Carbon-Based Nanocomposite Materials For Cold Cathode Sources
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Carbon-Based Nanocomposite Materials For Cold Cathode Sources Alexander V. Karabutov, Viktor G. Ralchenko, and Sergey K. Gordeev1. General Physics Institute, Vavilova str. 38, Moscow 119991, Russia (e-mail: [email protected]) 1 Central Research Institute of Materials, Paradnaya str. 8, St-Petersburg 191014, Russia ABSTRACT To find an alternative for CVD diamond films and carbon nanotubes for low-field electron emission sources and cold cathode applications, we have designed a novel class of nanomaterials with excellent field emission properties – dielectric/carbon nanocomposites, in which different insulating nanoparticles such as silicon oxide, boron nitride in cubic and hexagonal forms, and nanodiamond were used inside a pyrocarbon matrix. The thickness of pyrocarbon shells covering the dielectric particles can be controlled in a wide range during the CVD process. The best samples of the nanocomposites with all four kinds of dielectric material show excellent field emission properties with threshold fields of as low as 0.5-1 V/µm, good surface uniformity and long-term stability. An effect of post-growth treatment with oxygen and hydrogen plasma on the emission was also studied. A mechanism of the emission is discussed basing on quantum properties of nanostructured thin (two-dimensional) carbon covering the dielectric particles. The mechanism could be suitable for wide range of nanostructured sp2-bonded carbon objects. INTRODUCTION Some diamond and related carbon structures such as CVD diamond thin films, DLC film, diamond nanopowders, carbon nanotubes, etc. can show outstanding low-field electron emission with threshold fields of 1-3 V/µm [1-8]. Numerous microscopic studies of the emission centers show that the emission is often associated with diamond grain boundaries and diamond/sp2bonded carbon interfaces [5,9,10]. However, a role of the diamond phase (e. g., the negative electron affinity (NEA) of diamond [11]) for the emission is still not clear enough. Moreover, a common feature of those materials, which reveal the best emission characteristics, is that they contain a significant fraction of carbon with sp2 bonds [1,3-8], and a role of this phase for the emission is not well clear still. On the other hand, numerous studies of carbon nanotube-based field emitters supposed the low-field emission to be the only result of high field amplification effect of long and narrow nanotubes [8]. Here we call in question two important things related to the low-filed emission mechanisms for the above materials: (i) an importance of the diamond phase for effective carbon emitters (as NEA-material and so on) and (ii) an exclusive role of the field amplification (field enhancement) for carbon nanostructural materials (like nanotubes). We design a novel type of bulk material for effective cold cathode applications, in which different insulating particles such as nanopowders of silicon oxide, boron nitride, as well as nanodiamond were used to press the dielectric matrix and then saturated it with electrically conductive pyr
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