Kyushu University [Takeshi NAKAGAWA (Associate Professor) Faculty of Engineering Sciences, Department of Advanced Materials Science and Engineering]

Takeshi NAKAGAWA

Last modified date：2024.06.03

Associate Professor / Surface Science / Department of Advanced Materials Science and Engineering / Faculty of Engineering Sciences

Papers

1.	Xiaobin Chen, Dhiman Banik, Takeshi Nakagawa, Structural investigation of flat overlayer and surface alloy of Sn on Mo(110), SURFACE SCIENCE, 10.1016/j.susc.2022.122224, 729, 122224, 2023.03.
2.	Shahadat Hossain, Guansong Peng, Takeshi Nakagawa, Boron nanostructure formation on Mo(112) surface, Surface Science, 10.1016/j.susc.2022.122145, 2022.07, [URL].
3.	Farhana Jesmin Tuli, Guansong Peng, Shahadat Hossain, Kakeru Ninomiya, Rezwan Ahmed, Takeshi Nakagawa, Seigi Mizuno, Formation of ordered B structure on W(100), Surface Science, 10.1016/j.susc.2021.121906, 2021.07.
4.	Farhana Jesmin Tuli, Mohammad Tawheed Kibria, Takeshi Nakagawa, and Seigi Mizuno, Interfacial Magnetic Behaviors and Chemical States of Fe Grown on MoS2, physica status solidi (pss), 10.1002/pssb.202100124, 2021.05, [URL].
5.	Noguchi, A., Takamura, Y., Nakagawa, T., Rokuta, E. Mizuno, S., Structural analysis of clean LaB6(100), (111), and (110) surfaces via quantitative low-energy electron diffraction, Surface Science, 10.1016/j.susc.2020.121686, 2020.11.
6.	Rezwan Ahmed, Takeshi Nakagawa, Seigi Mizuno, Structure determination of ultra-flat stanene on Cu(111) using low energy electron diffraction, Surface Science, 10.1016/j.susc.2019.121498, 691, 2020.01, The 2D hexagonal structure of tin atoms which is termed stanene is structurally determined on a Cu(111) substrate using low energy electron diffraction (LEED). The structural analysis of Cu{111}-p(2 × 2)-Sn at a coverage of 0.5 at low temperature reveals the relaxation of underlying Cu atoms, which stabilizes the formation of almost zero-buckled Sn atoms forming a honeycomb structure. Our results using quantitative LEED conclusively reveals an ultra-flat stanene structure that complements well with the previous calculations. The detailed structural analysis presented in this article is expected to give in-depth information for characterizing the properties of as-grown stanene..
7.	Mohammad Tawheed Kibria, Takeshi Nakagawa, Seigi Mizuno, Morphology and magnetism of Fe on graphene and thick graphite grown on SiC, Applied Surface Science, 10.1016/j.apsusc.2019.144209, 2020.01, We have studied growth and magnetism of Fe on graphene and graphite surfaces grown on SiC substrate. Magneto-optical Kerr effect (MOKE) results show that the magnetic dead layer exists on both surfaces. Fe on graphene exhibits larger magnetic anisotropy with almost perfect remanence magnetization above Fe deposition of nominal 7.5 Å thickness. On the other hand, Fe on graphite, with oval nanoparticles, has a low magnetic anisotropy, and hysteresis appears at Fe deposition of nominal 15 Å thickness. X-ray photoelectron measurements suggest that the higher anisotropy and thinner magnetic dead layer for Fe/graphene does not come from the difference in interface mixing. A structural investigation by scanning tunneling microscopy reveals that Fe forms nanoparticles on both carbonized surfaces and that on graphene the aspect ratio of the Fe particles between the height and width is much smaller compared with that on graphite. The shape anisotropy originating from the morphological changes is consistent with the MOKE results. The formation of the low-profile Fe nanoparticle on the graphene indicates the higher surface energy on the graphene/SiC. The different surface energy derived from the interaction between graphene layer and the substrate drastically modifies magnetic properties of Fe overlayers..
