Browsing by Author "Kawai, Shigeki"

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Atom manipulation on an insulating surface at room temperature
(2014) Kawai, Shigeki; Foster, Adam S.; Federici Canova, Filippo; Onodera, Hiroshi; Kitamura, Shin-ichi; Meyer, Ernst
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Atomic manipulation enables us to fabricate a unique structure at the atomic scale. So far, many atomic manipulations have been reported on conductive surfaces, mainly at low temperature with scanning tunnelling microscopy, but atomic manipulation on an insulator at room temperature is still a long-standing challenge. Here we present a systematic atomic manipulation on an insulating surface by advanced atomic force microscopy, enabling construction of complex patterns such as a ‘Swiss cross’ of substitutional bromine ions in the sodium chloride surface.
Atomic-scale dissipation processes in dynamic force spectroscopy
(2011) Kawai, Shigeki; Canova, Filippo Federici; Glatzel, Thilo; Foster, Adam S.; Meyer, Ernst
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A systematic distance-dependent measurement of the quasistatic tip-sample interactions reveals a hidden stochastic dissipative interaction of the atomic-scale contact in dynamic force microscopy. By comparison of experiment with detailed molecular dynamics simulations, we demonstrate that the infrequently observed hysteresis loops are attributed to the formation of atomic chains during tip retraction. These lead to a large magnitude of energy dissipation in a single cycle and dominate the average measured dissipation, while also leading to differences in the forces measured in static and dynamic force microscopy. This paper provides quantitative force measurements and insights into atomic-scale dissipation processes.
Atomically controlled substitutional boron-doping of graphene nanoribbons
(2015) Kawai, Shigeki; Saito, Shohei; Osumi, Shinichiro; Yamaguchi, Shigehiro; Foster, Adam S.; Spijker, Peter; Meyer, Ernst
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Boron is a unique element in terms of electron deficiency and Lewis acidity. Incorporation of boron atoms into an aromatic carbon framework offers a wide variety of functionality. However, the intrinsic instability of organoboron compounds against moisture and oxygen has delayed the development. Here, we present boron-doped graphene nanoribbons (B-GNRs) of widths of N=7, 14 and 21 by on-surface chemical reactions with an employed organoboron precursor. The location of the boron dopant is well defined in the centre of the B-GNR, corresponding to 4.8 atom%, as programmed. The chemical reactivity of B-GNRs is probed by the adsorption of nitric oxide (NO), which is most effectively trapped by the boron sites, demonstrating the Lewis acid character. Structural properties and the chemical nature of the NO-reacted B-GNR are determined by a combination of scanning tunnelling microscopy, high-resolution atomic force microscopy with a CO tip, and density functional and classical computations.
Competing Annulene and Radialene Structures in a Single Anti-Aromatic Molecule Studied by High-Resolution Atomic Force Microscopy
(2017-08-22) Kawai, Shigeki; Takahashi, Keisuke; Ito, Shingo; Pawlak, Rémy; Meier, Tobias; Spijker, Peter; Canova, Filippo Federici; Tracey, John; Nozaki, Kyoko; Foster, Adam S.; Meyer, Ernst
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
According to Hückel theory, an anti-aromatic molecule possessing (4n)π-electrons becomes unstable. Although the stabilization has been demonstrated by radialene-type structures - fusing aromatic rings to anti-aromatic rings - in solution, such molecules have never been studied at a single molecular level. Here, we synthesize a cyclobutadiene derivative, dibenzo[b,h]biphenylene, by an on-surface intramolecular reaction. With a combination of high-resolution atomic force microscopy and density functional theory calculations, we found that a radialene structure significantly reduces the anti-aromaticity of the cyclobutadiene core, extracting π-electrons, while the small four-membered cyclic structure keeps a high density of the total charge.
