| 1. |
- Zou, Yonggang, et al.
(author)
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Rotational dynamics of confined C60 from near-infrared Raman studies under high pressure
- 2009
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 106:52, s. 22135-22138
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Journal article (peer-reviewed)abstract
- Peapods present a model system for studying the properties of dimensionally constrained crystal structures, whose dynamical properties are very important. We have recently studied the rotational dynamics of C60 molecules confined inside single walled carbon nanotube (SWNT) by analyzing the intermediate frequency mode lattice vibrations using near-infrared Raman spectroscopy. The rotation of C60 was tuned to a known state by applying high pressure, at which condition C60 first forms dimers at low pressure and then forms a single-chain, nonrotating, polymer structure at high pressure. In the latter state the molecules form chains with a 2-fold symmetry. We propose that the C60 molecules in SWNT exhibit an unusual type of ratcheted rotation due to the interaction between C60 and SWNT in the “hexagon orientation,” and the characteristic vibrations of ratcheted rotation becomes more obvious with decreasing temperature.
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| 2. |
- Wang, Lin, et al.
(author)
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Synthesis and high pressure induced amorphization of C60 nanosheets
- 2007
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:10, s. 103112-
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Journal article (peer-reviewed)abstract
- C-60 nanosheets with thicknesses in the nanometer range were synthesized by a simple method. Compared to bulk C-60, the lattice of the nanosheets is expanded by about 0.4%. In situ Raman spectroscopy and energy-dispersive x-ray diffraction under high pressures have been employed to study the structure of the nanosheets. The studies indicate that the bulk modulus of the C-60 nanosheets is significantly larger than that of bulk C-60. The C-60 cages in nanosheets can persist at pressures over 30 GPa, 3 GPa higher than for bulk C-60. These results suggest that C-60 crystals in even small size will be a potential candidate of superhard materials.
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| 3. |
- Yao, Mingguang, et al.
(author)
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Raman signature to identify the structural transition of single-wall carbon nanotubes under high pressure
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 78:20
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Journal article (peer-reviewed)abstract
- Raman spectra of single-walled carbon nanotubes (SWNTs) with diameters of 0.6–1.3 nm have been studied under high pressure. A “plateau” in the pressure dependence of the G-band frequencies was observed in all experiments, both with and without pressure transmission medium. Near the onset of the G-band plateau, the corresponding radial breathing mode (RBM) lines become very weak. A strong broadening of the full width at half maximum of the RBMs just before the onset of the G-band plateau suggests that a structural transition starts in the SWNTs. Raman spectra from SWNTs released from different pressures also indicate that a significant structural transition occurs during the G-band plateau process. Simulations of the structural changes and the corresponding Raman modes of a nanotube under compression show a behavior similar to the experimental observations. Based on the experimental results and the theoretical simulation, a detailed model is suggested for the structural transition of SWNTs, corresponding to the experimentally obtained Raman results in the high-pressure domain.
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| 4. |
- Zou, Yonggang, et al.
(author)
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Raman spectroscopy study of carbon nanotube peapods excited by near-IR laser under high pressure
- 2007
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In: Physical Review B. - 0163-1829. ; 76:19, s. 195417-
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Journal article (peer-reviewed)abstract
- A resonant Raman spectroscopy study has been carried out under high pressure, using a diamond anvil cell,on carbon nanotube peapods (C60@SWNT) synthesized in high yield in our laboratory. The Raman signal wasexcited by a near IR laser (830 nm) to avoid photopolymerization of C60 and thus obtain the intrinsic vibrationalinformation on the C60 molecules in the nanotubes. It is found that the surrounding tubes create aneffective pressure on the encapsulated C60 due to tube-fullerene interactions, resulting in a shift of the intrinsicAg(2) vibrational mode to 1474 cm−1 at ambient pressure. High pressure Raman spectroscopy indicates that(C60)2 dimers form near 1 GPa, and that a further polymerization of C60 occurs near 23 GPa, creating linearchains of covalently linked C60 molecules in the tubes.
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| 5. |
- Falth, JF, et al.
(author)
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Influence of dislocation density on photoluminescence intensity of GaN
- 2005
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 278:01-Apr, s. 406-410
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Journal article (peer-reviewed)abstract
- The influence of dislocation density on photoluminescence intensity is investigated experimentally and compared to a model. GaN samples were grown by molecular beam epitaxy and metal-organic chemical vapour deposition. Different growth parameters and thicknesses of the layers resulted in different dislocation densities. The threading dislocation density, measured by atomic force microscopy, scanning electron microscopy and X-ray diffraction, covered a range from 5 x 10(8) to 3 x 10(10) cm(-2). Carrier concentration was measured by capacitance-voltage-, and Hall effect measurements and photoluminescence at 2 K was recorded. A model which accounts for the photoluminescence intensity as a function of dislocation density and carrier concentration in GaN is developed. The model shows good agreement with experimental results for typical GaN dislocation densities, 5 x 10(8)-1 x 10(10) cm(-2), and carrier concentrations 4 x 10(16)-1 x 10(18) cm(-3). ©, 2005 Elsevier B.V. All rights reserved.
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| 6. |
- Hou, Yuanyuan, et al.
(author)
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Comparative study of pressure-induced polymerization of C60 nanorods and single crystals
- 2007
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In: Journal of Physics Condensed Matter. - Bristol : Institute of Physics. - 0953-8984 .- 1361-648X. ; 19:42, s. 425207-
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Journal article (peer-reviewed)abstract
- In this paper, we report a comparative study of pressure-induced polymerization in C60 nanorods and bulk single crystals, treated simultaneously under various pressures and temperatures in the same experiment. For both materials, orthorhombic, tetragonal and rhombohedral phases have been produced under high pressure and high temperature. The structures have been identified and compared between the two sample types by Raman and photoluminescence spectroscopy. There are differences between the Raman and photoluminescence spectra from the two types of materials for all polymeric phases, but especially for the tetragonal phase. From the comparison between nanorods and bulk samples, we tentatively assign photoluminescence peaks for various polymeric phases.
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| 7. |
- Klionsky, Daniel J., et al.
(author)
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Guidelines for the use and interpretation of assays for monitoring autophagy in higher eukaryotes
- 2008
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In: Autophagy. - : Landes Bioscience. - 1554-8627 .- 1554-8635. ; 4:2, s. 151-175
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Research review (peer-reviewed)abstract
- Research in autophagy continues to accelerate,1 and as a result many new scientists are entering the field. Accordingly, it is important to establish a standard set of criteria for monitoring macroautophagy in different organisms. Recent reviews have described the range of assays that have been used for this purpose.2,3 There are many useful and convenient methods that can be used to monitor macroautophagy in yeast, but relatively few in other model systems, and there is much confusion regarding acceptable methods to measure macroautophagy in higher eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers of autophagosomes versus those that measure flux through the autophagy pathway; thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from fully functional autophagy that includes delivery to, and degradation within, lysosomes (in most higher eukaryotes) or the vacuole (in plants and fungi). Here, we present a set of guidelines for the selection and interpretation of the methods that can be used by investigators who are attempting to examine macroautophagy and related processes, as well as by reviewers who need to provide realistic and reasonable critiques of papers that investigate these processes. This set of guidelines is not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to verify an autophagic response.
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