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ANTON VISIKOVSKIY Last modified date:2019.06.24



Graduate School
Undergraduate School


E-Mail
Homepage
http://www.qpn.kyushu-u.ac.jp/Tanaka/English/Welcome.html
Phone
092-802-3536
Fax
092-802-3536
Academic Degree
Ph.D.
Field of Specialization
Surface Science (condensed matter)
Outline Activities
We research the surface structures by low-energy electron diffraction, scanning tunneling microscopy and other surface sensitive methods. Particularly we focus on structures formed on vicinal SiC surfaces. Slightly miscutted SiC surface can be arranged in the ordered array of terraces and facets providing an excellent template to grow one-dimensional structures such as nanowires or graphene nanoribbons. We would like to explore the formation such kind of spatially confined nano-structures because of its importance for physics and high potential for technological application.
The other research topic is graphene formation on SiC substrate and modification of its properties by interface engineering. Quantum mechanical calculation using density functional theory (DFT) and tight-binding (TB) methods are actively used in our research of material properties such as atomic and electronic structures.
Research
Research Interests
  • Ultra-thin aluminium oxide layer on SiC(0001)
    keyword : oxide, semiconductors
    2018.10~2019.10.
  • Periodic modulation of substrate interaction on graphene's electronic properties
    keyword : semiconductor, surface, nanomaterals, spin, graphene
    2018.03~2019.06.
  • 2D triangular dense atomic layers of group III, IV, and V elements on SiC(0001) surface and their peculiar electronic properties.
    keyword : semiconductor, surface, nanomaterals, spin, graphene
    2017.06~2019.06.
  • Graphene/SiC interface structure manipulation by atom intercalation.
    New graphene-like 2D materials on SiC surfaces.
    keyword : surface, SiC, graphene, interface
    2015.04~2017.03.
  • Study of metal overlayers on silicon surfaces
    keyword : silicon, superstructure, surface
    2003.10~2009.03.
  • Origins of catalytic activity of metal nanoparticles
    keyword : nanoparicles, electronic structure, catalysis
    2009.04~2012.03.
Academic Activities
Papers
1. Koichiro Yaji, Anton Visikovskiy, Takushi Iimori, Kenta Kuroda, Singo Hayashi, Takashi Kajiwara, Tanaka Satoru, Fumio Komori, Shik Shin, Coexistence of Two Types of Spin Splitting Originating from Different Symmetries, Physical Review Letters, 10.1103/PhysRevLett.122.126403, 122, 12, 126403, 2019.03, The symmetry of a surface or interface plays an important role in determining the spin splitting and texture of a two-dimensional band. Spin-polarized bands of a triangular lattice atomic layer (TLAL) consisting of Sn on a SiC(0001) substrate is investigated by spin- and angle-resolved photoelectron spectroscopy. Surprisingly, both Zeeman- and Rashba-type spin-split bands, without and with spin degeneracy, respectively, coexist at a K point of the Sn TLAL. The K point has a threefold symmetry without inversion symmetry according to the crystal structure including the SiC periodicity, meaning that the Zeeman-type is consistent with the symmetry of the lattice while the Rashba-type is inconsistent. Our density functional calculations reveal that the charge density distribution of the Rashba-type (Zeeman-type) band shows (no) inversion symmetry at the K point. Therefore, the symmetry of the charge density distribution agrees with both types of the spin splitting..
