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Time-resolved photoconductivity measurements were carried out on single-wall carbon nanotube (SWNT) films at various temperatures. Photoconductivity excitation spectra show two clear peaks around 0.7 and 1.2 eV. Observed peaks in the spectra correspond to the optical absorption between symmetrical bands of semiconducting SWNTs. The analysis of this feature allows insight into the transport properties of semiconducting SWNTs. Signal profiles in the photoresponse at low temperatures depend strongly on the sample, while intensity of the photoresponse monotonously increases with a decrease in temperature for all samples. Photo-induced current for a sample decays rapidly after the laser pulse irradiation. For another sample, on the other hand, it decreases gradually and remains up to a few hundred nano seconds, showing the existence of trapping sites in the nanotubes., identifier:00086223, identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/3358

Time-resolved photoconductivity measurements were carried out on single-wall carbon nanotube (SWNT) films at various temperatures. Photoconductivity excitation spectra show two clear peaks around 0.7 and 1.2 eV. Observed peaks in the spectra correspond to the optical absorption between symmetrical bands of semiconducting SWNTs. The analysis of this feature allows insight into the transport properties of semiconducting SWNTs. Signal profiles in the photoresponse at low temperatures depend strongly on the sample, while intensity of the photoresponse monotonously increases with a decrease in temperature for all samples. Photo-induced current for a sample decays rapidly after the laser pulse irradiation. For another sample, on the other hand, it decreases gradually and remains up to a few hundred nano seconds, showing the existence of trapping sites in the nanotubes.

Temperature dependence of photoconductivity has been investigated for single-wall carbon nanotube (SWNT) films at 0.7eV. In order to clarify the effect of atmosphere on photoconductivity, measurements have been performed under helium and nitrogen gas flow in the temperature range from 10 K to room temperature (R.T.) and from 100 K to R.T., respectively. Photoconductive response monotonously increases with a decrease in temperature and tends to saturate around 10 K. No clear difference in photoconductive response under different atmosphere was observed. We discuss the mechanism of photoconductivity at 0.7eV., identifier:14686996, identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/3357

We report an x-ray diffraction (XRD) analysis of the structural transformation from single-wall carbon nanotubes (SWNTs) to double-wall carbon nanotubes (DWNTs) via C_60-encapsulating SWNTs (C_<60> peapods). It was shown that the bundle structure of the starting SWNTs retains on this process. The thermal expansion coefficients of DWNTs hardly changed from the pristine SWNTs. The intertube spacing between inner and outer tubes of DWNTs was obtained as 0.36±0.01 nm. This spacing was shown to be determined by the discreteness of the SWNT diameter under a turbostratic constraint between the inner and outer tubes of DWNT at synthesis temperatures., identifier:10980121, identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/3373

Temperature dependence of photoconductivity has been investigated for single-wall carbon nanotube (SWNT) films at 0.7eV. In order to clarify the effect of atmosphere on photoconductivity, measurements have been performed under helium and nitrogen gas flow in the temperature range from 10 K to room temperature (R.T.) and from 100 K to R.T., respectively. Photoconductive response monotonously increases with a decrease in temperature and tends to saturate around 10 K. No clear difference in photoconductive response under different atmosphere was observed. We discuss the mechanism of photoconductivity at 0.7eV.

We report an x-ray diffraction (XRD) analysis of the structural transformation from single-wall carbon nanotubes (SWNTs) to double-wall carbon nanotubes (DWNTs) via C_60-encapsulating SWNTs (C_<60> peapods). It was shown that the bundle structure of the starting SWNTs retains on this process. The thermal expansion coefficients of DWNTs hardly changed from the pristine SWNTs. The intertube spacing between inner and outer tubes of DWNTs was obtained as 0.36±0.01 nm. This spacing was shown to be determined by the discreteness of the SWNT diameter under a turbostratic constraint between the inner and outer tubes of DWNT at synthesis temperatures.

