Improvement of a focused ion beam fabricated diamond pillar for scanning ensemble nitrogen-vacancy magnetometry probe using an ultrapure diamond

Scanning diamond nitrogen-vacancy probe microscopy (SNVM) is an important tool for studying nanoscale condensed-matter phenomena. Ga$^+$-ion-focused-ion-beam (FIB) milling has been introduced as an available method for fabricating SNVM, while the probe diameter is limited to a few micrometers due to the Ga$^+$-induced damage. We report a method for improving the SNVM probes' quality, with an 800-nm diameter probe of ultrapure diamond, through polyvinyl alcohol and Pt/Pd capping, followed by UV/ozone exposure. The effectiveness of the method is confirmed by NVs' spin-coherence property measurements and magnetic domain structure imaging with a few-hundred-nanometer resolution and a 6.7 $μ$T/Hz$^{1/2}$ sensitivity.