2. Shingo Hayashi, Anton Visikovskiy, Takashi Kajiwara, Takushi Iimori, Tetsuroh Shirasawa, Kan Nakastuji, Toshio Miyamachi, Shuhei Nakashima, Koichiro Yaji, Kazuhiko Mase, Fumio Komori, Tanaka Satoru, Triangular lattice atomic layer of Sn(1 × 1) at graphene/SiC(0001) interface, Applied Physics Express, 10.7567/APEX.11.015202, 11, 1, 2018.01, Sn atomic layers attract considerable interest owing to their spin-related physical properties caused by their strong spin-orbit interactions. We performed Sn intercalation into the graphene/SiC(0001) interface and found a new type of Sn atomic layer. Sn atoms occupy on-top sites of Si-terminated SiC(0001) with in-plane Sn-Sn bondings, resulting in a triangular lattice. Angle-resolved photoemission spectroscopy revealed characteristic dispersions at and points, which agreed well with density functional theory calculations. The Sn triangular lattice atomic layer at the interface showed no oxidation upon exposure to air, which is useful for characterization and device fabrication ex situ..
3. ANTON VISIKOVSKIY, Takashi KAJIWARA, Masamichi Yoshimura, Takushi IIMORI, Fumio KOMORI, 田中 悟, Graphene/SiC(0001) interface structures induced by Si intercalation and their influence on electronic properties of graphene, PHYSICAL REVIEW B, 10.1103/PhysRevB.94.245421, 94, 24, 245421, 2016.12, [URL], Epitaxial graphene growth on SiC surfaces is considered advantageous in terms of device application. However, the first graphitic layer on SiC transforms to a buffer layer because of strong coupling with the substrate. The properties of several subsequent layers are also significantly degraded. One method to decouple graphene from the substrate is Si intercalation. In the present work, we report observation and analysis of interface structures formed by Si intercalation in between the graphene layer and the SiC(0001) surface depending on Si coverage and influence of these interfaces on graphene electronic structure by means of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), and theoretical first-principles calculations. The STM appearance of observed periodic interface structures strongly resembles previously known Si-rich phases on the SiC(0001) surface. Based on the observed range of interface structures we discuss the mechanism of graphene layer decoupling and differences in stability of the Si-rich phases on clean SiC(0001) and in the graphene/SiC(0001) interface region. We also discuss a possibility to tune graphene electronic properties by interface engineering..
4. ANTON VISIKOVSKIY, K. Mitsuhara, M. Hazama, M. Kohyama, Y. Kido, The atomic and electronic structures of NiO(001)/Au(001) interfaces, JOURNAL OF CHEMICAL PHYSICS, 10.1063/1.4820823, 139, 14, 144705, 2013.10, [URL], The atomic and electronic structures of NiO(001)/Au(001) interfaces were analyzed by high-resolution medium energy ion scattering (MEIS) and photoelectron spectroscopy using synchrotronradiation-light. The MEIS analysis clearly showed that O atoms were located above Au atoms at the interface and the inter-planar distance of NiO(001)/Au(001) was derived to be 2.30 +/- 0.05 angstrom, which was consistent with the calculations based on the density functional theory (DFT). We measured the valence band spectra and found metallic features for the NiO thickness up to 3 monolayer (ML). Relevant to the metallic features, electron energy loss analysis revealed that the bandgap for NiO(001)/Au(001) reduced with decreasing the NiO thickness from 10 down to 5 ML. We also observed Au 4f lines consisting of surface, bulk, and interface components and found a significant electronic charge transfer from Au(001) to NiO(001). The present DFT calculations demonstrated the presence of an image charge beneath Ni atoms at the interface just like alkali-halide/metal interface, which may be a key issue to explain the core level shift and band structure..
5. Takashi Kajiwara, Yuzuru Nakamori, ANTON VISIKOVSKIY, Takushi Iimori, Fumio Komori, Kan Nakatsuji, Kazuhiko Mase, Tanaka Satoru, Graphene nanoribbons on vicinal SiC surfaces by molecular beam epitaxy, American Physical Society, 10.1103/PhysRevB.87.121407, 87, 12, 121407, 2013.03, [URL].
