
Keisuke FukutaniTohoku University | Tohokudai
Keisuke Fukutani
Ph.D. in Physics
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45
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352
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Publications
Publications (45)
Two-dimensional (2D) crystallization of chiral molecules on achiral crystal surfaces typically exhibits mirror-imaged growth, defined by the substrate’s mirror plane and the lattices of each enantiomer. While various commensurate molecular overlayers have shown such growth, the possibility of achieving substrate-defined enantiospecific structures i...
Artificial molecular machines, especially when based on wheel‐and‐axle complexes, can generate mechanical motions in response to external stimuli. Ferrocene (Fc) is a key component, but it decomposes at 300 K on metal surfaces. Here, a novel method is presented to construct and control the molecular complex composed of ammonium‐linked ferrocene (Fc...
Excitons in semiconductors and molecules are widely utilized in photovoltaics and optoelectronics, and high-temperature coherent quantum states of excitons can be realized in artificial electron–hole bilayers and an exotic material of an excitonic insulator (EI). Here, we investigate the band gap evolution of a putative high-temperature EI Ta2NiSe5...
Despite the rapid progresses in the field of organic semiconductors, aided by the development of high-mobility organic materials, their high carrier mobilities are often unipolar, being sufficiently high only for either electrons or holes. Yet, the basic mechanisms underlying such significant mobility asymmetry largely remains elusive. We perform a...
Two-dimensional (2D) covalent organic frameworks (COFs) fabricated through on-surface synthesis were investigated as a honeycomb nanopore template for the growth of 3d-transition-metal nanoclusters (NCs) with a size of 2 nm on a metallic substrate. The evolution of these NCs and their electronic characteristics were studied employing scanning tunne...
Owing to the location of the Dirac point, which is around the center of its wide bulk band gap, TlBiSe2 would be one of the most promising topological insulators for spintronics devices material. However, like many other topological insulators, defects, such as vacancy formed during the crystal growth, dope electrons into TlBiSe2 and make its bulk...
Excitons, quasiparticles of electrons and holes bound by Coulombic attraction, are created transiently by light and play an important role in optoelectronics, photovoltaics and photosynthesis. They are also predicted to form spontaneously in a small-gap semiconductor or a semimetal, leading to a Bose–Einstein condensate at low temperature, but ther...
Through the description of various surface terminations, the chain direction of In4Se3 in this paper [1] is implied to be in the plane of its surface. Even though the common convention for photoemission spectroscopy is to place z-axis along the surface normal, the axis perpendicular to the growth direction for this indium selenide is the crystallog...
Excitons, quasiparticles of electrons and holes bound by Coulombic attraction, are created transiently by light and play an important role in optoelectronics, photovoltaics and photosynthesis. While they are also predicted to form spontaneously in a small gap semiconductor or a semimetal, leading to a Bose-Einstein condensate at low temperature, th...
The surface termination of In4Se3(001) and the interface of this layered trichalcogenide, with Au, was examined using x-ray photoemission spectroscopy. Low energy electron diffraction indicates that the surface is highly crystalline, but suggests an absence of C2v mirror plane symmetry. The surface termination of the In4Se3(001 is found, by angle-r...
The surface termination of In4Se3(001) and the interface of this layered trichalcogenide, with Au, was examined using x-ray photoemission spectroscopy. Low energy electron diffraction indicates that the surface is highly crystalline, but suggests an absence of C2v mirror plane symmetry. The surface termination of the In4Se3(001) is found, by angle-...
We demonstrate that the excitonic insulator ground state of Ta2NiSe5 can be electrically controlled by electropositive surface adsorbates. Our studies utilizing angle-resolved photoemission spectroscopy reveal intriguing wave-vector-dependent deformations of the characteristic flattop valence band of this material upon potassium adsorption. The obs...
We demonstrate that the excitonic insulator ground state of Ta 2 NiSe 5 can be electrically controlled by electropositive surface adsorbates. Our studies utilizing angle-resolved photoemission spectroscopy reveal intriguing wave-vector-dependent deformations of the characteristic flattop valence band of this material upon potassium adsorption. The...
Super-steep two-terminal electronic devices using NbO2, that abruptly switch from insulator to metal at a threshold voltage (Vth), offers diverse strategies for energy-efficient and high-density device architecture to overcome fundamental limitation in current electronics. However, the tight control of stoichiometry and high-temperature processing...
