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Journal Articles

Evaluation of doped potassium concentrations in stacked two-Layer graphene using real-time XPS

Ogawa, Shuichi*; Tsuda, Yasutaka; Sakamoto, Tetsuya*; Okigawa, Yuki*; Masuzawa, Tomoaki*; Yoshigoe, Akitaka; Abukawa, Tadashi*; Yamada, Takatoshi*

Applied Surface Science, 605, p.154748_1 - 154748_6, 2022/12

https://doi.org/10.1016/j.apsusc.2022.154748
 Times Cited Count：4 Percentile：45.85(Chemistry, Physical)

Immersion of graphene in KOH solution improves its mobility on SiO$$_{2}$$/Si wafers. This is thought to be due to electron doping by modification with K atoms, but the K atom concentration C$$_{K}$$ in the graphene has not been clarified yet. In this study, the C$$_{K}$$ was determined by XPS analysis using high-brilliance synchrotron radiation. The time evolution of C$$_{K}$$ was determined by real-time observation, and the C$$_{K}$$ before irradiation of synchrotron radiation was estimated to be 0.94%. The C 1s spectrum shifted to the low binding energy side with the desorption of K atoms. This indicates that the electron doping concentration into graphene is decreasing, and it is experimentally confirmed that K atoms inject electrons into graphene.

Journal Articles

X-ray absorption magnetic circular dichroism of (La,Ce)MnO$$_{3}$$ thin films

Yanagida, Tsuyoshi*; Saito, Yuji; Takeda, Yukiharu; Fujimori, Atsushi*; Tanaka, Hidekazu*; Kawai, Tomoji*

Physical Review B, 79(13), p.132405_1 - 132405_4, 2009/04

AA2017-0612.pdf:0.42MB

https://doi.org/10.1103/PhysRevB.79.132405
 Times Cited Count：11 Percentile：45.08(Materials Science, Multidisciplinary)

Creating a bipolarity of semiconductors has been a key technology to develop recent advanced semiconductor devices. Although theoretical calculation predicts the presence of ferromagnetic electron-doped manganites with doping tetravalent cations, the ferromagnetic origin in experiments has been controversial due to the lack of direct experimental evidence. Here, we investigate the ferromagnetism in (La,Ce)MnO$$_{3}$$ thin films by measuring the magnetic circular dichroism in soft X-ray absorption (XMCD). The XMCD measurements clarified that the ferromagnetism is not caused by the presence of Mn$$^{2+}$$ but by self-hole doping for manganese.

Journal Articles

Electrical conductivity increase of Al-doped ZnO films induced by high-energy-heavy ions

Sugai, Hiroyuki; Matsunami, Noriaki*; Fukuoka, Osamu*; Sataka, Masao; Kato, Teruo; Okayasu, Satoru; Shimura, Tetsuo*; Tazawa, Masato*

Nuclear Instruments and Methods in Physics Research B, 250(1-2), p.291 - 294, 2006/09

https://doi.org/10.1016/j.nimb.2006.04.126
 Times Cited Count：15 Percentile：70.41(Instruments & Instrumentation)

We have investigated the effects on electrical properties of Al-doped ZnO (AZO) semiconductor films induced by high-energy heavy ion. The AZO films with c-axis on SiO$$_{2}$$ glass substrate were prepared by a RF-sputter-deposition method at 400 $$^{circ}$$C. Rutherford backscattering spectroscopy shows that the Al/Zn composition and the film thickness are 4 % and 0.3 $$mu$$m. We find that the conductivity monotonically increases from 1.5$$times$$10$$^{2}$$ to 8$$times$$10$$^{2}$$ S/cm with increasing the fluence up to 4$$times$$10$$^{13}$$/cm$$^{2}$$, as already been observed for 100 keV Ne irradiation. The fluence of 100 keV Ne at which the conductivity takes its maximum is 3$$times$$10$$^{16}$$/cm$$^{2}$$ (7 dpa). The dpa of 100 MeV Xe at 4$$times$$10$$^{13}$$/cm$$^{2}$$ is estimated as 0.008. Hence, the conductivity increase by 100 MeV Xe ion is ascribed to the electronic excitation effects.

