AVS2001 Session NT-TuP: Poster Session
Tuesday, October 30, 2001 5:30 PM in Room 134/135
Tuesday Afternoon
Time Period TuP Sessions | Topic NT Sessions | Time Periods | Topics | AVS2001 Schedule
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NT-TuP-1 Field Emission Microscopy Observation on Single-Walled Carbon Nanotubes with Atomic Resolution
Z.X. Zhang, G.M. Zhang, M. Du, X.X. Jin, S.M. Hou, Z.J. Shi, Z.N. Gu, W.M. Liu, X.Y. Zhao, Z.Q. Xue (Peking University, China) We assembled single-walled carbon nanotubes (SWCNs) onto tungsten carbide thin film on a tungsten tip surface, which was formed due to the segregation of carbon element in polycrystalline tungsten. Then by using Field-Emission Microscope (FEM) and quadrupole mass spectrometry, we respectively observed the field emission from the SWCNs and analyzed the components of the residual gas with the sample receiving heat treatment. The pattern of FEM image underwent obvious change as the heating temperature varied. The heat treatment at approximately 1000¡æ was found to result in the appearance of an FEM image with atomic resolution of an open-ended SWCN. The quadrupole mass spectrometry analysis showed the existence of carbon and oxygen atoms, which are believed to be released under high temperature from the spaces among the grains inside the polycrystalline tungsten. We think that these carbon and oxygen atoms imposed decoration upon the tube ends. Oxygen atoms reacted with amorphous carbon on the ends of the carbon nanotubes and generated CO and CO2, which than escaped into vacuum. Carbon atoms might fill the defects so that relatively perfect structures resulted. We further believe that this kind of decoration led to the protrusion of an individual SWCN, which made the atomic resolution of FEM image possible. |
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NT-TuP-2 Field Emission Properties of Carbon Nanotubes
Z.Q. Xue, M. Du, J.P. Sun, H. Zhang, W.M. Liu, S.M. Hou, G.M. Zhang, Z.X. Zhang, Z.J. Shi, Z.N. Gu, L.M. Peng (Peking University, China) SWCNTs have been synthesized and purified. Using a water colloid, SWCNTs have been assembled at the end of a tungsten tip that can be used as samples of field emission microscope (FEM) and field ion microscope (FIM). Images of a carbon nanotube open end were studied by the field ion microscope. Atomic resolution patterns of the tube open end were obtained. Field emission properties of SWCNTs have been studied exploiting the field emission microscope (FEM). A field emission pattern of an SWCNT at atomic resolution was observed, which was consistent with the calculated results of a (9,9) armchair SWCNT. Conventional field emission analysis utilizes the Fowler-Nordheim equation, a typical current versus voltage curve of SWCNT was measured. The plotting of ln(I/V 2) versus 1/V shown yielded a straight line in agreement with the Fowler-Nordheim equation, confirming the current resulted from field emission. |
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NT-TuP-4 Scanning Tunneling Microscopy of Single-walled Carbon Nanotubes with Metallo-phthalocyanine Adsorbates
J. Lee (Seoul National University, Korea); J.-Y. Park (Cornell University); H.J. Kim, H. Suh, Y. Kuk (Seoul National University, Korea); H. Kato, T. Okazaki, H. Shinohara (Nagoya University, Japan) Since the existence of carbon nanotubes are first reported in early 1990s, efforts have been made to characterize the electronic, transport and mechanical properties of this new form of carbonaceous material in various situations with views to exploit them as building blocks of useful nanoscale devices or sensors. One of the major usefulness of nanotubes lies in the fact that the electronic and transport properties of a nanotube as a metal or a semiconductor are very sensitive to chemical adsorbates whose concentration can be well controlled and modulated after the creation of the nanotube. Therefore it is an intuitively natural idea to dope the nanotubes with functional molecules sensitive to a few specific chemical ligands or physical environments (light, temperature, etc) to use them as physical, chemical or biological sensors. In this report we present the results of recent STM studies on nanotubes with metallo-phthalocyanine (M-Pc) molecule adsorbates. M-Pc's are chosen because they are chemically stable up to the sublimation temperature, immobile at room temperature on most host surfaces and have different electronic sensitivities to various toxic gases. Atomic resolution images and spectroscopic data on and near the adsorbed single M-Pc will be presented. |
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NT-TuP-5 In-situ Chemical Experiments in Carbon Nanotubes
N.N. Naguib, Y. Gogotsi (Drexel University); J.A. Libera (Northwestern University) Graphitic carbon nanotubes were synthesized by using a water-based mixture, such as equilibrated C-H-O fluid, in the presence of a catalyst, specifically Ni, at 700-800°C under 60-100 MPa pressure.1,2 TEM and electron diffraction analysis show that these carbon nanotubes are characterized by having high perfection of graphene layers, long and wide internal channels, Ni tips, and internal liquid inclusions trapped during the synthesis. During the growth of a tube, the synthesis fluid, which is a supercritical mixture of CO, CO2, H2O, H2, and CH4, exists inside the tube. After closure of the tube, aqueous liquid and gases are trapped inside. Closed hydrothermal nanotubes, unlike conventional nanotubes produced in vacuum or at ambient pressure, contain water and gases encapsulated under pressure. H2O, CO and CH4 are expected to dominate from thermodynamic calculations done using ChemSage 3.1 Gibbs energy minimization code. These nanotubes can be used as miniature pressure vessels for in-situ studies. Thus, they provide a unique opportunity for studying the behavior of fluids in nanosize channels, and for analysis of aqueous samples in TEM. The liquid inclusions were studied by using TEM, where apparent condensation and evaporation of liquid as well as a strong interaction between the liquid enclosed and the nanotube-s walls were observed. These experiments demonstrate the possible use of nanotubes for in-situ study of carbon chemistry