6. Tomoaki Nishimura, Kei Mitsuhara, ANTON VISIKOVSKIY, Yoshiaki Kido, Cross sections for medium energy He ions scattered from Hf and Au atoms, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 10.1016/j.nimb.2012.02.030, 280, 5, 2012.06, [URL], The elastic scattering cross sections for medium energy He ions incident on Ni, Hf and Au atoms were measured precisely using a toroidal electrostatic analyzer. We prepared the targets of Ni(similar to 1 nm)/HfO2(1.5 nm)/Si(001) and Ni(similar to 1 nm)/Au(similar to 0.5 nm)/Si(111) and performed in situ ion scattering measurement under ultrahigh vacuum condition. The absolute amounts of Ni, Hf and Au were determined by Rutherford backscattering using 1.5 MeV He ions at a scattering angle of 150 degrees. The scattering cross sections for Hf and Au were normalized by those for Ni to avoid the ambiguities of the number of incident particles, solid angle subtended by a detector, detection efficiency and the He fractions for the emerging He ions from the surfaces. The results obtained are compared with the simple Lee-Hart formula and the calculated values using the Moliere and ZBL potentials and the potentials derived from the Hartree-Fock-Slater wave functions. .
7. K. Mitsuhara, M. Tagami, T. Matsuda, A. Visikovskiy, M. Takizawa, Y. Kido, The mechanism of emerging catalytic activity of gold nano-clusters on rutile TiO2(110) in CO oxidation reaction, Journal of Chemical Physics, 10.1063/1.3697478, 136, 12, 124303, 2012.03, [URL], This paper reveals the fact that the O adatoms (O-ad) adsorbed on the 5-fold Ti rows of rutile TiO2(110) react with CO to form CO2 at room temperature and the oxidation reaction is pronouncedly enhanced by Au nano-clusters deposited on the above O-rich TiO2(110) surfaces. The optimum activity is obtained for 2D clusters with a lateral size of similar to 1.5 nm and two-atomic layer height corresponding to similar to 50 Au atoms/cluster. This strong activity emerging is attributed to an electronic charge transfer from Au clusters to O-rich TiO2(110) supports observed clearly by work function measurement, which results in an interface dipole. The interface dipoles lower the potential barrier for dissociative O-2 adsorption on the surface and also enhance the reaction of CO with the O-ad atoms to form CO2 owing to the electric field of the interface dipoles, which generate an attractive force upon polar CO molecules and thus prolong the duration time on the Au nano-clusters. This electric field is screened by the valence electrons of Au clusters except near the perimeter interfaces, thereby the activity is diminished for three-dimensional clusters with a larger size..
8. A. Visikovskiy, H. Matsumoto, K. Mitsuhara, T. Nakada, T. Akita, Y. Kido, Electronic d-band properties of gold nanoclusters grown on amorphous carbon, Physical Review B, 10.1103/PhysRevB.83.165428, 83, 16, 165428, 2011.04, [URL], Despite bulk gold is one of the most inert metals in periodic table, it exhibit excellent catalytic activity in the form of nano-particles and nano-clusters. There re many disputes about the origin of such catalytic properties. While many researchers claims the importance of cluster-support interaction, some stated that catalytic properties are intrinsic for gold particles and main role in this play electronic d-band structure of which changes with decreasing the size of the particle. No experimental reports on direct measurements of d-band structure depending on size of the clusters has been published so far. Here we used electron photoemission spectroscopy coupled with medium energy ion scattering technique to investigate the d-band propertied of the gold particles depending on their size. .
9. A. Visikovskiy, M. Yoshimura, and K. Ueda, Initial Stages of Platinum Silicide Formation on Si(110) Studied by Scanning Tunneling Microscopy, Japanese Journal of Applied Physics, 10.1143/JJAP.48.08Jb11, 48, 8, 08JB11, 2009.08, [URL], Si(110) surface is considered to be a candidate for future electronic devices because of its high hole mobility. It is important to study silicide formation on this surface for device application. Here we studied initial stages of Pt silicide foemation on Si(110) by scanning tunneling microscopy (STM). We found that PtSi form of the silicide is formed and determined its epitaxial relation with underlying substrate. The silicide forms in form of 3D island. However, at certain experimental conditions it is possible to produce very long (> 1 micrometer) and aligned nanowires of PtSi on Si(110)..
