Synthesis, doping and characterization of chemical vapor deposited polycrystalline diamond and nanostructured carbon thin films for electronic applications

The hot-filament chemical vapor deposition (HFCVD) technique was used to deposit microcrystalline diamond (p-D) and nanocrystalline carbon (n-C) thin films using methane (CH₄) and hydrogen (H₂) gas feedstocks on molybdenum substrates. These films were deposited under a variety of growth conditions including sulfur addition in order to narrow down and optimize the process window and synthesize specific microstructures for their practical utility, such as cold cathodes for flat panel displays. Since the physical properties of diamond show significant variations as a function of process variables, standard characterization tools such as scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) were utilized to obtain a coherent and comprehensive picture of these films and help establishing property-structure correlation. The entire research work consists of primarily four sets of experiments.; First, nanocrystalline carbon (n-C) thin films were deposited varying process parameters relevant to the secondary nucleation rate (methane concentrations, deposition temperatures, and continuous forward and reverse bias during growth) in order to control key material properties: surface morphology (faceted versus evenly smooth), grain size (microcrystalline versus nanocrystalline), surface roughness (from rough 150 rms to smooth 70 rms), and bonding configuration (sp3 C versus sp2 C).; Second, the electron field emission (EFE) properties (turn-on fields and emitted currents) of n-C films grown under various substrate biasing condition were studied. Films grown under electron bombardment showed lower turn-on fields, smoother surfaces and smaller grains than those grown under ion-bombardment or no bias.; The third set of experiment consists of two parts. In the first part, the influence of sulfur addition on growth behavior of the carbon-based films is investigated. These experiments demonstrate the anomalies in the growth rate and catalytic effect of sulfur addition, pointing at the unknown chemical reactions taking place either at the growing surface or in the gas phase. The second part of these experiments report the field emission properties of sulfur-incorporated nanocrystalline carbon (n-C:S) films. The lowest turn-on field achieved was observed at around ∼4.0 V/μm for the sample grown at T_S ≈ 900°C with 500 ppm of H₂S.; In the last set of experiments, the electron field emission measurements revealed that the sulfur-assisted microcrystalline diamond thin films have substantially lower turn-on fields and steep rising currents as compared to conventional diamond films. (Abstract shortened by UMI.)...