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- ItemStrong Wet and Dry Adhesion by Cupped Microstructures(Washington, DC : American Chemical Society, 2019) Wang, Y.; Kang, V.; Arzt, E.; Federle, W.; Hensel, R.Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are considerably weakened underwater, fibrillar adhesives are however far less effective in wet environments. Although various strategies have been proposed to achieve strong reversible underwater adhesion, strong adhesives that work both in air and underwater without additional surface treatments have yet to be developed. In this study, we report a novel design - cupped microstructures (CM) - that generates strong controllable adhesion in air and underwater. We measured the adhesive performance of cupped polyurethane microstructures with three different cup angles (15, 30, and 45°) and the same cup diameter of 100 μm in dry and wet conditions in comparison to standard mushroom-shaped microstructures (MSMs) of the same dimensions. In air, 15°CM performed comparably to the flat MSM of the same size with an adhesion strength (force per real contact area) of up to 1.3 MPa, but underwater, 15°CM achieved 20 times stronger adhesion than MSM (∼1 MPa versus ∼0.05 MPa). Furthermore, the cupped microstructures exhibit self-sealing properties, whereby stronger pulls lead to longer stable attachment and much higher adhesion through the formation of a better seal. © 2019 American Chemical Society.
- ItemImaging of buried 3D magnetic rolled-up nanomembranes(Washington, DC : American Chemical Society, 2014) Streubel, R.; Han, L.; Kronast, F.; Ünal, A.A.; Schmidt, O.G.; Makarov, D.Increasing performance and enabling novel functionalities of microelectronic devices, such as three-dimensional (3D) on-chip architectures in optics, electronics, and magnetics, calls for new approaches in both fabrication and characterization. Up to now, 3D magnetic architectures had mainly been studied by integral means without providing insight into local magnetic microstructures that determine the device performance. We prove a concept that allows for imaging magnetic domain patterns in buried 3D objects, for example, magnetic tubular architectures with multiple windings. The approach is based on utilizing the shadow contrast in transmission X-ray magnetic circular dichroism (XMCD) photoemission electron microscopy and correlating the observed 2D projection of the 3D magnetic domains with simulated XMCD patterns. That way, we are not only able to assess magnetic states but also monitor the field-driven evolution of the magnetic domain patterns in individual windings of buried magnetic rolled-up nanomembranes.
- ItemConfined crystals of the smallest phase-change material(Washington, DC : American Chemical Society, 2013) Giusca, C.E.; Stolojan, V.; Sloan, J.; Börrnert, F.; Shiozawa, H.; Sader, K.; Rümmeli, M.H.; Büchner, B.; Silva, S.R.P.The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales.
- ItemUltracompact three-dimensional tubular conductivity microsensors for ionic and biosensing applications(Washington, DC : American Chemical Society, 2014) Martinez-Cisneros, C.S.; Sanchez, S.; Xi, W.; Schmidt, O.G.We present ultracompact three-dimensional tubular structures integrating Au-based electrodes as impedimetric microsensors for the in-flow determination of mono- and divalent ionic species and HeLa cells. The microsensors show an improved performance of 2 orders of magnitude (limit of detection = 0.1 nM for KCl) compared to conventional planar conductivity detection systems integrated in microfluidic platforms and the capability to detect single HeLa cells in flowing phosphate buffered saline. These highly integrated conductivity tubular sensors thus open new possibilities for lab-in-a-tube devices for bioapplications such as biosensing and bioelectronics.
- ItemRolled-up functionalized nanomembranes as three-dimensional cavities for single cell studies(Washington, DC : American Chemical Society, 2014) Xi, W.; Schmidt, C.K.; Sanchez, S.; Gracias, D.H.; Carazo-Salas, R.E.; Jackson, S.P.; Schmidt, O.G.We use micropatterning and strain engineering to encapsulate single living mammalian cells into transparent tubular architectures consisting of three-dimensional (3D) rolled-up nanomembranes. By using optical microscopy, we demonstrate that these structures are suitable for the scrutiny of cellular dynamics within confined 3D-microenvironments. We show that spatial confinement of mitotic mammalian cells inside tubular architectures can perturb metaphase plate formation, delay mitotic progression, and cause chromosomal instability in both a transformed and nontransformed human cell line. These findings could provide important clues into how spatial constraints dictate cellular behavior and function.