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ABSTRACT: Organic modified silica sol was prepared by using (3,3,3-trifluoropropyl)trimethoxysilane (TFPTMS) as a precursor in ethanol solution under acidic condition. Infrared and Raman spectra were recorded for the silane coupling agent (SCA), TFPTMS sol and xerogel. Vibrational assignments have been suggested based on the spectral relative intensity, results from the vibrational study of trimethoxypropylsilane (TMPS), similar trifluorocompounds and group frequencies. Low temperature IR spectra revealed the presence of two conformers in TFPTMS. Only one conformer could be identified in the TFPTMS sol and xerogel. Thermal investigation of TFPTMS xerogel with infrared spectroscopic method indicated that the organic part remained essentially unchanged at or below 350°C but decomposed at or around 450°C, in agreement with the result from thermal gravimetric analysis (TGA). After the decomposition of the organic branch, the remaining part of the xerogel was composed of silica.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 12/2012; 105C:213-217. · 2.10 Impact Factor
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ABSTRACT: Graphene-like structures were formed on an oxidized SiC (0001) surface following thermal annealing in a vacuum at high temperatures.
The SiO2/SiC structure was annealed at 1350°C in 10−5Torr; the SiO2 layer was vaporized, and two layer graphene-like structures were formed on the SiC surface. This method of fabricating graphene
did not require an ultra-high vacuum. In the absence of the oxide layer, a film of vertical carbon nanotubes (CNTs) was grown
on the SiC surface in the same temperature range at 10−5Torr.
Journal of Electronic Materials 04/2012; 38(6):731-736. · 1.47 Impact Factor
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ABSTRACT: Graphene and carbon nanotube (CNT) structures have promise for many electronic device applications and both have been grown on SiC through the decomposition of the substrate. It is well known that both graphene and aligned CNTs are grown under similar conditions with overlapping temperature and pressure ranges, but a fundamental understanding of the two types of growths is actively being researched. Moreover, various technical challenges need to be overcome to achieve improvement in the electronic and structural quality of these carbon-based nanostructures on SiC. Specifically, an understanding and control of the SiC surface graphitization process and interface structure needs to be established. In this review, we focus on graphene growth on SiC (0 0 0 1) (Si-face) as a model system in comparison with aligned CNT growth on SiC. The experimental growth aspects for graphene growth, including vacuum and ambient growth environments, and growth temperature are summarized, then proposed decomposition and growth mechanisms are discussed. Both thermal and chemical decomposition processes are presented and special emphasis is given to the role of growth process variations between laboratories. The chemical reactions driving the graphitization process and ultimately the carbon nanostructure growth on SiC are discussed. It is suggested that the composition of the residual gases in the growth environment is a critical parameter and that gas composition at the growth temperature should be monitored.
Journal of Physics D Applied Physics 09/2010; 43(37):374004. · 2.54 Impact Factor
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ABSTRACT: Direct reaction of herringbone, platelet, or narrow, tubular herringbone graphitic carbon nanofibers (GCNFs) with molten potassium gives K/GCNF intercalates with stoichiometric control of potassium loading. Intercalate formation is confirmed by powder X-ray diffraction and micro-Raman spectroscopy. K/GCNF intercalates act as radical-anion alkene polymerization catalysts and reduce water with stoichiometric formation of hydrogen gas. Stage-1 K/narrow, tubular GCNF intercalate exhibits thermionic emission at 300 degrees C. Stage-1 K/herringbone GCNF intercalate is an excellent thermionic emitter having high thermal stability up to 1000 degrees C. K/GCNF intercalates have much reduced work functions of ca. 2.2 eV with localized emission showing a work function of 1.6 eV.
Journal of Nanoscience and Nanotechnology 05/2008; 8(4):1942-50. · 1.56 Impact Factor
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ABSTRACT: The synthesis, characterization, and electrical measurements of graphitic carbon nanofiber (GCNF)/carbon paper composite materials are reported. GCNF/carbon paper composites having relatively weak GCNF/carbon paper and GCNF/SiO2/carbon paper interfacial binding are prepared by growing carbon nanofibers directly from growth catalyst nanoparticles distributed throughout the carbon paper support. Carbothermal reduction of GCNF/SiO2/carbon paper composites effectively “spot welds” carbon nanofibers to carbon paper fibers affording mechanically robust GCNF/SiC/carbon paper composite materials. Characterization methods include scanning electron microscopic imaging, chemical composition and elemental mapping by energy-dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy for phase identification, BET surface-area analysis, and measurement of in-plane and contact electrical resistance. Plots of the pressure dependence of the contact resistance of GCNF/carbon paper and GCNF/SiC/carbon paper composites fall between those of commercial plain carbon paper and wet-proofed carbon paper with the GCNF/SiC/carbon paper composite having a contact resistance similar to that of plain carbon paper. A method for instilling a nano/microscale hierarchical architecture to carbon paper without incurring significant increase of contact resistance is reported.