8.	Mohammad Tawheed Kibria, Md Amirul Islam, Bidyut Baran Saha, Takeshi Nakagawa, Seigi Mizuno, Assessment of environmental impact for air-conditioning systems in Japan using HFC based refrigerants, Evergreen, 6, 3, 246-253, 2019.09, Air-conditioning system notably contributes to global warming owing to the huge amount of energy consumption. Moreover, this system uses HFC based refrigerants, which have high global warming potential (GWP). This work investigates the direct and indirect impacts of GWP for commercial and residential air-conditioning systems considering the three widely used HFC based refrigerants. The warming impacts are assessed in terms of cooling load, co-efficient of performance (COP), evaporation temperature, and condensation temperature for three different locations in Japan. The indirect emission of the air-conditioning systems (commercial and residential) for different major cities of Japan is estimated in terms of energy demand and hours of operation. The results of this work indicate that the HFC based refrigerants such as R134a and R32 have lower warming impact compared to that of R410A refrigerant. Furthermore, the economic loss due to refrigerant leakage is also assessed..
9.	Koutaro Nishihara, Tatsushi Nomitsu, Takeshi Nakagawa, Seigi Mizuno, Structural investigation and magnetic properties of oxygen adsorption on ultrathin Fe(110) film, Surface Science, 10.1016/j.susc.2019.03.001, 685, 34-39, 2019.07, We have investigated oxygen induced surface structures on Fe(110) thin film and their magnetic properties using low energy electron diffraction (LEED) and surface magneto-optic Kerr effect (SMOKE). We have determined two chemisorbed structures, p(2 × 2) at 0.25 monolayer (ML) and p(3 × 2) at 0.33 ML using a dynamical LEED analysis. We found that oxygen atoms adsorb in long bridge sites on p(2 × 2) and move to three fold hollow sites on p(3 × 2) due to a steric repulsion. During chemisorption, proceeding the formation of FeO, the topmost surface of Fe film is ferromagnetic and with further oxygen adsorption the surface loses ferromagnetism in accordance with the oxide formation..
10.	Hiroshi Ando, Anton Visikovskiy, Takeshi Nakagawa, Seigi Mizuno, Satoru Tanaka, Structure determination of hydrogen-terminated 4H -SiC(0001) by LEED, Physical Review B, 10.1103/PhysRevB.99.235434, 99, 23, 2019.06, SiC(0001)-(1×1)-H consisting of monohydride is a preferred starting surface structure for synthesis of the two-dimensional materials on SiC(0001). Here we report preparation of the SiC(0001)-(1×1)-H by atomic hydrogen exposure and structure determination of the SiC(0001)-(1×1)-H by a quantitative LEED analysis. Our data show that the SiC(0001)-(1×1)-H is indeed a bulk terminated unreconstructed SiC(0001) surface. The sample morphology was also investigated using AFM. The dominance of one of two possible inequivalent surface terminations of 4H polytype of SiC crystal was confirmed..
11.	Md Kabiruzzaman, Takeshi Nakagawa, Seigi Mizuno, Optimization of growth procedure for silicon oxinitride (Si₄O₅N₃) single-layer on SiC(0001), Joint 7th International Conference on Informatics, Electronics and Vision and 2nd International Conference on Imaging, Vision and Pattern Recognition, ICIEV-IVPR 2018 2018 Joint 7th International Conference on Informatics, Electronics and Vision and 2nd International Conference on Imaging, Vision and Pattern Recognition, ICIEV-IVPR 2018, 10.1109/ICIEV.2018.8641044, 218-221, 2019.02, Optimized growth of Silicon Oxynitride (Si4O5N3) has been obtained in ultrahigh vacuum and growth conditions are confirmed by observing the low-energy electron diffraction (LEED) patterns and Auger electron spectroscopy (AES). All the steps to produce the perfect Si4O5N3 are clarified separately. Specially, initial Si, time for deposition, nitridation and oxidation are crucial points for getting the clear LEED pattern. By observing the LEED patterns and according to the suggestions of previous report to get ideal insulator and SiC interface, we are expecting that the surface is free from the extra-Si or the least amount of Si remains which can be confirmed by scanning tunneling microscopy (STM)..
