Search

Your search keyword '"Hitosugi, T."' showing total 240 results
Start Over Author "Hitosugi, T."
240 results on '"Hitosugi, T."'

2. Van Hove Singularity and Lifshitz Transition in Thickness-Controlled Li-Intercalated Graphene

Author

Ichinokura, S., Toyoda, M., Hashizume, M., Horii, K., Kusaka, S., Ideta, S., Tanaka, K., Shimizu, R., Hitosugi, T., Saito, S., and Hirahara, T.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We demonstrate a new method to control the Fermi level around the van Hove singularity (VHS) in Li-intercalated graphene on the SiC substrate. By angle-resolved photoemission spectroscopy, we observed a clear Lifshitz transition in the vicinity of the VHS by increasing the graphene thickness. This behavior is unexpected in a free-standing Li-intercalated graphene model. The calculation including the substrate suggests that the surface state stabilizes the Fermi level around the VHS of the Dirac bands via hybridization. In addition, we found that a sizable Schottky barrier is formed between graphene and the substrate. These properties allow us to explore the electronic phase diagram around the VHS by controlling the thickness and electric field in the device condition.

Published
2021
Full Text
View/download PDF

3. Observation of momentum space semi-localization in Si-doped $\beta$-Ga$_2$O$_3$

Author

Richard, P., Sato, T., Souma, S., Nakayama, N., Liu, H. W., Iwaya, K., Hitosugi, T., Aida, H., Ding, H., and Takahashi, T.

Subjects
Condensed Matter - Materials Science
Abstract

We performed an angle-resolved photoemission spectroscopy study of Si-doped $\beta$-Ga$_2$O$_3$. We observed very small photoemission intensity near the Fermi level corresponding to non-dispersive states assigned to Si impurities. We show evidence for a quantization of these states that is accompanied by a confinement in the momentum space consistent with a real-space finite confinement observed in a previous scanning tunneling microscopy study. Our results suggest that this semi-localization in the conjugate spaces plays a crucial role in the electronic conduction of this material., Comment: 4 pages, 4 figures. Copyright (2012) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters and may be found at http://apl.aip.org/resource/1/applab/v101/i23/p232105_s1

Published
2012
Full Text
View/download PDF

4. Valence evaluation of LiMnO2 and related battery materials by x-ray absorption spectroscopy

Author

Wadati, H., Hawthorn, D. G., Regier, T. Z., Chen, G., Hitosugi, T., Mizokawa, T., Tanaka, A., and Sawatzky, G. A.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons
Abstract

We present an x-ray absorption study of the oxidation states of transition-metal-ions of LiMnO2 and its related materials, widely used as cathodes in Li-ion batteries. The comparison between the obtained spectrum and the configuration-interaction cluster-model calculations showed that the Mn3+ in LiMnO2 is a mixture of the high-spin and low-spin states. We found that Li deficiencies occur in the case of Cr substitution, whereas there are no Li deficiencies in the case of Ni substitution. We conclude that the substitution of charge-transfer-type Ni or Cu is effective for LiMnO2 battery materials., Comment: 3 pages, 3 figures

Published
2010
Full Text
View/download PDF

5. Efficiency of electron doping to monolayer hexagonal boron nitride by alkali metals

Author

Ichinokura, S, Hemmi, Adrian, Cun, Huanyao; https://orcid.org/0000-0002-5225-9861, Tanaka, K, Shimizu, R, Hitosugi, T, Greber, Thomas, Hirahara, T, Ichinokura, S, Hemmi, Adrian, Cun, Huanyao; https://orcid.org/0000-0002-5225-9861, Tanaka, K, Shimizu, R, Hitosugi, T, Greber, Thomas, and Hirahara, T

Abstract

We investigated electron doping of monolayer hexagonal boron nitride (hBN) on metallic substrates by doping alkali metals (AMs). The valence band maximum (VBM) of hBN/Rh after doping with Li and Cs was directly observed using angle-resolved photoemission spectroscopy in a wide wavenumber space. The valence band shift resulting from doping confirms the vacuum level alignment model. Furthermore, when the same AM is used, the resultant binding energy of VBM was almost identical regardless of the substrate, even if it differs by eV before doping, which we found by comparison with the literature. This independence from the substrate is explained by an extension of the vacuum level alignment model, wherein the VBM is determined by the work function of the AM when it intercalates to the interface as well as adsorbs on surfaces of hBN. It means that the doping of Cs, which has the lowest work function, gives the deepest binding energy at VBM. This is evaluated as 5.7 eV in our experiments.