10. A. Visikovskiy, S. Mizuno and H. Tochihara, Structure of the Si(001)-(2x2)-Tl phase at 0.5 monolayer coverage, Physical Review B, 10.1103/PhysRevB.71.245407, 71, 24, 245407-245413, 2005.07, [URL], Thallium is a peculiar element. Being metal of group III of periodic table, it exhibit variable valence in chemical compounds. We have studied atomic reconstructions Tl induce on Si(001) surface by low-energy electron diffraction (LEED). It has been shown the structure formed at 0.5 monolayer coverage is very similar to the typical group III metal reconstructions on Si(001), thus at this particular conditions Tl behaves as trivalent metal. The precise coordinates of the atoms were determined. .
11. A. Visikovskiy, S. Mizuno, H. Tochihara, Reversible electromigration of Thallium adatoms on the Si(111) surface, Surface Science Letters, 10.1016/j.susc.2006.05.039, 600, 15, L189, 2006.09, [URL], In our study it has been found that Tl atoms can migrate macroscopic distances (the width of the sample) on relatively flat Si(111) surface by applying direct current to the sample. This kind of macroscopic electromigration has never been reported before. The migrating Tl produces gradient of surface coverage resulting in different surface phases along the sample..
12. V. Zavodinsky, A. Visikovskiy, I. Kuyanov, J. Dabrowski, Nitrogen trapping of boron and phosphorus in silicon, Physics of Low-Dimensional Structures, 3/4, 13-17, 2000.02, One of the problems occurred in metal-oxide field-effect transistors (MOSFET) is the diffusion of active dopants, such as boron and phosphorous from Si channel into oxide layer. This degrades the properties of insulating oxide. Introducing nitride or oxynitride buffer layer may solve the problem by trapping the diffusing dopant atoms. In the present work we have studied by density functional theory (DFT) calculations the possibility of such trapping of the boron and phosphorous by nitrogen atoms in bulk silicon..
Presentations
1. Shingo HAYASHI, Takashi KAJIWARA, Anton VISIKOVSKIY, Takushi IIMORI, Tetsuroh SHIRASAWA, Kan NAKATSUJI, Toshio MIYAMACHI, Shuhey NAKASHIMA, Kazuhiko MASE, Fumio KOMORI, Satoru TANAKA, Sn atomic layer by intercalation at graphene/SiC interface, International Symposium on Epitaxial Graphene 2017 (ISEG-2017), 2017.11, Researches on atomic layer materials of group IV elements attracts great attention. Among them, stanene, an atomic layer of Sn, is expected to exhibit such unique characteristics as a two dimensional topological insulator [1] and quantum anomalous Hall effect [2]. The growth of stanene on Bi2Te3 has been achieved [3] but no experimental evidence on such characteristics is yet reported. On the other hand, since Sn shows a large spin orbit coupling (SOC), the spin and electronic states in terms of Rashba splitting, antiferromagnetic order and Mott insulator transition etc. are investigated. Adatom Sn (√3×√3) R30° (R3) structure on semiconductor substrates (Ge, SiC) has been reported [4, 5]. Thus, we have been aiming at forming stanene on SiC(0001) surfaces. Here, we tried Sn intercalation at graphene/SiC interfaces, which are advantageous to any ex-situ measurements of a Sn interlayer.