12.	Md Kabiruzzaman, Rezwan Ahmed, Takeshi Nakagawa, Seigi Mizuno, Ordered mixed rows of (Pb + Sn) and (Pb + Sb) on Cu(001) A coadsorption study and structure determination using low energy electron diffraction, Surface Science, 10.1016/j.susc.2018.06.002, 677, 128-134, 2018.11, The surface alloys of (Pb, Sn) and (Pb, Sb) on Cu(001) obtained via the coadsorption method were independently determined using tensor low-energy electron diffraction (LEED). Both surface alloys were obtained under the p(4 × 4) phase. The determined structures consisted of mixed rows of the adsorbates in a one-dimensional chain arrangement. These mixed rows are buckled differently in each row. The best-fit structure indicates that the Sn or Sb atoms are located on the four-fold hollow sites while the Pb atoms are displaced toward the vacancies. The bond lengths of Sn or Sb atoms with Cu underneath of the alternative mixed chains are reduced by 4.8% or 5.9%, respectively, compared to the bulk values. We consider that, the large reductions of these bond lengths and the tendency of the adsorbates to make alloy at the surface stabilize the structure. The other structural parameters, bonding effects of the surrounding Cu atoms with the adsorbates, and similar characteristics of the elements located in the same period of periodic table are discussed in detail. On the basis of the structural characterization, the mechanisms of the formation of the p(4 × 4) phase are proposed..
13.	Mohammad Tawheed Kibria, Tatsushi Nomitsu, Takeshi Nakagawa, Seigi Mizuno, Investigation of Magnetic Dead Layer on Iron Silicide Surfaces^∗, e-Journal of Surface Science and Nanotechnology, 10.1380/ejssnt.2018.101], 16, 101-104, 2018.04, We report the magnetic dead layer at the interfaces between Fe and Si(111) surfaces. We prepared two ultrathin iron-silicides, c(8×4) prepared at 900 K and p(2×2) at 700 K, and clean reconstructed 7×7 surface for the silicon templates. By using magneto-optical Kerr effect, we found that at room temperature the ferromagnetic order appears at 5.5 ML, 8.2 ML, and 10.9 ML for Fe/c(8×4) silicide, Fe/p(2×2) silicide, and Fe/Si(111)-7×7 surface, respectively. From the thickness dependent magnetization measurements, we decided the magnetic dead layer for Fe/c(8×4) silicide, Fe/p(2×2) silicide, and Fe/Si(111)-7×7 to be 3.0 ML, 5.0 ML, and 7.5 ML, respectively. Our results indicate that the c(8×4) iron silicide surface prevents further silicide formation more effectively than the p(2×2) silicide and Si(111)-7×7 surface..
14.	Md Kabiruzzaman, Rezwan Ahmed, Takeshi Nakagawa, Seigi Mizuno, Coadsorption study of Pb and Sb on Cu(001) by low energy electron diffraction, 6th International Conference on Informatics, Electronics and Vision and 2017 7th International Symposium in Computational Medical and Health Technology, ICIEV-ISCMHT 2017 2017 6th International Conference on Informatics, Electronics and Vision and 2017 7th International Symposium in Computational Medical and Health Technology, ICIEV-ISCMHT 2017, 10.1109/ICIEV.2017.8338577, 1-5, 2018.04, Room temperature coadsorption of Pb and Sb on Cu(001) has been studied by low energy electron diffraction (LEED). A p(4×4) structure has been obtained by Pb and Sb at coverages of ∼0.25 and ∼0.125, respectively. This coverage combination is similar to the Pb and Bi study on Cu(001) [1]. This phase is confirmed by clear LEED patterns up to 250 eV. Above this energy some points of p(4×4) phase has been disappeared and only c(4×4) points remain. Based on LEED theory, using computer simulation and similarity of the coverage combination with Pb and Bi study, here a surface alloy model has been proposed and determined. The best-fit structure of the model and its consistency with the experimental results has been discussed in detail..
15.	Mohammad Tawheed Kibria, Tatsushi Nomitsu, Takeshi Nakagawa, Seigi Mizuno, Investigation of magnetic dead layer on iron silicide surfaces, e-Journal of Surface Science and Nanotechnology, 10.1380/ejssnt.2018.101, 16, 101-104, 2018.04, We report the magnetic dead layer at the interfaces between Fe and Si(111) surfaces. We prepared two ultrathin iron-silicides, c(8×4) prepared at 900 K and p(2×2) at 700 K, and clean reconstructed 7×7 surface for the silicon templates. By using magneto-optical Kerr effect, we found that at room temperature the ferromagnetic order appears at 5.5 ML, 8.2 ML, and 10.9 ML for Fe/c(8×4) silicide, Fe/p(2×2) silicide, and Fe/Si(111)-7×7 surface, respectively. From the thickness dependent magnetization measurements, we decided the magnetic dead layer for Fe/c(8×4) silicide, Fe/p(2×2) silicide, and Fe/Si(111)-7×7 to be 3.0 ML, 5.0 ML, and 7.5 ML, respectively. Our results indicate that the c(8×4) iron silicide surface prevents further silicide formation more effectively than the p(2×2) silicide and Si(111)-7×7 surface..
