Fabrication and characterization of nanopore array.
A nanopore array with diameter of approximately 30 nm was fabricated by use of focused ion beam (FIB) scanning and thin film coating on Si(100). A thin film of SiO2 with thickness of 200 nm (used as sacrificial layer) was coated by physical evaporation deposition (PVD) first. Next, the thin films of Aluminum with thickness of 500 nm were coated on the surface of SiO2 thin film. A window with an area of 2 x 2 mm2 was opened by reactive ion etching from bottom side and reached to the thin film of SiO2. After that, a fine controlled FIB milling with bitmap function (milling according to a designed pattern in a defined area) was used to scan the area. Signal is obtained by a sensor inside the vacuum chamber collecting secondary electrons emitted from the sputtered material when the beam reach the layer of SiO2. Stopping the milling process at this moment, the nanopore array was derived after removing the sacrificial layer by wet chemical etching. The nanopore arrays were characterized using transmission electron microscopy (TEM) after the FIB drilling.