Journal Articles

Irradiation effects with 100 MeV Xe ions on optical properties of Al-doped ZnO films

Fukuoka, Osamu*; Matsunami, Noriaki*; Tazawa, Masato*; Shimura, Tetsuo*; Sataka, Masao; Sugai, Hiroyuki; Okayasu, Satoru

Nuclear Instruments and Methods in Physics Research B, 250(1-2), p.295 - 299, 2006/09

https://doi.org/10.1016/j.nimb.2006.04.146
 Times Cited Count：24 Percentile：82.92(Instruments & Instrumentation)

We have investigated the effects on electrical and optical properties of Al-doped ZnO (AZO) semiconductor films induced by high-energy heavy ion. The AZO films with c-axis on SiO$$_{2}$$ glass substrate were prepared by a RF-sputter-deposition method at 400 $$^{circ}$$C. Rutherford backscattering spectroscopy shows that the Al/Zn composition and the film thickness are 4 % and 0.3 $$mu$$m. No appreciable change was observed in optical transparency. We find that the conductivity monotonically increases from 1.5$$times$$10$$^{2}$$ to 8$$times$$10$$^{2}$$ S/cm with increasing the fluence up to 4$$times$$10$$^{13}$$/cm$$^{2}$$, as already been observed for 100 keV Ne irradiation. The fluence of 100 keV Ne at which the conductivity takes its maximum is 3$$times$$10$$^{16}$$/cm$$^{2}$$ (7 dpa). The dpa of 100 MeV Xe at 4$$times$$10$$^{13}$$/cm$$^{2}$$ is estimated as 0.008. Hence, the conductivity increase by 100 MeV Xe ion is ascribed to the electronic excitation effects.

Journal Articles

Structural analysis of (Ga,Mn)N epilayers and self-organized dots using MeV ion channeling

Kuroda, Shinji*; Marcet, S.*; Bellet-Amalric, E.*; Cibert, J.*; Mariette, H.*; Yamamoto, Shunya; Sakai, Takuro; Oshima, Takeshi; Ito, Hisayoshi

Physica Status Solidi (A), 203(7), p.1724 - 1728, 2006/05

https://doi.org/10.1002/pssa.200565396
 Times Cited Count：6 Percentile：31.16(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Evidence for a hard gap and Wigner lattice in heavily boron-doped synthetic diamond

Sudo, Tomoko*; Ohashi, Kazutoshi*; Sato, Toshimaro*; Ota, Eiji*; Okayasu, Satoru; Sugai, Hiroyuki

Physical Review B, 71(4), p.045211_1 - 045211_7, 2005/01

https://doi.org/10.1103/PhysRevB.71.045211
 Times Cited Count：1 Percentile：7.19(Materials Science, Multidisciplinary)

We have measured low frequency generation-recombination noise (g-r moise) spectra of a heavily boro-doped diamond crystal over the temperature range 20-300 K. The experimental results show that there are two peaks in the g-r noise spectrum at 120 K and 67 K, respectively. The 120 K peak corresponds to experimental evidence for the existence of hard gap having width of 10.4 meV. We interpret the 67 K peak as evidence for Wigner lattice formation whose gap width is 5.8 meV.