16.	Md Kabiruzzaman, Rezwan Ahmed, Takeshi Nakagawa, Seigi Mizuno, 1D chain formation by coadsorption of Pb and Bi on Cu(001) Determination using low energy electron diffraction, Surface Science, 10.1016/j.susc.2017.05.017, 664, 70-75, 2017.10, Coadsorption of two heavy metals, Pb and Bi, on Cu(001) at room temperature has been studied using low energy electron diffraction (LEED). c(4 × 4), c(2 × 2), and c(92×2) phases are obtained at different coverages; here, we have determined the best-fit structure of c(4 × 4) phase. This structure can be described as a 1D substitutional chain arrangement of Pb and Bi atoms between the Cu rows along the [110] direction. The unit cell in the two-dimensional (2D) surface consists of one Bi atom, two Pb atoms, and four Cu atoms with one vacancy at the center. The optimal structure parameters demonstrate that Bi atoms are located at fourfold-hollow sites and that Pb atoms are laterally displaced by 0.78 Å from the fourfold-hollow site toward the vacancy. The reasons for the formation of the c(4 × 4) structure upon deposition of Pb and Bi on Cu(001) are discussed in comparison with a similar structure formed by the individual adsorption of Pb on the same substrate..
17.	Seigi Mizuno, Tomomi Matsuo, Takeshi Nakagawa, Step-by-step growth of an epitaxial Si₄O₅N₃ single layer on SiC(0001) in ultrahigh vacuum, Surface Science, 10.1016/j.susc.2017.03.004, 661, 22-27, 2017.07, An epitaxial single Si₄O₅N₃ layer was formed on a SiC(0001) surface using a step-by-step growth method in an ultrahigh vacuum condition. First, a silicon adsorbed SiC(0001) surface was prepared. The surface was then exposed to NO gas at 950 °C in order to form a Si₂ON₃ layer. Silicon was deposited on this surface and annealed to adjust the amount of adsorbed Si atoms. Finally, the surface was oxidized at 800 °C. The formation of a Si₄O₅N₃ layer was confirmed by low-energy electron diffraction analysis, Auger electron spectroscopy, and scanning tunneling microscopy. Using this procedure, we were able to suppress the growth of graphite-like clusters on the surface, although silicate-like clusters still remained..
18.	Md Kabiruzzaman, Rezwan Ahmed, Takeshi Nakagawa, Seigi Mizuno, Investigation of_C(2×2) phase of Pb and Bi coadsorption on Cu(001) by low energy electron diffraction, Evergreen, 4, 1, 10-15, 2017.01, The surface phases formed by coadsorption of Pb and Bi on a single crystal Cu(001) surface have been investigated using low energy electron diffraction (LEED). The complete phase chart is developed after the coadsorption of Pb and Bi with various coverages. Some notable phases obtained are (1×1), c(2×2), c(4×4) and c(9√2×√2). In this study, we have determined the c(2×2) phase. For individual adsorption of both Pb and Bi, we reconfirmed the c(2×2) structure with more accuracy by a tensor LEED analysis that they both occupy the four fold hollow sites. By comparing the structural parameters of coadsorption and individual adsorption, we conclude that the c(2×2) phase of coadsorption is the mixture of separate domains of the c(2×2) phases of Pb and Bi. This study opens a new window of further research into the surface phase determination of coadsorption of Pb and Bi on Cu(001)..
19.	Md. Sazzadur Rahman, NAKAGAWA Takeshi, Seigi Mizuno, Structure determination of the ordered (2 × 1) phase of NiSi surface alloy on Ni(111) using low-energy electron diffraction, Jpn. J. Appl. Phys. 54, 125701(2015), http://iopscience.iop.org/1347-4065/54/12/125701, 54, 125701, 2015.11.