Diacetylene Linked Anthracene Oligomers Synthesized by One-Shot Homocoupling of Trimethylsilyl on Cu(111)
(2018-08-07) Kawai, Shigeki; Krejci, Ondrej; Foster, Adam; Pawlak, Rémy; Xu, Feng; Peng, Lifen; Orita, Akihiro; Meyer, Ernst
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
On-surface chemical reaction has become a very powerful technique to conjugate small precursor molecules and several reactions have been proposed with the aim to fabricate functional nanostructures on surfaces. Here we present an unforeseen adsorption mode of 9,10-bis-((trimethylsilyl)ethynyl)anthracene on a Cu(111)surface and the resulting one-shot desilylative homocoupling of of the adsorbate by annealing at 400 K. With a combination of high-resolution atomic force microscopy and density functional theory calculations, we found that the triple bonds and silicon atoms of the monomer chemically interact with the copper surface. After the oligomerization, we discovered that the anthracene units are linked to each other via buta-1,3-diynediyl fragments while keeping the surface clean. Furthermore, the force measurement revealed the chemical nature at the center of anthracene unit.
Direct quantitative measurement of the C=O center dot center dot center dot H-C bond by atomic force microscopy
(2017-05) Kawai, Shigeki; Nishiuchi, Tomohiko; Kodama, Takuya; Spijker, Peter; Pawlak, Remy; Meier, Tobias; Tracey, John; Kubo, Takashi; Meyer, Ernst; Foster, Adam S.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The hydrogen atom-the smallest and most abundant atom-is of utmost importance in physics and chemistry. Although many analysis methods have been applied to its study, direct observation of hydrogen atoms in a single molecule remains largely unexplored. We use atomic force microscopy (AFM) to resolve the outermost hydrogen atoms of propellane molecules via very weak C=O center dot center dot center dot H-C hydrogen bonding just before the onset of Pauli repulsion. The direct measurement of the interaction with a hydrogen atom paves the way for the identification of three-dimensional molecules such as DNAs and polymers, building the capabilities of AFMtoward quantitative probing of local chemical reactivity.
Energy Loss Triggered by Atomic-Scale Lateral Force
(2013) Federici Canova, Filippo; Kawai, Shigeki; de Capitani, Christian; Kanno, Ken-ichi; Glatzel, Thilo; Such, Bartosz; Foster, Adam S.; Meyer, Ernst
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We perform bimodal atomic force microscopy measurements on a Br-doped NaCl (001) surface to investigate the mechanisms behind frequency shift and energy dissipation contrasts. The peculiar pattern of the dissipated energy in the torsional channel, related to frictional processes, is increased at the positions of Br impurities, otherwise indistinguishable from Cl ions in the other measured channels. Our simulations reveal how the energy dissipates by the rearrangement of the tip apex and how the process is ultimately governed by lateral forces. Even the slightest change in lateral forces, induced by the presence of a Br impurity, is enough to trigger the apex reconstruction more often, thus increasing the dissipation contrast; the predicted dissipation pattern and magnitude are in good quantitative agreement with the measurements.
Local probe-induced structural isomerization in a one-dimensional molecular array
(2023-11-25) Kawai, Shigeki; Silveira, Orlando J.; Kurki, Lauri; Yuan, Zhangyu; Nishiuchi, Tomohiko; Kodama, Takuya; Sun, Kewei; Custance, Oscar; Lado, Jose L.; Kubo, Takashi; Foster, Adam S.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Synthesis of one-dimensional molecular arrays with tailored stereoisomers is challenging yet has great potential for application in molecular opto-, electronic- and magnetic-devices, where the local array structure plays a decisive role in the functional properties. Here, we demonstrate the construction and characterization of dehydroazulene isomer and diradical units in three-dimensional organometallic compounds on Ag(111) with a combination of low-temperature scanning tunneling microscopy and density functional theory calculations. Tip-induced voltage pulses firstly result in the formation of a diradical species via successive homolytic fission of two C-Br bonds in the naphthyl groups, which are subsequently transformed into chiral dehydroazulene moieties. The delicate balance of the reaction rates among the diradical and two stereoisomers, arising from an in-line configuration of tip and molecular unit, allows directional azulene-to-azulene and azulene-to-diradical local probe structural isomerization in a controlled manner. Furthermore, our theoretical calculations suggest that the diradical moiety hosts an open-shell singlet with antiferromagnetic coupling between the unpaired electrons, which can undergo an inelastic spin transition of 91 meV to the ferromagnetically coupled triplet state.
