Isotopically pure 13C homoepitaxial diamond layer was grown on top of a brilliant cut diamond anvil using a microwave plasma chemical vapor deposition process for application as a stress sensor. To generate high pressure on a soft sample containing carbon nanotubes to 100 GPa, the isotopically pure diamond tip was used in conjunction with a natural abundance 12C diamond anvil. It was observed that the 13C diamond Raman signal remained a distinct single peak showing that the mean normal stress experienced by the thin layer is uniform to the highest pressure. A ruby pressure sensor was used to relate the stress-induced shift of the 13C layer to the quasihydrostatic pressure in the sample chamber.
