ZnO nanostructures with different
morphologies (nanowires, nanodisks,
and nanostars) were synthesized hydrothermally. Gas sensing properties
of the as-grown nanostructures were investigated under thermal and
UV activation. The performance of the ZnO nanodisk gas sensor was
found to be superior to that of other nanostructures (Sg ∼ 3700% to 300 ppm ethanol and response time
and recovery time of 8 and 13 s). The enhancement in sensitivity is
attributed to the surface polarities of the different structures on
the nanoscale. Furthermore, the selectivity of the gas sensors can
be achieved by controlling the UV intensity used to activate these
sensors. The highest sensitivity value for ethanol, isopropanol, acetone,
and toluene are recorded at the optimal UV intensity of 1.6, 2.4,
3.2, and 4 mW/cm2, respectively. Finally, the UV activation
mechanism for metal oxide gas sensors is compared with the thermal
activation process. The UV activation of analytes based on solution
processed ZnO structures pave the way for better quality gas sensors.
The fabrication of highly functional materials for practical devices requires a deep understanding of the association between morphological and structural properties and applications. A controlled hydrothermal method to produce single crystal ZnO hexagonal nanodisks, nanorings, and nanoroses using a mixed solution of zinc sulfate (ZnSO4) and hexamethylenetetramine (HMTA) without the need of catalysts, substrates, or templates at low temperature (75 °C) is introduced. Metal-semiconductor-metal (MSM) ultraviolet (UV) detectors were fabricated based on individual and multiple single-crystal zinc oxide (ZnO) hexagonal nanodisks. High quality single crystal individual nanodisk devices were fabricated with inkjet-printed silver electrodes. The detectors fabricated show record photoresponsivity (3300 A/W) and external quantum efficiency (1.2 × 10(4)), which we attribute to the absence of grain boundaries in the single crystal ZnO nanodisk and the polarity of its exposed surface.
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