Manipulation of Spin Polarization in Boron-Substituted Graphene Nanoribbons
(2022-07-26) Sun, Kewei; Silveira, Orlando J.; Saito, Shohei; Sagisaka, Keisuke; Yamaguchi, Shigehiro; Foster, Adam S.; Kawai, Shigeki
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The design of magnetic topological states due to spin polarization in an extended πcarbon system has great potential in spintronics application. Although magnetic zigzag edges in graphene nanoribbons (GNRs) have been investigated earlier, real-space observation and manipulation of spin polarization in a heteroatom substituted system remains challenging. Here, we investigate a zero-bias peak at a boron site embedded at the center of an armchair-type GNR on a AuSiX/Au(111) surface with a combination of low-temperature scanning tunneling microscopy/spectroscopy and density functional theory calculations. After the tip-induced removal of a Si atom connected to two adjacent boron atoms, a clear Kondo resonance peak appeared and was further split by an applied magnetic field of 12 T. This magnetic state can be relayed along the longitudinal axis of the GNR by sequential removal of Si atoms.
Measuring Electric Field Induced Subpicometer Displacement of Step Edge Ions
(2012) Kawai, Shigeki; F. Canova, Filippo; Glatzel, Thilo; Hynninen, Teemu; Meyer, Ernst; Foster, Adam S.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We provide unambiguous evidence that the applied electrostatic field displaces step atoms of ionic crystal surfaces by subpicometers in different directions via the measurement of the lateral force interactions by bimodal dynamic force microscopy combined with multiscale theoretical simulations. Such a small imbalance in the electrostatic interaction of the shifted anion-cation ions leads to an extraordinary long-range feature potential variation and is now detectable with the extreme sensitivity of the bimodal detection.
Multiple heteroatom substitution to graphene nanoribbon
(2018-04-13) Kawai, Shigeki; Nakatsuka, Soichiro; Hatakeyama, Takuji; Pawlak, Rémy; Meier, Tobias; Tracey, John; Meyer, Ernst; Foster, Adam S.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Substituting heteroatoms into nanostructured graphene elements, such as graphene nanoribbons, offers the possibility for atomic engineering of electronic properties. To characterize these substitutions, functionalized atomic force microscopy (AFM)-a tool to directly resolve chemical structures-is one of themost promising tools, yet the chemical analysis of heteroatoms has been rarely performed. We synthesized multiple heteroatom-substituted graphene nanoribbons and showed that AFM can directly resolve elemental differences and can be correlated to the van der Waals radii, as well as the modulated local electron density caused by the substitution. This elemental-sensitive measurement takes an important step in the analysis of functionalized two-dimensional carbon materials.
On-Surface Synthesis of a π-Extended Diaza[8]circulene
(2020-05-15) Nakamura, Kimihiro; Li, Qiang Qiang; Krejčí, Ondřej; Foster, Adam S.; Sun, Kewei; Kawai, Shigeki; Ito, Shingo
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Heterocyclic [8]circulenes are an important class of polycyclic aromatic hydrocarbon molecules because of their unique structural properties and promising applications. However, the synthesis of heterocyclic [8]circulenes is still limited and thus is an important synthetic challenge. Here we describe the first example of a π-extended diaza[8]circulene surrounded by and fused with six hexagons and two pentagons, which was successfully synthesized only by a combined in-solution and on-surface synthetic strategy. State-of-the-art scanning tunneling microscopy with a CO-functionalized tip and density functional theory calculations revealed its planar conformation and unique electronic structure.
