Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Tanaka Satoru Last modified date:2019.06.21

Professor / Applied Physics / Department of Applied Quantum Physics and Nuclear Engineering / Faculty of Engineering


Papers
1. Sean W. King, Tanaka Satoru, Robert F. Davis, Robert J. Nemanich, Hydrogen desorption from hydrogen fluoride and remote hydrogen plasma cleaned silicon carbide (0001) surfaces, Journal of Vacuum Science and Technology A, 10.1116/1.4921526, 33, 5, 2015.09, Due to the extreme chemical inertness of silicon carbide (SiC), in-situ thermal desorption is commonly utilized as a means to remove surface contamination prior to initiating critical semiconductor processing steps such as epitaxy, gate dielectric formation, and contact metallization. In-situ thermal desorption and silicon sublimation has also recently become a popular method for epitaxial growth of mono and few layer graphene. Accordingly, numerous thermal desorption experiments of various processed silicon carbide surfaces have been performed, but have ignored the presence of hydrogen, which is ubiquitous throughout semiconductor processing. In this regard, the authors have performed a combined temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) investigation of the desorption of molecular hydrogen (H2) and various other oxygen, carbon, and fluorine related species from ex-situ aqueous hydrogen fluoride (HF) and in-situ remote hydrogen plasma cleaned 6H-SiC (0001) surfaces. Using XPS, the authors observed that temperatures on the order of 700-1000 °C are needed to fully desorb C-H, C-O and Si-O species from these surfaces. However, using TPD, the authors observed H2 desorption at both lower temperatures (200-550 °C) as well as higher temperatures (>700 °C). The low temperature H2 desorption was deconvoluted into multiple desorption states that, based on similarities to H2 desorption from Si (111), were attributed to silicon mono, di, and trihydride surface species as well as hydrogen trapped by subsurface defects, steps, or dopants. The higher temperature H2 desorption was similarly attributed to H2 evolved from surface O-H groups at ∼750 °C as well as the liberation of H2 during Si-O desorption at temperatures >800 °C. These results indicate that while ex-situ aqueous HF processed 6H-SiC (0001) surfaces annealed at <700 °C remain terminated by some surface C-O and Si-O bonding, they may still exhibit significant chemical reactivity due to the creation of surface dangling bonds resulting from H2 desorption from previously undetected silicon hydride and surface hydroxide species..
2. Ayhan Yurtsever, Jo Onoda, Takushi Iimori, Kohei Niki, Toshio Miyamachi, Masayuki Abe, Seigi Mizuno, Tanaka Satoru, Fumio Komori, Yoshiaki Sugimoto, Graphene
Effects of Pb Intercalation on the Structural and Electronic Properties of Epitaxial Graphene on SiC (Small 29/2016), Small, 10.1002/smll.201670142, 2016.08.
3. Ayhan Yurtsever, Jo Onoda, Takushi Iimori, Kohei Niki, Toshio Miyamachi, Masayuki Abe, Seigi Mizuno, Tanaka Satoru, Fumio Komori, Yoshiaki Sugimoto, Effects of Pb Intercalation on the Structural and Electronic Properties of Epitaxial Graphene on SiC, Small, 10.1002/smll.201600666, 3956-3966, 2016.08, The effects of Pb intercalation on the structural and electronic properties of epitaxial single-layer graphene grown on SiC(0001) substrate are investigated using scanning tunneling microscopy (STM), noncontact atomic force microscopy, Kelvin probe force microscopy (KPFM), X-ray photoelectron spectroscopy, and angle-resolved photoemission spectroscopy (ARPES) methods. The STM results show the formation of an ordered moiré superstructure pattern induced by Pb atom intercalation underneath the graphene layer. ARPES measurements reveal the presence of two additional linearly dispersing π-bands, providing evidence for the decoupling of the buffer layer from the underlying SiC substrate. Upon Pb intercalation, the Si 2p core level spectra show a signature for the existence of PbSi chemical bonds at the interface region, as manifested in a shift of 1.2 eV of the bulk SiC component toward lower binding energies. The Pb intercalation gives rise to hole-doping of graphene and results in a shift of the Dirac point energy by about 0.1 eV above the Fermi level, as revealed by the ARPES measurements. The KPFM experiments have shown that decoupling of the graphene layer by Pb intercalation is accompanied by a work function increase. The observed increase in the work function is attributed to the suppression of the electron transfer from the SiC substrate to the graphene layer. The Pb intercalated structure is found to be stable in ambient conditions and at high temperatures up to 1250 °C. These results demonstrate that the construction of a graphene-capped Pb/SiC system offers a possibility of tuning the graphene electronic properties and exploring intriguing physical properties such as superconductivity and spintronics..
