The structural, optical, and gas-sensing properties of spray pyrolysis deposited Cu doped ZnO thin films were investigated. Gas response of the undoped and doped films to N02 (oxidizing) gas shows an increase and decrease in resistance, respectively, indicating p-type conduction in doped samples. The UV-Vis spectra of the films show decrease in the bandgap with increasing Cu concentration in ZnO. The observed p-type conductivity is attributed to the holes generated by incorporated Cu atoms on Zn sites in ZnO thin films. The X-ray diffraction spectra showed that samples are polycrystalline with the hexagonal wurtzite structure and increasing the concentration of Cu caused a decrease in the intensity of the dominant (002) peak. The surface morphology of films was studied by scanning electron microscopy and the presence of Cu was also confirmed by X-ray photoelectron spectroscopy. Seebeck effect measurements were utilized to confirm the p-type conduction of Cu doped ZnO thin films. Copyright © 2009 American Scientific Publishers All rights reserved

The breadth and depth of applications for two-dimensional (2D) materials which, by their nature, are nanoscale and layer structured with a high surface to volume ratio, are extensive and rapidly transforming the field of gas sensing. Facile preparation methods, as well as novel electronic and surface properties that enable functionalisation, provide high sensitivity for gases commonly encountered in natural and industrial environments. Gas sensors that are operational at room temperature offer low power demand and thermal safety during analysis. This review focuses on room-temperature gas sensing performance of conductometric devices employing 2D hybrid nanomaterials including layered transition metal dichalcogenides (TMDs) and graphene materials. The effect of hybridisation of 2D nanomaterials on gas sensing performance and their sensing mechanisms are studied. Hybrid forms of 2D materials occur by the addition of metals, or polymers to surface sites, or by combining two or more different materials (i.e. nanocomposites) or by developing a heterojunction layer, which lead to enhanced collective performance. Gas sensing mechanisms depend on the type and format of 2D material but fundamentally involve gas adsorption on an active surface with a resultant change in the resistive property of the material.