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Investigation of the magnetic and transport properties of single-walled small-diameter carbon nanotubes embedded in a zeolite matrix revealed that at temperatures below 20 kelvin, 4 angstrom tubes exhibit superconducting behavior manifest as an anisotropic Meissner effect, with a superconducting gap and fluctuation supercurrent. The measured superconducting characteristics display smooth temperature variations owing to one-dimensional fluctuations, with a mean-field superconducting transition temperature of 15 kelvin. Statistical mechanic calculations based on the Ginzburg-Landau free-energy functional yield predictions that are in excellent agreement with the experiments., Superconductivity in organic conductors was first reported in pressurized quasi-one-dimensional (1D) tetramethyltetraselenafulvalene (TMTSF) Bechgaard salt [(TMTSF).sub.2]P[F.sub.6] (1, 2). After the discovery of the fullerenes, superconductivity was observed in alkali metal-doped [...]

The relationship between band gap and biaxial stress in wurtzite ZnO thin films is examined by side-inclination x-ray diffraction technique and optical absorbance spectrum as well as ab initio calculation. The difference between ZnO and GaN is because of the large valence-band maximum (VBM) offset of ZnO to low energy and the strong p-d coupling in valence band of ZnO is responsible for the large VBM offset.

Phase transition of Se species incorporated in the AlPO4-5 nanoporous matrix was investigated by differential scanning calorimetry and temperature dependent vibrational spectra. The thermal absorption/desorption process showed that the confined Se species structure transformations at temperature range 320-350 K.

Abstract: We report the hydrothermal synthesis of AlPO4-5 crystals using TBAOH as template. The resulting product sensitively depends on the gel compositions and synthesis procedure. By treating the tri-isopropylate aluminum gel solution with ultrasonic, and adding HF acid to adjust the gel pH value, perfect hexagonal-shaped AlPO4-5 crystals are obtained. At high TBAOH content, some centrosymmetric intersecting crystals are observed in the products, this can be interpreted by the polar growth of AlPO4-5 crystals. The decomposition of template TBAOH in the channels of AlPO4-5 crystals has been studied by FTIR and TG analysis. [Copyright &y& Elsevier]

Abstract: In this paper, we reviewed our recent study on ultraviolet stimulated emission and lasing observed at room temperature from nano-structured ZnO thin films. The nano-structured ZnO thin films were grown on sapphire substrates using Laser-Molecular-Beam-Epitaxy (L-MBE). The thin film was consisted of regularly arrayed hexagonal nano-crystallite columns, whose facets form natural micro-cavities. These nano-crystallites confine the centre-of-mass motion of excitons. As a result of the quantum size effect, the oscillation strength of the excitons is largely enhanced, which is favored to the radiate recombination of exciton at room temperature. Excited using the frequency-tripled output of a YAG laser, the nano-structured ZnO thin film showed strong ultraviolet lasing at room temperature with a threshold as low as 24kW/cm2. At a moderate pumping intensity, the room temperature stimulated emission is associated with an exciton-exciton collision process. At higher pumping density, the excitons are dissociated, and the ultraviolet stimulated emission is dominated by an electron-hole plasma recombination process. Because of the large enhancement of oscillator strength of the excitons, the optical gain of the stimulated emission measured at room temperature reaches as high as 320 cm-1, which is an order higher than that observed in bulk ZnO crystals. In comparison with the electron-hole plasma stimulated emission in most of commercial semiconductor lasers, the excitonic stimulated emission can be realized at relatively low external pumping density. The observation of excitonic lasing effect at room temperature might be valuable in realization of practical ultraviolet semiconductor laser devices. [Copyright &y& Elsevier]

The second-order non-linear susceptibility components were measured using 1.064 μm incident light for ZnO thin films of various thicknesses from 24.4 to 283 nm self-assembled on sapphire substrates by laser molecular beam epitaxy. It was found that the values of the non-linear susceptibility for the films are almost the same as those of bulk material, except the samples with thicknesses ranging from 35 to 64.8 nm, which show a large enhancement effect. For the sample with a thickness of 44.4 nm, the second-order non-linear susceptibility components were found to be approximately 14.7 pm/v for d31, 15.2 pm/v for d15, and −83.7 pm/v, a value approximately 14 times that of the bulk material, for d33. The second-order non-linear coefficient enhancement in the thin films may be resulted from the microcrystallite structures. [Copyright &y& Elsevier]

A detailed synthesis process of ultra-small single-walled carbon nanotubes (SWNTs) aligned in the channels of AlPO4-5 zeolite single crystals is reported. The structure of such ultra-small SWNTs was analyzed by means of transmission electron microscopy (TEM) and polarized Raman scattering. TEM images showed that the diameter of the SWNTs is as small as 0.4 nm, which is the size of three possible structures: the zigzag (5,0), armchair (3,3) and chiral (4,2). The polarization dependence of the Raman lines indicates that the structures of the nanotubes are dominated by the zigzag (5,0) form. Line-shape analysis of the tangential A1g Raman mode shows that the SWNTs are metallic with a finite electronic density-of-state near the Fermi energy level, which is in agreement with the band structural calculation using local-density function approximation (LDA) as well as the electric transport measurement. [ABSTRACT FROM AUTHOR]

Abstract. Mono-sized single-wall carbon nanotubes were formed in one-dimensional channels of ALPO[sub 4-5] single crystal (AFI) by pyrolysis of tripropylamine (TPA). Raman spectra have been measured for the TPA-AFI crystals thermally processed at different conditions. TPA molecules are carbonized at 400 Celsius, and carbon nanotubes were formed at 500 Celsius or above. The radial-breathing mode, which is special for carbon nanotube geometry, was observed. Three Raman-active modes with symmetry A[sub 1g], E[sub 1g], and E[sub 2g] were identified by detailed symmetrical analysis for the polarized-Raman spectra. [ABSTRACT FROM AUTHOR]

Raman spectra of single-wall carbon nanotubes produced in the channels of zeolite AFl single crystals have been analyzed in the light of the full symmetry group, the line group. The phonon dispersion curves of the tubes (5,0), (3,3), and (4,2) are calculated based on the lattice dynamical model and the phonon branches are assigned to their quantum numbers (irreducible representations). The structures of Raman spectra of different samples are reproduced well by the density of states of relevant Raman-active phonons. The result is useful to evaluate the contents of these tubes in real crystals where the contents are not well defined before. [ABSTRACT FROM AUTHOR]

Reports on the measurement of third-order optical nonlinearity of ZnO microcrystallite thin films near the excitonic resonance at various temperatures. Use of the femtosecond degenerate four-wave-mixing technique in the study; Response times measured.