Nanomaterial synthesis and nanodevice fabrication by laser chemical processing

The main objective of this dissertation is to explore the possibility and extend the capability of laser-technology into nanoscale material processing. The research focused on three novel laser chemical processing techniques for nanomaterials processing, including (1) near-field-induced spatially-confined photochemical deposition of diamond-like carbon (DLC) films on nanostructures; (2) pulsed-laser disintegration of inorganic compounds as nanocatalysts for large-area carbon nanotube (CNT) growth; and (3) laser-assisted chemical vapor deposition (LCVD) growth of CNTs and direct fabrication of CNT field-effect transistors. In the study of near-field induced photochemical deposition of DLC films on nanostructures, DLC was deposited on tungsten nanotips as well as Mo nanowedges using benzene as the precursor. Theoretical as well as experimental results confirmed the prediction of spatially confined and phase graded deposition of DLC film on sharp edges due to local intensity gradient of optical near field. We also developed a method to produce nanocatalysts by irradiating dispersed NiSO4 microclusters on silicon substrates using a KrF excimer laser. Under appropriate laser fluences and multiple laser pulses, the disintegrated NiSO4 nanocatalysts were used for large-area uniform multi-walled carbon nanotube (MWNT) growth. In the study of LCVD synthesis of CNTs, we have developed controlled synthesis of vertically-aligned CNFs, large-area high-quality MWNTs, and defect-free single-walled nanotubes (SWNTs) with different catalysts, carbon feedstock, and laser parameters. The synthesis could be achieved by both far-infrared CO2 laser (10.6 μm) and near-infrared Nd:YAG laser (1064 nm) in a localized manner. The LCVD technique was also applied for direct fabrication of field-effect devices. Due to the unique advantages of the LCVD process, such as fast and local heating, as well as its potential to select chiralities during the growth, it may provide new features and versatilities in device fabrications