Hetero-apertured micro/nanostructured ordered porous array: Layer-by-layered construction and structure-induced sensing parameter controllability

The double-layer hetero-apertured porous films with hierarchical micro/nanoarchitectures were fabricated on a desired substrate, based on a simple and flexible strategy alternately using the monolayer colloidal crystal with different sizes of colloidal spheres as templates. Such films are of biperiodic ordered structures and can be fully lifted off from the substrate and present a freestanding property. The structures and morphologies of the films can be controlled by combination of the colloidal monolayers with different sphere sizes. The corresponding gas sensing devices were also built. Representatively, the In₂O₃ hierarchically micro/nanostructured porous film-based sensors have shown both higher sensitivity and much faster response to NH₃ atmosphere than the corresponding conventional nanostructured ones. Importantly, the gas-sensing parameters (i.e., response time and the sensitivity) can be well-controlled separately in a large range simply by changing the pore sizes in different layers of the porous film. Further, for the application, a diagram of gas-sensing parameters (f_R-5 diagram) was presented, which can not only give a measurement of sensing performances but also well guide design and fabrication of the hierarchically structure-based sensors with desired sensing performances. This work is an important step toward the practical application of the nanostructured porous film sensors.