11/2007;
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ABSTRACT: Thermal decomposition on SiC surface at high temperature and at low residual oxygen pressure yields a thin film of metal-free carbon nanotubes (CNTs) aligned on the SiC. In this study, CNT films on carbon-face 4H-SiC are produced under vacuum from 10−3 to 10−7 Torr and at temperatures ranging from 1400 to 1700 °C. Ex situ spectroscopic ellipsometry (SE) technique is applied to investigate the structure of the CNT films. It is found that two thin interfacial layers on the top and bottom of the CNTs are crucial in modeling the film structure from the SE data. We suggest a five layer structural model that consists of a CNT film as the main component, two interfacial layers, an amorphous carbon layer, and a surface roughness layer. This structural model based on the SE measurements is confirmed by cross-section transmission electron microscopy and can be applied for all CNT/SiC structures grown at various pressures and temperatures. At the growth pressure of 10−5 Torr, the CNT layer on SiC consists of 30%–50% CNTs, 35%–60% voids, and 5%–12% amorphous carbon in volume.
Journal of Applied Physics. 05/2007; 101(10):104311-104311-5.
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ABSTRACT: The surface interaction between ZrO2 and TiO2 in physical mixtures was studies using laser Raman spectroscopy (LRS). The characteristic peaks of ZrO2 disappeared after mixing ZrO2 and TiO2 with a loading ZrO2 of less than 25 wt.% and calcination at 773 K for 12 h. Surface polyhedrally coordinated Zr on TiO2 could not be detected by LRS. Therefore, MoO3 was used as a molecular probe to detect the nature of the interactions between ZrO2 and TiO2. The results revealed that ZrO2 could disperse on the surface of TiO2 and its interaction with TiO2 is different from that of MoO3 and TiO2.
Journal of Raman Spectroscopy 04/2005; 22(6):345 - 347. · 3.09 Impact Factor
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ABSTRACT: To study the effect of the high molecular weight polyethylene on the periprosthetic tissue in vivo as to give some reference to treatment of loosening hip arthroplasty.
Every lower limb of 20 New Zealand white rabbits was implanted a Co-Cr-Mo plug in femur by intercondylar notch. 15 mg polyethylene particles, dispersed in 1.5 ml normal saline solution, were injected into one knee joint. The other knee joint was injected 1.5 ml normal saline solution as control. This procedure was repeated 2,4,6,8 and 10 weeks after the implantation. Both of two lower limbs were given a X-ray examination 10 weeks to assess if there were periprosthetic osteolysis and loosening of the plugs. All animals were killed 2 weeks afer the last injection. The distribution of polyethylene in the knee joint capsule was examined to understand if there were loosening of implants or tissue change around implants. Knee joint capsule tissues and periprosthetic tissues were examined by optical microscope.
Nine cases formed fibrous membrane and four cases formed new bone around prostheses in experiment group. Eleven cases formed new bone and two cases formed fibrous membrane in control group (P < 0.05) The X-ray results indicated that the plugs were in distal medulla of femur. There was no sign of periprosthetic osteolysis, implants loosening or new bone formation. Optical microscope study indicated that there were a lot of polyethylene particles inside the capsule. The polyethylene particles were surrounded by multinucleated foreign-body giant cells and fibroblast. In some cases, there were fibroblasts and fibrous tissue around plug. There were no polyethylene particles and multinucleated foreign-body giant cells around plug in the marrow. There were a lot of polyethylene particles on the joint surface. The bone surface that contacted multinucleated foreign-body giant cells was coarse.
Maximizing ultra high molecular weight polyethylene can restrain rabbit periprosthetic bone formation.
Zhongguo xiu fu chong jian wai ke za zhi = Zhongguo xiufu chongjian waike zazhi = Chinese journal of reparative and reconstructive surgery 02/2005; 19(1):54-7.
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ABSTRACT: Graphitic features are detected on 4H-SiC surface following oxidation and etching using surface enhanced Raman spectroscopy (SERS). The electronic state of the carbon is sp2 on both the Si- and C-faces of 4H-SiC. The structures of the “carbon clusters” consist of two-dimensional graphitic flakes less than 2 nm and one-dimensional polyenes. The degree of graphitization on the C-face SiC is higher than those on the Si-face SiC. This study provides experimental evidence for “carbon clusters” existing on SiC surfaces following oxidation at atmospheric pressure and demonstrates that SERS is an effective technique to probe low concentration species on the SiC surface.
Applied Physics Letters 10/2004; 85(16):3495-3497. · 3.84 Impact Factor
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ABSTRACT: Carbon nanofiber/silica aerogel composites are prepared by sol-gel processing of surface-enhanced herringbone graphitic carbon nanofibers (GCNF) and Si(OMe)4, followed by supercritical CO2 drying. Heating the resulting GCNF/silica aerogel composites to 1650 degrees C under a partial pressure of Ar gas initiates carbothermal reaction between the silica aerogel matrix and the carbon nanofiber component to form SiC/silica nanocomposites. The SiC phase is present as nearly spherical nanoparticles, having an average diameter of ca. 8 nm. Formation of SiC is confirmed by powder XRD and by Raman spectroscopy.
