Light‐Induced Buckles Localized by Polymeric Inks Printed on Bilayer Films. Issue 20 (16th April 2018)

• Record Type: Journal Article
• Authors: Park, Sungjune; Nallainathan, Umaash; Mondal, Kunal; Sen, Pratik; Dickey, Michael D.
• Is Part Of: Small. Volume 14:Issue 20(2018)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-04-16
• Subjects: bilayer films -- light‐induced buckles -- localized instability -- polymeric inks; Nanotechnology -- Periodicals; Nanoparticles -- Periodicals; Microtechnology -- Periodicals; 620.5
• DOI: 10.1002/smll.201704460
• Languages: English
• ISSNs: 1613-6810

Abstract

Abstract: Buckling instabilities generate microscale features in thin films in a facile manner. Buckles can form, for example, by heating a metal/polymer film stack on a rigid substrate. Thermal expansion differences of the individual layers generate compressive stress that causes the metal to buckle over the entire surface. The ability to dictate and confine the location of buckle formation can enable patterns with more than one length scale, including hierarchical patterns. Here, sacrificial "ink" patterned on top of the film stack localizes the buckles via two mechanisms. First, stiff inks suppress buckles such that only the non‐inked regions buckle in response to infrared light. The metal in the non‐inked regions absorbs the infrared light and thus gets sufficiently hot to induce buckles. Second, soft inks that absorb light get hot faster than the non‐inked regions and promote buckling when exposed to visible light. The exposed metal in the non‐inked regions reflects the light and thus never get sufficiently hot to induce buckles. This second method works on glass substrates, but not silicon substrates, due to the superior thermal insulation of glass. The patterned ink can be removed, leaving behind hierarchical patterns consisting of regions of buckles among non‐buckled regions. Abstract : An approach to achieve localized surface topography is presented. Stiff polymeric inks patterned on a metal/polymer bilayer via microcontact printing physically suppress the formation of buckles, resulting in surface buckling only in nonpatterned regions. In contrast, soft and light‐absorbing polymer inks printed on the bilayer promote buckling only in patterned regions when exposed to visible light.