We report the discovery of two-dimensional electron gas (2DEG) at the surface of thermoelectric material In$_4$Se$_3$ by angle-resolved photoemission spectroscopy. The observed 2DEG exhibits a nearly isotropic band dispersion with a considerably small effective mass of m* = 0.16 m_0, and its carrier density shows a significant temperature dependenc...
We report the discovery of two-dimensional electron gas (2DEG) at the surface of thermoelectric material In4Se3 by angle-resolved photoemission spectroscopy. The observed 2DEG exhibits a nearly isotropic band dispersion with a considerably small effective mass of m*=0.16 m0, and its carrier density shows a significant temperature dependence, leadin...
We present a comprehensive characterization of the electronic structure of anisotropic layered semiconductor In 4 Se 3 by means of high-resolution angle-resolved photoemission spectroscopy. Our study reveals the quasi-one-dimensionality in the electronic structure of In 4 Se 3 and provides a direct estimate of its band gap (0.86 ± 0.05 eV). The ide...
We report the experimental identification of a symmetry-protected surface state on Mo(1 1 2). The utilization of photon-energy- and polarization-dependent angle-resolved photoemission spectroscopy clearly demonstrates that this true surface state preserves its two-dimensional character despite the fact that it resides within the projection of the b...
We report the experimental identification of a symmetry-protected surface state on Mo(1 1 2). The utilization of photon-energy- and polarization-dependent angle-resolved photoemission spectroscopy clearly demonstrates that this true surface state preserves its two-dimensional character despite the fact that it resides within the projection of the b...
We find that Gd2O3 thin films strongly favor a (−402) texture growth on a variety of substrates and will form heterojunction diodes with silicon, especially when doped with oxygen vacancies. Even in the thin film limit, these heterojunction diodes appear to be sensitive to gamma radiation, likely from the X-rays created by scattering events, adding...
The effects of lack of in-plane C2 invariance of the crystal
on the angle-resolved photoemission spectra are investigated for
Mo(112). The results indicate that, for Mo(112), the absence of
C2 symmetry gives rise to noticeable asymmetry in the ARPES
band mapping along the 1 1 -1direction. The apparent differences in the
experimental band structure...
We find that Gd2O3 thin films strongly favor a (-402) texture growth on a variety of substrates and will form heterojunction diodes with silicon, especially when doped with oxygen vacancies. Even in the thin film limit, these heterojunction diodes appear to be sensitive to gamma radiation, likely from the X-rays created by scattering events, adding...
A detailed investigation of the electronic structure and electron-phonon coupling for a Au monolayer on the Mo(112) surface is presented. The electronic states of bulk Mo and the (112) surface-derived states are seen to strongly hybridize with those of the Au overlayer, resulting in the formation of surface resonance states localized near the surfa...
A detailed investigation of the electronic structure and electron-phonon coupling for a Au monolayer on the Mo(112) surface is presented. The electronic states of bulk Mo and the (112) surface-derived states are seen to strongly hybridize with those of the Au overlayer, resulting in the formation of surface resonance states localized near the surfa...
The electronic structures, many-body interactions and Fermi surface topologies of Au/Mo(112) were investigated in detail and were found to play important roles in the newly discovered order-disorder structural phase transition of the system. First, the high-resolution angle-resolved photoemission spectroscopy was utilized to characterize the electr...
A comprehensive examination of the Fermi surface of Mo(112) is presented. The Fermi surface contours for the Mo(112) surface, obtained by density functional theory calculations, agree well with the direct observations via angle-resolved photoemission spectroscopy and indicate the existence of flattened segments in the Fermi contours perpendicular t...
A comprehensive examination of the Fermi surface of Mo(112) is presented. The Fermi surface contours for the Mo(112) surface, obtained by density functional theory calculations, agree well with the direct observations via angle-resolved photoemission spectroscopy and indicate the existence of flattened segments in the Fermi contours perpendicular t...
We present a comprehensive examination of the occupied surface-weighted band structure of Mo(112) along the two high-symmetry directions of the surface Brillouin zone, both from theoretical and experimental perspectives. The band structures are found to be significantly different for the states along the two high-symmetry directions and for the sta...
We present a comprehensive examination of the occupied surface-weighted band structure of Mo(112) along the two high-symmetry directions of the surface Brillouin zone, both from theoretical and experimental perspectives. The band structures are found to be significantly different for the states along the two high-symmetry directions and for the sta...