Initially, the graphene buffer layer was grown on SiC (0001)(Si-face) in UHV. Sn irradiation was done at room temperature and annealed at 700℃. The LEED pattern in Fig 1(a) before Sn irradiation shows (6√3×6√3) R30°(6R3) spots due to the buffer layer formation. After Sn irradiation in Fig. 1(b) the 6R3 diffraction is weakened and graphene (1×1) is clearly visible, suggesting the growth of Sn (1×1) structure at the interface. Surface X-ray diffraction analysis also supports Sn (1x1) formation. Thus, possible Sn sites on Si-terminated SiC(0001) surface are T1, where Sn is located above Si, which is further confirmed by XPS, DFT, and ARPES. The structural model of the Sn interlayer is shown in Fig. 2 (a) as compared to the honeycomb lattice. A Sn atom forms in-plane bondings with neighboring Sn atoms due to relatively shorter Sn-Sn distance than in the case of Sn(R3) at T4 sites, resulting in triangular lattice (TL) (1x1). Total energy calculation using DFT indicates TL is most stable configuration under Sn-rich chemical potentials. We investigated the electronic structure by ARPES, which is in good agreement with the DFT calculation shown in Fig. 2(b). Further, the DFT calculation including SOC terms shows Rashba type spin splitting at K points, which was actually observed by spin polarized ARPES, to be discussed in the future.
The Sn triangular lattice atomic layer (TLAL) was formed at the graphene/SiC interface via intercalation. TLAL is a new structure and is expected to show unique properties. Finally, we should emphasize the advantage of the TLAL at the interface is robustness against the atmospheric environment..
2. Anton VISIKOVSKIY, Shingo HAYASHI, Fumio KOMORI, Satoru TANAKA, Sn and Pb triangular lattice atomic layers on SiC(0001) and at graphene/SiC(0001) interface, International Symposium on Epitaxial Graphene 2017 (ISEG-2017), 2017.11, The research of 2D Dirac materials has been one of the main topics in recent material science, because of wide possible device application and fascinating physics. Most studies, however, are concentrated on graphene-like honeycomb lattice materials (graphene, silicene, germanene, stanene, etc.)1,2, though other lattice types may possess similar electronic structure features. Dense triangular lattice atomic layers (TLAL) of heavy group IV elements (Sn, Pb) on SiC(0001) surface and at graphene/SiC(0001) interface could be such materials (Fig. 1a,b). Additionally, heavy group IV elements exhibit strong spin-orbit coupling (SOC) which may significantly contribute to electronic structure of 2D layers and result in spin-polarized states. Previous studies did consider sparse triangular systems of group IV adatoms on SiC surface in terms of frustrating magnetic order, spin liquids, and Mott-type insulator state3. However, dense atomic layers where Sn (or Pb) atoms directly interconnected by in-plane bonds are unexplored.
Here we present computational results on such systems. We show that TLALs indeed could be stable on bare SiC(0001) (Fig. 1a). The exotic for group IV elements bonding configuration results in formation of Dirac cone feature in electronic structure, which originates from px and py type orbitals, rather than pz orbital as in graphene. Strong SOC results in spin-polarized electronic states, some of which on SiC substrate at K points of Brillouin zone exhibit Rashba-type splitting with in-plane spin texture, while other demonstrate non-Rashba type splitting with spin components normal to the surface (Fig. 1c). Growth of such triangular layers at graphene-buffer-layer/SiC interface (Fig. 1b) results in complete graphene decoupling from SiC substrate and induce spin-polarization in graphene states. While Sn and Pb layers shows similarities, due to the lattice mismatch the difference in atomic structure is predicted. While Sn TLALs exhibit planar structure with (1x1) periodicity, Pb TLALs buckled resulting in (√3x√3) period on SiC(0001)..
3. ANTON VISIKOVSKIY, Shin-Ichi KIMOTO, Takashi KAJIWARA, Masamichi YOSHIMURA, Fumio KOMORI, Tanaka Satoru, Graphene/SiC(0001) interfaces induced by Si intercalation, 18th International Conference on Crystal Growth and Epitaxy (ICCGE-18), 2016.08, [URL], Graphene is an important 2D material with extremely useful properties for device applications. Growth of graphene on substrates faces the problem of interface influence on graphene's properties. In particular, graphene forms buffer layer when growing on SiC(0001) which does not possess characteristic graphene band dispersion and affect, often negatively, subsequent graphene layers. The interface between graphene and SiC can be modified by different atoms intercalation. In the present work, we consider one of the simplest cases of Si intercalation. Various amounts of Si atoms were intercalated into graphene/SiC(0001) interface and studied by means of electron diffraction (LEED, RHEED), scanning tunneling microscopy (STM), angle-resolved photoemission (ARPES) and first principals calculations. We have shown that interface structures are similar to those formed by Si adsorption on clean SiC(0001) surface. The formation of these interface structures decouples graphene layer from substrate and restore it's linear electronic band dispersion.