Journal Articles

Magnetic field effect on the static antiferromagnetism of the electron-doped superconductor Pr$$_1-x$$LaCe$$_x$$CuO$$_4$$ (x=0.11 and 0.15)

Fujita, Masaki*; Matsuda, Masaaki; Katano, Susumu; Yamada, Kazuyoshi*

Physical Review Letters, 93(14), p.147003_1 - 147003_4, 2004/10

https://doi.org/10.1103/PhysRevLett.93.147003
 Times Cited Count：24 Percentile：72.09(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Static antiferromagnetic correlations under magnetic fields in electron-doped high-${it T}$$$_{c}$$ cuprate superconductor Pr$$_{0.89}$$LaCe$$_{0.11}$$CuO$$_{4}$$

Fujita, Masaki*; Matsuda, Masaaki; Katano, Susumu; Yamada, Kazuyoshi*

Physica B; Condensed Matter, 345(1-4), p.19 - 22, 2004/03

https://doi.org/10.1016/j.physb.2003.11.011
 Times Cited Count：1 Percentile：7.1(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Improvement of luminescence capability of Tb$$^{3+}$$-related emission by Al$$_{x}$$Ga$$_{1-x}$$N

Nakanishi, Yasuo*; Wakahara, Akihiro*; Okada, Hiroshi*; Yoshida, Akira*; Oshima, Takeshi; Ito, Hisayoshi

Physica Status Solidi (B), 240(2), p.372 - 375, 2003/11

https://doi.org/10.1002/pssb.200303479
 Times Cited Count：19 Percentile：65.52(Physics, Condensed Matter)

Luminescence propeties of Tb-doped Al$$_{x}$$Ga$$_{1-x}$$N were studied. The samples were grown on sapphire substrates using OMVPE. Tb implantation was cariied out to introduce Tb into samples. After implantation, samples were annealed at 1000 to 1150 $$^{o}$$C in 10% NH$$_{3}$$ diluted with N$$_{2}$$. The luminescence intensity for Al$$_{x}$$Ga$$_{1-x}$$N x=0.1 is 5 times stronger than that for x=0 at 14 K. The luminesecence intensity for GaN rapidly decreases with temperature and its activation enegy is 7.8 meV. With increasing Al content, the activation enegy increases, and the activation energy for Al$$_{0.1}$$Ga$$_{0.9}$$N is 70 meV.

Journal Articles

Effects of Al composition on luminescence properties of europium implanted Al$$_{x}$$Ga$$_{1-x}$$N(0$$<$$x$$<$$1)

Nakanishi, Yasuo*; Wakahara, Akihiro*; Okada, Hiroshi*; Yoshida, Akira*; Oshima, Takeshi; Ito, Hisayoshi; Shibata, Tomohiko*; Tanaka, Mitsuhiro*

Physica Status Solidi, 0(7), p.2623 - 2626, 2003/07

In our previous study, it was reported that Eu-doped Nitride semiconductors show luminescence propetires. In this study, we investigate the relationship between luminescence properties and Al composition using Al$$_{x}$$Ga$$_{1-x}$$N(0$$<$$x$$<$$1). Al$$_{x}$$Ga$$_{1-x}$$N were grown using OMVPE. Eu atoms were doped into the samples by ion implantation (200keV). After implantation, the samples were annealed to remove residual damege. Luminescence propreties of the samples were measured using photoluminescence and cathodeluminescence. As a result, luminescence at 621 nm which relates 4f-4f transition were observed for all samples (x=0 to 1). As for intensity, samples with x=0.5 show the strongest luminescence. This result can be interpreted in terms of the internal stress of crystals by the existence of Al atoms.

Journal Articles

UV-ray photoelectron and ab initio band calculation studies on electronic structures of Cr- or Nb-ion implanted titanium dioxide

Umebayashi, Tsutomu; Yamaki, Tetsuya; Sumita, Taishi*; Yamamoto, Shunya; Tanaka, Shigeru; Asai, Keisuke*

Nuclear Instruments and Methods in Physics Research B, 206, p.264 - 267, 2003/05

https://doi.org/10.1016/S0168-583X(03)00740-7
 Times Cited Count：24 Percentile：81.79(Instruments & Instrumentation)

