- Chaos Control on the Nanoscale
The burgeoning field of nanotechnology opens windows between science and art. Exploration of this interplay encourages interaction among scientists, artists and educators. Color Plate A No. 2 serves as an example demonstrating the fertile ground for exchange.
The substrate that this image captures is made of silicon, the material from which computer chips are made. I homogeneously applied a thin silane chemical coating (about 1 nm thick) to the silicon substrate, after which I locally removed specific regions of the coating that were 600 nm wide (approximately 125 times smaller than the diameter of a human hair), using a technique known as photocatalytic nanolithography (PCNL) [1,2]. PCNL engages light, such as from a light-emitting diode or an ultraviolet source, to activate molecules that are swabbed from a volatile solution onto a transparent mask positioned above the silicon substrate. These molecules can be compounds similar to chlorophyll, the photoactive material that aids plants in photosynthesis, or may be semiconductor materials such as TiO2. Once these molecules are activated, chemical reactions result in local destruction of the coating on the silicon. Thus, only regions of the coated silicon in close contact with the mask are affected. I then grafted a non-fouling polymer hydrogel (about 10 nm thick) to the retained silane coating.
Hydrogels are superabsorbent and are therefore used on a bulk scale in common items, including contact lenses and disposable diapers. They also are used in topical drug delivery and tissue engineering applications. Because the hydrogel is so absorbent, exposing the silicon chip with patterned hydrogel to water vapor from one’s breath reveals the pattern that the lithography dictates . The myriad colors seen in the image are due to optical interference. The thickness of the swollen layer determines the colors that are visible. While the field of view immediately following hydration appears like a big drop of oil shining in the sun, the oil drop appearance breaks up into many small domains as the water vapor evaporates. The base silicon does not retain the water in the same way that the hydrogel does, due to differences in surface tension. Thus, the pattern stands out from the background.
In addition to bringing together nanotechnology, polymer chemistry, materials science and optics, this image suggests the imposition of order on an otherwise chaotic world. This is a repeated theme in nature across multiple orders of magnitude. The interface of this order and chaos is amorphous and renders a Klimt-like vision of reflected light. As this image is just a still in time, it also reminds us that all things and states are transient and that the materials of the earth, like ourselves as individuals, are constantly evolving.
National Laboratory, University of California, P.O. Box 808, Livermore, CA, 94550. E-mail: <email@example.com>
This paper is presented as part of the Leonardo special section Nanotechnology, Nanoscale Science and Art, guest edited by Tom Rockwell and Tami I. Spector. Published in collaboration with the Exploratorium and the Nanoscale Informal Science Education (NISE) Network. Partial support for publication of this article provided by the National Science Foundation under cooperative agreement #ESI-0532536. Any opinions, findings, and conclusions or recommendations expressed in this article are those of the authors and do not necessarily reflect the views of the Foundation.
Unedited references as provided by the author.
1. J.P. Bearinger, G. Stone, et al. (2008). “Porphyrin Based Photocatalytic Lithography.” Langmuir, accepted.
2. J.P. Bearinger, A. L. Hiddessen, et al. (2005). Biomolecular Patterning via Photocatalytic Lithography. NSTI Nanotech 2005, Anaheim, CA.
3. G.P. Lopez, H.A. Biebuyck, et al. (1993). “Imaging of Features on Surfaces by Condensation Figures.” Science 260 (5108): 647–649. [End Page 361]