Fig. 2. The fabrication process to realize self-aligned patterning and based sensor arrays.

(A) Schematic of fabrication steps. (I) Spin-coating PMGI ~270-nm (yellow) and PMMA ~210-nm (pink) double layers on diamond and making holes array in the PMMA layer by electron beam lithography. (II) Isotropic wet etching of PMGI layer with 2.38% tetramethylammonium hydroxide (TMAH). (III) Doping nitrogen into diamond by ion implantation through hole array in PMMA layer. (IV) Removing the PMMA layer with acetone. (V) Coating titanium of ~100 nm (blue) by electron beam evaporation (VI) liftoff processing in N-methyl pyrrolidone. (VII) Forming conical cylinder by CHF₃ + O₂ reactive ion etching (CHF₃:O₂, 5:30 standard cubic centimeters per minute). (VIII) Removing the Ti layer with a buffered oxide etch. (IX) Converting nitrogen to NV center by annealing at 1000°C. (B) Verification of ion implanted region in (III) by metal deposition and scanning electron microscopy (SEM) characterization (scale bar, 100 nm). The metal position in the center of the image represents the ion implantation region (see the Supplementary Materials for details). (C) SEM imaging contrast shows that the radius of ion implantation region is ~15 nm. (D) SEM image of a metal Ti mask in VI (scale bar, 200 nm). (E) SEM image of a conical cylinder by CHF₃ + O₂ reactive ion etching in VII (scale bar, 200 nm). (F) SEM image of an array of conical cylinders (scale bar, 2 μm).