Showing papers by "Yury Gogotsi published in 2001"
TL;DR: In this paper, a closed carbon nanotubes with an encapsulated multiphase aqueous fluid is shown to offer an attractive test platform for unique in situ nanofluidic experiments in the vacuum of a transmission electron microscope.
Abstract: Hydrothermal multiwall closed carbon nanotubes are shown to contain an encapsulated multiphase aqueous fluid, thus offering an attractive test platform for unique in situ nanofluidic experiments in the vacuum of a transmission electron microscope. The excellent wettability of the graphitic inner tube walls by the aqueous liquid and the mobility of this liquid in the nanotube channels are observed. Complex interface dynamic behavior is induced by means of electron irradiation. Strong atomic-scale interactions between the entrapped liquid phase and the wetted terminated graphite layers are revealed by means of high-resolution electron microscopy. The documented phenomena in this study demonstrate the potential of implementing such tubes in future nanofluidic devices.
249 citations
TL;DR: The synthesis of nano- and micro-crystalline diamond-structured carbon is reported by extracting silicon from silicon carbide in chlorine-containing gases at ambient pressure and temperatures not exceeding 1,000 °C, with promising mechanical properties.
Abstract: Synthetic diamond is formed commercially using high-pressure1, chemical-vapour-deposition2 and shock-wave3 processes, but these approaches have serious limitations owing to low production volumes and high costs. Recently suggested alternative methods of diamond growth include plasma activation4, high pressures5, exotic precursors6,7 or explosive mixtures8, but they suffer from very low yield and are intrinsically limited to small volumes or thin films. Here we report the synthesis of nano- and micro-crystalline diamond-structured carbon, with cubic and hexagonal structure, by extracting silicon from silicon carbide in chlorine-containing gases at ambient pressure and temperatures not exceeding 1,000 °C. The presence of hydrogen in the gas mixture leads to a stable conversion of silicon carbide to diamond-structured carbon with an average crystallite size ranging from 5 to 10 nanometres. The linear reaction kinetics allows transformation to any depth, so that the whole silicon carbide sample can be converted to carbon. Nanocrystalline coatings of diamond-structured carbon produced by this route show promising mechanical properties, with hardness values in excess of 50 GPa and Young's moduli up to 800 GPa. Our approach should be applicable to large-scale production of crystalline diamond-structured carbon.
219 citations
TL;DR: In this article, a diamond turning machine was used to make grooves on (111) p-type single-crystal silicon wafers at room temperature, and the surface of the groove, after machining, was covered by a mixture of metastable, high-pressure silicon phases and amorphous silicon.
Abstract: A single-point diamond turning machine was used to make grooves on (111) p-type single-crystal silicon wafers at room temperature. Scratch tests have been performed with both sharp (Vickers and conical) diamond tools, and a spherical (Rockwell) diamond tool. Our results showed that material removal mechanisms differed between these tools. Pressure-induced metallization of Si allows the ductile regime mechanical micromachining of wafer surfaces. Raman microspectroscopy and electron microscopy were used to determine the machining parameters that do not introduce cracking or other types of damage. The surface of the groove, after machining, was covered by a mixture of metastable, high-pressure silicon phases and amorphous silicon. Further, these phases can be transformed into cubic silicon by annealing. The maximum depth of cut in the ductile regime has been determined for the given scratch test conditions and tools. The developed technique can be used to machine Ge, GaAs and other semiconductors. Applications drawing from this research are many. For example, channels for microfluidic devices can be engraved with a channel cross-section that is determined by the shape of the tool, which allows patterns that cannot be produced using etching. There are no limitations on the channel length or direction, and the channel width can vary from potentially a few nanometres to several micrometres.
119 citations
TL;DR: In this paper, the authors describe the synthesis of carbon nanotubes from 70 to 1300 nm in diameter which were synthesized hydrothermally in the C-H-O-Ni system at 100 MPa and 730-800°C by first establishing a post-pyrolysis C−H−O equilibrium followed by an increase in pressure during which time growth of graphitic carbon occurred.
