In thermal Dip Pen Nanolithography (tDPN) a heated atomic force microscope cantilever regulates the deposition of an ink through controlled melting, acting like a nanoscale soldering iron. Control over writing is exceptional-deposition may be turned on or off and the deposition rate easily changed without breaking surface contact. In addition, imaging with a cool tip does not contaminate the surface, thereby allowing in situ confirmation of the deposited pattern. tDPN has been successful at depositing materials ranging from semiconductors to insulators to metals.
Thermal DPN is particularly suited to the deposition of polymers. Many different polymers (e.g., mylar, poly(3-dodecylthiophene) [PDDT], polyvinylidene fluoride [PVDF], etc.) have all been successfully deposited, leading to our belief that tDPN is a generic tool for polymer deposition. Importantly, nanopatterning via tDPN provides outstanding control over the purity, dimensions, and structure of the deposited polymer. For instance, well-ordered PDDT nanostructures have been deposited on silicon oxide and gold surfaces with layer-by-layer thickness control 1. By adjusting the tip heating power and the writing speed, we can vary the polymer thickness from a single monolayer (~2.6 nm) to tens of monolayers with lateral dimensions below 70 nm. Moreover, the shearing of the polymer between the tip and substrate appears to align the polymer strands along the path of the AFM tip. A significant benefit of this technique is that the low vapor pressure of solvent-free polymers enables deposition in ultra high vacuum (UHV). We have deposited in UHV single monolayers of highly-ordered PDDT nanostructures on clean Si(001)-(2x1). Deposition in UHV is allowing the full range of surface characterization tools to be brought to bear on this important class of materials. Finally, we will present modeling which allows the rheological behavior of the deposited polymer to be interrogated on the nanometer length scale.
1. M. Yang, P. E. Sheehan, W. P. King, and L. J. Whitman, J. Amer. Chem. Soc. 128, 6774 (2006).
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