Muneyuki Motoyama

Electrical and structural properties of indium tin oxide films prepared by pulsed laser deposition

The relation between electrical and structural properties of indium tin oxide (ITO) films prepared by pulsed laser deposition with and without in situ laser irradiation is examined. The residual stresses of the films were estimated from x-ray diffraction patterns measured by grazing-incidence asymmetric Bragg and grazing-incidence x-ray diffraction geometries. For the films prepared without in situ irradiation, the residual stress depended on oxygen pressure (PO2) during deposition and had minimum around PO2 of 1.3 Pa, which coincided with the optimum PO2 for growing the lowest resistivity films. The resistivity was only slightly improved with an increase of substrate temperature (Ts) because a large residual stress was introduced. In contrast, the ITO films prepared with in situ laser irradiation showed very low resistivity (ρ<10−4 Ω cm) which can be attributed to the high crystallinity and low residual stress.

Pulsed Laser Deposition of Low-Resistivity Indium Tin Oxide Thin Films at Low Substrate Temperature

Indium tin oxide (ITO) thin films were grown on SiO2 glass and silicon (Si) substrates from a 95 wt% In2O3–5 wt% SnO2 sintered ceramic target by pulsed laser deposition (PLD). The films were deposited under different oxygen pressures (Po2) of 5×10-3 to 5×10-2 Torr at room temperature (RT) and 200°C. Po2 was found to have a critical influence on the optical and the electrical properties of the ITO films. Under a Po2 of 1×10-2 Torr, ITO films with resistivity as low as 4.5×10-4 and 1.8×10-4 Ωcm were obtained on glass at RT and 200°C, respectively. Moreover, by increasing the substrate temperature (Ts) to 350°C, the resistivity was further reduced to 1.3×10-4 Ωcm. Optical transmittance in visible light greater than 85% was attained in all the films deposited under Po2 above 5× 10-3 Torr. However, a reduction in the transmittance to less than 80% was observed as Po2 decreased. The films deposited at RT were amorphous, whereas those produced at 200°C were polycrystalline.

Electrical properties of crystalline ITO films prepared at room temperature by pulsed laser deposition on plastic substrates

Electrical properties of crystalline indium-tin-oxide (ITO) films, which were grown on polycarbonate (PC) substrates at room temperature by pulsed laser deposition (PLD) with in situ laser irradiation onto the substrates, were studied. The PC substrates were colored by in situ laser irradiation when the ITO films were prepared on the substrates directly, and the resistivity of the ITO films was extremely high. While the PC substrates were prevented from coloring by pre-deposition of CeO 2 film, the resistivity was still high. The introduction of a thin Al 2 O 3 layer between the PC substrate and CeO 2 film resulted in marked decreasing of the resistivity of the ITO film.

Highly conducting indium tin oxide (ITO) thin films deposited by pulsed laser ablation

Abstract Highly conducting and transparent indium tin oxide (ITO) thin films were prepared on SiO2 glass and silicon substrates by pulsed laser ablation (PLA) from a 90 wt.% In2O3-10 wt.% SnO2 sintered ceramic target. The growths of ITO films under different oxygen pressures (PO2) ranging from 1×10 −4 –5×10 −2 Torr at low substrate temperatures (Ts) between room temperature (RT) and 200°C were investigated. The opto-electrical properties of the films were found to be strongly dependent on the PO2 during the film deposition. Under a PO2 of 1×10 −2 Torr, ITO films with low resistivity of 5.35×10 −4 and 1.75×10 −4 Ω cm were obtained at RT (25°C) and 200°C, respectively. The films exhibited high carrier density and reasonably high Hall mobility at the optimal PO2 region of 1×10 −2 to 1.5×10 −2 Torr. Optical transmittance in excess of 87% in the visible region of the solar spectrum was displayed by the films deposited at P o 2 ≥1×10 −2 Torr and it was significantly reduced as the PO2 decreases.

Structure of fluorine-graphite intercalation compounds

Abstract Fluorine-graphite intercalation compounds have been prepared from HOPG and natural graphite powder in the presence of a fluoride such as AgF, WF 6 , or SbF 5 at room temperature. The C x F samples obtained were quasi stage 1, 2, and 3 compounds with compositions of C 2.7 F-C 9.6 F. The stage 1 phases in the admixtures of stages 1 and 2 prepared from HOPG show large I c values of 10.5 to 11.9 A. X-ray powder diffraction indicates the existence of an in-plane superlattice with a 0 = 2 a g in the stage 3 and 2 compounds, but no superlattice at quasi stage 1. Electron diffraction for the same samples also reveals an in-plane superlattice at stages 3 and 2. Based on these results, c -axis and inplane structure models have been proposed for sage 1 through 3, C x F. The phase with a large I c value is a bi-intercalation phase in which two kinds of ionically and semi-ionically bonded fluorines with different sizes are inserted between every other carbon layer. For the in-plane structures, the proposed models are that stage 3 and 2 compounds consist of C 4n F and C 2.7n F with a 0 = 2 a g , which lead to the C 2n F structure and/or some disordered one with a 0 = a g at stage 1.