Chromium (Cr) and niobium (Nb) were implanted into single-crystalline titanium dioxide (TiO$$_{2}$$; rutile). After annealing at 600$$^{circ}$$C for the Cr-implanted sample or at 1000$$^{circ}$$C for the Nb-implanted sample, the radiation damage was recovered. The implanted metals occupied titanium (Ti) sites in TiO$$_{2}$$ to form metal-oxygen bonds. According to the ultraviolet-ray photoelectron spectra, a localized level due to the implanted metals was formed in band gap of both the crystals. This position was close to the VB edge for the Cr-doped TiO$$_{2}$$, while the Nb-doped TiO$$_{2}$$ had the small peak far from the edge. This is in good agreement with the ab-initio band calculation results. It is considered that the midgap states of Cr- and Nb-doped TiO$$_{2}$$ consist of the Cr t$$_{2g }$$ or Ti t$$_{2g }$$ state, respectively.

Journal Articles

Fluorine-doping in titanium dioxide by ion implantation technique

Yamaki, Tetsuya; Umebayashi, Tsutomu; Sumita, Taishi*; Yamamoto, Shunya; Maekawa, Masaki; Kawasuso, Atsuo; Ito, Hisayoshi

Nuclear Instruments and Methods in Physics Research B, 206(1-4), p.254 - 258, 2003/05

https://doi.org/10.1016/S0168-583X(03)00735-3
 Times Cited Count：136 Percentile：98.9(Instruments & Instrumentation)

Single crystalline titanium dioxide (TiO$$_{2}$$) rutile were implanted with 200keV F$$^{+}$$ at a nominal fluence of 1$$times$$10$$^{16}$$ to 1$$times$$10$$^{17}$$ ions cm$$^{-2}$$ and then thermally annealed in air up to 1200$$^{circ}C$$ for 5h. The radiation damage and its recovery during the subsequent annealing were analyzed by Rutherford backscattering spectrometry in channeling geometry and variable-energy positron annihilation spectroscopy. The lattice disorder was completely annealed at 1200$$^{circ}C$$ by the diffusion of point defects to the surface acting as a sink. According to the secondary ion mass spectrometry, the F depth profile was shifted to a shallower region along with the damage recovery, finally producing an F-doped layer where the impurity concentration increased steadily towards the surface. The F doping proved to provide a small modification to the conduction-band edge of TiO$$_{2}$$, as assessed by theoretical band calculations.

Journal Articles

Absence of a magnetic field effect on static magnetic order in the electron-doped superconductor Nd$$_{1.86}$$Ce$$_{0.14}$$CuO$$_{4}$$

Matsuda, Masaaki; Katano, Susumu; Uefuji, T.*; Fujita, Masaki*; Yamada, Kazuyoshi*

Physical Review B, 66(17), p.172509_1 - 172509_4, 2002/11

https://doi.org/10.1103/PhysRevB.66.172509
 Times Cited Count：17 Percentile：62.71(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Analysis of electronic structures of 3d transition metal-doped TiO$$_{2}$$ based on band calculations

Umebayashi, Tsutomu; Yamaki, Tetsuya; Ito, Hisayoshi; Asai, Keisuke*

Journal of Physics and Chemistry of Solids, 63(10), p.1909 - 1920, 2002/10

https://doi.org/10.1016/S0022-3697(02)00177-4
 Times Cited Count：627 Percentile：99.67(Chemistry, Multidisciplinary)

The electronic structures of titanium dioxide (TiO$$_{2}$$) doped with 3d transition metals (V, Cr, Mn, Fe, Co and Ni) have been analyzed by ab-initio band calculations based on the density functional theory with the full-potential linearized-augmented-plane-wave methods. When TiO$$_{2}$$ is doped with V, Cr, Mn, Fe or Co, an occupied level occurs and the electrons localized around each dopant. As the atomic number of the dopant increases, the localized level shifts to lower energy. In contrast, the electrons from Ni dopant are somewhat delocalized, thus significantly contributing to the formation of the valence band with O p and Ti 3d electrons. Based on a comparison with the absorption and photoconductivity data previously reported, we show that the t$$_{2g}$$ state of the dopant plays a significant role in the photoresponse of TiO$$_{2}$$ under visible light irradiation.

