The present invention relates to a method for growing diamond on a diamond substrate by chemical vapor deposition. The inventive method comprises alternatingly contacting at elevated temperature said diamond substrate with a gas having the formula C.sub.n X.sub.m and then with a gas having the formula C.sub.l Z.sub.p. X and Z each form single bonds with carbon. X and Z also are reactable to form ZX or a derivative thereof. The Z--X bond is stronger than the C--X bond and also is stronger than the C--Z bond. In the formulas, n, m, l, and p are integers. If C.sub.n X.sub.m and C.sub.l Z.sub.p do not react in the gas phase, then a gas mixture of them can be used to grow diamond instead of the alternating exposure of one and then the other.