Oriented Carbon Nanotube Growth for Field Emission Applications
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A.N. OBRAZTSOV , I. PAVLOVSKY, A.P. VOLKOV, **o** V.L. KUZNETSOV , and A.L. CHUVILIN *Physics Department of Moscow State University, [email protected], http ://carbon.phys.msu.su Institute of Catalysis, Novosibirsk 630090, RUSSIA
Moscow
119899,
RUSSIA,
ABSTRACT Oriented carbon nanotube films were grown using a method of chemical vapor deposition in hydrogen/methane plasma activated by glow discharge. The film phase composition and structural features were studied by Raman, SEM, TEM, and HRTEM techniques. Field emission properties of the films were examined to obtain I-V characteristics and the field emission site distribution. The I-V curves in Fowler-Nordheim coordinates were linear, that is typical for the field emission, with the threshold average field about 1.5 V/kLm and the emission current density up to 50 mA/cm 2 at the field of 5 V/pm. The emission site density reached 107 cm 2 at the same value of electrtic field. INTRODUCTION Chemically vapor deposited (CVD) diamond films are known as a material with negative electron affinity (NEA) which should signicantly decrease the voltage utilized in a vacuum device to force electrons escape from its cathode [1,2]. Other important properties of diamond in view of its possible application as a field emissive (FE) cathode matrial are its chemical inertness, high durability to particle bombardment and high thermal conductivity. However,
detailed investigations of CVD diamond films exhibited that their FE properties are enchanced with an increase of non-diamond carbon contaminations [3-5]. To explain this dependence a few models were proposed which could be joined into two basic conceptss. In accord with the first, FE properties of CVD diamond are believed to be essentially a result of NEA at diamond surface, and a role of non-diamond inclusions is to provide the conductivity in dielectric diamond material [6]. Other point of view consists in idea that FE from CVD diamond originates from a local field enchancement onto the ends of conductive non-diamond carbon tiplike structures and, consequently, NEA of diamond has not any significance in this phenomenon [7]. The latter concept is very close to usual explanations of FE from other carbon materials and esspecially from carbon nanotubes [8,9]. This paper describes a comparative investigation of FE, carbon phase composition and structural properties of carbon films fabricated by using the CVD technique. Having an improvement of FE properties of polycrystalline diamond films grown by chemical vapor deposition (CVD) techniques as an initial motivation of our work, we have shown that the best emission properties are achieved for completely nondiamond carbon material which possesses structural characteristics similar to those of carbon nanotubes and/or nanosized graphite crystallites. We propose a model explaining FE from these CVD films which could also be applied to other kinds of carbon materials from diamond to polymers.
111 Mat. Res. Soc. Symp. Proc. Vol. 558 ©2000 Materials Research Society
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