Pretreatment process for forming a smooth surface diamond film on a carbon-coated substrate

DETAILED DESCRIPTION OF THE INVENTION The invention comprises a pretreatment process for carbon-coated substrates which provides a uniform and high density of nucleation sites thereon for the subsequent growth of a continuous diamond film thereon, wherein a carbon-coated substrate is exposed, in a microwave plasma enhanced chemical vapor deposition system, to a mixture of hydrogen and methane gases, having a higher concentration of methane gas than normally used in the deposition or growth of a diamond film on the substrate, while maintaining the substrate at a lower pressure than normally used in the deposition of a diamond film on the substrate.
The carbon-coated substrate used for the pretreatment, and for the subsequent deposition of the continuous diamond film on the pretreated surface, may comprise any solid surface capable of being coated with a carbon-containing coating.
The substrate may be an insulator, a semiconductor, or a conductive material.
For example, fused silica, silicon, and copper have all been successfully used as substrates in the pretreatment process.
The carbon-containing coating which is applied to the surface of the substrate prior to the pretreatment may comprise any one of a number of carbon-containing coating materials.
For example, fullerene coatings respectively comprising a 9:1 wt.
% mixture of C.
sub.
60 and C.
sub.
70, and a pure C.
sub.
70 coating have been successfully used; as have coatings made from amorphous carbon and colloidal graphite having a particle size of approximately 8 nanometers.
The carbon-containing coating may be applied to the substrate by first dispersing (or optionally dissolving in the case of fullerenes) the carbonaceous material in a liquid which serves as a vehicle for application of the carbon coating to the substrate.
For convenience, the liquid may be any easily evaporatable liquid.
However, the liquid must be compatible with the underlying substrate, i.
e.
, be chemically nonreactive with the underlying substrate material(s).
The carbon-coating may also be applied, in some cases such as the fullerenes, by evaporation of the coating material in powder form, and subsequent deposition of the condensed coating material from the vapor state on the substrate