Published
2023

16. Absence of ferromagnetism in MnBi2Te4/Bi2Te3 down to 6 K

Author

Fukasawa, T., primary, Kusaka, S., additional, Sumida, K., additional, Hashizume, M., additional, Ichinokura, S., additional, Takeda, Y., additional, Ideta, S., additional, Tanaka, K., additional, Shimizu, R., additional, Hitosugi, T., additional, and Hirahara, T., additional

Published
2021
Full Text
View/download PDF

22. Thickness-dependent local surface electronic structures of homoepitaxial SrTiO3 thin films.

Author

Ohsawa, T., Iwaya, K., Shimizu, R., Hashizume, T., and Hitosugi, T.

Subjects
THIN films, HETEROSTRUCTURES, SUPERLATTICES, PULSED laser deposition, HOMOEPITAXY, SURFACES (Technology)
Abstract

We have investigated the atomically-resolved substrate and homoepitaxial thin film surfaces of SrTiO3(001) using low-temperature scanning tunneling microscopy/scanning tunneling spectroscopy (STS) combined with pulsed laser deposition. It was found that a typical annealing treatment for preparation of SrTiO3 substrates, unexpectedly, resulted in a disordered surface on an atomic scale. In contrast, homoepitaxial SrTiO3 thin films grown on this disordered substrate exhibited a (2×2) surface reconstruction. The STS measurements revealed a number of surface defects in a 10 unit cell thick SrTiO3 film but much fewer in a 50 unit cell thick film, indicating nonuniform stoichiometry along the growth direction. These results suggest the possibility of using homoepitaxial SrTiO3 film surfaces as idealized substrates, opening a way to extract novel functionalities in complex oxides heterostructures. [ABSTRACT FROM AUTHOR]

Published
2010
Full Text
View/download PDF

23. Properties of TiO2-based transparent conducting oxide thin films on GaN(0001) surfaces.

Author

Kasai, J., Hitosugi, T., Moriyama, M., Goshonoo, K., Hoang, N. L. H., Nakao, S., Yamada, N., and Hasegawa, T.

Subjects
*PHYSICS research, *SEMICONDUCTOR industry, *SEMICONDUCTOR doping, *THIN films, *TITANIUM dioxide, *LIGHT emitting diodes
Abstract

Anatase Nb-doped TiO2 transparent conducting oxide has been formed on GaN(0001) surfaces using a sputtering method. Amorphous films deposited at room temperature were annealed at a substrate temperature of 500 °C in vacuum to form single-phase anatase films. Films with a thickness of 170 nm exhibited a resistivity of 8×10-4 Ω cm with absorptance less than 5% at a wavelength of 460 nm. Furthermore, the refractive index of the Nb-doped TiO2 was well matched to that of GaN. These findings indicate that Nb-doped TiO2 is a promising material for use as transparent electrodes in GaN-based light emitting diodes (LEDs), particularly since reflection at the electrode/GaN boundary can be suppressed, enhancing the external quantum efficiency of blue LEDs. [ABSTRACT FROM AUTHOR]

Published
2010
Full Text
View/download PDF

24. Thickness-dependent local surface electronic structures of homoepitaxial SrTi[O.sub.3] thin films

Author

Ohsawa, T., Iwaya, K., Shimizu, R., Hashizume, T., and Hitosugi, T.

Subjects
Ablation (Vaporization technology) -- Usage, Scanning tunneling microscopy -- Usage, Strontium -- Electric properties, Strontium -- Optical properties, Titanium compounds -- Electric properties, Titanium compounds -- Optical properties, Titanium compounds -- Structure, Physics
Abstract

Atomatically-resolved substrate and homoepitaxial thin film surfaces of SrTi[O.sub.3](001) are examined by using low-temperature scanning tunneling microscopy/scanning tunneling spectroscopy (STS) combined with pulsed laser deposition. The results have shown the possibility of using homoepitaxial SrTi[O.sub.3] film surfaces as idealized substrates, thus providing a way to extract novel functionalities in complex oxides heterostructures.