4. Anton Visikovskiy, Shin Ichi Kimoto, Takashi Kajiwara, Masamichi Yoshimura, Takushi Iimori, Fumio Komori, Tanaka Satoru, 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, 2016.12, 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..
5. R. Dagher, S. Matta, R. Parret, M. Paillet, B. Jouault, L. Nguyen, M. Portail, M. Zielinski, T. Chassagne, Tanaka Satoru, J. Brault, Y. Cordier, A. Michon, High temperature annealing and CVD growth of few-layer graphene on bulk AlN and AlN templates, Physica Status Solidi (A) Applications and Materials Science, 10.1002/pssa.201600436, 214, 4, 2017.04, Graphene and AlN are promising materials, interesting to combine together. In this study, we will present first results for direct growth of graphene on bulk AlN and on AlN templates using chemical vapor deposition, including the annealing of these substrates at high temperatures. Atomic force microscopy (AFM) enabled us to study the evolution of the AlN surface morphology after annealing and growth. Few-layer graphene deposition is demonstrated on the basis of X-ray photoemission and Raman spectroscopy. AFM view of graphene wrinkles on the N-face of bulk AlN..
6. Koichiro Ienaga, Takushi Iimori, Koichiro Yaji, Toshio Miyamachi, Shuhei Nakashima, Yukio Takahashi, Kohei Fukuma, Shingo Hayashi, Takashi Kajiwara, Anton Visikovskiy, Kazuhiko Mase, Kan Nakatsuji, Tanaka Satoru, Fumio Komori, Modulation of Electron-Phonon Coupling in One-Dimensionally Nanorippled Graphene on a Macrofacet of 6H-SiC, Nano Letters, 10.1021/acs.nanolett.7b00606, 17, 6, 3527-3532, 2017.06, Local electron-phonon coupling of a one-dimensionally nanorippled graphene is studied on a SiC(0001) vicinal substrate. We have characterized local atomic and electronic structures of a periodically nanorippled graphene (3.4 nm period) prepared on a macrofacet of the 6H-SiC crystal using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy (ARPES). The rippled graphene on the macrofacets distributes homogeneously over the 6H-SiC substrate in a millimeter scale, and thus replica bands are detected by the macroscopic ARPES. The STM/STS results indicate the strength of electron-phonon coupling to the out-of-plane phonon at the K̄ points of graphene is periodically modified in accordance with the ripple structure. We propose an interface carbon nanostructure with graphene nanoribbons between the surface rippled graphene and the substrate SiC that periodically modifies the electron-phonon coupling in the surface graphene..
7. 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..
8. Ashraful Hossain Howlader, Md Sherajul Islam, Tanaka Satoru, Takayuki Makino, Akihiro Hashimoto, Vacancy and curvature effects on the phonon properties of single wall carbon nanotube, Japanese Journal of Applied Physics, 10.7567/JJAP.57.02CB08, 57, 2, 2018.02, Single wall carbon nanotube (SWCNT) is considered as an ideal candidate for next-generation nanoelectronics owing to its unusual properties. Here we have performed an in-depth theoretical analysis of the effect of vacancy defects and curvature on the phonon properties of (10; 0)and (10; 10)SWCNTs using the forced vibrational method. We report that Raman active E2g mode softens towards the low-frequency region with increasing vacancies and curvature in both types of CNTs. Vacancy induces some new peaks at low-frequency region of the phonon density of states. Phonon localization properties are also manifested. Our calculated mode pattern and localization length show that optical phonon at Raman D-band frequency is strongly localized in vacancy defected and large curved CNTs. Our findings will be helpful in explaining the thermal conductivity, specific heat capacity, and Raman spectra in vacancy type disordered CNTs, as well as electron transport properties of CNT-based nanoelectronic devices..