100 citations
TL;DR: In this paper, carbon layers were formed on various types of sintered and CVD silicon carbide (SiC) using a novel technique involving a reaction with chlorine and chlorine-hydrogen gas mixtures at 1000 °C.
Abstract: Carbon coatings are widely used to modify surfaces of materials and improve their tribological properties. In this work, carbon layers were formed on various types of sintered and CVD silicon carbide (SiC) using a novel technique involving a reaction with chlorine and chlorine-hydrogen gas mixtures at 1000 °C. Following the work done on powders and fibers, this method successfully produced adherent coatings on SiC ceramics, which could be grown to thickness above 200 µm. Highly disordered carbon with contributions from nanocrystalline graphite was identified by Raman spectroscopy, x-ray diffraction, and energy dispersive spectroscopy. The kinetics of the chlorination reaction at 1000 °C for different gas mixtures fit to a linear reaction rate equation. Coatings produced in pure Cl2 are graphitic and demonstrate a low hardness (1.8 GPa), Young’s modulus (18 GPa), low wear rate, and a friction coefficient of ∼0.1, which is almost constant for any testing conditions in dry or humid air. Coatings produced in Cl2/H2 mixtures have microhardness up to 50 GPa and Young’s modulus up to 800 GPa. Although the presence of hydrogen had little effect on the Raman spectrum of the carbon layers, its presence changed the structure and permeability of the carbon film.
99 citations
TL;DR: Basavalingu et al. as discussed by the authors used a fine-grained b-SiC powder with a 2.21-morphs inside the capsule for the synthesis of carbon polymorphs.
52 citations
Patent•
02 Apr 2001
TL;DR: Isolated graphitic polyhedral crystal and methods for their isolation are provided in this article, where the crystals have graphite sheets arranged in a plurality of layers to form an elongated structure having a long axis and a diameter and having 7 or more external facets running substantially the length of the long axis, and take a variety of forms, such as needles, giant nanotubes, nanorods, whiskers, rings, cones, double tipped pyramids and others.
Abstract: Isolated graphitic polyhedral crystal and methods for their isolation are provided wherein the crystals have graphite sheets arranged in a plurality of layers to form an elongated structure having a long axis and a diameter and having 7 or more external facets running substantially the length of the long axis, and take a variety of forms, such as needles, giant nanotubes, nanorods, whiskers, rings, cones, double tipped pyramids and others, as well as their use in a variety of nanoscale devices and endproducts.
32 citations
TL;DR: The behavior of fullerenes C60 under hydrothermal conditions between 200 and 800°C, and under 100 MPa pressure, in the absence and in the presence of nickel is reported in this paper.
26 citations
TL;DR: The morphology of the platinum dispersion, its effect on the carbon layer, and its proposed formation mechanism are presented in this paper, where a platinum sample holder was employed (instead of fused silica), and the platinum was found dispersed in a carbon layer concentrated near the SiC/C interface.
Abstract: Highly disordered graphitic carbon layers were formed on various types of commercially available silicon carbide (SiC) ceramics by reaction with chlorine and chlorine-hydrogen gas mixtures at 1000°C. The carbon was produced ranging from only a few micrometers to hundreds of micrometers thick. When a platinum sample holder was employed (instead of fused silica), platinum was found dispersed in the carbon layer concentrated near the SiC/C interface. This process can be used for incorporating platinum in porous carbon films for catalytic and other applications. In addition, the platinum resulted in a smoother physical interface between the SiC and carbon sublayer. The morphology of the platinum dispersion, its effect on the carbon layer, and its proposed formation mechanism are presented in this paper.
21 citations
TL;DR: In this article, the deformation-induced phase transformations in contact loading of a simple elemental semiconductor have been investigated using Raman micro-spectroscopy, which can also provide information on residual stresses and/or chemical changes in the surface layers.
