Duangrut Julthongpiput and Michael J. Fasolka
Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8542
We present a new class of micropatterning techniques that incorporates a surface energy gradient on a single substrate. By combining microcontact printing and vapor deposition methods, this technique provides fast, reproducible, and high-quality micro-scale gradient patterns on silicon substrates.
For creating chemical patterns, elastomeric stamps with an array of stripes 1-25 m m wide are used to create a stationary contact with a silicon substrate. This substrate is then immersed in a chlorosilane vapor for 1 hour. Organosilane molecules in a vapor phase react with OH groups on areas of substrate not covered by the elastomer stamp, resulting in the formation of a patterned organosilane self-assembled monolayers (SAMs). The substrate is then exposed to a gradient of UV-ozone radiation, which gradually changes the hydrophobic SAMs layer to hydrophilic species. The resulting gradient shows a range of contact angles from 25-95° .
These gradient energy substrates with chemical patterns are developed to (1) serve the development and calibration of next generation SPM techniques and (2) generate libraries for combinatorial studies of thin film phenomenology, where a systematic variation of interfacial surface energy is significant parameter along one axis. The graded oxidation process presents a systematic variation of surface chemical composition. We have utilized contact angle measurements and Atomic Force Microscopy (AFM) to investigate the influence of the chemical gradient and pattern size on the morphology of ultrathin dewetting polystyrene films. We show that the dewetting patterns are correlated to the surface energies and pattern period leading to the formation of droplet arrays.
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