Direct-Write Molecular Layer Epitaxy by Thermal Dip-Pen Nanolithography

Achieving nanometer-scale control of structure in organic thin films is crucial to understand charge transport and thereby develop reliable devices such as organic FETs and LEDs. Although a variety of methods can be used to reliably deposit thin polymer films, fabrication of polymer nanostructures remains a significant challenge. We have developed a new technique, thermal dip-pen nanolithography (tDPN),$^{1}$ that can be used to directly write such nanostructures. In tDPN a custom AFM cantilever with an integral tip heater is pre-coated with a solid ``ink,'' which can then be precisely deposited onto a substrate by heating the tip above the ink’s melting temperature. Using this technique, poly(3-dodecylthiophene) nanostructures have been deposited on silicon oxide surfaces with layer-by-layer thickness control. By adjusting the tip heating power and the writing speed, we can vary the polymer thickness from a single monolayer (about 2.8 nm) to tens of monolayers with lateral dimensions $<200$ nm. \\ $^{1}$P. A. Sheehan, {\em et al.}, Appl. Phys. Lett. {\bf 85}, 1589 (2004).