Abstract: Publisher Summary Interaction between two material surfaces in a real environment is a complex process that may involve material fracture, deformation, mechanochemical interactions, and phase transformations These processes must be considered together because of the existing synergy between them Both static and dynamic interactions between two hard surfaces may result in phase transformations Hydrostatic and deviatoric stresses must be taken into account and phase transformations in contact loading can be described as deformation-induced transformations At the same time, the transformation pressures for silicon obtained in indentation tests are in good agreement with the results from high-pressure cell experiments, which utilize hydrostatic loading Phase transformations in semiconductors, including pressure-induced metallization, are described in this chapter Currently, only silicon has been studied thoroughly enough However, even for this simple elemental semiconductor, not all issues concerning identification of new phases, transformations mechanisms, and transformation paths have been resolved Raman microspectroscopy is the fastest and most powerful tool for the analysis of phase transformations in contact loading It can additionally provide information on residual stresses and/or chemical changes in the surface layers
17 citations
TL;DR: In this paper, the synthesis of nano-and micro-crystalline diamond-structured carbon, with cubic and hexagonal structure, by extracting silicon from silicon carbide in chlorine-containing gases at ambient pressure and temperatures not exceeding 1,000
Abstract: Synthetic diamond is formed commercially using high-pressure1, chemical-vapour-deposition2 and shock-wave3 processes, but these approaches have serious limitations owing to low production volumes and high costs. Recently suggested alternative methods of diamond growth include plasma activation4, high pressures5, exotic precursors6,7 or explosive mixtures8, but they suffer from very low yield and are intrinsically limited to small volumes or thin films. Here we report the synthesis of nano- and micro-crystalline diamond-structured carbon, with cubic and hexagonal structure, by extracting silicon from silicon carbide in chlorine-containing gases at ambient pressure and temperatures not exceeding 1,000 °C. The presence of hydrogen in the gas mixture leads to a stable conversion of silicon carbide to diamond-structured carbon with an average crystallite size ranging from 5 to 10 nanometres. The linear reaction kinetics allows transformation to any depth, so that the whole silicon carbide sample can be converted to carbon. Nanocrystalline coatings of diamond-structured carbon produced by this route show promising mechanical properties, with hardness values in excess of 50 GPa and Young's moduli up to 800 GPa. Our approach should be applicable to large-scale production of crystalline diamond-structured carbon.
01 Jan 2001
TL;DR: In this article, the authors describe a technique that can produce a broad range of potentially important carbon nanostructures that may be used in future technologies, including fibers, powders and components with complex shapes and surface morphologies.
Abstract: Nanotechnology has been recognized as an emerging technology of the new century. Control over the structure of materials on nanoscale can open opportunities for the development of nanostructured materials with controlled properties, if the structure/property relations are known. This paper describes a technique that can produce a broad range of potentially important carbon nanostructures that may be used in future technologies. Nanostructured carbon coatings can be obtained either by deposition from the gas phase onto a substrate, or by surface treatment of a carbon-containing substrate. The method presented in this paper is accomplished through the extraction of metals from carbides (SiC and TiC) using chlorine or chlorine-hydrogen mixtures. This is a versatile technology because a variety of carbon structures can be obtained on the surface of carbides in the same reactor. Not only simple shapes, but also fibers, powders and components with complex shapes and surface morphologies can be coated. This technology allows the control of coating growth on the atomic level, monolayer by monolayer, with high accuracy and controlled structures.
TL;DR: The recent discovery of graphite polyhedral crystals, having shapes of faceted needles, rods, rings, barrels, and double-tipped pyramids with 7-fold, 9-fold or more complex morphological symmetry, suggests the possibility of growing complex crystal shapes on nanoscale and microscale as discussed by the authors.
Abstract: Recent discovery of graphite polyhedral crystals, having shapes of faceted needles, rods, rings, barrels, and double-tipped pyramids with 7-fold, 9-fold, or more complex morphological symmetry, suggests the possibility of growing complex crystal shapes on nanoscale and microscale. Appropriate crystal design may result in more diverse and better controlled morphologies grown “to size” from the material that best suits the application.
TL;DR: In this article, a model of oxide scale growth on Si 3 N 4 ceramics has been developed, which accounts for the formation of a porous SiO 2 layer between the dense SiO2 scale and porosity.
01 Jan 2001
TL;DR: In this paper, the phase transformations in semiconductors, including pressure-induced metallization and deformation-induced amorphization, have been studied for both classes of materials.
