Journal
ACS NANO
Volume 3, Issue 12, Pages 3977-3986Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn900750w
Keywords
surface energy; surface chemistry; monolayer; gradient morphology; block copolymer; thin film
Categories
Funding
- National Science Foundation [DMR-0645586]
- National Science Foundation Graduate Research Fellowship
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We utilize a vapor deposition setup and cross-diffusion of functionalized chlorosilanes under dynamic vacuum to generate a nearly linear gradient in surface energy and composition on a silicon substrate. The gradient can be tuned by manipulating chlorosilane reservoir sizes and positions, and the gradient profile is independent of time as long as maximum coverage of the substrate is achieved. Our method is readily amenable to the creation of gradients on other substrate surfaces, due to the use of vapor deposition, and with other functionalities, due to our use of functionalized chlorosilanes. Our gradients were characterized using contact angle measurements and X-ray photoelectron spectroscopy. From these measurements, we were able to correlate composition, contact angle, and surface energy. We generated a nearly linear gradient with a range in mole fraction of one component from 0.15 to 0.85 (34 to 40 mJ/m(2) in surface energy) to demonstrate its utility in a block copolymer thin film morphology study. Examination of the copolymer thin film surface morphology with optical and atomic force microscopy revealed the expected morphological transitions across the gradient.
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