Silicon nitride nanosieve membrane

An array of very uniform cylindrical nanopores with a pore diameter as small as 25 nm has been fabricated in an ultrathin micromachined silicon nitride membrane using focused ion beam (FIB) etching. The pore size of this nanosieve membrane was further reduced to below 10 nm by coating it with another silicon nitride layer. This nanosieve membrane possesses adequate mechanical strength up to several bars of transmembrane pressure, and it can withstand high temperatures up to 900 degreesC. In addition, it is inert to many aggressive chemicals such as hot concentrated potassium hydroxide (KOH), piranha (H2SO4 + H2O2), and nitric acid (HNO3).