Design of a Compact Biaxial Tensile Stage for Fabrication and Tuning of Complex Micro and Nano scale Wrinkle Patterns

Abstract

Wrinkling of thin films is a straindriven process that enables scalable and lowcost fabrication of periodic microand nanoscale patterns. In the past, singleperiod sinusoidal wrinkles have been applied for thinfilm metrology and microfluidics applications. However, realworld adoption of this process beyond these specific applications is limited by the inability to predictively fabricate a variety of complex functional patterns. This is primarily due to the inability of current tools and techniques to provide the means for applying large, accurate, and nonequal biaxial strains. For example, the existing biaxial tensile stages are inappropriate because they are too large to fit within the vacuum chambers that are required for thinfilm deposition/growth during wrinkling. Herein, we have designed a compact biaxial tensile stage that enables (i) applying large and accurate strains to elastomeric films and (ii) in situ visualization of wrinkle formation. This stage enables one to stretch a 37.5 mm long film by 33.5% with a strain resolution of 0.027% and maintains a registration accuracy of 7 خ¼m over repeated registrations of the stage to a customassembled vision system. Herein, we also demonstrate the utility of the stage in (i) studying the wrinkling process and (ii) fabricating complex wrinkled patterns that are inaccessible via other techniques. Specifically, we demonstrate that (i) spatial nonuniformity in the patterns is limited to 6.5%, (ii) onedimensional (1D) singleperiod wrinkles of nominal period 2.3 خ¼m transition into the perioddoubled mode when the compressive strain due to prestretch release of plasmaoxidized polydimethylsiloxane (PDMS) film exceeds ∼18%, and (iii) asymmetric twodimensional (2D) wrinkles can be fabricated by tuning the strain state and/or the actuation path, i.e., the strain history. Thus, this tensile stage opens up the design space for fabricating and tuning complex wrinkled patterns and enables extracting empirical process knowledge via in situ visualization of wrinkle formation.