20.	Md Sazzadur Rahman, Mohammad Tawheed Kibria, Takeshi Nakagawa, Seigi Mizuno, Surface structure study and structure determination of (√3 × √3)R 30° phase of Si-adsorption on Ni(111) by LEED, 4th International Conference on Informatics, Electronics and Vision, ICIEV 2015 2015 4th International Conference on Informatics, Electronics and Vision, ICIEV 2015, 10.1109/ICIEV.2015.7334025, 2015.11, The phase evolution of Si on Ni (111) was studied by LEED and AES. A new phase of Si on Ni (111) was found along with the previously reported (√3 × √3)R 30° phase. The surface structure of (√3 × √3)R 30° phase had determined, with chemical composition of Ni₂Si, by using low-energy electron diffraction (LEED) analysis. The obtained nickel silicide would be helpful for understanding the formation of Schottky barrier at semiconductor-metal interface..
21.	Md Sazzadur Rahman, Takeshi Nakagawa, Seigi Mizuno, Structure determination of the ordered (√3 × √3)R30° phase of Ni₂Si and Ni₂Ge surface alloys on Ni(111) via low-energy electron diffraction, Surface Science, 10.1016/j.susc.2015.07.024, 642, 1-5, 2015.08, Abstract The 3×3R30°structures of 2-D nickel silicide and nickel germanide surface alloys on Ni(111) were investigated using quantitative low-energy electron diffraction analysis. The unit cells of the determined silicide and germanide structures contain two Ni atoms and one Si or Ge atom, corresponding to the chemical compositions Ni₂Si and Ni₂Ge, respectively. Both the Si and Ge atoms adopt substitutional face-centered cubic hollow sites to sit on the Ni(111) substrates, and the alloy surfaces exhibit a slight corrugation. The NiSi and NiGe distances were 2.44 and 2.56 Å, respectively, and corresponded well to their respective empirical radii. It was also found that the Ni atoms in the second and third layers moved toward the Si or Ge atom sites from their bulk crystal positions. These results indicate rather strong interactions of the Ni atoms with both the Si and Ge atoms at the surface, leading to trapping of the Si and Ge atoms at the substitutional sites without diffusion into the bulk..
22.	Md Sazzadur Rahman, Takeshi Nakagawa, Seigi Mizuno, Growth of Si on Ag(111) and determination of large commensurate unit cell of high-temperature phase, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.54.015502, 54, 1, 2015.01, We studied the structural transition for silicon adsorption on Ag(111) by using low-energy electron diffraction (LEED) and Auger electron spectroscopy at various substrate temperatures during deposition. We obtained a single phase of the (4 × 4) structure at 520 K, which was reported as a silicene. At 620 K, the (4 × 4) structure changed to a high-temperature phase which was determined as ( √133 × √133) R 4.3° by LEED, while in preceding works, it was assigned to a quasi (2√3 × 2√3) R 30° or (3.5 × 3.5) R 26° structure. Although the high-temperature phase had not been observed as a single phase, we obtained LEED patterns with a single phase for it, which enabled us to explain all the diffraction spots on the basis of the kinematic theory including double diffraction. The (√133 × √133) R 4.3° was obtained by the multiplication of a (1.35 × 1.35) R 9.9° subunit cell. We concluded that the (2 √3 × 2√3) R 30° and (3.5 × 3.5) R 26° phases could instead be represented as a ( √133× √133) R 4.3° phase, and we proposed a possible atomic model..
23.	Md Sazzadur Rahman, Md Amirul Islam, Bidyut Baran Saha, Takeshi Nakagawa, Seigi Mizuno, Structure determination of the ordered (2 × 1) phase of NiSi surface alloy on Ni(111) using low-energy electron diffraction, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.54.125701, 54, 12, 2015.01, The (2 × 1) structure of the two-dimensional nickel silicide surface alloy on Ni(111) was investigated using quantitative low-energy electron diffraction analysis. The unit cell of the determined silicide structure contains one Si and one Ni atom, corresponding to a chemical formula of NiSi. The Si atoms adopt substitutional face-centered cubic hollow sites on the Ni(111) substrate. The Ni-Si bond lengths were determined to be 2.37 and 2.34 Å. Both the alloy surface and the underlying first layers of Ni atoms exhibit slight corrugation. The Ni-Si interlayer distance is smaller than the Ni-Ni interlayer distance, which indicates that Si atoms and underlying Ni atoms strongly interact..
