Honeycomb type ZnO nanostructures for sensitive and selective CO detection

Excellent sensing performance for CO gas is demonstrated using inexpensive sensor devices based on honeycomb type ZnO nanostructures, fabricated by colloidal lithography and lift-off process. This newly proposed method for gas sensors is cost effective and provides significant enhancement of both sensitivity and selectivity of CO detection. Honeycomb type ZnO nano films developed in ∼21 nm ZnO layer consisting of 1 μm period hexagonal lattice of air-holes with diameter varying from ∼600–900 nm are investigated for CO sensing. These structures are fabricated by a combination of self-assembly of polystyrene (PS) spheres, their size reduction by oxygen plasma and magnetron-sputtering of ZnO followed by PS mask removal. The hole diameter and hence the width of ZnO honeycomb walls are determined by size reduction of PS spheres. Fabricated ZnO honeycomb type sensors show superior sensing performance compared to planar ZnO films, and response as high as ∼81.2% at 300 °C for a 3 ppm CO with a detection resolution of 500 ppb and response and recovery times of ∼180 and ∼210 s, respectively, were obtained. The repeatability of the observed results is confirmed and in addition, the CO selectivity is shown for gas mixtures consisting of CH₄, H₂S, CO₂, NO₂, SO₂ and H₂. The developed nanostructuring method is generic and can be adapted for improving performance of other metal-oxide based gas sensors.