A Carbon Nanotube Field-Emission Electron Source
17 Nov 1995-Science (American Association for the Advancement of Science)-Vol. 270, Iss: 5239, pp 1179-1180
TL;DR: In this paper, a high-intensity electron gun based on field emission from a film of aligned carbon nanotubes has been made, which consists of a nanotube film with a 1-millimeter-diameter grid about 20 micrometers above it.
Abstract: A high-intensity electron gun based on field emission from a film of aligned carbon nanotubes has been made. The gun consists of a nanotube film with a 1-millimeter-diameter grid about 20 micrometers above it. Field-emission current densities of about 0.1 milliampere per square centimeter were observed for applied voltages as low as 200 volts, and current densities greater than 100 milliamperes per square centimeter have been realized at 700 volts. The gun is air-stable, easy and inexpensive to fabricate, and functions stably and reliably for long times (short-term fluctuations are on the order of 10 percent). The entire gun is only about 0.2 millimeter thick and can be produced with virtually no restrictions on its area, from less than 1 square millimeter to hundreds of square centimeters, making it suitable for flat panel display applications.
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TL;DR: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects.
Abstract: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.
9,693 citations
TL;DR: The nanotubes sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature and the mechanisms of molecular sensing with nanotube molecular wires are investigated.
Abstract: Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO 2 or NH 3 , the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated.
5,908 citations
TL;DR: In this paper, the authors describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of diamond-like carbon.
Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).
5,400 citations
TL;DR: The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported and the mechanisms of nanotube growth and self-orientation are elucidated.
Abstract: The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported. The approach involves chemical vapor deposition, catalytic particle size control by substrate design, nanotube positioning by patterning, and nanotube self-assembly for orientation. The mechanisms of nanotube growth and self-orientation are elucidated. The well-ordered nanotubes can be used as electron field emission arrays. Scaling up of the synthesis process should be entirely compatible with the existing semiconductor processes, and should allow the development of nanotube devices integrated into silicon technology.
3,093 citations
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References
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TL;DR: In this paper, the authors studied the bond-orientational order in molecular-dynamics simulations of supercooled liquids and in models of metallic glasses and found that the order is predominantly icosahedral, although there is also a cubic component which they attribute to the periodic boundary conditions.
Abstract: Bond-orientational order in molecular-dynamics simulations of supercooled liquids and in models of metallic glasses is studied. Quadratic and third-order invariants formed from bond spherical harmonics allow quantitative measures of cluster symmetries in these systems. A state with short-range translational order, but extended correlations in the orientations of particle clusters, starts to develop about 10% below the equilibrium melting temperature in a supercooled Lennard-Jones liquid. The order is predominantly icosahedral, although there is also a cubic component which we attribute to the periodic boundary conditions. Results are obtained for liquids cooled in an icosahedral pair potential as well. Only a modest amount of orientational order appears in a relaxed Finney dense-random-packing model. In contrast, we find essentially perfect icosahedral bond correlations in alternative "amorphon" cluster models of glass structure.
2,832 citations
TL;DR: In this paper, a detailed study of the phase diagram of suspensions of colloidal spheres which interact through a steep repulsive potential is presented. But it is not a detailed analysis of the colloidal glass phase.
Abstract: Suspensions of spherical colloidal particles in a liquid show a fascinating variety of phase behaviour which can mimic that of simple atomic liquids and solids. ‘Colloidal fluids’1–4, in which there are significant short-range correlations between the positions of neighbouring particles, and ‘colloidal crystals’5–7, which have long-range spatial order, have been investigated extensively. We report here a detailed study of the phase diagram of suspensions of colloidal spheres which interact through a steep repulsive potential. With increasing particle concentration we observed a progression from colloidal fluid, to fluid and crystal phases in coexistence, to fully crystallized samples. At the highest concentrations we obtained very viscous samples in which full crystallization had not occurred after several months and in which the particles appeared to be arranged as an amorphous ‘colloidal glass’. The empirical phase diagram can be reproduced reasonably well by an effective hard-sphere model. The observation of the colloidal glass phase is interesting both in itself and because of possible relevance to the manufacture of high-strength ceramics8.
1,881 citations
TL;DR: In this article, a set of polyhedral subunits essentially inverse to the packing in real space is derived, and several possible descriptive parameters are proposed to characterize an irregular array in formal mathematical terms.
Abstract: In his Bakerian Lecture, Bernal (1964) discussed those ideas of restricted irregularity which are physically realized in random packings of equal hard spheres, with particular reference to the structure of simple liquids. He stressed the need for a science of ‘statistical geometry ’, and took the first steps himself by proposing possible ways of describing such arrays. In this paper, these and other associated ideas are briefly described and extended by deriving an equivalent set of polyhedral subunits essentially inverse to the packing in real space. Examination of two independent high density arrays demonstrates the repro-ducibility of certain metrical and topological properties of these polyhedra, and their correlations over larger elements of volume. As a result, several possible ‘descriptive parameters’ are proposed. Although these essentially ‘numerical’ characteristics facilitate sensitive structural descriptions of any assembly of micro- and macroscopic subunits, we are still unable to characterize an irregular array in formal mathematical terms. Such a formulation of statistical geometry could be a powerful tool for tackling important problems in many branches of science and engineering.
1,237 citations
TL;DR: The notion of a crystal or a solid in general as an arrangement of molecules in rank and file, as Newton put it, is, in fact, older than Newton yet its quantitative statement was made possible only through the work of Born and others in our own century.
Abstract: A satisfactory picture of the structure of liquids has lagged far behind that of other states of matter. Ever since the time of Euler in the eighteenth century or, in a more precise form, since that of Maxwell in the nineteenth, we have had a convincing qualitative and quantitative picture of the chaos that is represented by the movements of the ideal gas molecules. The notion of a crystal or a solid in general as an arrangement of molecules ‘ in rank and file’, as Newton put it, is, in fact, older than Newton yet its quantitative statement was made possible only through the work of Born and others in our own century. But it is admitted even by those who work most in the field that the study of the structure of liquids or any exposition of their properties in atomic terms is still largely to be sought. This is not for want of trying. A vast number of researches have been devoted to attempts to analyze the structure of liquids, either directly by the diffraction methods which have proved so successful in crystalline solids, or, indirectly, through the construction of models and their thermodynamic testing. But we still lack either an adequate picture of the arrangement of molecules in a liquid or the necessary quantitative theory to explain their thermal and other properties.
866 citations
TL;DR: A general survey of glass transition phenomena and concepts is presented in an introductory section as discussed by the authors, and the physical significance of computer simulations of glass transitions in simple liquids and the question of a hidden phase transition underlying an observed glass transition are examined critically.
Abstract: The different physical aspects of glass transitions are reviewed and models aiming at their explanation are described. The following three main aspects are distinguished: the degree of stability of supercooled liquids with respect to crystallisation; the variation of physical properties of supercooled liquids in metastable equilibrium above the glass transition; the arrest of structural relaxation at the glass transition. The physical significance of computer simulations of glass transitions in simple liquids and the question of a hidden phase transition underlying an observed glass transition are examined critically. In relation to the stability problem, the geometrical constraints operative in typical disordered structures, such as random sphere packings and random covalent networks, are also discussed. A general survey of glass transition phenomena and concepts is presented in an introductory section.
777 citations