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- ItemSelf-assembly as a tool to study microscale curvature and strain-dependent magnetic properties(London : Springer Nature, 2022) Singh, Balram; Otálora, Jorge. A.; Kang, Tong H.; Soldatov, Ivan; Karnaushenko, Dmitriy D.; Becker, Christian; Schäfer, Rudolf; Karnaushenko, Daniil; Neu, Volker; Schmidt, Oliver G.The extension of 2D ferromagnetic structures into 3D curved geometry enables to tune its magnetic properties such as uniaxial magnetic anisotropy. Tuning the anisotropy with strain and curvature has become a promising ingredient in modern electronics, such as flexible and stretchable magnetoelectronic devices, impedance-based field sensors, and strain gauges, however, has been limited to extended thin films and to only moderate bending. By applying a self-assembly rolling technique using a polymeric platform, we provide a template that allows homogeneous and controlled bending of a functional layer adhered to it, irrespective of its shape and size. This is an intriguing possibility to tailor the sign and magnitude of the surface strain of integrated, micron-sized devices. In this article, the impact of strain and curvature on the magnetic ground state and anisotropy is quantified for thin-film Permalloy micro-scale structures, fabricated on the surface of the tubular architectures, using solely electrical measurements.
- ItemStress‐Actuated Spiral Microelectrode for High‐Performance Lithium‐Ion Microbatteries(2020) Tang, Hongmei; Karnaushenko, Dmitriy D.; Neu, Volker; Gabler, Felix; Wang, Sitao; Liu, Lixiang; Li, Yang; Wang, Jiawei; Zhu, Minshen; Schmidt, Oliver G.Miniaturization of batteries lags behind the success of modern electronic devices. Neither the device volume nor the energy density of microbatteries meets the requirement of microscale electronic devices. The main limitation for pushing the energy density of microbatteries arises from the low mass loading of active materials. However, merely pushing the mass loading through increased electrode thickness is accompanied by the long charge transfer pathway and inferior mechanical properties for long‐term operation. Here, a new spiral microelectrode upon stress‐actuation accomplishes high mass loading but short charge transfer pathways. At a small footprint area of around 1 mm2, a 21‐fold increase of the mass loading is achieved while featuring fast charge transfer at the nanoscale. The spiral microelectrode delivers a maximum area capacity of 1053 µAh cm−2 with a retention of 67% over 50 cycles. Moreover, the energy density of the cylinder microbattery using the spiral microelectrode as the anode reaches 12.6 mWh cm−3 at an ultrasmall volume of 3 mm3. In terms of the device volume and energy density, the cylinder microbattery outperforms most of the current microbattery technologies, and hence provides a new strategy to develop high‐performance microbatteries that can be integrated with miniaturized electronic devices.