HIGH-QUALITY INDIUM OXIDE FILMS AT LOW SUBSTRATE TEMPERATURE

Low-resistivity (ρ) and highly transparent pure indium oxide (In2O3) thin films grown on glass substrates by pulsed laser deposition at substrate temperature (Ts) between room temperature and 200 °C are reported. As-deposited films with resistivity (ρ) of ∼3×10−4 Ω cm and transmittance (visible), above 87% were obtained within a narrow range of PO2 (1×10−2–1.5×10−2 Torr). Hall effect measurements showed that the low ρ resulted from the high carrier concentration (n)∼7×1020 cm−3, whereas modest Hall mobility (μ<45 cm2 V−1 s−1) was measured. X-ray diffraction indicated that the films prepared at Ts⩽100 °C were amorphous, while at Ts⩾150 °C polycrystalline films were obtained.

Effect of Sn doping on the electronic transport mechanism of indium–tin–oxide films grown by pulsed laser deposition coupled with substrate irradiation

Low-resistivity indium–tin–oxide (ITO) films (8.9×10−5–2.3×10−4 Ω cm), 80±20 nm thick grown by combining pulsed laser deposition and laser irradiation of the substrate were studied in relation to tin (Sn) doping content. Films with Sn doping content over the range 0–10 wt % were deposited at room temperature (RT) and 200 °C at a fixed oxygen pressure of 1×10−2 Torr. The laser beam with energy density of 70 mJ/cm2 was directed at the middle portion of the substrate during growth. At RT, the laser-irradiated and nonirradiated parts of the films exhibited crystalline and amorphous phase, respectively. The amorphous films indicated a steady resistivity, carrier concentration, and Hall mobility of ∼2.4×10−4 Ω cm, 8×1020 cm−3, and ∼32 cm2/V s, respectively, and showed no significant change over 0–10 wt % Sn doping content. The crystalline films deposited at RT by laser irradiation and 200 °C indicated a strong dependence of the resistivity, carrier concentration, and Hall mobility on Sn doping content over the ...

NQR and NMR studies of Cu in the superconducting La2CuO4+δ

Abstract In the superconducting La2CuO4+δ obtained by annealing in high pressure mixture gas of oxygen and argon, nuclear quadrupole resonance (NQR) signals of 63Cu and 65Cu have been observed around 33.1 and 36.0 MHz together with the antiferromagnetic Cu NMR signal around 70–100 MHz. The ratio of the resonance frequency of 63Cu and 65Cu is the same as that of the quadrupole moment of each Cu nucleus, indicating no internal magnetic field (paramagnetic) at Cu site. The nuclear spin-lattice relaxation time, T1, of Cu NQR indicates that the paramagnetic phase is in the superconducting state at low temperatures. The NQR intensity is roughly proportional to the partial pressure of the oxygen gas. The NQR result suggests that the volume fraction of paramagnetic phase in La2CuO4+δ increases with increasing oxygen content.

Superconducting properties of La2CuO4+δ annealed in high pressure oxygen gas

Abstract Electrical and magnetic properties of (La1−xSrx)2CuO4+δ annealed in high pressure oxygen gas up to 400 bar are studied. The superconducting La2CuO4+δ includes two separate phases: one is the superconducting phase with extra oxygen, and the other is the well known antiferromagnetic phase with Neel temperature TN at 240–300 K depending on the annealing atmosphere. The superconducting phase in the undoped sample becomes unstable by Sr doping. In the high pressure oxygen annealed La2CuO4+δ, a temperature dependent paramagnetism is observed even below TN, and spontaneous vortices are considered to be induced in the zero magnetic field cooling.

Pulsed Laser Deposition of Crystalline Indium Tin Oxide Films at Room Temperature by Substrate Laser Irradiation

Crystalline tin (Sn)-doped indium oxide (ITO) films grown at room temperature (RT) using pulsed laser deposition (PLD) coupled with laser irradiation of the growing films are discussed. The energy of the laser irradiation beam was ~0.07 Jcm-2. The films were deposited from Sn-doped (0–10 wt%) In2O3 targets under oxygen pressure (PO2 ) of 10-2 Torr. At RT, the laser-irradiated and nonirradiated portions of the films yielded resistivities of ~1.2×10-4 and ~2.5×10-4 Ωcm, respectively. At 200°C, a resistivity of 8.9×10-5 Ωcm was observed for the laser-irradiated part of the ITO films.