Published
2010

25. Properties of Ti[O.sub.2]-based transparent conducting oxide thin films on GaN(0001) surfaces

Author

Kasai, J., Goshonoo, K., Hoang, N.L.H., Nakao, S., Yamada, N., Hasegawa, T., Hitosugi, T., and Moriyama, M.

Subjects
Titanium compounds -- Electric properties, Gallium nitrate -- Electric properties, Lead compounds -- Electric properties, Light-emitting diodes -- Research, Physics
Abstract

A sputtering method is used for preparing anatase Nb-based Ti[O.sub.2] transparent conducting oxide on GaN(0001) surfaces. The studies have shown that Nb-doped T[O.sub.2] is a good material for use as transparent electrodes in GaN-based light emitting diodes (LEDs), since reflection at the electrode/GaN boundary is suppressed, enhancing the external quantum efficiency of blue LEDs.

Published
2010

26. Carrier induced ferromagnetism in Nb doped Co:Ti[O.sub.2] and Fe:Ti[O.sub.2] epitaxial thin films

Author

Hitosugi, T., Nakajima, K., Chikyow, T., Shimada, T., Hasegawa, T., Hirose, Y., Kinoda, G., Furubayashi, Y., Yamamoto, Y., and Inaba, K.

Subjects
Ferromagnetism -- Analysis, Niobium -- Magnetic properties, Ablation (Vaporization technology) -- Analysis, Physics
Abstract

Carrier induced ferromagnetism in Nb and transition metal codoped anatase [Ti.sub.1-x-y][Nb.sub.x][M.sub.y][O.sub.2] (M=Co, Fe) epitaxial films grown by pulsed laser deposition method was investigated. The results of the investigation reveal that the charge carriers are spin polarized and mediate ferromagnetic interaction between local spins on transition metal ions.

Published
2006

30. Carrier induced ferromagnetism in Nb doped Co:TiO2 and Fe:TiO2 epitaxial thin film.

Author

Hitosugi, T., Kinoda, G., Yamamoto, Y., Furubayashi, Y., Inaba, K., Hirose, Y., Nakajima, K., Chikyow, T., Shimada, T., and Hasegawa, T.

Subjects
*THIN films, *FERROMAGNETISM, *EPITAXY, *MAGNETIC properties, *MAGNETISM
Abstract

We have investigated the carrier induced magnetic properties of anatase Ti1-x-yNbxMyO2 (M=Co,Fe) epitaxial films grown by the pulsed laser deposition technique. For Ti0.95-xNbxCo0.05O2, the n-type carrier density could be controlled in a wide range (4.9×1017 cm-3 to 2.7×1021 cm-3) by Nb doping (x=0–0.2). The temperature dependence of the resistivity showed metallic behavior, suggesting that Ti0.95-xNbxCo0.05O2 undergoes a semiconductor to metal transition along with a slight carrier doping less than x<0.03. In both Co-doped and Fe-doped films, we have confirmed hysteresis in M-H curves, and the anomalous Hall effect at room temperature. This strongly suggests that the charge carriers are spin polarized and mediate ferromagnetic interaction between local spins on transition metal ions. In the case of Ti0.94-xNbxFe0.06O2, ferromagnetism is sensitive to carrier concentration. That is, the x=0.002 film is nonmagnetic even at 3 K, while room-temperature ferromagnetism appears at x=0.01. [ABSTRACT FROM AUTHOR]

Published
2006
Full Text
View/download PDF

31. 8Liβ-NMR study of epitaxial LixCoO2films

Author

Sugiyama, J, primary, Harada, M, additional, Oki, H, additional, Shiraki, S, additional, Hitosugi, T, additional, Ofer, O, additional, Salman, Z, additional, Song, Q, additional, Wang, D, additional, Saadaoui, H, additional, Morris, G D, additional, Chow, K H, additional, MacFarlane, W A, additional, and Kiefl, R F, additional

Published
2014
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results