Laser-assisted diamond deposition in open atmosphere.

摘要

Diamond, with the unique combinational properties of extreme hardness, high thermal conductivity and electrical resistivity, low coefficient of friction, and high degrees of chemical inertness, etc., can be used as surface coatings for optimizing substrate performance. In spite of the extensive study of diamond synthesis in the past decades, an efficient process for depositing diamond coatings in open atmosphere is still lacking. In this dissertation, efforts are extended to explore the capability of a laser-assisted open-atmospheric diamond deposition technique for controlled deposition of diamond in open atmosphere. Fundamental understandings of the process mechanisms and their implications are addressed. The research project mainly focused on using lasers to assist diamond deposition with a combustion flame in open atmosphere, including: (1) laser surface processing of substrates before diamond deposition; (2) laser processing of as-grown diamond films during deposition for improving quality; (3) laser processing of diamond films after the deposition process for improving film adherence; and (4) in-situ laser resonant excitation of precursor molecules and reactive radicals for promoting diamond nucleation and growth. Laser-assisted deposition of diamond-like carbon (DLC) thin films from liquid precursors was also studied. A method for real-time monitoring of diamond nucleation and growth was developed.;Diamond thin films have been deposited on cemented tungsten carbide (WC-Co) and copper (Cu) substrates with the laser-assisted combustion-flame technique in open atmosphere. A krypton fluoride (KrF) excimer laser, a carbon dioxide (CO2) laser, and a tunable optical parameter oscillator (OPO) laser were used in the process. Observations from experimental results confirmed that under certain conditions laser irradiation could promote diamond nucleation and growth, and enhance coating adherence.;Optical emission spectra of the flames were studied to obtain information on the reactive species involved in diamond formation. The coating properties were related to the flame properties and substrate surface conditions to understand the diamond formation process. A balance among the concentrations of C 2, CH, and OH radicals is believed to account for diamond deposition using a combustion flame, in the presence or absence of the laser irradiation.