Nanometer-Thick Films of Aligned ZnO Nanowires Sensitized with Au Nanoparticles for Few-ppb-Level Acetylene Detection

Wireless devices for environmental and health monitoring require the development of stable and highly sensitive thin metal oxide gas-sensing films. This paper reports one-step Langmuir-Blodgett assembly of ultrathin (20 nm) nanostructured films of aligned ZnO nanowires with 10 nm-wide v-grooves on the surface, followed by sensitization with Au nanoparticles (Au NPs) by sputtering and postannealing. The ridges of the nanopatterns are revealed as diffusion barriers capable of preventing Au NPs from sintering via particle migration and growth (PMC). The resulting ZnO Langmuir-Blodgett film decorated with high dispersion of small Au NPs functions as a highly responsive conductance switch, which demonstrates unprecedented sensitivity (37 ppm-1) and detection limit (3 ppb) toward acetylene (C2H2), a key marker gas for air pollution caused by anthropogenic emission. The fabrication method for the stabilized nanometric metal on the Langmuir-Blodgett film reported in this work not only provides a general strategy to improve the sensitivity of the thin sensing film but also can be applied to many metal nanodot-based applications, such as solar cells, plasmon-resonance waveguides, and biosensors.