9. Md Sherajul Islam, Khalid N. Anindya, Ashraful G. Bhuiyan, Tanaka Satoru, Takayuki Makino, Akihiro Hashimoto, Effect of 10B isotope and vacancy defects on the phonon modes of two-dimensional hexagonal boron nitride, Japanese Journal of Applied Physics, 10.7567/JJAP.57.02CB04, 57, 2, 2018.02, We report the details of the effects of the 10B isotope and those of B and N vacancies combined with the isotope on the phonon modes of two-dimensional hexagonal boron nitride (h-BN). The phonon density of states and localization problems are solved using the forced vibrational method, which is suitable for an intricate and disordered system. We observe an upward shift of Raman-active E2g-mode optical phonons (32 cm-1) for a 100% 10B isotope, which matches well with the experiment and simple harmonic oscillator model. However, a downward shift of E2g-mode phonons is observed for B or N vacancies and the combination of the isotope and vacancy-type disordered BN. Strong localized eigenmodes are found for all types of defects, and a typical localization length is on the order of ∼7 nm for naturally occurring BN samples. These results are very important for understanding the heat dissipation and electron transport properties of BN-based nanoelectronics..
10. 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, 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..
11. Ashraful Hossain Howlader, Md Sherajul Islam, Tanaka Satoru, Takayuki Makino, Akihiro Hashimoto, Vacancy and curvature effects on the phonon properties of single wall carbon nanotube, Japanese Journal of Applied Physics, 10.7567/JJAP.57.02CB08, 57, 2, 2018.02, Single wall carbon nanotube (SWCNT) is considered as an ideal candidate for next-generation nanoelectronics owing to its unusual properties. Here we have performed an in-depth theoretical analysis of the effect of vacancy defects and curvature on the phonon properties of (10; 0)and (10; 10)SWCNTs using the forced vibrational method. We report that Raman active E2g mode softens towards the low-frequency region with increasing vacancies and curvature in both types of CNTs. Vacancy induces some new peaks at low-frequency region of the phonon density of states. Phonon localization properties are also manifested. Our calculated mode pattern and localization length show that optical phonon at Raman D-band frequency is strongly localized in vacancy defected and large curved CNTs. Our findings will be helpful in explaining the thermal conductivity, specific heat capacity, and Raman spectra in vacancy type disordered CNTs, as well as electron transport properties of CNT-based nanoelectronic devices..
12. 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, 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..
13. Md. Sherajul Islam, Khalid N. Anindya, Ashraful G. Bhuiyan, Satoru Tanaka, Takayuki Makino, Akihiro Hashimoto, Effect of 10B isotope and vacancy defects on the phonon modes of two-dimensional hexagonal boron nitride, Japanese Journal of Applied Physics, 57, 02CB04, 2017.12, We report the details of the effects of the 10B isotope and those of B and N vacancies combined with the isotope on the phonon modes of two- dimensional hexagonal boron nitride (h-BN). The phonon density of states and localization problems are solved using the forced vibrational method, which is suitable for an intricate and disordered system. We observe an upward shift of Raman-active E2g-mode optical phonons (32 cm%1) for a 100% 10B isotope, which matches well with the experiment and simple harmonic oscillator model. However, a downward shift of E2g-mode phonons is observed for B or N vacancies and the combination of the isotope and vacancy-type disordered BN. Strong localized eigenmodes are found for all types of defects, and a typical localization length is on the order of >7 nm for naturally occurring BN samples. These results are very important for understanding the heat dissipation and electron transport properties of BN-based nanoelectronics..
14. Shingo Hayashi, Anton Visikovskiy, Takashi Kajiwara, Takushi Iimori, Tetsuroh Shirasawa, Kan Nakastuji, Toshio Miyamachi, Shuhei Nakashima, Koichiro Yaji, Kazuhiko Mase, Fumio Komori, Satoru Tanaka, Triangular lattice atomic layer of Sn(1 × 1) at graphene/SiC(0001) interface, Applied Physics Express, 11, 1, 015202, 2017.12, 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 K" and M" 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..
15. Koichiro Ienaga, Takushi Iimori, Koichiro Yaji, Toshio Miyamachi, Shuhei Nakashima, Yukio Takahashi, Kohei Fukuma, Shingo Hayashi, Takashi Kajiwara, Anton Visikovskiy, Kazuhiko Mase, Kan Nakatsuji, Tanaka Satoru, Fumio Komori, Modulation of Electron-Phonon Coupling in One-Dimensionally Nanorippled Graphene on a Macrofacet of 6H-SiC, Nano Letters, 17, 6, 3527-3532, 2017.06, Local electron−phonon coupling of a one-dimen-sionally nanorippled graphene is studied on a SiC(0001) vicinal substrate. We have characterized local atomic and electronic
structures of a periodically nanorippled graphene (3.4 nm period) prepared on a macrofacet of the 6H-SiC crystal using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy (ARPES). The rippled graphene on the macrofacets distributes homogeneously over the 6H-SiC substrate in a millimeter scale, and thus replica bands are detected by the macroscopic ARPES. The STM/STS results indicate the strength of electron−phonon coupling to the out-of-plane phonon at the K̅ points of graphene is periodically modified in accordance with the ripple structure. We propose an interface carbon nanostructure with graphene nanoribbons between the surface rippled graphene and the substrate SiC that periodically modifies the electron−phonon coupling in the surface graphene.