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NT-TuP-7 Characteristic of Carbon Nanotube Tip in UHV-STM
K. Ojima, M. Ishikawa, M. Yoshimura, K. Ueda (Toyota Technological Institute, Japan) Recently much attention is paid to carbon nanotube (CNT) because of its unique structural and electric properties. Field emitter, nano-tweezers and probe in scanning probe microscopy are expected for future application using CNTs, and have been extensively studied. In terms of the last application, most of reports are devoted to in the fields of atomic force microscopy. However, there is few study to use CNT in scanning tunneling microscopy (STM). Here we report on the application of CNT for STM probes in ultrahigh vacuum in order to investigate its capability. CNTs are attached to the tungsten tip using a new preparation method we recently proposed [unpublished]. The presence of CNT at the apex of the tip is confirmed before and after the STM experiment by scanning electron microscope. Before STM measurement, the contamination on the tip is removed by radiant heating. The Si(100)2x1 surface is used as the reference specimen, as is prepared by conventional method. STM images of Si(100)2x1 surface using CNT tip reveal individual silicon atoms in dimer units. However the image is a little bit vaguer than the case without CNT. This is probably related to the electric property of CNT. In order to image the surface structure clearly, the sample bias voltage and the tunneling current should be set at larger than 1.5V and lower than 0.1nA, respectively, which is apparently different condition from the tungsten tip without CNT. It is also noted that in the images obtained by CNT, no ghost such as double tip effect is observed. The voltage dependence of STM images will be presented in order to clarify the electric property of the CNT tip. |
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NT-TuP-8 Catalyst Effects in Its Deposition Rate and Kinds on Growth and Emission Characteristics of Carbon Nanotubes
J.H. Han, S.H. Choi, T.Y. Lee, Y.W. Jin, J.E. Jung, J.B. Yoo, C.Y. Park (Sungkyunkwan University, Korea); H.J. Kim, Y.J. Park, I.T. Han, N.S. Lee, J.M. Kim (Samsung Advanced Institute of Technology, Korea) Research on carbon nanotubes (CNTs) has been extensively carried out in past few years because of their own unique physical properties and their potential applications such as flat panel displays and vacuum microelectronics. In practical applications, a role of metal-catalyst has been very important for growth of CNTs in various synthesis methods. Among effects of metal-catalyst, an initial formation and various kinds of metal-catalyst film may have great effects on CNTs growth. Recently we observed that Ni film used as the catalyst-layer was differently formed according its deposition rate condition and thus CNTs were differently grown on it, hence this was systematically studied. Moreover, effects of a variety of metal-catalyst and buffer-metal on growth and emission characteristics of CNTs were investigated. In our experiments, the deposition rates of Ni film were varied from 1 Å/sec to 10 Å/sec. The metal-catalyst such as Ni, Co, Fe, Co-Fe and the buffer-metal such as Cr, Ti for improvement the adhesion between metal-catalyst and glass substrate were used. We have grown the vertically aligned CNTs on metal-catalyst coated glass with buffer-metal-layer at low temperatures below 550 °C by plasma enhanced chemical vapor deposition (PECVD). A DC plasma was employed, and C2H2 and NH3 was used as a carbon source and a catalyst gas. We examined morphologies of CNTs using field emission scanning electron microscopy (FESEM). Microstructures of CNTs were investigated by high resolution transmission electron microscopy (HRTEM) and emission characteristics of CNTs were evaluated in vacuum chamber below 10-6 Torr using phosphor-coated anode. |
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NT-TuP-9 Conversion of Carbon Nanotube from Diamond-Like Carbon Films
D. Sarangi, C. Godon, A. Granier, A. Goullet, G. Turban, O. Chauvet (CNRS, France) A simple route to synthesize carbon nanotube (CNT) has been reported in this article. Vacuum annealing of diamond-like carbon (DLC) films, grown by microwave (MW - 2.45 GHz) excited electron cyclotron resonance (ECR) technique with a radio frequency (RF) bias applied to the substrate, mixed with catalyst in argon atmosphere leads to the formation of carbon nanotube. High-resolution transmission electron microscopy studies reveal highly graphitized multi-walled nanotubes (MWNT) or amorphous fibre like structures, depending on the catalyst amount. This synthesis process may give a new approach to understand the phase transition of different carbon allotropes into nanotube or nanostructure. D. Sarangi's Present Address: Institut de Physique Experimentale, EPFL - Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland. C. Godon and O. Chauvet - Laboratoire de Physique Cristalline. |