Bilayer Au nanoparticle-decorated WO3 porous thin films: On-chip fabrication and enhanced NO2 gas sensing performances with high selectivity

We present the on-chip fabrication of bilayer Au NP-decorated WO3 nanoporous thin films (B-Au/WO3) via layer-by-layer stacking of a sacrificial colloidal template with periodic Au sputtering deposition. Technical analysis shows that the B-Au/WO3 film is homogeneous and consists of a hexagonally ordered bowl-like structure, whose surface is uniformly decorated with crystalline Au NPs. The B-Au/WO3 sensing film shows a sensitivity of 96.0, a response time of 9.0 s and a recovery time of 16.0 s for 1 ppm NO2 at a low operating temperature of 150 degrees C. This significantly exceeds performances of bare WO3 counterpart. Also, the B-Au/WO3 sensor demonstrates obviously enhanced sensing responses over operating temperature ranges of 75-225 degrees C and perfect selectivity to NO2 gas. We proposed a combined sensing mechanism, the surface Au NPs dominated chemical sensitization and interbedded Au NP-induced electronic sensitization, to explain the perfect sensing performances in sensitivity, response, and selectivity. The template-mediated approach focuses on precise single-layer control and facilitates direct integration of the sensing film onto the required sensor substrate. The addressed on-chip fabrication strategy along with Au NPs decoration technique might provide promising applications in construction of advanced chemiresistive gas sensors, photocatalysts and electrochromic smart windows.