Direct Writing on Phosphate Glass Using Atomic Force Microscopy for Rapid Fabrication of Nanostructures

Abstract

Rapid and cost effective fabrication of nanostructures is critical for experimental exploration and translation of results for commercial development. While conventional techniques such as E-beam or Focused Ion beam lithography serve some prototyping needs for nano-scale experimentations, cost and rate considerations prohibit use for manufacturing. Specialized lithographic processes [e.g. nanosphere lithography or interference lithography] are also powerful tools in creating nanostructures but provide limited shapes, positioning and size control of nanostructures. In this work, we demonstrated a liquid-free and mask-less electrochemical writing approach using atomic force microscopy (AFM) that is capable of making arbitrary shapes of silver nanostructures in seconds on a solid state super-ionic (AgI)x (AgPO3)(1−x) glass. Under ambient conditions. silver is extracted selectively on super-ionic (AgI)x (AgPO3)(1−x) glass surface by negatively biasing an AFM probe relative to an Ag film counter electrode. Both voltage controlled and current controlled writings demonstrated localized extraction of silver. The current controlled approach is shown to be the preferred writing approach to make repeatable and uniform patterns of silver on (AgI)x AgPO3(1−x), where x represents the mole fraction of AgI in the mixture and the control parameter that tunes the conductivity of the sample. We demonstrated current controlled printing of silver on two different compositions of the material (i.e. (AgI)0.125 (AgPO3 )0.875 and (AgI)0.25(AgPO3)0.75 ). Depending on the magnitude of the constant current and tip speed, line-width of the silver pattern can be ∼150 nm. The length of these patterns are limited to the maximum distance the tip can be moved using the AFM position controls. The substrate being optically transparent allows the use of this writing technique for rapid prototyping plasmonic devices. By using the patterned substrate as a template for replica molding of soft materials such as polydimethylsiloxane (PDMS), this writing technique can also be utilized for high throughput nano-channel fabrication in biofluidics and microfluidics devices.