We utilize an innovative vapor deposition set-up and cross-diffusion of functionalized chlorosilanes under dynamic vacuum to generate a 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. This 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 diiodomethane and ethylene glycol contact angle measurements and X-ray photoelectron spectroscopy (XPS). From these measurements we were able to correlate composition, diiodomethane contact angle, and surface energy. We generated a linear gradient with a range in mole fraction of one component from 0.15 to 0.80 (34 mN/m to 40 mN/m in surface energy) to demonstrate its utility in a block copolymer thin film morphology study. Examination of the thin film surface morphology with atomic force microscopy (AFM) revealed the expected morphological transitions across the gradient.
Citation: ACS Nano
Pub Type: Journals
gradient, monolayer, block copolymer, thin films, surface energy