Irradiation-induced structural modifications in multifunctional nanocarbons
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0956-J14-01
Irradiation-induced structural modifications in multifunctional nanocarbons Sanju Gupta Electrical and Computer Engineering, University of Missouri-Columbia, 6th St. 303 EBW, Columbia, MO, 65211-2300 ABSTRACT Severe environmental tolerability is the prime factor in the development of novel space materials exhibiting excellent physical properties accompanied by lightweight, reusability, and multifunctional capabilities. Diamond is known for its reputation being radiation hard besides a range of outstanding properties (electronic, optical, mechanical, and chemical) and hence it is preferable in radiation harsh environments. Carbon nanotubes are also of great interest because of several unsurpassable physical properties and it needs to be shown that they are physically stable and structurally unaltered when subjected to irradiation. In the present work, a family of novel nanocarbon (nanodiamond and nanotubes) films deposited by microwave plasma chemical vapor deposition (MWCVD) technique was subjected to gamma radiation (1, 5, and 20 Mrads) and to medium energy electron-beam, respectively to investigate their effects on the microscopic structure and corresponding physical properties to establish property-structure relationship. Dramatic improvement in the field emission properties for microcrystalline diamond and relatively small but systematic behavior for nanocrystalline diamond with increasing radiation dose is discussed in terms of the critical role of defects. The results also indicate that nanocrystalline carbon tends to reach a state of damage saturation they are discussed in terms of sp3, sp2+δ sp2 C inter-conversion. The effects of electron beam irradiation on the carbon nanotube show that multi–walled nanotubes tend to be relatively more robust than those of their single–walled counterparts. This is because increased exposure on an individual bundle of single-walled nanotubes promoted graphitization, pinching, and cross-linking similar to polymers forming intra-molecular junction (IMJ) within the area of electron beam focus, possibly through aggregates of amorphous carbon. Formation of novel nanostructures (nano– ring and helix– like) due to irradiation is also observed. These studies glean information about on the dynamics of nano-manufacturing and a regime of possible relevance to these materials for a) short-term space missions; b) radiation hard programmable logic circuits; and c) radiation pressure sensors. I. INTRODUCTION Advanced nanostructured carbon-based materials continue to attract attention because of their unique combination of structural and physical properties and therefore offering multifunctionality. Diamond and nanodiamond, in particular, exhibit exceptional structural (high aspect ratio of ~ 1000), physical (electrical, electronic, mechanical), and chemical properties, which have resulted in their continued investigations since they were discovered [1, 2]. Carbonbased materials continue to attract attention because of their unique combination of physical properties [3]. Inc
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