Nanosensors Research Papers - Academia.edu (original) (raw)

Recent developments on the synthesis of networked nanostruc-tures have added new amplitudes for designing multifunc-tional devices, including sensors and UV photodetectors. The importance of UV detectors is growing because of the demand for wide range of environmental, military, industrial, fl ame sensing, water sterilization, and early missile plume detection applications. [ 1 ] With their high performances, but own drawbacks , Si-, GaN-or III–V-compound-based UV detectors are available on the market. Although the Si-based photo-devices are known for quick responses compared with ZnO-based UV detectors, they exhibit severe limitations, such as poor selectivity towards visible and infrared (IR) light, which demands complex fi lters, ultra-high vacuum condition, and high voltage. [ 2 ] By contrast, for ZnO-based UV detectors, these types of limitations are easily ruled out because of their wide and direct band-gaps and ability to operate in harsh environmental conditions. In this work, we demonstrate two novel fl ame transport synthesis (FTS) methods, namely, burner fl ame transport synthesis (B-FTS) and crucible fl ame transport synthesis (C-FTS) for fabrication of the ZnO nano-microstructure-based UV photodetec-tors. The FTS approach utilizes Zn microparticles in contrast to many conventional fl ame synthesis methods that are based on precursor gases. Both of the techniques allow facile and cost-effective growth of ZnO nano-microstructures, bridging the 2–10 μ m size gaps between two Au contacts on pre-patterned chips. High crystalline qualities of the fabricated nano-micro-structures grown by rapid B-FTS and C-FTS approaches were confi rmed by XRD and Raman studies. The SEM investigations revealed interpenetrating nanojunctions between the bridging ZnO nano-microstructures grown on the gaps between two Au contacts. The B-FTS approach exhibits the unique feature of ultra-rapid growth of ZnO nanotetrapods within few milliseconds and simultaneously in situ bridging electrical contacts. These bridging nanotetrapods were directly integrated on a chip and demonstrated signifi cantly improved performances as a UV photodetector. Comparison of the UV photodetectors performances built from interpenetrating ZnO nano-microstruc-tures fabricated by B-FTS and C-FTS techniques are presented. Fastest response/recovery time constant (≈32 ms) under 365 nm UV light irradiation of B-FTS-made photodetectors (on/off ratio ≈4.5 × 10 3 at 2.4 V) is reported. Different type of nanojunctions formed between neighbor nanowires or nanotet-rapods (with 'arm' thickness <50 nm) could be the reason for such improved characteristics. The role of nanojunctions in fast UV photodetectors from networked ZnO nanowires and nano-tetrapods is discussed. On the basis of the rapid B-FTS fabrication process and fast UV photodetection capabilities, such networked ZnO nanotetrapods can be potential candidates for various nanosensor applications. Metal oxide nanostructures, such as nanorods, nano wires, and nanotetrapods, have gained a lot of research interest for multifunctional device applications owing to their electrical , optical, and mechanical properties. [ 3–6 ] With wide direct bandgap (3.37 eV) and large exciton binding energy (≈60 meV) at room temperature, ZnO nanostructures are one of the most investigated materials for different nanotechnological