Journal Articles

Effect of 3 MeV electron irradiation on the photoluminescence properties of Eu-doped GaN

Nakanishi, Yasuo*; Wakahara, Akihiro*; Okada, Hiroshi*; Yoshida, Akira*; Oshima, Takeshi; Ito, Hisayoshi

Applied Physics Letters, 81(11), p.1943 - 1945, 2002/09

https://doi.org/10.1063/1.1504873
 Times Cited Count：19 Percentile：59.2(Physics, Applied)

Eu-doped GaN samples were irradiated with 3MeV-electrons at RT at 10$$^{16}$$ - 3x10$$^{17}$$/cm$$^{2}$$. Photoluminescence (PL) propeties related to $$^{5}$$D$$_{0}$$-$$^{7}$$F$$_{2}$$ in Eu$${3+}$$ were studied using He-Cd laser as excitation source. As the results, it is found that PL intensity is not affected by electron irradiation.Considering that PL peak related to near-band-edge strongly decreases due to electron irradiation, we can conclude that PL related to $$^{5}$$D$$_{0}$$-$$^{7}$$F$$_{2}$$ in Eu$${3+}$$ has very strong radiation resistance.

Journal Articles

$$^{151}$$Eu-M$"o$ssbauer spectroscopic study of the fluorite-type oxide solid solutions, Eu$$_{y}$$M$$_{1-y}$$O$$_{2-y/2}$$ (M=Zr,Ce)(0$$leq$$y$$leq$$1.0)

Masaki, Nobuyuki; Guillermo, N. R. D.; Otobe, Haruyoshi; Nakamura, Akio; Izumiyama, Yuki*; Hinatsu, Yukio*

Advances in Science and Technology, 29, p.1233 - 1240, 2000/00

no abstracts in English

Journal Articles

Molybdenum substitutional doping and its effects on phase transition properties in single crystalline vanadium dioxide thin film

Wu, Z. P.*; Miyashita, Atsumi; Yamamoto, Shunya; Abe, Hiroaki; Nashiyama, Isamu; Narumi, Kazumasa; Naramoto, Hiroshi

Journal of Applied Physics, 86(9), p.5311 - 5313, 1999/00

https://doi.org/10.1063/1.371519
 Times Cited Count：59 Percentile：88.47(Physics, Applied)

no abstracts in English

Journal Articles

Development of a synthetic diamond radiation detector with a boron doped CVD diamond contact

Kaneko, Junichi; Katagiri, Masaki; Ikeda, Yujiro; Nishitani, Takeo

Nuclear Instruments and Methods in Physics Research A, 422, p.211 - 215, 1999/00

https://doi.org/10.1016/S0168-9002(98)01096-1
 Times Cited Count：24 Percentile：83.9(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Pressure effects on spin-gap and antiferromagnetism in the hole-doped spin ladder system Sr$$_{2.5}$$Ca$$_{11.5}$$Cu$$_{24}$$O$$_{41}$$

Katano, Susumu; *; *; Akimitsu, Jun*; Nishi, Masakazu*; Kakurai, Kazuhisa*

Physica B; Condensed Matter, 259-261, p.1046 - 1047, 1999/00

https://doi.org/10.1016/S0921-4526(98)00692-9
 Times Cited Count：10 Percentile：51.88(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Magnetic phase diagram of the spin-peierls and artiferromagnetic system CuGe$$_{1-x}$$Si$$_{x}$$O$$_{3}$$

Katano, Susumu; *; Akimitsu, Jun*; Nishi, Masakazu*; Kakurai, Kazuhisa*; Fujii, Yasuhiko*

Physical Review B, 57(17), p.10280 - 10283, 1998/05

https://doi.org/10.1103/PhysRevB.57.10280
 Times Cited Count：12 Percentile：55.69(Materials Science, Multidisciplinary)

no abstracts in English

30 (Records 1-20 displayed on this page)