By exploiting the thermoplastic and photosensitive nature of SU-8 photoresists, different types of hierarchical pillar arrays with variable aspect ratios are fabricated through capillary force lithography (CFL), followed by photopatterning. The thermoplastic nature of SU-8 enables the imprinting of micropillar arrays with variable aspect ratios by CFL using a single poly(dimethylsiloxane) mold, simply by tuning the initial film thickness of SU-8 on a substrate. The pillar array is subsequently photopatterned through a photomask, followed by post-exposure baking above the glass transition temperature (T(g)) of SU-8. The pillars in the exposed region become highly crosslinked and, therefore, neither soluble nor able to reflow above T(g), whereas the pillars in the unexposed regions can reflow and flatten out. Two developing strategies are investigated after UV exposure of the SU-8 pillar arrays including i) solvent development and drying and ii) thermal reflow to create bilevel hierarchical structures with short pillars and single-level, dual-scaled, high-aspect-ratio (up to 7.7) pillars in a microdot array, respectively.
The cover image illustrates an array of high‐aspect‐ratio (up to 7.7) polymer pillars from SU‐8 photoresists imprinted by capillary force lithography (CFL), followed by photopatterning and a thermal reflow process. Because of the thermoplastic nature of SU‐8, pillars with variable aspect ratios are created through CFL using a single poly(dimethylsiloxane) membrane as the mold, simply by tuning the initial film thickness of SU‐8 on a substrate. The pillars are subsequently photopatterned through a photomask with a square dot array, followed by post‐exposure bake above the glass‐transition temperature (Tg) of SU‐8. The pillars in the exposed region become highly crosslinked, and thus neither soluble nor reflowable, whereas the pillars in the unexposed regions can reflow and flatten out above Tg. In this way, a single‐level, dual‐scaled, high‐aspect‐ratio SU‐8 pillar array is “developed” in the exposed region without the use of solvent. Such high‐aspect‐ratio pillar arrays may find applications in biomimetic superhydrophobic surfaces and dry adhesion, microfluidics, diagnosis, tissue engineering, force sensing, and actuation. For more information, please read the Full Paper “Fabrication of Hierarchical Pillar Arrays from Thermoplastic and Photosensitive SU‐8” by S. Yang et al., beginning .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.