What gasses are used for CVD Diamonds?
Mostly a mixture of hydrogen and methane gasses are used for the making of CVD Diamonds.
For CVD Diamonds around 700-900° C. Also lower temperatures are possible but at strongly reduced growth rates.
Actually, it is a very slow process. At growth rates between 0.1 and 10 microns per hour usually deposited on large areas (>100 cm2) diamond where much higher growth rates (>100 microns per hour) have been demonstrated for small areas (<1 cm2).