Papers

ICMCTF2005 Session D3: Low-dimensional Carbon Nanostructured Materials

Tuesday, May 3, 2005 1:30 PM in Room Royal Palm 1-3

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		D3-1 Carbon Nanotubes for HDTVs and Progress J.M. Kim (Samsung Inc., South Korea)
2:10 PM		D3-3 Evolution of Structure and Morphology during PECVD Growth of Carbon Nanosheets B.L. French, J. Wang, M. Zhu, D.M. Manos, B.C. Holloway (College of William and Mary) Carbon nanostructures are currently under intense investigation for their extraordinary electronic and mechanical properties. Among these structures, carbon nanosheets hold promise for field emission and catalysis due to their sharp edges, upright orientation, and high surface area. Carbon nanosheets consist of thin stacks of graphene layers that often have a length 1000 times greater than their thickness. In this study the temperature-dependence of microstructure was investigated in nanosheets grown by inductively coupled radio-frequency plasma enhanced chemical vapor deposition. Using x-ray diffraction and scanning electron microscopy the distribution of nanosheet thickness and length was probed, both parallel and perpendicular to the substrate. All samples measured consisted mainly of turbostratic graphite, although a small amount of ordered graphite was detected in the lowest-temperature specimen. The degree of corrugation was found to increase with temperature in nanosheets synthesized at 670, 750, 800, and 950°C, while the distribution of sheet thickness remained nearly constant. These results are explained within the context of existing models of nanosheet formation, and suggest that microstructure can be adjusted during a given deposition through temperature variation.
2:30 PM		D3-4 Low Temperature Growth of Carbon Nanotubes by Microwave CVD with Sm-Co Catalyst J.T. Tsai (Tatung University, Taiwan) This paper describes the work carried out to produce multi-wall carbon nanotubes (MWCNTs) using a liquid catalyst and a microwave plasma technique. By this method we can reduce the CNT growth temperature at ~550°C yet maintain a very high CNT growth rate (~10 µm per minute). The catalyst is made by hydrochloric acid solution which contains high concentration of ferromagnetic metal such as Sm-Co magnet. Upon dispersing the liquid catalyst on a glass substrate, the catalyst only precipitates on the hydrophilic sites (i.e. CF₄ plasma etched surface). After performing the CNT growth in a microwave reactor with CH₄/N₂ mixture plasma, nanotubes can only be found to grow on etched pits instead of the whole area. This method allows us to produce multi-wall carbon nanotubes on the selective area such as in the glass trenches, concavities and thin film edges.
2:50 PM		D3-5 On the Characteristics of Iron-Silicon Thin Film Catalysts for Rapid, Low-Temperature Growth of Carbon Nanotubes K.-H. Liao, S.-W. Hung, W.-J. Liu (Mina Materials Lab, Taiwan); J.-M. Ting (National Cheng Kung University, Taiwan) We have reported previously very fast growth (13 ?-m/min) of aligned carbon nanotubes (CNT) at low temperature (less than 370â"f) in the presence of Fe-Si thin film catalyst (Jyh-Ming Ting, Kun-Hou Liao, ? oLow-temperature, Nonlinear Rapid Growth of Aligned Carbon Nanotubes, ? CPL, in press, 2004). The very fast, low temperature growth was attributed to the addition of Si into Fe. However, further understanding of the relationship between the nature of the catalyst and the CNT growth requires additional studies. Among them, we have addressed in this study the characteristics the Fe-Si thin film catalyst. A DC magnetron sputter deposition unit was used to deposit Fe-Si thin films under different deposition conditions to obtain thin films with various characteristics. The deposition parameters that were varied include working pressure, electrode distance, DC power wattage, and deposition time. The resulting Fe-Si thin films were examined using high-resulotion transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Fe-Si thin films exhibiting different thicknesses, compositions, crystallinity, and microstructure, and topography were obtained. Selected Fe-Si thin films were also used for the growth of CNT using a microwave plasma chemical vapor deposition method.
3:10 PM		D3-6 Gigahertz Carbon Nanotube/Fiber Cathodes K.B.K. Teo (University of Cambridge, United Kingdom); O. Groening (EMPA, Switzerland); E. Minoux (Thales Research and Technology, United Kingdom); L. Gangloff (University of Cambridge, United Kingdom); J.P. Schnell, P. Legagneux (Thales Research and Technology, United Kingdom); D. Dieumegard, F Peauger (Thales Electron Devices, United Kingdom); D.G. Hasko, GAJ Amaratunga, W.I. Milne (University of Cambridge, United Kingdom) We investigate the application of carbon nanotubes/fibers (CN) produced by plasma enhanced chemical vapour deposition as directly-modulated microwave cathodes. Using lithographic means to define the catalyst for growth, arrays of CN are grown. The structural uniformity and field emission uniformity of individual CN in the array are assessed. A model, based on the distribution of emitters and their maximum current, is then used to predict the emission characteristics and maximum current density for an array of CN array. This is shown to be highly accurate when compared with the experimental data of an array of CN. In dc operation, high current densities of around 1 Amp per square centimeter can be obtained from the array of CN. Finally, we demonstrate the operation of a radio frequency diode using CN operating at 1.2 Amp per square centimeter at 1.5 Gigahertz.
3:50 PM		D3-8 First Principles Calculation of the Field Emission of Nitrogen/Boron-Doped Carbon Nanotube H.-S. Ahn (Seoul National University, South Korea); S. Han (Ewha Womans University, South Korea); K.-R. Lee (Korea Institute of Science and Technology, South Korea); D.-Y. Kim (Seoul National University, South Korea) The effect of nitrogen and boron doping in carbon nanotubes (CNTs) on the field emission behavior were studied by first-principle calculations of electron transport. Emission currents were obtained from the time-dependent Schrödinger equations. The electronic structure of the pure CNT consists of two distinctive states: localized state originated from the defective sites of the CNT cap and extended state produced by the graphitic characteristics of CNT wall. In pure CNTs, the field emission from the localized states at the tip is more relevant than those from the extended metallic (π and π*) states. Nitrogen doping substantially changes the electronic structure. Some of the localized and the extended state are combined to provide a hybrid energy state and the energy levels of the localized states are shifted to the Fermi level. Electron emission from these states mainly contribute to the enhanced emission from nitrogen doped CNTs. On the other hand, boron doping has an opposite effect on the electronic structure. Boron doping pushes the localized state from Fermi level to a higher energy and seems to suppress the formation of the hybrid energy state, which result in the less electron emission. However, it must be noted that an irregular electron emission is observed in boron doped CNTs, because the shift in the energy level of localized states due to the external electric field is much more significant than in pure CNTs.