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16. Ayhan Yurtsever, Jo Onoda, Takushi Iimori, Kohei Niki, Toshio Miyamachi, Masayuki Abe, Seigi Mizuno, Satoru Tanaka, Fumio Komori, Yoshiaki Sugimoto , Effects of Pb Intercalation on the Structural and Electronic Properties of Epitaxial Graphene on SiC, Small, 12, 29, 3956-3966, 2016.10, The effects of Pb intercalation on the structural and electronic properties of epitaxial single-layer graphene grown on SiC(0001) substrate are investigated using scanning tunneling microscopy (STM), noncontact atomic force microscopy, Kelvin probe force microscopy (KPFM), X-ray photoelectron spectroscopy, and angle-resolved photoemission spectroscopy (ARPES) methods. The STM results show the formation of an ordered moiré superstructure pattern induced by Pb atom intercalation underneath the graphene layer. ARPES measurements reveal the presence of two additional linearly dispersing π-bands, providing evidence for the decoupling of the buffer layer from the underlying SiC substrate. Upon Pb intercalation, the Si 2p core levelspectrashowasignaturefortheexistenceofPb Sichemicalbondsattheinterface region, as manifested in a shift of 1.2 eV of the bulk SiC component toward lower binding energies. The Pb intercalation gives rise to hole-doping of graphene and results in a shift of the Dirac point energy by about 0.1 eV above the Fermi level, as revealed by the ARPES measurements. The KPFM experiments have shown that decoupling of the graphene layer by Pb intercalation is accompanied by a work function increase. The observed increase in the work function is attributed to the suppression of the electron transfer from the SiC substrate to the graphene layer. The Pb intercalated structure is found to be stable in ambient conditions and at high temperatures up to 1250 °C. These results demonstrate that the construction of a graphene-capped Pb/SiC system offers a possibility of tuning the graphene electronic properties and exploring intriguing physical properties such as superconductivity and spintronics..
17. 田中 悟, ANTON VISIKOVSKIY, 梶原隆司, 小森 文夫, 吉村, 飯盛 たくし, 木本 真一, Graphene/SiC(0001) interface structures induced by Si intercalation and their influence
on electronic properties of graphen, PHYSICAL REVIEW B, 94, 245421, 2016.12, 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..
18. H. A. Hafez, I. Al-Naib, M. M. Dignam, Y. Sekine, K. Oguri, F. Blanchard, D. G. Cooke, Tanaka Satoru, F. Komori, H. Hibino, T. Ozaki, Nonlinear terahertz field-induced carrier dynamics in photoexcited epitaxial monolayer graphene, Phys. Rev. B, 91, 035422, 2015.10.
19. A. Endo, F. Komori, K. Morita, T. Kajiwara, Tanaka Satoru, Highly Anisotropic Parallel Conduction in the Stepped Substrate of Epitaxial Graphene Grown on Vicinal SiC, J. Low Temp. Phys., 179, 237, 2015.09.
20. S. W. King, Tanaka Satoru, R. F. Davis, R. J. Nemanich, Hydrogen desorption from hydrogen fluoride and remote hydrogen plasma cleaned silicon carbide (0001) surfaces, J. Vac. Sci. Tech. A, 33, 5, 05E105, 2015.07.
21. H. Tochihara, T. Shirasawa, T. Suzuki, T. Miyamachi, T. Kajiwara, K. Yagyu, S. Yoshizawa, T. Takahashi, Tanaka Satoru, F. Komori, Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(000-1) surfaces, Appl. Phys. Lett. , 104, 051601, 2015.04.
22. Md. Sherajul Islam, Kenji Ushida, Tanaka Satoru, Akihiro Hashimoto, Effect of vacancy defects on phonon properties of hydrogen passivated graphene nanoribbons, Carbon, 80, 146, 2014.10.