24.	Md. Sazzadur Rahman, NAKAGAWA Takeshi, Seigi Mizuno, Growth of Si on Ag(111) and determination of large commensurate unit cell of high-temperature phase , Jpn. J. Appl. Phys , doi:10.7567/JJAP.54.015502, 54, 015502 , 2014.10.
25.	K.Eguchi　, NAKAGAWA Takeshi, Y. Takagi, T. Yokoyama, Magnetic Interactions of Vanadyl Phthalocyanine with Ferromagnetic Iron, Cobalt, and Nickel Surfaces, J. Phys. Chem. C, 2014, 118 (31), pp 17633–17637 , 10.1021/jp503851k, 118 , 31, 2014.08.
26.	Ryo Kohmatsu, NAKAGAWA Takeshi, Seigi Mizuno, Growth and surface structure analysis of a new SiON single layer on SiC(0001) , Surface Science, 628, October 2014, Pages 148–152 , 0.1016/j.susc.2014.06.007, 628, 31, 148-152, 2014.08.
27.	NAKAGAWA Takeshi, Oscillations of the Orbital Magnetic Moment due to d-Band Quantum Well States, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.113.067203, 113, 6, 2014.08.
28.	Md Sazzadur Rahman, Takeshi Nakagawa, Seigi Mizuno, Germanene Experimental study for graphene like two dimensional germanium, Evergreen, 1, 2, 25-29, 2014.01, Inspired by the fruitful results based on graphene, two dimensional structures of group-IV elements (Si, Ge) are currently the most investigated materials in physics and nano science. Silicene, the silicon analogy of graphene, had already been synthesized experimentally, but the germanium analogy of graphene has not been synthesized experimentally yet. Only a few theoretical works predicted that graphene like 2-D honeycomb structure of germanium is stable with low buckling. We experimentally observed the phase evolutions for germanium growth on Ag(111) by low energy electron diffraction. We observed that the phase evolutions were strongly dependent on the amount of germanium coverage on Ag(111). We obtained a (9√3 × 9√3)R 30° pattern by germanium adsorption on Ag(111) at RT and the pattern become clear after annealing at 415 K. The (9√3 × 9√3)R 30° pattern is analogous to the (6√3 × 6√3)R 30° pattern of graphene formation on SiC(0001). We also observed the atomically resolved STM image after one monolayer germanium adsorption on Ag(111). By the observation on the STM image, we observed a honeycomb structure and by further close observation on larger area, we observed the (9√3 × 9√3)R 30° moire structure. On the basis of the LEED and STM results, we have proposed an atomic model for germanene, the germanium analogy of graphene, growth on Ag(111)..
29.	Ryo Kohmatsu, Takeshi Nakagawa, Seigi Mizuno, Growth and surface structure analysis of a new SiON single layer on SiC(0001), Surface Science, 10.1016/j.susc.2014.06.007, 628, 148-152, 2014.01, A new silicon oxynitride layer was formed on a 6H-SiC(0001) surface by a nitrogen oxide treatment. The atomic structure of this single layer on the SiC(0001) substrate was determined by means of low-energy electron diffraction (LEED) analysis. The surface layer has a (3×3) R30° periodicity. Its LEED I(E) spectra are different from those of the previously reported silicon oxynitride layer which has a Si₄O₅N₃ composition [Phys. Rev. Lett. 98 (2007) 136105]. The best-fit structure has a single layer of Si₂ON₃ composition terminated by O bridges. The Si-N layer of the determined structure has the same structure as that in the Si₄O₅N₃ surface. The obtained Si₂O₃ structure would be useful for preparing an ideal SiC-insulator interfaces with a low interfacial density of states..
30.	NAKAGAWA Takeshi, Molecular Orientation and Electronic States of Vanadyl Phthalocyanine on Si(111) and Ag(111) Surfaces, 10.1021/jp406906k, 117, 22843-22851, 2013.10.
31.	NAKAGAWA Takeshi, Keitaro Eguchi, Toshihiko Yokoyama, Yasumasa Takagi, Passivating effect of Si(111)-(root 3x root 3)Ag and Si3N4/Si(111)-(8x8) buffer layers, Journal of Physics Conference Series, 430, 012129 (2013) [6 pages], 10.1088/1742-6596/430/1/012129, 2013.06.
