Recent Advances in Unconventional Lithography for Challenging 3D Hierarchical Structures and Their Applications

Figure 3

Applications of 3D hierarchical structures fabricated by combined top-down lithographical techniques. (a-b) (a) SEM image of the rice leaf-like hierarchical Pd structures (after heat treatment) with primary lines of 1.7 mm and secondary pillars of 90 nm and corresponding height of 170 nm and 60 nm, respectively, from AFM profiles. (b) The different contact angles in parallel and perpendicular direction of the metallic rice leaf structure due to anisotropic wetting property (left). After hexadecanethiol absorption, the contact angle is increased in both directions (right). Reproduced with permission from [82]. Copyright 2013 Macmillan Publishers Ltd. (c–f) (c) Conceptual illustration (left), SEM image (top right), and photograph (bottom right) of bioinspired dry adhesive as medical skin patch. (d) Photographs show the use of dry adhesive patch to monitor electrocardiograms (ECGs) on the volunteer’s chest (top) and wrist (bottom). The inset images show the corresponding ECG signals from the volunteer’s heart. (e) Photographs show the skin condition after use of acrylic adhesive (left) and bioinspired dry adhesive during 48 hours. (f) Variations in normal adhesion strength of acrylic adhesive and bioinspired dry adhesive on the skin with 30 repeating cycles. Both adhesives were cleaned every 5 times. Reproduced with permission from [90, 91]. Copyright 2011 and 2013 WILEY-VCH Verlag GmbH & Co. KGaA. (g–j) Large-area photograph (g) and SEM images (h) of the three-level hierarchical apertures (800 nm/20 μm/500 μm apertures) at different magnifications. (i) Photographs of the three-level polymeric membrane with hierarchical apertures onto a tip of a syringe. The inset illustration depicts the reorganization process near the apertures. (j) Size distributions of emulsions before and after the filtration of apertures having two different diameters (800 nm apertures and 350 nm apertures). Reproduced with permission from [107]. Copyright 2014 Macmillan Publishers Ltd.

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