Abstract: Interaction between two material surfaces in a real environment is a complex process that may involve material fracture, deformation, mechanochemical interactions, and phase transformations. These processes must be considered together because of the existing synergy between them. Interaction between two material surfaces in a real environment is a complex process that may involve material fracture, deformation, mechanochemical interactions, and phase transformations. These processes must be considered together because of the existing synergy among them. This chapter reviews phase transformations in semiconductors, including pressure-induced metallization. Mechanisms of phase transformations in ceramics can be different from those in semiconductors, but pressure- or deformation-induced amorphization has been observed for both classes of materials.
TL;DR: In this article, a new class of low-angle conical carbon crystals has been described and their characteristics are reported, which are found in pores of a glassy carbon along with cylindrical multiwall nanotubes and graphite polyhedral crystals.
Abstract: A new class of low-angle conical carbon crystals has been described and their characteristics are reported here. These carbon nanocones were found in pores of a glassy carbon (GC) along with cylindrical multiwall nanotubes and graphite polyhedral crystals. The largest cones reach 2 to 3 microns in length, although most are in the submicron range. Scanning Electron Microscopy (SEM) reveals cones protruding from the inner pore surfaces with the tips oriented toward the inside of the pores. Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) show that cones are made of thick (up to several hundred layers), highly-ordered graphitic walls. Their tips are graphitic as well, and exhibit a dome-like morphology. These cones also differ from any carbon cones observed earlier in that they have a much smaller apex angle, sometimes less than 3°. Small angle carbon nanocones can potentially be used for probes and field emission elements.
01 Jan 2001
TL;DR: In this article, a closed-end multi-wall carbon nanotubes are used as a test platform for unique in-situ nanofluidic experiments in TEM.
Abstract: Closed-end multi-wall carbon nanotubes, which contain an encapsulated aqueous multi-phase fluidunder high pressure, have been produced by hydrothermal synthesis. These nanotubes are leak-tight by virtue of holding the fluid at the high vacuum of a transmission electron microscope (TEM) and can be used as a testplatform for unique in-situ nanofluidic experiments in TEM. They form an experimental apparatus, which is at least two orders of magnitude smaller than the smallest capillaries used in fluidic experiments so far. Excellent wettability of the carbon tube walls by the liquid and a dynamic behavior similar to that in micro-capillaries demonstrates the possibility of use of nanoscale (<100 nm) tubes in nanofluidic devices.However, complex interface behavior that can potentially create hurdles to fluid transport is also demonstratedherein.
01 Jan 2001
TL;DR: A combination of depth-sensing indentation and Raman microspectroscopy has been used for the identification of pressure-induced phase transformations in silicon, germanium, boron carbide and partially stabilized zirconia single crystals as discussed by the authors.
Abstract: A combination of depth-sensing indentation and Raman microspectroscopy has been used for the identification of pressure-induced phase transformations in silicon, germanium, boron carbide and partially stabilized zirconia single crystals. Phase transformations during nanoindentation may be revealed through deviations in the shape of the load-displacement curves from that of a perfect elastoplastic material. Such deviations are often more readily identified if the nanoindentation data are presented as average contact pressure vs. contact depth curves, allowing assessment of the corresponding transformation pressures.
Patent•
13 Apr 2001
TL;DR: In this paper, an isolated graphite polyhedral crystalline body has plural layers of graphite sheets arranged to form an elongated structure having >=7 external wall surfaces extending along the major axis.
Abstract: PROBLEM TO BE SOLVED: To provide a nanotube or carbon whisker which has a stable structure, has high strength and is of a polyhedron in the cross section having a twist along a major axis. SOLUTION: An isolated graphite polyhedral crystalline body has plural layers of graphite sheets which have the major axis and diameter and area arranged to form an elongated structure having >=7 external wall surfaces extending along the major axis. The isolated graphite polyhedral crystalline body the crystal of which has various shapes of needles, macronanotubes, rings, cones, double pyramids, nanorods, whiskers, or the like, and which is made into various kinds of nanoscale devices and products is provided.