A New Method of AFM‐Based Nanolithography Using Frequency Enhanced Electrochemical Pressure Solution Etching

A new method of direct‐write nanolithography that is able to rapidly etch silica surfaces under a scanning atomic force microscopy (AFM) probe in tapping mode (TM) is reported. In this lithography technique, silica surfaces are etched using a recently described electro‐chemo‐mechanical phenomenon of frequency enhanced electrochemical pressure solution (FEEPS). In FEEPS, the tapping of the AFM tip generates oscillations of the Stern potential at the silica‐water interface that can accelerate the silica dissolution kinetics by more than 5–6 orders of magnitude when surface resonance states are achieved; i.e., when the oscillation frequency is in phase with the dynamics of interfacial chemical reaction steps. By scanning silica surfaces in TM, silica is selectively dissolved below the tapping tip as it is scanned. The FEEPS accelerated silica dissolution rates can generate etched features with depths of more than 60 nm in a single AFM tip pass. The rate of etching can be controlled easily by varying the scanning rate or by modulating the tapping frequency. This fine control over the silica etching process and because material is removed (dissolved) rather than displaced as with nanoscratching, the FEEPS process lends itself to gray‐scale nanolithography which is demonstrated. This work details a new method of atomic force microscopy (AFM)‐based lithography which utilizes a new chemical phenomenon of “frequency enhanced electrochemical pressure solution” (a.k.a. “FEEPS”) that greatly enhances the rate of silica dissolution under an oscillating AFM tip undergoing tapping in pure water. FEEPS greatly reduces tip wear and eliminates unwanted features like hillocks common to other AFM lithography techniques like nanoscratching.