STUDY ON THE EFFECT OF PLASMA PARAMETERS AND CATALYST ON GROWTH AND FIELD EMISSION PROPERTIES OF CARBON NANOTUBES(CNTs)

Abstract

ABSTRACT Carbon nanotubes are allotropes of carbon with cylindrical nano structure. The structure of a nanotube is similar to graphite, with a difference that the sheets are rolled to form a tube and capped at least one end. CNTs have found applications in field emission displays, nanoscale electronic devices, biosensors and hydrogen storage medium. There are various techniques through which CNTs can be synthesized but CNT synthesized in a plasma medium are known to be vertically aligned at low growth temperatures. The present thesis is a rigorous and detailed study of parameters affecting CNT growth in plasma and the consequent field emissions from them. In the research work, we have developed a theoretical model describing the growth of CNT in plasma with and without catalyst, separately. The model detailing CNT growth in plasma without catalyst is extended to study the effect of plasma parameters, plasma compositions, different plasma mediums, and negative ions on the growth of CNT and the results obtained have been extended to present an estimate of the behavior of field enhancement factor of CNT. The broad outcomes of the research are that the plasma parameters (electron density and temperature , ion density and temperature), relative density of negative ions, fractional concentration of light positive ion, decreases the radius of CNT and since the field enhancement factor is inversely proportional to radius , it can be estimated that field enhancement factor would increase with all the above parameters. The CNT growth on a catalyst-substrate surface in a plasma environment is a complex process and therefore a model is developed underlining the numerous complex growth processes in a plasma iii environment. The impact of plasma parameters, plasma power, substrate bias, substrate temperatures, different carrier gases and their flow rates on the height and radius of CNT is thoroughly studied. The outcomes of present research can be extended to improve field emission from the CNTs at low temperatures.