Proton-Fountain Electric-Field-Assisted Nanolithography (PEN): Fabrication of Polymer Nanostructures that Respond to Chemical and Electrical Stimuli. An Overview in the Context of the Top-Down and Bottom-Up Approaches to Nanotechnology
Nanolithography -- Methodology, Nanostructures, Biomimetics
The development of chemically functionalized materials, such that their physical properties can vary in response to external mechanical, chemical, or optical stimuli, offers potential applications in a wide range of fields, namely microfluidics, electronic memory devices, sensors and actuators. In particular, patterned structures built with stimuli-responsive polymer materials are attractive due to their inherent lower cost production and for building soft scaffolds that mimic closer natural bio-environments. In addition, harnessing the construction of patterns with nanoscale dimensions would not only a) allow building lab-on-a-chip devices that require minimal chemical reactants volumes, but also b) find applications in the area of nano-electronics for fabricating flexible, low-cost, and low-voltage-operation integrated logic circuits devices. To address these potential applications of stimuli-responsive polymer nanomaterials in the bio and nano-electronics arena, this article provides first a brief review of radiation and non-radiation based lithography methods used for fabricating nanopatterns. This introduction helps to put in context a more general description of the Proton-fountain Electricfield- assisted Nanolithography (PEN) technique, a recently introduced scanning-based method able to fabricate patterns of nanoscale dimensions using responsive polymer films. We also outline potential avenues for the outgrowth of PEN by replacing its current top-down fabrication approach with a bottom-up modality. The proposed outgrowth is to improve the fabrication speed and the lateral dimensions of the patterns. More specifically, we address the fact that, since PEN capitalizes on the reversible swelling-response of poly(4-vinylpyridine) (P4VP) films upon spatially-localized injection of protons (hydronium ions H3O+), the diffusion of the positive charges inside the polymer film matrix limits the patterns lateral resolution. This shortcoming can be remediated by the integration of ultra-fast optical activation into the PEN technique in order to gain much finer control over the functionalized sample area where the polymer molecules are selectively attached to the substrate, which would allow implementing a diffusion free, nanometer resolution, self-assembly method for fabricating erasable polymer nanostructures.
A. La Rosa, M. Yan, R. Fernandez, X. Wang, and E. Zegarra, "An overview of Proton-fountain Electric-field-assisted Nanolithography (PEN) in the context of top-down and bottom-up approaches to nanotechnology," REVCIUNI 15, 87-129 (2012)