The chemistry of halogens on diamond: effects on growth and electron emission

Abstract

Portions of this ABSTRACTThe feasibility of diamond growth using halogenated precursors was studied in several diamond growth reactors. In a conventional microwave plasma reactor, diamond growth using the following gas mixtures was studied: CF4/H,, CH4/H,, CH,F/H,, and CH,Cl/H,. Both' the diamond growth measurements (film growth rate, film quality, etc.) and in-situ near-surface gas composition measurements demonstrated ineffective transport of halogen radicals to the diamond surface during the growth process. In order to transport radical halogen species to the diamond surface during growth, a flow-tube reactor was constructed which minimized gas phase reactions. In addition, the flow-tube reactor enabled pulsed gas transport to the diamond surface by fast-acting valves. Molecular beam mass spectroscopy was used to find conditions which resulted in atomic hydrogen and/or atomic fluorine transport to the growing diamond surface. Although such conditions were found, they required very low pressures (.5 Torr and below); these low pressures produce radical fluxes which are too low to sustain a reasonable diamond growth rate. Due to the limitations of both the conventional plasma reactor and the flow-tube reactor, the sequential reactor at Stanford University was modified to add a halogen-growth step to the conventional atomic hydrogerdatomic carbon diamond growth cycle. Since the atomic fluorine, atomic hydrogen, and atomic carbon environments are independent in the sequential reactor, the effect of fluorine on diamond growth could be studied independently of gas phase reactions. Although the diamond growth rate was increased by the use of fluorine (compared to growth without fluorine under similar conditions), the film quality was seen to deteriorate as well as the substrate surface. Moreover, materials incompatibilities with fluorine significantly limited the use of fluorine in this reactor.A diamond growth model incorporating both gas phase and surface reactions was developed for the halocarbon system concurrent with the film growth efforts. In this experiments done to understand fluorine interaction with diamond surfaces. In addition, fluorine modification of diamond surfaces after growth is used to prepare cesiated-diamond cathodes which have field emission characteristics that are both air stable and thermally stable (200°C).