Light Emission from Carbon Nanotubes Induced by Field Electron Emission from Oriented MWCNT Arrays Accompanied by Re-Dep
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Light Emission from Carbon Nanotubes Induced by Field Electron Emission from Oriented MWCNT Arrays Accompanied by Re-Deposition R. Nanjundaswamy, Al. A Zakhidov*, M. Zhang, S.B. Lee, W.M. Sampson, A. N. Obraztsov*, A. Cunningham, A. A. Zakhidov UTD-Nanotech Institute, University of Texas at Dallas, Richardson, TX, 75086 *Physics Department, Moscow State University, Moscow Abstract Well-ordered aligned arrays of multiwalled carbon nanotubes were synthesized by the catalytic thermal chemical vapor deposition (CVD) in acetylene gas at the atmospheric pressure. Abrupt spark–type light emission spots and release of the carbon nanotubes from the cathode and succeeding deposition onto the anode without decomposition has been detected above the threshold electron emission current. Spectral analysis of the light showed that the spectra consist of a background similar to blackbody radiation and a set of sharp lines identified with the radiative transitions of excited carbon and iron atoms. Light emission spectra were found to be essentially different depending on the type (AC or DC) of the applied bias voltage and its value. As-grown and re-deposited materials were characterized by Raman spectroscopy and scanning electron microscopy. It was found that the structural properties of the re-deposited carbon nanotubes remained intact, with only negligible amorphization. A mechanism of the spark emission and re-deposition processe is proposed and discussed in terms of fast overheating of CNT, after explosion type melting of Fe-catalyst nanoclusters, followed by CNT transfer from cathode to anode . Introduction Carbon nanotubes (CNT) have attracted significant interest as cold electron field emitters (FE) for displays, soft X-ray sources, RF amplifiers and highly efficient luminescent lamps [1-3]. However in order to evaluate CNT cathode applicability, and to optimize their characteristics, other physical processes associated with FE effect in such emitters still need to be further investigated. One of these is light emission from CNT cathodes associated with the electron emission [4-8]. Light emission coupled with field emission phenomenon was observed for the first time by G. Rinzler et al. on individually opened multiwalled carbon nanotubes (MWCNT) at high FE emission currents, above 0.5 to 1 µA [4]. This light was associated with the heating of 1D chains of carbon atoms formed due to pulling these chains out of the open ends of MWCNT [4]. Succeeding studies of this interesting effect have been interpreted in terms of electroluminescence from the local discrete electronic states on the surface of carbon nanotubes [5]. This effect is similar to electroluminescence effects associated with FE from a carbon fiber micro-point emitter [6]. More recent studies of different types of tube arrays performed at the same time have reported, controversially, blackbody type [7-9] continuous spectra due to incandescence. Another phenomena coupled with FE from CNT material is degradation of the cathode due to a self-heating process [10]
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