Journal of Nanoscience and Nanotechnology 10/2004; 4(7):803-8. · 1.56 Impact Factor
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ABSTRACT: Electrical contact properties and graphitic structures of metal/carbon/4H–SiC structures are investigated. Metals studied include Ni, Co, Cr, NiCr, Ti, W, Mo, Al, and Au. Ohmic contacts are formed on Ni/C, Co/C, Cr/C, and NiCr/C films on 4H–SiC with n-type, C-face, and a doping concentration of 1.8×1019 cm−3 . Only Ni/C and Co/C films exhibit Ohmic contact behavior on SiC with n-type, Si-face, and a doping concentration of 1.6×1018 cm−3. Ni and Co are well known as excellent graphitization catalysts. Raman spectra show that the formation of graphitic carbon is related to the formation of Ohmic contacts in the annealed metal/carbon/SiC structures. Generally accepted catalytic graphitization mechanisms are applied to explain the scanning electron microscopy images, which demonstrate a relationship between the catalytically reacted morphology and Ohmic contact behavior. This study provides evidence that the metals with better catalytic graphitization activities form better Ohmic contacts on metal/carbon/SiC structures. © 2003 American Institute of Physics.
Journal of Applied Physics. 04/2003; 93(9):5397-5403.
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ABSTRACT: The structural properties of sputtered carbon films on SiC are investigated using X-ray photoelectron spectroscopy (XPS) and
Raman scattering. The as-deposited films are amorphous with an sp2/sp3 ratio of 1. The sp2 carbon structures gradually increase with increasing temperatures and consist of amorphous aromatic-like carbon, polyene-like
carbon, and nano-size graphite flakes. Schottky contacts on carbon/SiC are converted to ohmic contacts after annealing. The
concentration of nano-graphitic flakes relative to the aromatic-like and polyene-like carbon increases nearly linearly with
annealing temperature. Stacked graphitic structures are not observed. The specific contact resistivities are at 10−3–10−4Ωcm2 on the carbon/SiC after annealing from 1050°C to 1350°C.
Journal of Electronic Materials 01/2003; 32(5):426-431. · 1.47 Impact Factor
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ABSTRACT: Polyethylene terephthalate (PET) is a widely used polymeric material. In this work, the microstructural features before and after the solid-state polymerization (SSP) of several DuPont PET products were investigated by low-voltage scanning electron microscopy (LV-SEM) and atomic force microscopy (AFM). The microstructural features on the cross section of various PET samples included crystallites, voids, boundaries, defects, and amorphous phases. The SEM images revealed layered and stepped structural features at the micron and 10-micron scales that are highly crystallized at the near-edge region of the cross section for both linear and branched PET samples after the SSP process. The AFM images demonstrate that the degree of crystallization for the linear and branched PET samples increases gradually from the central area to the edge on the cross section. The linear crystallized PET has a higher degree of orientation than the branched crystallized PET in the 10-micron to micron scales, but their crystalline structures have no significant differences in the submicron to nanometer scales. The PET crystallization process occurs when the molecular chains in the amorphous phase are aligned and folded to form straight molecular chains at the nanometer scale, and small crystallites are formed. The crystallites aggregate and align together into a polygon rod-like-shaped crystallites at the submicron scale. Finally, large crystallites at the micron size are formed that appear on the edge area of the cross section. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 245–254, 2002
Journal of Polymer Science Part B Polymer Physics 12/2001; 40(3):245 - 254. · 1.53 Impact Factor
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ABSTRACT: Preparation procedures and thermionic emission properties of graphitic carbon nanofibres (GCNFs) supported on Si wafer or commercial carbon felt supports are reported. GCNF/native-oxide Si wafer, GCNF/oxidized Si wafer, GCNF/Ni-coated Si wafer and GCNF/carbon felt nanocomposites are obtained by growing GCNFs from growth catalyst nanoparticles supported on these supports. Narrow herringbone GCNF/SiO2/carbon felt mats are prepared from growth catalyst nanoparticles supported on fumed silica flakes. Due to weak GCNF-to-support binding in GCNF/Si wafer mats, GCNF/carbon felt mats and GCNF/SiO2/carbon felt mats, mechanical loss of the GCNF component is facile. However, carbothermal reduction of GCNF/SiO2/carbon felt nanocomposites affords mechanically robust GCNF/SiC/carbon felt mats. Thermionic electron energy distribution profiles recorded for these new nanofibre compositions indicate classic free-electron emission with estimated work functions (4.25-4.91 eV) slightly lower than those observed for un-doped graphite or carbon nanotubes. Electron energy distributions along the low energy leading region of the profiles display a cascade of emission peaks equally spaced by ca 0.014 eV, tentatively attributed to electron emission from localized GCNF edge sites.
Birck and NCN Publications.
