Deposition of carbon layers from cyclohexane by thermal Chemical Vapor Deposition

The overall aim of this thesis is to deposit carbon layers by thermal Chemical Vapor Deposition (CVD) and investigate the effects of process parameters on the morphology and structure of the deposited carbon layers. Cyclohexane (C6H12) hydrocarbon is the precursor material used as the source of carbon. A 20% Cu- 80% Ni alloy, deposited by RF magnetron sputtering and annealed at the growth temperature either in an argon flow or in 10% hydrogen-90% argon flow, is used as a catalyst prior to carbon film deposition by CVD. The CVD temperature is varied between 550 0C and 800 0C. The Cu-Ni film thickness for CVD is varied from 2 nm to 80 nm. Carbon layers obtained after each CVD growth run of 12 min are characterized by scanning electron microscopy (SEM). The most likely temperature for carbon nanotube (CNT) growth seems to be 725 0C. Growth of fibers and rods is found to occur on CuNi films deposited on oxide coated silicon substrates and not on silicon substrates. The Cu-Ni film on oxide should not be more than 15 nm thick for argon anneal to produce CNTs upto 150 nm in diameter. Cu-Ni catalytic films of thicknesses 6 nm, 12 nm and 24 nm on patterned oxidized substrates are annealed in Ar and Ar-H2 flows for 15 and 30 min at 760 Torr. Smallest size catalyst particles are observed on oxide coated substrates. CVD growth is carried out on the 6 nm and 12 nm catalytic Cu-Ni films for 12 min on oxide coated substrates at 725 0C in Ar-H2 atmosphere. In the first case, 50 nm diameter carbon fibers are produced while 160 nm diameter carbon fibers are observed for the 12 nm thick Cu-Ni film. Transmission electron microscopy (TEM) analysis on the carbon fibers revealed multi-walled structures, 50 nm and 130 nm in diameters indicating the growth of CNTs comparable to the average size of the catalyst particles after annealing. Resistivity measurements on the carbon layers on 6 nm and 12 nm Cu-Ni films show sheet resistivity values of 293 §Ù/square and 85 §Ù/square respectively