  We demonstrate highly-tunable formation of nitrogen-vacancy (NV) centers
using 20 keV 15N+ ion implantation through arrays of high-resolution apertures
fabricated with electron beam lithography. By varying the aperture diameters
from 80 to 240 nm, as well as the average ion fluences from 5 x 10^10 to 2 x
10^11 ions/cm^2, we can control the number of ions per aperture. We analyze the
photoluminescence on multiple sites with different implantation parameters and
obtain ion-to-NV conversion yields of 6 to 7%, consistent across all ion
fluences. The implanted NV centers have spin dephasing times T2* ~ 3
microseconds, comparable to naturally occurring NV centers in high purity
diamond with natural abundance 13C. With this technique, we can
deterministically control the population distribution of NV centers in each
aperture, allowing for the study of single or coupled NV centers and their
integration into photonic structures.
