title: Ink-on-probe hydrodynamics in atomic force microscope deposition of liquid inks.
abstract: The controlled deposition of attolitre volumes of liquids may engender novel applications such as soft, nano-tailored cell-material interfaces, multi-plexed nano-arrays for high throughput screening of biomolecular interactions, and localized delivery of reagents to reactions confined at the nano-scale. Although the deposition of small organic molecules from an AFM tip, known as dip-pen nanolithography (DPN), is being continually refined, AFM deposition of liquid inks is not well understood, and is often fraught with inconsistent deposition rates. In this work, the variation in feature-size over long term printing experiments for four model inks of varying viscosity is examined. A hierarchy of recurring phenomena is uncovered and there are attributed to ink movement and reorganisation along the cantilever itself. Simple analytical approaches to model these effects, as well as a method to gauge the degree of ink loading using the cantilever resonance frequency, are described. In light of the conclusions, the various parameters which need to be controlled in order to achieve uniform printing are dicussed. This work has implications for the nanopatterning of viscous liquids and hydrogels, encompassing ink development, the design of probes and printing protocols.
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, Innovation Campus, University of Wollongong, NSW, 2522, Australia.
authors.forename: Cathal D
authors.initials: CD
authors.lastname: O'Connell
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Higgins
authors.forename: Ryan P
authors.initials: RP
authors.lastname: Sullivan
authors.forename: Simon E
authors.initials: SE
authors.lastname: Moulton
authors.forename: Gordon G
authors.initials: GG
authors.lastname: Wallace
keywords: AFM lithography; dip-pen nanolithography; hydrodynamics; liquid nano-dispensing; nanofluidics