The catalytic effect of nitrogen during the homoepitaxial diamond growth on a diamond anvil was investigated using isotopically enriched carbon-13 methane in a feed-gas mixture in a microwave plasma chemical vapor deposition reactor. The use of isotopically enriched carbon-13 allows us to precisely measure the film thickness in this homoepitaxial growth process by Raman spectroscopy. It is found that the addition of 0.4 sccm of nitrogen to an H2/CH4/O2 gas-phase mixture increases the growth rate by a factor of 2.3. This enhanced growth rate with the addition of trace amounts of nitrogen allows for a quick encapsulation of embedded sensors in the designer diamond anvils and is a key control parameter in the fabrication process. Photoluminescence spectroscopy reveals nitrogen-vacancy defect centers in the high-growth-rate diamonds. Atomic force microscopy reveals dramatic changes in the surface microstructure as is indicated by a total loss of step-flow growth morphology on the addition of nitrogen in the plasma. © 2007 Materials Research Society.