The experiments were carried out on off-axis (4o-off) SiC(0001) substrates prepared by hydrogen etching and high temperature annealing in UHV to obtain uniform buffer layer coverage exhibiting well-known 6√3 reconstruction. Vicinal samples were used to promote intercalation process near the step edges, where graphene layer is believed to have a lot of defects. Intercalation was performed by Si deposition on hot (700-800oC) surface, as well as room temperature deposition with subsequent annealing. Both methods give identical results. As observed by diffraction and STM, the interface reconstruction changes as follows 6√3 → “2 x 2” → (2√3 x 4) → (3 x 3). Low-bias STM scans have revealed decoupled graphene layer being on top of these structures. The structure of (3 x 3) phase of Si on Si(0001) is well-established. We used the same model with graphene on-top to calculate electronic properties of such system by means of density functional theory (DFT) and DFT-based tight-binding methods. The results are in good agreement with experimental data. Such ability to engineer different interfaces between graphene and the substrate may allow to tune graphene's electronic properties to the ones desired by applications..
4. ANTON VISIKOVSKIY, TAKASHI KAJIWARA, Tanaka Satoru, MASAMICHI YOSHIMURA, STM study of graphene nanodots array on SiC, 23rd International Colloquium on Scanning Probe Microscopy (ICSPM23), 2015.12, [URL].
5. ANTON VISIKOVSKIY, Kei Mitsuhara, Masayuki Hazama, Yoshiaki Kido, Experimental and computational study of NiO(001)/Au(001) interface, IUMRS-ICA, 2014.08, [URL], The electronic contact between metal and oxide is an important issue in terms of oxide electronics, which has recently attracted much attention. It has been also revealed that electronic charge transfers between metal and oxide supports play a crucial role in catalytic activities, in particular, for Au nano-particles on oxide supports. NiO is one of the most frequently utilized supports in catalysis and a model transition oxide. Indeed, Au nano-particles grown on NiO supports work well as catalyst in CO oxidation and other reactions. Although there are a number of reports on NiO/Ag interface, Au interaction with NiO stays much out of focus, in spite of its importancy. In the present work the atomic and electronic structures of NiO(001)/Au(001) interface were analyzed by medium-energy ion scattering spectroscopy, (MEIS), photoelectron spectroscopy (PES) and DFT calculations.
We first revealed by MEIS that the O atoms were located above Au atoms at the NiO(001)/Au(001) interface (Fig. 1). This was supported by the DFT calculations. Concerning the electronic properties of the NiO/Au interface, we observed metallic features for NiO(001)/Au(001) for NiO thickness up to 3 ML. Relevant to the metallic features, the bandgap decreased with decreasing the NiO thickness from 10 down to 5 ML. We also observed the interface component for Au 4f core level, which shifted by 0.35 eV to higher binding energy side compared with that for bulk Au. Despite that, the DFT calculations demonstrated no significant charge transfer. We, however, found out the presence of image charge beneath the Ni atoms at the NiO(001)/Au(001) interface (Fig. 2), which may be a key issue to explain the core level shift and band structure.
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Membership in Academic Society
  • Japanese Society of Applied Physics
  • Physical Society of Japan
Educational
Educational Activities
Student guidance, help with experiments and discussion of the results.
Help students to write and submit papers, guidance in thesis writing.
Lectures on some topics of solid-state physics, and quantum mechanical calculations.