the presence of nitrogen in the reactive gas mixture is that it keeps the walls of the reaction chamber clean during the diamond growth run normally some deposits form on the walls of the quartz tube chamber during a long run and must be cleaned after a number of runs or the tube becomes opaque contemplated equivalents to utilizing nitrogen are methods wherein a portion or all of the nitrogen is replaced by a functionally equivalent gas for example ammonia or hydrogen cyanide the reactive gas mixture may optionally be diluted with an inert gas such as argon neon xenon and or helium pressures for the reactive gas mixture generally range from about 0 01 1000 torr advantageously about 1 760 torr and preferably about 10 torr details on conventional process conditions suitable for use can also be found in angus et al 34 low pressure metastable growth of diamond and diamondlike phases 34 science 241 913 921 aug 19 1988 u s pat no 4 707 384 provides further details concerning cvd conditions and techniques the reactive gas mixture of hydrogen nitrogen and hydrocarbon most often methane is preferably 34 energized 34 or excited utilizing conventional techniques preferably by passing the reactive gas over a hot filament at a conventional temperature preferably in the range of 1700 u00b0 2400 u00b0 c once energized the excited reactive gas mixture is contacted with the surface of the substrate to be coated with diamond film the substrate is desirably heated to a conventional temperature the substrate temperature utilized for diamond growth typically ranges from 500 u00b0 1100 u00b0 c and preferably is in the range of 850 u00b0 950 u00b0 c it is often desirable to maintain the substrate at temperatures in the range of about.