On-surface synthesis of disilabenzene-bridged covalent organic frameworks
(2023-01) Sun, Kewei; Silveira, Orlando J.; Ma, Yujing; Hasegawa, Yuri; Matsumoto, Michio; Kera, Satoshi; Krejčí, Ondřej; Foster, Adam S.; Kawai, Shigeki
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Substituting carbon with silicon in organic molecules and materials has long been an attractive way to modify their electronic structure and properties. Silicon-doped graphene-based materials are known to exhibit exotic properties, yet conjugated organic materials with atomically precise Si substitution have remained difficult to prepare. Here we present the on-surface synthesis of one- and two-dimensional covalent organic frameworks whose backbones contain 1,4-disilabenzene (C4Si2) linkers. Silicon atoms were first deposited on a Au(111) surface, forming a AuSix film on annealing. The subsequent deposition and annealing of a bromo-substituted polyaromatic hydrocarbon precursor (triphenylene or pyrene) on this surface led to the formation of the C4Si2-bridged networks, which were characterized by a combination of high-resolution scanning tunnelling microscopy and photoelectron spectroscopy supported by density functional theory calculations. Each Si in a hexagonal C4Si2 ring was found to be covalently linked to one terminal Br atom. For the linear structure obtained with the pyrene-based precursor, the C4Si2 rings were converted into C4Si pentagonal siloles by further annealing.
On-Surface Synthesis of Silole and Disila-Cyclooctene Derivatives
(2024-04-24) Sun, Kewei; Kurki, Lauri; Silveira, Orlando J.; Nishiuchi, Tomohiko; Kubo, Takashi; Foster, Adam S.; Kawai, Shigeki
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The incorporation of Si atoms into organic compounds significantly increases a variety of functionality, facilitating further applications. Recently, on-surface synthesis was introduced into organosilicon chemistry as 1,4-disilabenzene bridged nanostructures were obtained via coupling between silicon atoms and brominated phenyl groups at the ortho position on Au(111). Here, we demonstrate a high generality of this strategy via syntheses of silole derivatives and nanoribbon structures with eight-membered sila-cyclic rings from dibrominated molecules at the bay and peri positions on Au(111), respectively. Their structures and electronic properties were investigated by a combination of scanning tunneling microscopy/spectroscopy and density functional theory calculations. This work demonstrates a great potential to deal with heavy group 14 elements in on-surface silicon chemistry.
On-Surface Synthesis of Triaza[5]triangulene through Cyclodehydrogenation and its Magnetism
(2024-11-04) Li, Donglin; Silveira, Orlando J.; Matsuda, Takuma; Hayashi, Hironobu; Maeda, Hiromitsu; Foster, Adam S.; Kawai, Shigeki
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Triangulenes as neutral radicals are becoming promising candidates for future applications such as spintronics and quantum technologies. To extend the potential of the advanced materials, it is of importance to control their electronic and magnetic properties by multiple graphitic nitrogen doping. Here, we synthesize triaza[5]triangulene on Au(111) by cyclodehydrogenation, and its derivatives by cleaving C−N bonds. Bond-resolved scanning tunneling microscopy and scanning tunneling spectroscopy provided detailed structural information and evidence for open-shell singlet ground state. The antiferromagnetic arrangement of the spins in positively doped triaza[5]triangulene was further confirmed by density function theory calculations. The key aspect of triangulenes with multiple graphitic nitrogen is the extra pz electrons composing the π orbitals, favoring charge transfer to the substrate and changing their low-energy excitations. Our findings pave the way for the exploration of exotic low-dimensional quantum phases of matter in heteroatom doped organic systems.
Synthesis of azahexabenzocoronenium salts through a formal [3 + 3] cycloaddition strategy
(2024-10) Zhang, Xinjiang; Li, Donglin; Tan, Cheryl Cai Hui; Hanindita, Fiona; Hamamoto, Yosuke; Foster, Adam S.; Kawai, Shigeki; Ito, Shingo
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Heteroatom-embedded hexa-peri-hexabenzocoronene (HBC) molecules exhibit interesting properties depending on the number and position of the introduced heteroatoms and are promising materials for applications in organic electronics and supramolecular chemistry. However, their synthesis is quite limited because of the difficulty in selectively introducing heteroatoms into the HBC core, which poses a challenge in organic synthesis. Here we report a strategy for the in-solution synthesis of 3a2-azahexa-peri-hexabenzocoronenium salts, which are cationic nitrogen-embedded HBC derivatives. The synthesis was enabled by the formal [3 + 3] cycloaddition of polycyclic aromatic azomethine ylides with cyclopropenes, as a three-atom dipolarophile, followed by mechanochemical intramolecular cyclization. Furthermore, on-surface polymerization of aza-HBC precursors was performed to synthesize aza-HBC-based chevron-like graphene nanoribbons. This study provides the possibility for the further use of nitrogen-embedded HBC derivatives in a variety of potential applications. (Figure presented.)