We have measured local electronic transport through a junction of single-wall carbon nanotube (SWNT) bundles by Atomic force microscopy (AFM)/Scanning tunneling spectroscopy (STS) dual probe method. We found that 1) the sudden decrease in current near the junction of SWNT bundles 2) the current actually flow through the junction of SWNT bundles. From the observed topographic current image, we can expect our method will be a powerful technique for investigation of functions of the devices in the nanometer scale., identifier:09214526, identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/3362

We have measured local electronic transport through a junction of single-wall carbon nanotube (SWNT) bundles by Atomic force microscopy (AFM)/Scanning tunneling spectroscopy (STS) dual probe method. We found that 1) the sudden decrease in current near the junction of SWNT bundles 2) the current actually flow through the junction of SWNT bundles. From the observed topographic current image, we can expect our method will be a powerful technique for investigation of functions of the devices in the nanometer scale.

We have measured the local current density on individual single-wall carbon nanotubes (SWNTs) with the conducting tip of an atomic force microscope; the SWNTs make up a nanometer-scale electronic circuit on an insulating substrate. Scanning tunneling spectroscopy measurements at certain positions on a SWNT bundle show that both metallic and semiconducting nanotubes can coexist in a bundle. The approach applied in this experiment appears as a powerful technique for the investigation of the spatial variation of current density and electronic states of nanometer-scale electronic devices.

type:text, Dc-magnetization and NMR measurements were carried out on a layered superconductor Li0.48(THF)yHfNCl having Tc∼26 K. For the magnetic field applied perpendicular to the basal plane (ab plane) above 10 kOe, we found a pronounced broadening of the superconducting transition in temperature dependence of magnetization and the substantial diamagnetic signals were observed as high as 2Tc, indicating the existence of superconducting fluctuations. Analysis based on the anisotropic Ginzburg-Landau model reveals that the present system is a highly anisotropic superconductor. 7Li-NMR signals were observed around zero Knight shift, indicating that the local Fermi-level density of states, N(EF), at Li site is practically nothing and the superconductivity is derived from the HfNCl layer. We have shown the unambiguous evidence for the quasi-two-dimensional superconducting character in this system.

Dc-magnetization and NMR measurements were carried out on a layered superconductor Li0.48(THF)yHfNCl having Tc∼26 K. For the magnetic field applied perpendicular to the basal plane (ab plane) above 10 kOe, we found a pronounced broadening of the superconducting transition in temperature dependence of magnetization and the substantial diamagnetic signals were observed as high as 2Tc, indicating the existence of superconducting fluctuations. Analysis based on the anisotropic Ginzburg-Landau model reveals that the present system is a highly anisotropic superconductor. 7Li-NMR signals were observed around zero Knight shift, indicating that the local Fermi-level density of states, N(EF), at Li site is practically nothing and the superconductivity is derived from the HfNCl layer. We have shown the unambiguous evidence for the quasi-two-dimensional superconducting character in this system.

Thermal expansion coefficient in single-walled carbon nanotube bundles was determined as (－0.15±0.20)×10^<－5> (1/K) for the tube diameter and (0.75±0.25)×10^<－5> (1/K) for the triangular lattice constant by means of x-ray scattering between 300 K to 950 K. The value for the intertube gap was (4.2±1.4) ×10^<－5> (1/K), which is larger than 2.6×10^<－5> (1/K) for the c-axis thermal expansion in graphite. The results reveal the presence of a remarkably larger lattice anharmonicity in nanotube bundles than that of graphite. The small value for the tube diameter is consistent with the seamless tube structure formed by a strong covalent bond between carbon atoms comparable to that in graphite., identifier:10980121, identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/3359

Dc-magnetization and NMR measurements were carried out on a layered superconductor Li0.48(THF)yHfNCl having Tc∼26 K. For the magnetic field applied perpendicular to the basal plane (ab plane) above 10 kOe, we found a pronounced broadening of the superconducting transition in temperature dependence of magnetization and the substantial diamagnetic signals were observed as high as 2Tc, indicating the existence of superconducting fluctuations. Analysis based on the anisotropic Ginzburg-Landau model reveals that the present system is a highly anisotropic superconductor. 7Li-NMR signals were observed around zero Knight shift, indicating that the local Fermi-level density of states, N(EF), at Li site is practically nothing and the superconductivity is derived from the HfNCl layer. We have shown the unambiguous evidence for the quasi-two-dimensional superconducting character in this system.

