Showing papers by "Yury Gogotsi published in 2003"
747 citations
TL;DR: In this article, the formation mechanisms of diamond as well as the transformation of diamond to graphite and onion-like carbon upon heating were analyzed. But the mechanism of diamond formation has not been previously analyzed.
Abstract: Synthesis of nano- and microcrystalline sp3-bonded carbon (diamond) with cubic and hexagonal structure by extraction of silicon from silicon carbide in chlorine-containing gases has been reported recently. This process is attractive because it can produce diamond at ambient pressure and temperatures below 1000 °C. No plasma or other high-energy activation is required, thus providing an opportunity for large-scale synthesis. However, the mechanism of diamond formation has not been previously analyzed. This work reports on the formation mechanisms of diamond as well as the transformation of diamond to graphite and onionlike carbon upon heating. Study of SiC/carbon interfaces showed that direct epitaxial growth of diamond on SiC is possible, in agreement with previous molecular-dynamics simulation. However, random nucleation of diamond from amorphous sp3-bonded carbon produced as the result of extraction of Si from SiC has also been demonstrated. It has been shown that the presence of hydrogen in the environ...
144 citations
TL;DR: More than 2500 indentations were made on a silicon wafer surface using a range of different unloading rates and maximum applied loads, and the unloading curves were examined for characteristic events (popout, kink popout, elbow followed by pop-out, and elbow) that were assigned to different phase transitions within the affected material based on Raman microspectroscopy analysis of residual imprints.
Abstract: More than 2500 indentations were made on a silicon wafer surface using a range of different unloading rates and maximum applied loads. The unloading curves were examined for characteristic events (pop-out, kink pop-out, elbow followed by pop-out, and elbow) that were assigned to different phase transitions within the affected material based on Raman microspectroscopy analysis of residual imprints. The effect of unloading rate and maximum applied load on the average contact pressure at the beginning of the event was found. A permissible range for each event to occur was established.
118 citations
TL;DR: In this paper, the first known natural occurrence of large arrays of conical graphite crystals were reported, which occur on the surfaces of millimeter-sized polycrystalline spheroidal aggregates of graphite Cone heights range from less then a micron to 40 μm.
97 citations
TL;DR: In this paper, a mixture of metastable Si-III and Si-XII phases was observed by both selected area diffraction in TEM and Raman analysis, and a mechanism of dislocation-induced lattice rotation that leads to a phase transition and distortion-induced amorphization in nanoindentation was proposed.
Abstract: Plan-view transmission electron microscopy (TEM) and Raman microspectroscopy were used to identify metastable silicon phases in nanoindentation. A mixture of metastable Si-III and Si-XII phases was observed by both selected area diffraction in TEM and Raman analysis. High resolution TEM observations provided detailed structural information about the metastable phases of silicon and the interfaces between different silicon structures. A mechanism of dislocation-induced lattice rotation that leads to a phase transition and distortion-induced amorphization in nanoindentation is proposed.
87 citations
01 Nov 2003
TL;DR: In this article, a simulation of pressure-induced phase transformations in monocrystalline silicon is presented, where contact mechanics models are used to account for phase transformations and contact loading is used to simulate phase transformations.
Abstract: Introduction. High Pressure Surface Science and Engineering - A New Area of Research (Y Gogotsi, Drexel University, USA) Chapter 1 Phase Transitions Induced by Mechanical Compression (JJ Gilman, University of California at Los Angeles, USA) Chapter 2 Simulation of Pressure-Induced Phase Transformations 2,1 Contact Mechanics Models Accounting for Phase Transformations (BA Galanov and V. Kindrachuk, National Academy of Sciences, Ukraine) 2,2 Molecular Dynamics Simulation of Phase Transformations in Monocrystalline Silicon (L Zhang and WCD Cheong, University of Sydney, Australia) 2,3 High-Pressure Phases of Group IV and III-V Semiconductors (G Ackland, University of Edinburgh, UK) Chapter 3 Continuum Mechanical Fundamentals of Mechanochemistry (VI Levitas, Texas Tech University, USA) Chapter 4 Experimental Techniques in High Pressure Surface Science 4,1 Depth-Sensing Nanoindentation (A Fischer-Cripps, CSIRO, Australia) 4,2 Nanomechanical Characterization of Ceramic Materials (B Bhushan, Ohio State University, USA X Li, University of South Carolina, USA) 4,3 Raman Microspectroscopy (V Domnich and Y Gogotsi, Drexel University, USA) 4,4 Transmission Electron Microscopy (D Ge and Y Gogotsi, Drexel University, USA) Chapter 5 Experimental Studies of Phase Transformations Induced by Contact Loading 5,1 Indentation Induced Phase Transformations in Semiconductors (V Domnich, D Ge and Y Gogotsi, Drexel University, USA) 5,2 Indentation Induced Phase Transformations in Ceramics (V Domnich and Y Gogotsi, Drexel University, USA) 5,3 Zirconia Ceramics: Phase Transformations and Micro Raman Spectroscopy (M Dorn and KG Nickel, University of Tubingen, Germany) 5,4 Phase Transformations Under Dynamic Loading (T Juliano, V Domnich and Y Gogotsi, Drexel University, USA) Chapter 6 Ductile Regime Machining of Semiconductors and Ceramics (J Patten and H Cherukuri, University of North Carolina at Charlotte, USA J Yan, Kitami Institute of Technology, Japan)
66 citations
TL;DR: The effect of humidity on the tribological behavior of carbide-derived carbon (CDC) films prepared by high-temperature chlorination of silicon carbide was examined in this article.