23. Md. Sherajul Islam, Kenji Ushida, Tanaka Satoru, Akihiro Hashimoto, Numerical experiments on phonon properties of isotope and vacancy-type disordered graphene, Diamond & Related Materials, 40, 115-122, 2013.10, We have studied phonon properties of graphene theoretically with different concentrations of 13C isotope and vacancy-type defects. The forced vibrational method, which is based on the mechanical resonance to extract
the pure vibrational eigenmodes by numerical simulation, has been employed to compute the phonon density of states (PDOSs) and mode pattern of isotope-disordered graphene as well as a combined isotope and vacancy-type defective graphene structure. We observe a linear reduction of the E2g mode frequencies with an increase in 13C concentration due to the reduced mass variation of the isotope mixture.We find a downshift of the E2g mode of 65 cm−1, which is a very good agreement with the experimental results, and the phonon frequencies described by the simple harmonic oscillator model. The vacancy-type defects break down the phonon degeneracy at the Г point of the LO and TOmodes, distort and shift down the phonon density of states significantly. The PDOS peaks for the combined isotope and vacancy-type defects showthe remarkable increase in the low frequency region induced by their defect formations. Due to phonon scattering by 13C isotope or vacancies, some graphene phonon wave functions become localized in the real space. Our numerical experiments reveal that the lattice vibrations in the defective graphene show the remarkably different properties such as spatial localization of lattice vibrations due to their random structures from those in the perfect graphene. The calculated typical mode patterns for in-plane K point optical phonon modes indicate that the features of strongly localized state depend on the defect density, and the phonon is localized stronglywithin a region of several nanometers in the random percolation network structures. In particular, for in-plane K point optical phonon modes, a typical localization length is on the order of ≈7 nm for isotope impurities, ≈5 nm for vacancy-type defects and ≈6nm for mixed-type defects at high defect concentrations of 30%. Our findings can be useful for the interpretation
of experiments on infrared, Raman, and neutron-diffraction spectra of defective graphene, aswell as in the study of a wide variety of other physical properties such as thermal conductivity, specific heat capacity, and electron–phonon interaction..
24. Md. Sherajul Islam, Kenji Ushida, Tanaka Satoru, Akihiro Hashimoto, Numerical analysis on vacancy induced vibrational properties of graphene nanoribbons, Computational Materials Science, 79, 356-361, 2013.07, The effect of vacancy-type defects on the vibrational properties of graphene nanoribbons has been
discussed numerically. We have computed the phonon density of states and mode pattern over a broad
range of vacancies using the forced vibrational method which is based on the mechanical response to
extract the pure vibrational eigenmodes by numerical simulation. We find that the armchair-edge and
the vacancy-type defects break down the phonon degeneracy at the U point of the LO and TO mode,
distort and shift down the phonon density of states significantly. The phonon density of states in the
armchair graphene nanoribbons with vacancy-type defects show the remarkable increase in the low
frequency region induced by their defect formations. The mode patterns obtained by our numerical
experiments reveal that the in-plane optical phonon modes in the K point are localized near the armchair-
edges which are in good agreement with the high intensity D peak in the Raman spectra originate
from the armchair-edge. The simulation results also demonstrate that the lattice vibrations in the defective graphene nanoribbons show the remarkably different properties such as spatial localizations of lattice vibrations due to their random structures from those in the perfect graphene nanoribbons. These differences manifest themselves in the predicted temperature behavior of the constant-volume specific heat capacity of both structures..
25. Hagihara Yoshihito, Tanaka Satoru, Graphene nanoribbons grown on epitaxial SixCyOz layer on vicinal SiC(0001) surfaces by chemical vapor deposition, Appl. Phys. Express, 6, 055102, 2013.04.
26. Kajiwara Kakashi, Tanaka Satoru, Graphene nanoribbons on vicinal SiC surfaces by molecular beam epitaxy, Physical Review B 87, 121407 (2013). , 87, 121407, 2013.03, We present a method of producing a densely ordered array of epitaxial graphene nanoribbons (GNRs) using vicinal SiC surfaces as a template, which consists of ordered pairs of (0001) terraces and nanofacets. Controlled selective growth of graphene on approximately 10 nm wide (0001) terraces with 10 nm spatial intervals allows GNR formation. By selecting the vicinal direction of SiC substrate, [1¯100], well-ordered GNRs with predominantly armchair edges are obtained. These structures, the high-density GNRs, enable us to observe the electronic structure at K points by angle-resolved photoemission spectroscopy, showing a clear band-gap opening of at least 0.14 eV..
