Laser-grown ZnO nanowires for room-temperature SAW-sensor applications

ZnO nanowires were grown on the active sensor surface of a surface acoustic wave (SAW) sensor via a vapour–liquid–solid (VLS) technique using pulsed laser deposition (PLD) as the particle source. The fabricated sensors were “delay-line” type (quartz substrate; ∼69.4-MHz central frequency). The nanowire length and diameter were controlled by the growth time and temperature, respectively. The sensor response at room temperature to various hydrogen (H2) concentrations was recorded for different ZnO morphologies and nanowire thicknesses and compared with the performance of a thin-film sensor with a comparable amount of ZnO material. The sensor response depended on the ZnO volume and the morphology of the active surface. An increase in the ZnO volume enhanced the frequency shift for the same H2 concentration, while the larger surface area of the longer nanowires enhanced the sensor response to low H2 concentrations, enabling detection of concentrations as low as 0.01%.