|The Nanoscale Deposition and Organization of Polymers using Heatable AFM Cantilevers |
Laboratory for Surface Modification
|Paul E. Sheehan|
Naval Research Laboratory
12:00 Noon Rm 260 Wright-Rieman Chemistry
In thermal Dip Pen Nanolithography (tDPN), a heatable AFM cantilever regulates the deposition of an ink through controlled melting, much 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. Moreover, the technique may be performed in UHV and is compatible with standard CMOS processing. tDPN has been successful at depositing materials ranging from semiconductors to insulators to metals at speeds up to 200 µm/s.
A critical aspect of creating nanostructures by tDPN is that the deposited material can be highly ordered. For instance, during deposition a polymer ink is simultaneously sheared between the tip and the substrate while being annealed by the hot tip. This leads to polymer strands that are aligned along the deposition path and whose thicknesses may be precisely controlled. This precise ordering reveals properties that are otherwise unobtainable. For the conducting polymer poly(3-dodecylthiophene) [PDDT], the polymer nanostructures may be deposited monolayer-by-monolayer and show a pronounced increase in conductivity when exposed to an electron beam—an effect not observed in spin-coated material. A second example is the temperature-responsive polymer poly(N-isopropylacrylamide) [pNIPAAM] that undergoes a phase change from hydrophilic to hydrophobic when heated above 32 °C. To date, pNIPAAM nanostructures always collapsed during this transition. By stretching the polymer, we could decouple the change in hydrophilicity from the structural change.
We will discuss the wide range of materials that may be deposited via tDPN, the novel properties of the deposited structures, and how tDPN is a general tool for studying the rheology of nanoscale polymer structures.