27. Susumu Kamoi, Kenji Kisoda, Noriyuki Hasuike, Hiroshi Harima, Kouhei Morita, Satoru Tanaka, Akihiro Hashimoto, Hiroki Hibino, A Raman imaging study of growth process of few-layer epitaxial graphene on vicinal 6H–SiC, Diamond & Related Materials, 25, 80-83, 2012.03, Few-layer epitaxial graphenes grown on vicinal 6H–SiC (0001) were characterized by confocal Raman imaging.
In the beginning of the growth, the surface of SiC substrate was covered with monolayer graphene. Next,
few-layer graphenes started to grow toward directions perpendicular to [11–20] of the SiC substrate. The
shift in the G-peak was not straightforward with the increase in number of graphene layers. This result can
be interpreted that the in-plane compressive stress from the substrate depends on the domain size of graphene.
The 2D-peak frequency shifted to higher frequency side due to strong compressive strain from the
substrate with increasing of the growth times..
28. Yoshimine Kato, Masaki Goto a, Ryota Sato a, Kazuhiro Yamada a, Akira Koga b, Kungen Teii, Chenda Srey, Satoru Tanaka, Formation of epitaxial 3C-SiC layers by microwave plasma-assisted carbonization, Surface & Coatings Technology, 206, 990–993, 2011.08, Epitaxial 3C-SiC (β-SiC) thin layers are grown on Si (001) substrates by carbonization in moderate-pressure
microwave plasmas, typically used for diamond film deposition. The substrate temperature and the CH4 gas
concentration diluted in H2 gas are varied from 1000 to 1200 °C and from 2 to 8 vol.%, respectively. The grown
layers are characterized by scanning electron microscopy, Raman spectroscopy, x-ray diffraction, Fourier
transform infrared spectroscopy, reflection high energy electron diffraction, and energy-dispersive x-ray
spectroscopy. For 2% CH4, epitaxial 3C-SiC about 10 nm thick is grown only when the temperature is increased
to 1200 °C, while polycrystalline 3C-SiC is grown for temperatures less than 1200 °C. For 8% CH4, epitaxial
3C-SiC is grown even for temperatures less than 1200 °C, but the thickness of the SiC layer is reduced. Some
amounts of amorphous carbon and diamond phases are found to grow on the SiC layers..
29. K. Hayashi, S. Mizuno, S. Tanaka, LEED analysis of graphite films on vicinal 6H-SiC(0001) surface, Journal of Novel Carbon Resource Sciences, 2, 0001, 17, 2010.08.
30. Kan Nakatsuji, Yuki Shibata, Ryota Niikura, Fumio Komori, Kouhei Morita, Satoru Tanaka, Shape, width, and replicas of π bands of single-layer graphene grown on Si-terminated vicinal SiC(0001), Phys. Rev. B, 82, 4, 045428, 2010.07.
31. K. Kisoda, S. Kamoi, N. Hasuike, H. Harima, K. Morita, S. Tanaka, A. Hashimoto, Few-layer epitaxial graphene grown on vicinal 6H–SiC studied by deep ultraviolet Raman spectroscopy, Appl. Phys. Lett., 97, 3, 033108, 2010.05.
32. S. Tanaka, K. Morita, H. Hibino, Anisotropic layer-by-layer growth of graphene on vicinal SiC(0001) surfaces, Phys. Rev. B, Rapid Communication, 81, 041406(R), 2010.01.
33. S. Odaka, H. Miyazaki, S.-L. Li, A. Kanda, K. Morita, S. Tanaka, Y. Miyata, H. Kataura, K. Tsukagoshi, Y. Aoyagi, Anisotropic transport in graphene on SiC substrate with periodic nanofacets, Appl. Phys. Lett., 96, 062111, 2010.01.
34. T. Shirasawa, K. Hayashi, H. Yoshida, S. Mizuno, S. Tanaka, T. Muro, Y. Tamenori, Y. Harada, T. Tokushima, Y. Horikawa, E. Kobayashi, T. Kinoshita, S. Shin, T. Takahashi, Y. Ando, K. Akagi, S. Tsuneyuki, H. Tochihara, Atomic-layer-resolved bandgap structure of an ultrathin oxynitride-silicon film epitaxially grown on 6H-SiC(0001), Phys. Rev. B, 79, 24, 241301(R), 2009.06.
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