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- ItemPresent and future of surface-enhanced Raman scattering(Washington, DC : ACS Publications, 2020) Langer, Judith; de Aberasturi, Dorleta Jimenez; Aizpurua, Javier; Alvarez-Puebla, Ramon A.; Auguié, Baptiste; Baumberg, Jeremy J.; Bazan, Guillermo C.; Bell, Steven E.J.; Boisen, Anja; Brolo, Alexandre G.; Choo, Jaebum; Cialla-May, Dana; Deckert, Volker; Fabris, Laura; Faulds, Karen; de Abajo, F. Javier García; Goodacre, Royston; Graham, Duncan; Haes, Amanda J.; Haynes, Christy L.; Huck, Christian; Itoh, Tamitake; Käll, Mikael; Kneipp, Janina; Kotov, Nicholas A.; Kuang, Hua; Le Ru, Eric C.; Lee, Hiang Kwee; Li, Jian-Feng; Ling, Xing Yi; Maier, Stefan A.; Mayerhöfer, Thomas; Moskovits, Martin; Murakoshi, Kei; Nam, Jwa-Min; Nie, Shuming; Ozaki, Yukihiro; Pastoriza-Santos, Isabel; Perez-Juste, Jorge; Popp, Juergen; Pucci, Annemarie; Reich, Stephanie; Ren, Bin; Schatz, George C.; Shegai, Timur; Schlücker, Sebastian; Tay, Li-Lin; Thomas, K. George; Tian, Zhong-Qun; Van Duyne, Richard P.; Vo-Dinh, Tuan; Wang, Yue; Willets, Katherine A.; Xu, Chuanlai; Xu, Hongxing; Xu, Yikai; Yamamoto, Yuko S.; Zhao, Bing; Liz-Marzán, Luis M.The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.
- ItemA Design Strategy for Mushroom-Shaped Microfibrils With Optimized Dry Adhesion: Experiments and Finite Element Analyses(New York, NY : ASME, 2021) Zhang, Xuan; Wang, Yue; Hensel, René; Arzt, EduardEnhanced dry adhesion of micropatterned polymeric surfaces has been frequently demonstrated. Among the design parameters, the cap geometry plays an important role to improve their performance. In this study, we combined experiments on single polyurethane mushroom-shaped fibrils (with a stalk diameter of 80 µm and height of 125 µm) against flat glass, with numerical simulations implementing a cohesive zone. We found that the geometry of the mushroom cap strongly affects the interfacial crack behavior and the pull-off stress. The experimental and numerical results suggest that optimal adhesion was accompanied by the appearance of both edge and interior interfacial cracks during separation. Finite elemental analyses revealed the evolution of the interfacial stress distributions as a function of the cap thickness and confirmed the distinct detachment mechanisms. Furthermore, the effect of the stalk diameter and the Young's modulus on the adhesive force was established, resulting in an optimal design for mushroom-shaped fibrils.
- ItemZirconium-Catalyzed Atom-Economical Synthesis of 1,1-Diborylalkanes from Terminal and Internal Alkenes(Weinheim : Wiley-VCH, 2020) Wang, Xianjin; Cui, Xin; Li, Sida; Wang, Yue; Xia, Chungu; Jiao, Haijun; Wu, LipengA general and atom-economical synthesis of 1,1-diborylalkanes from alkenes and a borane without the need for an additional H2 acceptor is reported for the first time. The key to our success is the use of an earth-abundant zirconium-based catalyst, which allows a balance of self-contradictory reactivities (dehydrogenative boration and hydroboration) to be achieved. Our method avoids using an excess amount of another alkene as an H2 acceptor, which was required in other reported systems. Furthermore, substrates such as simple long-chain aliphatic alkenes that did not react before also underwent 1,1-diboration in our system. Significantly, the unprecedented 1,1-diboration of internal alkenes enabled the preparation of 1,1-diborylalkanes. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemSwitchable Underwater Adhesion by Deformable Cupped Microstructures(Weinheim : Wiley-VCH, 2020) Wang, Yue; Kang, Victor; Federle, Walter; Arzt, Eduard; Hensel, RenéSwitchable underwater adhesion can be useful for numerous applications, but is extremely challenging due to the presence of water at the contact interface. Here, deformable cupped microstructures (diameter typically 100 µm, rim thickness 5 µm) are reported that can switch between high (≈1 MPa) and low (<0.2 MPa) adhesion strength by adjusting the retraction velocity from 100 to 0.1 µm s–1. The velocity at which the switch occurs is determined by specific design parameters of the cupped microstructure, such as the cup width and angle. The results are compared with theoretical estimates of water penetration into the contact zone and expansion of the cup during retraction. This work paves the way for controlling wet adhesion on demand and may inspire further applications in smart adhesives.