32.	T. Nakagawa, and T. Yokoyama, Laser induced threshold photoemission magnetic circular dichroism and its application to photoelectron microscope, Journal of Electron Spectroscopy and Related Phenomena, 186, 356, 2012.12, This work enlightens the threshold photoemission magnetic circular dichroism (MCD) and its adaption on photoemission electron microscopy (PEEM) using lasers. MCD is a simple and efficient way to investigate magnetic properties since it does not need any spin analyzers with low efficiency, and thus the MCD related techniques have developed to observe magnetic domains. Usually, MCD in a total yield measurement in the valence band with weak spin–orbit coupling (SOC) excited by low photon energy (hν≤ 6 eV) does not compete with the X-ray magnetic circular dichroism (XMCD) with strong SOC. XMCD PEEM observation of magnetic domains has been successfully established while MCD PEEM derived from valence bands has not been. However, using angle and energy resolved photoelectron, valence band MCD provides large asymmetry similar to that by XMCD. Threshold measurement of photoelectron in a total electron yield procedure can take advantage of the measurement of photoelectrons with a limited angle and energy mode. This restriction of the photoelectron makes the threshold MCD technique an efficient way to get magnetic information and gives more than 10% asymmetry for Ni/Cu(0 0 1), which is comparable to that obtained by angle resolved photoemission. Thus the threshold MCD technique is a suitable method to observe magnetic domains by PEEM. For threshold MCD, incident angle dependence and high sensitivity to out-of-plane magnetized films compared with in-plane ones are discussed. Ultrashort pulse lasers make it feasible to measure two photon photoemission MCD combined with PEEM, where resonant excitation has a possibility to enhance dichroic asymmetry. Recent results for valence band magnetic dichroism PEEM are presented..
33.	T. Nakagawa, Y. Takagi, T. Yokoyama, T. Methfessel, S. Diehl, H.J. Elmers, Giant Magnetic Anisotropy Energy and Coercivity in Fe island and atomic wire on W(110), Phys. Rev. B, 86, 144418, 2012.11, We have directly investigated the giant magnetic anisotropy energy and coercivity of monolayer (ML) Fe islands and stripes on flat and stepped W(110) surfaces using x-ray magnetic circular dichroism. Both for islands and stripes, the magnetic anisotropy energy is ∼1.0 meV/atom, independent of the coverage below 0.5 ML. On the contrary, the coercive field of the islands rapidly drops from 4.3 T at 0.25 ML to 1.9 T at 0.50 ML, while that of the stripes moderately degrades from 3.5 T at 0.15 ML (∼3 atom rows) to 3.0 T at 0.50 ML. We explain the contrastive behavior for the islands and stripes by different nucleation and remagnetization processes. Considering the enhanced Fe moment, we find an unprecedented large value of the energy product BHmax=5 MJ/m3..
34.	Photoemission Magnetic Circular Dichroism using Laser We report magnetic circular dichroism (MCD) on ultrathin films using lasers as excitation sources. By using threshold photoemission, we can obtain high MCD asymmetry. On the other hand, when the laser photon energy is far away from the threshold, the MCD asymmetry is small. The MCD asymmetry depends also on the magnetization, and MCD is larger for the perpendicularly magnetized films. The reason for the enhanced MCD asymmetry near the threshold is spontaneous momentum and energy selection in the photoelectron excitation. The MCD dependence on the magnetization direction is explained by the polarization change of reflected light, which is negligible for x-ray MCD. Also shown is the photoemission electron microscope observation of magnetic domains using lasers. .
35.	Photoemission Electron Microscopy using Magnetic Circular Dichroism with Laser We report on laser photoemission electron microscopy (PEEM) using magnetic circular dichroism (MCD). Although MCD asymmetry in valence band is generally very small, it can be enhanced using threshold photoemission. We give experimental results for Ni/Cu(001) to show enhanced MCD effect near the threshold. Possible reasons for the mechanism of the enhancement are its energy and angle limited measurement of a specific electron energy state in the threshold photoemission, which can be achieved without an energy analyzer. As an application of the enlarged MCD using laser, we show magnetic domain imaging using PEEM. Due to its high brilliance, the laser MCD PEEM can measure the magnetic domain in a real time, but its explosive photoemission in a short period would deteriorate the special resolution. Finally we show our effort to make time resolved MCD-PEEM experiment in sub ps time resolution, whose time resolution would be much better than that of the state-of-art experiment using synchrotron with MCD-PEEM..

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