H2 sensing properties in highly oriented SnO2 thin films

Highly oriented polycrystalline SnO2 films were deposited on the sapphire substrates with various orientations using rf magnetron sputtering, and the effects of the crystallographic orientation on the H, gas sensing performance were investigated. The orientation of the SnO2 films was varied with the substrate orientation such that (10 1), (0 0 2), and (1 0 1) oriented films were grown on (1 1 (2) over bar 0) (a-cut), (1 0 (1) over bar 0) (m-cut), and (1 (1) over bar 0 2) (r-cut) Al2O3 substrates, respectively. More than one preferred orientation was observed in the films deposited on (0 0 0 1) (c-cut) Al2O3, quartz, and SiO2 (20,000 angstrom)/Si substrates. All the films had a similar thickness (similar to 115 nm), root-mean-square (rms) roughness (similar to 1 nm), and surface area, and therefore the sensing performance of each film was little affected by the microstructure. The (1 0 1) SnO2, films grown on (1 (1) over bar 0 2) Al2O3 exhibited the highest H-2 gas response (R-o/R-g) of similar to 300 to 1.0% H-2/air, and the other films showed an order of magnitude lower gas response. The chemical composition and surface state of the films were further examined by AES and XPS to find out the reasons for the different H, gas response of the (10 1) films grown on (1 1 (2) over bar 0) and (1 (1) over bar 0 2) Al2O3. (C) 2007 Elsevier B.V. All rights reserved.