Provided is a process for the rapid deposition of highly conformal molybdenum- or tungsten-containing films onto microelectronic device substrates under vapor deposition conditions. In the practice of the invention, a first nucleation step is conducted, while utilizing a generally lower concentration of metal precursor than would ordinarily be utilized in the reaction zone. This utilization of lower metal precursor concentrations can be achieved by way of regulating the temperature of the ampoule (housing the precursor), the concentration of the precursor, pressure in the reaction zone, and the duration of the pulse. In this fashion, a generally lower concentration is utilized to form a nucleation layer of greater than or equal to about 3 Å, or up to about 9, 15, or 25 Å, at which time, the conditions for introducing the precursor are advantageously changed and the concentration of the precursor in the reaction zone is increased for the purpose of bulk deposition.