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A simple yet scalable strategy for fabricating dry adhesives with mushroom-shaped micropillars is achieved by a combination of the roll-to-roll process and modulated UV-curable elastic poly(urethane acrylate) (e-PUA) resin. The e-PUA combines the major benefits of commercial PUA and poly(dimethylsiloxane) (PDMS). It not only can be cured within a few seconds like commercial PUA but also possesses good mechanical properties comparable to those of PDMS. A roll-type fabrication system equipped with a rollable mold and a UV exposure unit is also developed for the continuous process. By integrating the roll-to-roll process with the e-PUA, dry adhesives with spatulate tips in the form of a thin flexible film can be generated in a highly continuous and scalable manner. The fabricated dry adhesives with mushroom-shaped microstructures exhibit a strong pull-off strength of up to ∼38.7 N cm(-2) on the glass surface as well as high durability without any noticeable degradation. Furthermore, an automated substrate transportation system equipped with the dry adhesives can transport a 300 mm Si wafer over 10,000 repeating cycles with high accuracy.

known as denticles that are thought to be multifunctional. It has been hypothesized that these surface features prevent biofouling and, more importantly, reduce fluid friction drag, which enables more efficient swimming. This has inspired the development of commercially successful products such as the Fastskin swimming suit by Speedo. Shark skin structures could also be applied to ships, underwater vehicles, airplanes, and pipelines to reduce energy waste from friction drag.Many studies have been conducted over the past few decades to understand the mechanism of drag reduction over shark skin-inspired surfaces. The physical causes responsible for drag reduction are reasonably well understood. [2][3][4] However, fabrication of such multifunctional surfaces remains a challenge. Although various methods have been used to reproduce shark skin geometry, a trade-off between throughput and resolution always exists and severely hinders the progress in this field. Some high-throughput methods include textured liners, [5,6] molding from real shark skin samples, [7] microcasting and wax printing, sampling from real shark skin, [8] and laser cutting. [9] However, these methods suffer from low resolution or difficulty in accurately reproducing the 3D geometry of shark skin, comprising dermal denticles attached to the surface. More importantly, given the vast design spaces involved, it is difficult to flexibly and quickly fabricate many different modified shapes and sizes that may be required in biomimetic studies. High-resolution digital fabrication methods such as two-photon lithography [10] have successfully fabricated highly detailed and accurate 3D shark skin denticles. [9] However, such fabrication processes can only produce samples with small areas. The small building extent, coupled with extremely low throughput, limits the value of such fabrication techniques for research purposes. As an emerging manufacturing technology, 3D printing has been playing an increasingly important role in various industries due to its advantages in high customization and fast prototyping, as well as the ability to fabricate complex shapes. [11][12][13][14][15][16][17] The flexibility of 3D printing also makes it very appealing for biomimetic studies. For example, 3D printing enables the development of artificial shark skin with textures of varying shape and size on arbitrary surface shapes. Indeed, some recent studies have successfully utilized 3D printing to fabricate shark skin structures. [9,18,19] Nevertheless, Additive manufacturing has many advantages in creating highly complex customized structures. In this study, a low-cost multiscale stereolithography technology that can print a macroscale object with microscale surface structures with high throughput is demonstrated. The developed multiscale stereolithography is realized by dynamic switching of laser spot size and adaptively sliced layer thickness. An optical filter based on subwavelength resonance grating is used to modify laser spot size for lasers with different wavelengths an...

Catalytic interface of semiconductor photoelectrodes is critical for high-performance photoelectrochemical solar water splitting because of its multiple roles in light absorption, electrocatalysis, and corrosion protection. Nevertheless, simultaneously optimizing each of these processes represents a materials conundrum owing to conflicting requirements of materials attributes at the electrode surface. Here we show an approach that can circumvent these challenges by collaboratively exploiting corrosion-resistant surface stoichiometry and structurally-tailored reactive interface. Nanoporous, density-graded surface of ‘black’ gallium indium phosphide (GaInP 2 ), when combined with ammonium-sulfide-based surface passivation, effectively reduces reflection and surface recombination of photogenerated carriers for high efficiency photocatalysis in the hydrogen evolution half-reaction, but also augments electrochemical durability with lifetime over 124 h via strongly suppressed kinetics of corrosion. Such synergistic control of stoichiometry and structure at the reactive interface provides a practical pathway to concurrently enhance efficiency and durability of semiconductor photoelectrodes without solely relying on the development of new protective materials.

Large-scale deployment of GaAs solar cells in terrestrial photovoltaics demands significant cost reduction for preparing device-quality epitaxial materials. Although multilayer epitaxial growth in conjunction with printing-based materials assemblies has been proposed as a promising route to achieve this goal, their practical implementation remains challenging owing to the degradation of materials properties and resulting nonuniform device performance between solar cells grown in different sequences. Here we report an alternative approach to circumvent these limitations and enable multilayer-grown GaAs solar cells with uniform photovoltaic performance. Ultrathin single-junction GaAs solar cells having a 300-nm-thick absorber (i.e., emitter and base) are epitaxially grown in triple-stack releasable multilayer assemblies by molecular beam epitaxy using beryllium as a p-type impurity. Microscale (∼500 × 500 μm) GaAs solar cells fabricated from respective device layers exhibit excellent uniformity (<3% relative) of photovoltaic performance and contact properties owing to the suppressed diffusion of p-type dopant as well as substantially reduced time of epitaxial growth associated with ultrathin device configuration. Bifacial photon management employing hexagonally periodic TiO nanoposts and a vertical p-type metal contact serving as a metallic back-surface reflector together with specialized epitaxial design to minimize parasitic optical losses for efficient light trapping synergistically enable significantly enhanced photovoltaic performance of such ultrathin absorbers, where ∼17.2% solar-to-electric power conversion efficiency under simulated AM1.5G illumination is demonstrated from 420-nm-thick single-junction GaAs solar cells grown in triple-stack epitaxial assemblies.