The isomeric effects on the adsorption geometry of di-halobenzene
(C6H4X2; X = F, Cl, Br, I) and
pentacene (C22H14) on the idealized
non-interacting substrate are analyzed both qualitatively and
quantitatively by means of Monte Carlo simulations. The shape of
pentacene isomers and the relative positions of halogen atoms in
di-halobenzene may be imp...
Manipulation of magnetically ordered states by electrical means is among
the most promising approaches towards novel spintronic devices. Electric
control of the exchange bias can be realized when the passive
antiferromagnetic pinning layer is replaced by a magneto-electric
antiferromagnet, like the prototypical magneto-electric
Cr2O3(0001), so long...
Electrons may experience inelastic coupling with the organic spacer layer during tunneling between two ferromagnetic electrodes. To probe the transport behavior of spin-polarized electrons in organic materials, organic spin valves were fabricated utilizing a relatively thin organic barrier of 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) dus...
We investigated the electron–phonon coupling (EPC), in the vicinity of the Fermi level, for the surface states of the Au-covered Mo(112) surface from high-resolution angle resolved photoemission data taken parallel to the surface corrugation (i.e. 〈1_ 1_1〉). The changes of the widths of the surface weighted bands, induced by Au layers, are discusse...
Order-disorder overlayer phase transitions are observed at the surface of Au/Mo(112) for the nominal Au coverages of 1.66 and 1.75 monolayers. These transitions are characterized by the abrupt change in the surface Debye temperature. In the search for the detailed mechanism of this phase transition, we investigated the electron-phonon coupling (EPC...
We report on the inelastic scattering characteristics of an
organic-based spin valve with a thin organic barrier of
3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) dusted with alumina
at organic/ferromagnetic interfaces. Spin injection with
magnetoresistance up to 12% at room temperature was achieved. In the
inelastic tunneling spectrum, the o...
A 2.5 monolayer (ML) thick graphene film grown by chemical vapor deposition of thermally dissociated C(2)H(4) on MgO(111), displays a significant band gap. The apparent six-fold low energy electron diffraction (LEED) pattern actually consists of two three-fold patterns with different 'A' and 'B' site diffraction intensities. Similar effects are obs...
We investigated the electron–phonon coupling (EPC), in the vicinity of the Fermi level, for
the surface-weighted states of Mo(112) from high resolution angle-resolved photoemission
data taken parallel to the surface corrugation (i.e. ). The surface-weighted bandwidth may be discussed in terms of electron–electron interactions,
electron impurity sca...
Atomic-scale structure of the growth of a gold film on (1 1 2) plane of Mo single crystal was investigated by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) up to two monolayers (ML) of gold coverage. Both LEED and STM results establish that Au grows on Mo(1 1 2) in a layer-by-layer mode, for at least the fi...
Differences are seen in the adsorption of 1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene on graphite, as a function of exposure, using core level photoemission. The isomer 1,3-di-iodobenzene exhibits significant differences from 1,2-di-iodobenzene, and 1,4-di-iodobenzene in apparent sticking coefficients and core level binding energ...
Differences are seen in the adsorption of 1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene on graphite, as a function of exposure, using core level photoemission. The isomer 1,3-di-iodobenzene exhibits significant differences from 1,2-di-iodobenzene, and 1,4-di-iodobenzene in apparent sticking coefficients and core level binding energ...
We studied the adsorption of isomers of halogenated benzene on graphite. We found difference in the behavior of three different symmetry types, (1,2), (1,3), and (1,4), of diiodobenzene (C6H4I2) and 1,4-bromoiodobenzene (C6H4IBr) adsorbed on graphite surface at 95K by X-ray photoemission spectroscopy. Although the molecules are expected to be simil...
Reversible bromoform adsorption on crystalline polyvinylidene fluoride with 30% of trifluoroethylene, P(VDF-TrFE 70:30) was examined by photoemission and inverse photoemission spectroscopies. The adsorption of bromoform on this polymer surface is associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K...
Questions
Question (1)
If there is surface band-bending whose strength depends on temperature, does it make direct contribution to the Seebeck coefficient at the surface? For example, if at the surface, the band-bending changes by 1 meV within the temperature range of 10 K, does it contribute 100uV/K to the Seebeck coefficient at the surface?