Abstract: The effect of humidity on the tribological behavior of carbide-derived carbon (CDC) films prepared by high-temperature chlorination of silicon carbide was examined. Pin-on-disk tribological tests indicate that CDC, unlike graphite or glassy carbon, performs better in dry nitrogen (less than 0.05 friction coefficient at 0% humidity) than in humid air. This versatility is explained by the onion-like structure of the nanoporous CDC coating.
52 citations
TL;DR: In this paper, pure BN coatings have been synthesized on the surface of SiC powders and fibers by a novel carbothermal nitridation method, which is simple, cost-effective, and less toxic due to the use of H3BO3 and NH3 as precursors at atmospheric pressure compared with most commonly used chemical vapor deposition (CVD) methods.
Abstract: Pure BN coatings have been synthesized on the surface of SiC powders and fibers by a novel carbothermal nitridation method. Three stages are involved in the process: first, formation of a carbon layer on the SiC by the extraction of Si with chlorine; second, infiltration of the resulting nanoporous carbide-derived carbon (CDC) coating by a saturated boric acid solution; and finally, nitridation in ammonia at atmospheric pressure to produce the pure BN coating. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS) were used to characterize the phase, elemental composition, and surface morphology of the coatings. The intermediate carbon layer acts as a template for BN growth, facilitates the formation of BN, and prevents the degradation of SiC fibers during nitridation. The whole process is simple, cost-effective, and less toxic due to the use of H3BO3 and NH3 as precursors at atmospheric pressure compared with most commonly used chemical vapor deposition (CVD) methods. Uniform BN coatings obtained by this method prevent the bridging of fibers in the tow. The coating of powders is possible, which cannot be achieved by conventional CVD methods.
51 citations
TL;DR: In this paper, the safe properties of nanotubes and other nanofilaments were investigated and the authors concluded that they are safe. But they did not specify how safe they are.
Abstract: (2003). How safe are nanotubes and other nanofilaments? Materials Research Innovations: Vol. 7, No. 4, pp. 192-194.
47 citations
TL;DR: In this article, a contact mechanics model is developed which takes into account possible phase transformations in materials induced by hydrostatic and shear stresses associated with indentation, allowing prediction of the average thickness and approximate shape of the phase transformation zone in semiconductors and ceramics under various types of diamond indenters.
Abstract: A contact mechanics model is developed which takes into account possible phase transformations in materials induced by hydrostatic and shear stresses associated with indentation. The proposed model allows prediction of the average thickness and approximate shape of the phase transformation zone in semiconductors and ceramics under various types of diamond indenters. The results of theoretical calculation are in good agreement with the available experimental data.
22 citations
TL;DR: In this article, single wall and multi-wall carbon nanotubes (MWNT) were electrostatically assembled into nanofibers through an electrospinning process in order to increase the strength and toughness of polyacrylonitrile (PAN)-derived carbon fibers.
Abstract: Single wall (SWNT) and multi-wall carbon nanotubes (MWNT) were electrostatically assembled into nanofibers through an electrospinning process in order to increase the strength and toughness of polyacrylonitrile (PAN)-derived carbon fibers. It was found that the effectiveness of carbon nanotubes (CNT) in reinforcing the PAN precursor is highly dependent on the dispersion and the alignment of the CNT. Alignment was achieved during electrospinning by the flow of polymer, electrostatic charge and diameter confinement. Up to 10 wt. % SWNT coelectrospun with PAN was successfully produced with fiber diameters in the range of 40 nm to 400 nm. With the addition of 1 wt. % SWNT, a two-fold increase in strength and modulus was obtained in the as-spun nanofibers mat. These encouraging results show a promising pathway to produce the next generation of high performance carbon fibers that will help bridge dimensional and properties gap between nanoscopic and macroscopic structures.
