| In this study, we investigated several novel methods to synthesize carbon nanotubes and nanowires of various compositions with controlled properties, utilized electron microscopy and microanalysis techniques to study their growth mechanisms and effects of growth parameters on their internal structures and morphologies, and set up a field emission microscope and a field emission probe system to study field emission properties of single nanotube/nanowires and thin films of nanostructures.; The introduction of H2 during catalyst activation and nanotube growth periods thermodynamically and kinetically facilitates the formation of high quality nanotubes. With the inclusion of H2, the nanotube diameter decreased from 300 nm to 15 nm and growth rate increased from 78 nm/s to 145 nm/s.; The growth location and orientation of carbon nanotubes to substrates can be controlled by the position and density of catalysts, respectively. Focused Ion Beam (FIB) techniques were utilized to confine catalyst locations and to directly deposit patterned catalyst precursors.; Nanotube internal structures including graphitization and number of graphite layers can be tailored using different hydrocarbon gases (CH4 or C2H2) as carbon sources or by varying catalyst elements (Fe, Ni, or Co).; Besides effects of nanoscale radius and high aspect ratio, the internal structures of carbon nanotubes greatly affects their field mission properties including turn-on field, threshold field and enhancement factor. Carbon nanotubes from Fe or Co demonstrate better field emission properties than those from Ni. At high electric fields, nanotube emission deviates from the Fowler-Nordheim (F-N) theory due to space charge and field emission-induced temperature effects. Also, an abnormal noise power spectral density (PSD) peak was observed at the space charge regime and PSD decreases with the increase of emission current due to Joule self-heating.; In order to investigate field emission properties of nanostructures with different work functions and explore new emitter candidates, nanowires with various compositions (CdS, ZnO, SiOx, WOx, and WS 2), diameters, morphologies and crystal structures were synthesized on tungsten substrates. In comparison to carbon nanotubes, these nanowires exhibit higher turn-on fields and threshold fields, but demonstrate similar noise power spectral of a 1/f3/2 characteristic from 1 Hz to 6 KHz. |
