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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]

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]

Examines the temperature dependence of the optical absorption spectra of isolated selenium chains stabilized in channels of AlPO[sub 4]-5 crystals. Linear shift of the excitonic energy with increasing chain temperature; Attribution of the temperature dependence to interchain interaction and electron-optical-phonon coupling weakening.

Detailed synthesis process of selenium species incorporated in the channels of AlPO4-5 zeolite single crystals is reported. X-ray scattering experiments show diffuse planes which can be analyzed in terms of a partial filling of the channels by helical selenium chains. Polarized Raman and polarized absorption spectra confirm that the helical chains are highly aligned along the channel direction, while the rings appear randomly distributed in the channels. The helical chains have a lowest optical absorption band at 2.6 eV that is strongly polarization dependent, while the rings have a lowest absorption band at 3.0 eV that varies slowly with the light polarization. [Copyright &y& Elsevier]

Abstract: Single-walled 0.4nm carbon nanotubes (SWNTs) were fabricated using various metal cation substituted AlPO4-5 (MeAPO-5) molecular sieves as the template. The catalytic behavior varies with different metal incorporation. The incorporation of metal cations (Mn, Mg, Co) and Si gives rise to the formation of negatively charged frameworks and Brønsted acid sites. These frameworks thus play an important catalytic role in the pyrolysis and conversion of the organic molecules to SWNTs within the crystal channels. It is shown that the MeAPO-5 single crystals have a higher density of SWNTs than those crystals without the metal cations. The experimental results agree with the predictions of first-principles calculations, which show the metal-incorporated frameworks to be favorable for the SWNTs formation. [Copyright &y& Elsevier]

Abstract: We report the effects of gel composition and crystallization condition on the hydrothermal synthesis of optical-clear large AlPO4-5 crystals. By using a gel with excessive Al species and high HF content, large perfect hexagonal-shaped AlPO4-5 crystals (size 1.25mm×0.65mm) were obtained, at a synthesis temperature of 453K with a crystallization period of 36h. The optical quality of the crystals is sensitive to the crystallization temperature and time duration. [Copyright &y& Elsevier]

Single wall carbon nanotubes with diameter 0.4 nm grown in the channels of AlPO4-5 crystals were studied by Raman spectroscopy. Up to 21 different laser lines were used to characterize vibrational properties. Spectra depend strongly on the energy of the laser line used for excitation. It was found that only two types of nanotubes with different chiralities, (5,0) and (4,2), are responsible for the spectra observed. The frequencies of the radial breathing modes were reliable assigned. A strong response was also observed for frequencies ∼1250 cm−1. The positions of two such peaks assigned to the (5,0) do not depend on the laser energy whereas only one such a peak was observed for the (4,2) nanotube. Its frequency shifts with the laser energy like the D line of large diameter nanotubes, but the rate of the shift is only a half of the value known for the latter. We did not observe a radial breathing mode of the (3,3) tube even though a laser line close to the predicted resonance energy was used. On the other hand, we detected a possible presence of the (5,1) tube in the spectrum excited with the UV laser line. [Copyright &y& Elsevier]