Diamond film deposition using laser-assisted combustion flames.

摘要

Due to the wide range of the superior properties, diamonds are of great interest in industry applications and scientific research. The inherent shortcomings of conventional chemical vapor deposition methods and the ever-increasing demand for diamonds urge extended efforts for further enhancement of diamond deposition without compromising the diamond quality. Conventional chemical vapor deposition processes, which rely on thermal heating, are inefficient energy coupling routes to drive gas reactions. As an intensive, coherent and monochromatic light, laser is an ideal candidate for exploring alternative energy coupling pathways. To address these challenges, the research efforts in this dissertation mainly focused on laser incorporation in combustion chemical vapor deposition of diamond films, which led to: 1) promotion of energy coupling efficiency; 2) enhancement of diamond deposition; 3) control of the crystallographic orientation; and 4) identification of active species roles in combustion chemical vapor deposition of diamond films.;Pure diamond and nitrogen-doped diamond films were deposited using combustion flames assisted by infrared-laser vibrational excitations of ethylene and ammonia molecules, respectively. Vibrational excitations of precursor molecules were realized using a kilowatt wavelength-tunable CO 2 laser with a spectrum range from 9.2 to 10.9 mum. On-resonance excitation of the CH2-wagging mode of ethylene molecules was demonstrated to be more efficient than off-resonance excitations in promoting the deposition rate and improving the diamond quality attributed to a higher energy coupling efficiency. Ro-vibrational excitations of ethylene molecules enabled crystallographic control in {100}-textured diamond film deposition. Micro-crystalline nitrogen-doped diamond films with a high doping concentration were deposited using an ammonia-added oxyacetylene flame assisted by infrared-laser vibrational excitations of the NH-wagging mode of ammonia molecules.;Another form of laser incorporation, a femtosecond laser induced gas breakdown, was introduced into the combustion chemical vapor deposition of diamonds as well. The diamond deposition rate was increased by a factor of 1.13 with a femtosecond laser induced gas breakdown occurred at the inner flame tip.;Optical emission spectroscopy and mass spectrometry were performed to achieve an in-depth understanding of laser effects on diamond deposition and to identify active species roles in diamond formation.