- ItemSliding Mechanism for Release of Superlight Objects from Micropatterned Adhesives(Weinheim : Wiley-VCH, 2022) Wang, Yue; Zhang, Xuan; Hensel, René; Arzt, EduardRobotic handling and transfer printing of micrometer-sized superlight objects is a crucial technology in industrial fabrication. In contrast to the precise gripping with micropatterned adhesives, the reliable release of superlight objects with negligible weight is a great challenge. Slanted deformable polymer microstructures, with typical pillar cross-section 150 µm × 50 µm, are introduced with various tilt angles that enable a reduction of adhesion by a switching ratio of up to 500. The experiments demonstrate that the release from a smooth surface involves sliding of the contact during compression and subsequent peeling of the object during retraction. The handling of a 0.5 mg perfluorinated polymer micro-object with high accuracy in repeated pick-and-place cycles is demonstrated. Based on beam theory, the forces and moments acting at the tip of the microstructure are analyzed. As a result, an expression for the pull-off force is proposed as a function of the sliding distance and a guide to an optimized design for these release structures is provided.
- ItemBioinspired Underwater Adhesion to Rough Substrates by Cavity Collapse of Cupped Microstructures(Weinheim : Wiley-VCH, 2021) Wang, Yue; Hensel, RenéUnderwater or wet adhesion is highly desirable for numerous applications but is counteracted by the liquids in the contact which weaken intermolecular attraction. The problem is exacerbated in conjunction with surface roughness when liquids partially remain in grooves or dimples of the substrate. In the present study, a cupped microstructure with a cavity inspired by suction organs of aquatic animals is proposed. The microstructures (cup radius of 100 µm) are made from polyurethane using two-photon lithography followed by replica molding. Adhesion to rough substrates is emulated experimentally by a micropatterned model substrate with varying channel widths. Pull-off stresses are found to be about 200 kPa, i.e., twice atmospheric pressure. Evaluation of force–displacement curves together with in situ observations reveal the adhesion mechanism, which involves adaptation to surface roughness and an elastic force induced by the collapse of the cavity that holds sealed contact with the substrate during retraction. This new microarchitecture may pave the way for next generation microstructures applicable to real, rough surfaces under wet conditions.
- ItemA bioinspired snap-through metastructure for manipulating micro-objects(Washington, DC [u.a.] : American Association for the Advancement of Science, 2022) Zhang, Xuan; Wang, Yue; Tian, Zhihao; Samri, Manar; Moh, Karsten; McMeeking, Robert M.; Hensel, René; Arzt, EduardMicro-objects stick tenaciously to each other—a well-known show-stopper in microtechnology and in handling micro-objects. Inspired by the trigger plant, we explore a mechanical metastructure for overcoming adhesion involving a snap-action mechanism. We analyze the nonlinear mechanical response of curved beam architectures clamped by a tunable spring, incorporating mono- and bistable states. As a result, reversible miniaturized snap-through devices are successfully realized by micron-scale direct printing, and successful pick-and-place handling of a micro-object is demonstrated. The technique is applicable to universal scenarios, including dry and wet environment, or smooth and rough counter surfaces. With an unprecedented switching ratio (between high and low adhesion) exceeding 104, this concept proposes an efficient paradigm for handling and placing superlight objects.
- ItemWater as a "glue" : Elasticity-enhanced wet attachment of biomimetic microcup structures(Washington, DC [u.a.] : Assoc., 2022) Wang, Yue; Li, Zhengwei; Elhebeary, Mohamed; Hensel, René; Arzt, Eduard; Saif, M. Taher A.Octopus, clingfish, and larva use soft cups to attach to surfaces under water. Recently, various bioinspired cups have been engineered. However, the mechanisms of their attachment and detachment remain elusive. Using a novel microcup, fabricated by two-photon lithography, coupled with in situ pressure sensor and observation cameras, we reveal the detailed nature of its attachment/detachment under water. It involves elasticity-enhanced hydrodynamics generating “self-sealing” and high suction at the cup-substrate interface, converting water into “glue.” Detachment is mediated by seal breaking. Three distinct mechanisms of breaking are identified, including elastic buckling of the cup rim. A mathematical model describes the interplay between the attachment/detachment process, geometry, elasto-hydrodynamics, and cup retraction speed. If the speed is too slow, then the octopus cannot attach; if the tide is too gentle for the larva, then water cannot serve as a glue. The concept of “water glue” can innovate underwater transport and manufacturing strategies.