSFG spectroscopy. Our results reveal that interfacial water is structurally more homogeneous than previously thought [1]. Furthermore, ultrafast exchange of vibrational energy can occur between water surface and bulk water [2], but the occurrence of ultrafast resonant vibrational energy transfer depends critically on the details of the water interface [3]. Finally, we demonstrate a new type of two-dimensional surface spectroscopy that allows one to follow the structural evolution of interfacial molecular systems in real-time.[4]

References

• M. Sovago, R. Campen, G. Wurpel, M. Muller, H. Bakker and M. Bonn, Phys. Rev. Lett. 2008 100 173901
• M. Smits, A. Ghosh, M. Sterrer, M. Muller and M. Bonn Phys. Rev. Lett. 2007 98 098302.
• A. Ghosh, M. Smits, J. Bredenbeck and M. Bonn J. Am. Chem. Soc. 2007 129 9608.
• J. Bredenbeck, A. Ghosh, M. Smits and M. Bonn J. Am. Chem. Soc. 2008 130 2152.

Invited talk

Abstract

When gas atoms or molecules collide with clean and ordered surfaces, under many circumstances the energy-resolved scattering spectra exhibit two clearly distinct features, the first due to direct scattering and the second due to trapping in the physisorption well with subsequent desorption. James Clerk Maxwell is credited with being the first to describe this situation by invoking the simple assumption that when an impinging gas beam is scattered from a surface it can be divided into a part that reflects specularly with no energy transfer and another part that equilibrates or accommodates completely and then desorbs with an equilibrium distribution. In this talk a scattering theory is presented, using an iterative algorithm and classical mechanics for the collision process, that describes both direct scattering and trapping-desorption of the incident beam. The initially trapped particles can be followed as they continue to make further interactions with the surface until they are all eventually promoted back into the positive energy continuum and leave the surface region. Consequently, this theory allows a rigorous test of the Maxwell assumption and determines the conditions under which it is valid. The theory also gives quantitative explanations of recent experimental measurements [S. J. Sibener et al., J. Chem. Phys. 119, 13083 (2003)] which clearly exhibit both a direct scattering contribution and a trapping-desorption fraction in the energy-resolved spectra.

Invited talk

Contents

• はじめに
• 化学ポテンシャル（Energy Level Alignmentの駆動源）
• エネルギーレベルアライメント（Energy Level Alignment）
• 電荷中性準位（Charge Neutrality Level : CNL）
• 金属・有機半導体界面における真空レベルオフセットの理論的背景
• Carrier Injection Barriers
• 有機半導体FET（OFET）の概要
• まとめ

Invited talk

Abstract

Studies of elementary collision processes of H₂ with metal surfaces can provide benchmark tests of theoretical methods that are increasingly used to aid the design of new heterogeneous catalysts. Molecular beam and associative desorption experiments have been carried out to understand the main factors that govern H₂ dissociation at the surface. In addition, vibrationally inelastic and rotationally inelastic scattering experiments have provided useful information on how certain features of the potential energy surface (PES) control the experimental observations. A different point of view is provided by diffraction experiments. H₂ diffraction from metal surfaces is more complex than He diffraction, since the PES is six-dimensional and the coupling with the dissociative adsorption channels comes into play. Thus, H₂ diffraction is a verya promising technique to gauge the molecule-surface PES and dynamics. We have recently shown that this is possible by performing H₂ diffraction experiments on reactive Pd(111) and non reactive NiAl(110) surfaces at 70-150 meV. By comparing with six-dimensional quantum dynamics and classical trajectory calculations we showed for the first time that accurate diffraction patterns can be obtained from state-of-the-art PES based on density functional theory . Once the PESs are validated, they can be used to study in detail the relationship between the trajectories followed by the H₂ molecules and the different channels involved in reactivity, like direct dissociation and dynamic trapping. Finally, I will address the problem of the validity of the Born- Oppenheimer approximation for molecule-metal surface reactions, which has been recently questioned due to the possibility of electron-hole pair excitations . We have performed experiments and six-dimensional quantum dynamics calculations on the scattering of molecular hydrogen from Pt(111), obtaining absolute diffraction probabilities. The comparison for in-plane and out-of-plane scattering, and results for dissociative chemisorption in the same system, show that for hydrogen-metal systems, reaction and diffractive scattering can be accurately described using the Born-Oppenheimer approximation .

References

• G. J. Kroes and M. F. Somers, J. Theor. Comput. Chem. 4, 493 (2005).
• D. Farias and K.H. Rieder, Rep. Prog. Phys. 61, 1575 (1998).
• D. Farias, C. Diaz, P. Riviere, H. F. Busnengo, P. Nieto, M. F. Somers, G. J.Kroes, A. Salin and F. Martin, Phys. Rev. Lett. 93, 246104 (2004).
• J. D. White, J. Chen, D. Matsiev, D. J. Auerbach, A. M. Wodtke, Nature 433, 503 (2005).
• P. Nieto, E. Pijper, D. Barredo, G. Laurent, R. A. Olsen, E. J. Baerends, G. J. Kroes, and D. Farias, Science 312, 86 (2006); A. M. Wodtke, ibid. 64; D. Clary, Nature Materials 5, 345 (2006).