Sequential images of fabrication of nanostencil mask. (a) Low-stress silicon nitride film (50-nm thick) was deposited and patterned onto both sides of a 4-in. silicon wafer. (b) Silicon nitride membranes were released using KOH to anisotropically etch silicon. (c, d) Microscale and nanoscale FIB milling were performed on the membranes to form reference marks and apertures. Scale bars shown in (b), (c), and (d) are 100, 30, and 3 μm, respectively.