TL;DR: In this article, the authors used load-displacement derivative behavior and power-law curve fitting to find the location of events for a number of different materials during depth-sensing indentation.
Abstract: The use of load-displacement derivative behavior and power-law curve fitting is applied to find the location of events for a number of different materials during depth-sensing indentation. Load-displacement curves for Berkovich indentations on fused silica, fullerene thin film on sapphire, CdTe thin film on silicon, single crystal silicon, carbide derived carbon, and a polymethylmethacrylate/hydroxyapatite (PMMA/HA) particle composite are examined. The analysis is applied to quantify the location of different events that occur during material loading and unloading.
01 Jan 2003
TL;DR: In this article, the effect of humidity on the tribological behavior of carbide-derived carbon (CDC) films prepared under various experimental conditions was examined, and the results indicated that CDC, unlike graphite or glassy carbon, does not fail in dry environments.
Abstract: The problem of good wear resistance coupled with low friction coefficient has been studied extensively. Carbide-derived carbon (CDC) films have been demonstrated to show excellent friction and wear properties in air. in the present work, we examine the effect of humidity on the tribological behavior of CDC films prepared under various experimental conditions. We produced the films by high temperature chlorination of sintered silicon carbide, characterized them by Raman microspectroscopy and nanoindentation, and carried out pin-ondisk tribological tests in air and dry nitrogen (0% humidity) using silicon nitride counterbodies. Our results indicate that CDC, unlike graphite or glassy carbon, does not fail in dry environments. Moreover, it performs better in dry nitrogen than in humid laboratory air. The CDC coating on SiC can work for hours in dry nitrogen showing the friction coefficient of less than 0.05. Chlorination conditions and the surface condition of the test piece are other important parameters in tribological performance. These coatings may be used in dynamic seals and other tribological applications.
TL;DR: In this article, different formulations of a new material to be used as an insoluble anode for copper electrowinning, a Ti-Pb composite, were investigated for both mechanical and electrochemical properties.
Abstract: Different formulations of a new material to be used as an insoluble anode for copper electrowinning, a Ti-Pb composite, were investigated for both mechanical and electrochemical properties. Mechanical and metallographic characteristic tests, as well as short-term deposition tests were used to study the effect of the Ti/Pb ratio on anode performance. Yield strength and elastic modulus, obtained through tensile testing, significantly exceed that of lead. Metallographic procedures were used to assess the uniformity of lead distribution in the material, as well as porosity, which would be decreased below 1 % for most of the compositions under study. Short-term deposition tests were used to determine power consumption, deposit quality current efficiency and weight loss characteristics of the new anode material. The material with only 30 vol.% lead shows approximately the same electrochemical performance as a pure lead anode, but has much higher mechanical properties which prevent warping and extend the lifetime of the anode.
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TL;DR: In this paper, free standing carbon nanotubes about 300 nm in diameter and lengths 5-60 micrometers were obtained by pyrolyzing ethylene within alumina membranes.
Abstract: Free standing carbon nanotubes about 300 nm in diameter and lengths 5-60 micrometers were obtained by pyrolyzing ethylene within alumina membranes.
TL;DR: In this paper, a plan-view TEM work on silicon nano-identification is presented, which discusses phase transformation mechanisms during unloading and investigates the stability of metastable silicon phases during heating in TEM.
Abstract: The cubic diamond structure of silicon (Si-I) undergoes a phase transformation to a tetragonal structure (Si-II) at a pressure level of 11.2~12 GPa. This transition is not reversible; a mixture of body-centered cubic Si-III (bc8) and rhombohedral Si-XII (r8) structures or amorphous silicon (a-Si) may form during pressure release [1]. In the last decade, depth-sensing indentation has proven to be a powerful tool for studying phase transformations in silicon under highly deviatoric stresses. However, the transmission electron microscopy (TEM) analysis of various Si structures formed during nanoindentation has been largely inhibited by the difficulties involved in sample preparation. Recently, with the aid of focused ion beam and other advanced TEM sample preparation techniques, a few groups have performed successful TEM studies on residual silicon indentations [2-6]. However, the structures formed under load and the exact transformation mechanisms between different phases are still not fully understood. Furthermore, the thermal stabilities of metastable phases (such as Si-III and Si-XII) formed within nanoindentations have not been reported. In this paper, a plan-view TEM work on silicon nanoidentations is presented. This work is then used to discuss phase transformation mechanisms during unloading and to investigate the stability of metastable silicon phases during heating in TEM.