H₂ sensing properties of two-dimensional zinc oxide nanostructures.
In this work we have grown particular zinc oxide two-dimensional nanostructures which are essentially a series of hexagonal very thin sheets. The hexagonal wurtzite crystal structure gives them their peculiar shape, whose dimensions are few microns wide, with a thickness in the order of 25 nm. Such kind of nanostructure, grown by thermal oxidation of evaporated metallic zinc on a silica substrate, has been used to fabricate conductometric gas sensors, investigated then for hydrogen gas detection. The "depletion layer sensing mechanism" is clarified, explaining how the geometrical factors of one- and two-dimensional nanostructures affect their sensing parameters. The comparison with one-dimensional ZnO nanowires based structures shows that two-dimensional nanostructures are ideal for gas sensing, due to their tiny thickness, which is comparable to the depletion-layer thickness, and their large cross-section, which increases the base current, thus lowering the limit of detection. The response to H₂ has been found good even to sub-ppm concentrations, with response and recovery times shorter than 18s in the whole range of H₂ concentrations investigated (500 ppb-10 ppm). The limit of detection has been found around 200 ppb for H₂ gas even at relatively low working temperature (175 °C).
IMEM CNR, sede di Trento - FBK, Via alla Cascata 56/C, Povo - Trento, Italy. Electronic address: matteo.tonezzer@cnr.it.
Matteo
M
Tonezzer
IMEM CNR, Parco Area delle Scienze 37/A, I-43124 Parma, Italy.
Salvatore
S
Iannotta
D006859:Hydrogen / Q000032:analysis*; D049329:Nanostructures / Q000737:chemistry*; D056951:Photoelectron Spectroscopy / Q000379:methods; D015034:Zinc Oxide / Q000737:chemistry*
D006859:Hydrogen; D015034:Zinc Oxide
Gas sensor; Hydrogen; Nanostructure; Zinc oxide