Thermal expansion coefficient in single-walled carbon nanotube bundles was determined as (－0.15±0.20)×10^<－5> (1/K) for the tube diameter and (0.75±0.25)×10^<－5> (1/K) for the triangular lattice constant by means of x-ray scattering between 300 K to 950 K. The value for the intertube gap was (4.2±1.4) ×10^<－5> (1/K), which is larger than 2.6×10^<－5> (1/K) for the c-axis thermal expansion in graphite. The results reveal the presence of a remarkably larger lattice anharmonicity in nanotube bundles than that of graphite. The small value for the tube diameter is consistent with the seamless tube structure formed by a strong covalent bond between carbon atoms comparable to that in graphite.

type:text, 13C, 1H, and 39K-NMR measurements of (NH3)K3C60 unambiguously demonstrated that its magnetic properties are described as a S=1/2 localized spin system over the entire temperature range (300 K–4.2 K). A possible antiferromagnetic structure that appeared below 45 K is compatible with the orientational order of K-NH3 pairs on the octahedral (O) site. The present NMR study strongly suggests that the Mott-Hubbard localization occurs due to the removal of the C60 t1u-orbital degeneracy.

13C, 1H, and 39K-NMR measurements of (NH3)K3C60 unambiguously demonstrated that its magnetic properties are described as a S=1/2 localized spin system over the entire temperature range (300 K–4.2 K). A possible antiferromagnetic structure that appeared below 45 K is compatible with the orientational order of K-NH3 pairs on the octahedral (O) site. The present NMR study strongly suggests that the Mott-Hubbard localization occurs due to the removal of the C60 t1u-orbital degeneracy.

13C, 1H, and 39K-NMR measurements of (NH3)K3C60 unambiguously demonstrated that its magnetic properties are described as a S=1/2 localized spin system over the entire temperature range (300 K–4.2 K). A possible antiferromagnetic structure that appeared below 45 K is compatible with the orientational order of K-NH3 pairs on the octahedral (O) site. The present NMR study strongly suggests that the Mott-Hubbard localization occurs due to the removal of the C60 t1u-orbital degeneracy.

13C, 1H, and 39K-NMR measurements of (NH3)K3C60 unambiguously demonstrated that its magnetic properties are described as a S=1/2 localized spin system over the entire temperature range (300 K–4.2 K). A possible antiferromagnetic structure that appeared below 45 K is compatible with the orientational order of K-NH3 pairs on the octahedral (O) site. The present NMR study strongly suggests that the Mott-Hubbard localization occurs due to the removal of the C60 t1u-orbital degeneracy.

Dc-magnetization and NMR measurements were carried out on a layered superconductor Li0.48(THF)yHfNCl having Tc∼26 K. For the magnetic field applied perpendicular to the basal plane (ab plane) above 10 kOe, we found a pronounced broadening of the superconducting transition in temperature dependence of magnetization and the substantial diamagnetic signals were observed as high as 2Tc, indicating the existence of superconducting fluctuations. Analysis based on the anisotropic Ginzburg-Landau model reveals that the present system is a highly anisotropic superconductor. 7Li-NMR signals were observed around zero Knight shift, indicating that the local Fermi-level density of states, N(EF), at Li site is practically nothing and the superconductivity is derived from the HfNCl layer. We have shown the unambiguous evidence for the quasi-two-dimensional superconducting character in this system.