Synthesis of Regioisomeric Graphene Nanoribbon Junctions via Heteroprecursors
(2019-07-18) Sun, Kewei; Krejci, Ondrej; Foster, Adam S.; Okuda, Yasuhiro; Orita, Akihiro; Kawai, Shigeki
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Graphene nanoribbons are one of the most promising materials for nanoscale electronics. While various structures have successfully been synthesized by on-surface reactions, curved connections remain less investigated, yet they could prove highly useful in the development of copolymerization technology. Here, we present the synthesis of three different regioisomeric junctions on Au (111) by using 10,10'-dibromo-9,9'-bianthryl and 1,3,6,8-tetrabromopyrene. The chemical structures and the electronic properties of junctions were studied with a combination of scanning tunneling microscopy with a CO terminated tip, scanning tunneling spectroscopy, and density functional theory calculations. We found that two identical nanoribbon-junction interface electronic states appear within the band gaps of connected graphene nanoribbons.
Thermal control of sequential on-surface transformation of a hydrocarbon molecule on a copper surface
(2016-09-13) Kawai, Shigeki; Haapasilta, Ville; Lindner, Benjamin D.; Tahara, Kazukuni; Spijker, Peter; Buitendijk, Jeroen A.; Pawlak, Rémy; Meier, Tobias; Tobe, Yoshito; Foster, Adam S.; Meyer, Ernst
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
On-surface chemical reactions hold the potential for manufacturing nanoscale structures directly onto surfaces by linking carbon atoms in a single-step reaction. To fabricate more complex and functionalized structures, the control of the on-surface chemical reactions must be developed significantly. Here, we present a thermally controlled sequential three-step chemical transformation of a hydrocarbon molecule on a Cu(111) surface. With a combination of high-resolution atomic force microscopy and first-principles computations, we investigate the transformation process in step-by-step detail from the initial structure to the final product via two intermediate states. The results demonstrate that surfaces can be used as catalysing templates to obtain compounds, which cannot easily be synthesized by solution chemistry.
Three-dimensional graphene nanoribbons as a framework for molecular assembly and local probe chemistry
(2020-02-28) Kawai, Shigeki; Krejci, Ondrej; Nishiuchi, Tomohiko; Sahara, Keisuke; Kodama, Takuya; Pawlak, Rémy; Meyer, Ernst; Kubo, Takashi; Foster, Adam
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Recent advances in state-of-the-art probe microscopy allow us to conduct single molecular chemistry via tip- induced reactions and direct imaging of the inner structure of the products. Here, we synthesize three-dimensional graphene nanoribbons by on-surface chemical reaction and take advantage of tip-induced assembly to demon- strate their capability as a playground for local probe chemistry. We show that the radical caused by tip-induced debromination can be reversibly terminated by either a bromine atom or a fullerene molecule. The experimental results combined with theoretical calculations pave the way for sequential reactions, particularly addition reac- tions, by a local probe at the single-molecule level decoupled from the surface.
Van der Waals interactions and the limits of isolated atom models at interfaces
(2016-05-13) Kawai, Shigeki; Foster, Adam S.; Björkman, Torbjörn; Nowakowska, Sylwia; Björk, Jonas; Canova, Filippo Federici; Gade, Lutz H.; Jung, Thomas A.; Meyer, Ernst
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Understanding the resulting structural motifs and patterns has become increasingly important in studies of the nanoscale regime. Here we measure the paradigmatic van der Waals interactions represented by the noble gas atom pairs Ar-Xe, Kr-Xe and Xe-Xe with a Xe-functionalized tip of an atomic force microscope at low temperature. Individual rare gas atoms were fixed at node sites of a surface-confined two-dimensional metal-organic framework. We found that the magnitude of the measured force increased with the atomic radius, yet detailed simulation by density functional theory revealed that the adsorption induced charge redistribution strengthened the van der Waals forces by a factor of up to two, thus demonstrating the limits of a purely atomic description of the interaction in these representative systems.