Effects of electrons on the shape of nanopores prepared by focused electron beam inducedetching

Abstract

The fabrication of nanometric pores with controlled size is important for applicationssuch as single molecule detection. We have recently suggested the use of focusedelectron beam induced etching (FEBIE) for the preparation of such nanopores insilicon nitride membranes. The use of a scanning probe microscope as the electronbeam source makes this technique comparably accessible, opening the way towidespread fabrication of nanopores. Since the shape of the nanopores is criticallyimportant for their performance, in this work we focus on its analysis and study thedependence of the nanopore shape on the electron beam acceleration voltage. We showthat the nanopore adopts a funnel-like shape, with a central pore penetratingthe entire membrane, surrounded by an extended shallow-etched region at thetop of the membrane. While the internal nanopore size was found to dependon the electron acceleration voltage, the nanopore edges extended beyond theprimary electron beam spot size due to long-range effects, such as radiolysis anddiffusion. Moreover, the size of the peripheral-etched region was found to be lessdependent on the acceleration voltage. We also found that chemical etching is therate-limiting step of the process and is only slightly dependent on the accelerationvoltage. Furthermore, due to the chemical etch process the chemical compositionof the nanopore rims was found to maintain the bulk membrane composition.