Flexible Sensory Systems: Structural Approaches

Abstract

Biology is characterized by smooth, elastic, and nonplanar surfaces; as a consequence, soft electronics that enable interfacing with nonplanar surfaces allow applications that could not be achieved with the rigid and integrated circuits that exist today. Here, we review the latest examples of technologies and methods that can replace elasticity through a structural approach; these approaches can modify mechanical properties, thereby improving performance, while maintaining the existing material integrity. Furthermore, an overview of the recent progress in wave/wrinkle, stretchable interconnect, origami/kirigami, crack, nano/micro, and textile structures is provided. Finally, potential applications and expected developments in soft electronics are discussed.

Metal–Organic Framework-Derived Co-Doped ZnO Nanostructures Anchored on N-Doped Carbon as a Room-Temperature Chemiresistive Hydrogen Sensor

“…This clear distinction in the gas sensing properties highlights the role played by amorphous ZnO in the Co–ZnO–N/C material. The present sensor response and recovery times are faster than the reported literature under similar operating conditions for systems based on ZnO. − ,− Non-noble metal-based Co–ZnO–N/C could sense H 2 much faster even when compared to Pd-, Pt-, and Au-decorated ZnO nanostructures (Table S1).…”

“…This is remarkable as most of the studies reported for ZnO (nanopillars, nanorod arrays, nanoassemblies, and p–n homojunction) uses temperatures >200 °C for sensing H 2 . Several other nanostructures of ZnO, including nanopillar, nanorod arrays, nanoassemblies, and p–n homojunction, exhibited Δ R o / R a in the range of 0.1–10 S only at temperatures ≥300 °C. ,,,,, Precious metals such as Pd and Au are hybridized with ZnO for room-temperature sensing of H 2 . − As evident from Table S1, Pd-assisted ZnO nanowires and Au-decorated rGO/ZnO nanostructures exhibited recovery times several times higher (66–612 s) than found in this study at room temperature. , …”

“…In comparison with other nanostructures of ZnO given in Table S1, the response and recovery times are quite low. − ,− For example, in the case of 0.05 wt % Co 3 O 4 -loaded ZnO, both the response and recovery times were 70 s at 300 °C. For ZnO nanotubes when exposed to 1000 ppm H 2 concentration at 250 °C, the response and recovery times were reported to be 80 and 250 s, respectively.…”

“…In another study, the unique nanostructure of the Au–rGO/ZnO nanohybrid bestowed room-temperature H 2 sensing as rGO enhanced the free flow of electrons between ZnO and Au . These and other literature studies clearly emphasize the role played by the nanostructure of the material on the gas sensing characteristics. − ,− …”

“…Various nanostructures of ZnO have been utilized for sensing H 2 but only at high temperatures (>300 °C) (Table S1). − ,− Noble metals (Pd, Pt, and Au) have been used as catalysts/sensitizers with ZnO. − However, these noble metal@ZnO hybrids suffered from longer recovery times. − To note a few nanostructures, 2 atom % of Cd-doped ZnO nanorods showed enhanced sensitivity toward H 2 with a response of 6.13 and recovery times of 30 s at 220 °C . Herein, the Cd-doped ZnO nanorods possessed high surface-to-volume ratio due to the smaller grain size compared to the undoped one.…”