Paper NS-FrM3
Nanopatterning of Functional Polymers by Thermal Dip-Pen Nanolithography

Friday, October 19, 2007, 8:40 am, Room 616

Thermal dip-pen nanolithography (tDPN) uses a heated atomic force microscope (AFM) cantilever to deposit material that is solid at room temperature. The cantilever melts the solid ink on the tip, allowing precise control over its deposition onto the surface.¹ This method for nanolithography has proven particularly effective for depositing polymers.² Both the polymer thickness and lateral dimensions can be controlled to nanometer tolerances by controlling the tip heating power and the writing speed. Using tDPN, controlled layer-by-layer deposition of polymer has been achieved as well as molecular alignment along the writing direction of the cantilever. Many different functional polymers have been successfully deposited on silicon oxide substrates, including those that are temperature responsive, semiconducting, piezoelectric, and light-emitting, demonstrating that tDPN is a flexible nanolithography tool for polymer deposition and patterning. We will present our characterizations of the deposited polymers and report how tDPN can be used to optimize their properties. For example, poly(N-isopropylacrylamide) [pNIPAAM] nanostructures written by tDPN undergo a hydrophilic-to-hydrophobic phase transition induced by temperature that allows the structures to controllably capture and release proteins. We use carboxylic acid functionalized pNIPAAM as a tDPN "ink" that can be grafted onto an epoxy-terminated SAM substrate. We observe the temperature-dependent phase transition by monitoring the adhesion forces of the pNIPAAM with AFM. Finally, we will describe functional polymer patterns created by tDPN in ultra-high vacuum.

¹ Sheehan, et al., Appl. Phys. Lett. 85, 1589 (2004).
² Yang, et al., J. Amer. Chem. Soc. 128, 6774 (2006).