Synthesis and characterization of magnesium doped ZnO nanostructures: methane (CH4) detection

Synthesis of magnesium doped zinc oxide nanostructures has been carried out by vapor transport method and characterization of the samples have been performed regarding methane (CH4) gas sensing in addition to their structural, morphological, chemical composition and optical properties. The un-doped and magnesium doped zinc oxide nanostructures were synthesized on silicon substrates at 900 °C through vapor liquid solid mechanism. Powder X-ray diffraction study confirmed the growth of material exhibiting crystalline wurtzite (hexagonal) structure. Scanning electron microscopy revealed that morphology of grown material is in the form of nanorods and nanobelts with average diameter and thickness of 12.66 ± 3.72 µm and 1.88 ± 0.70 µm, respectively. Energy dispersive X-ray analysis was used to examine the stoichiometry of the samples. Optical characterizations were carried out by photoluminescence, diffused reflectance spectroscopy, voltage dependent photo-current response and Time dependent photocurrent response. A significant change in energy bandgap has been observed after Mg incorporation in ZnO. For doped ZnO samples, the observed value of band gap is 3.32 eV which is higher than that for undoped ZnO (3.18 eV).The nanostructures were tested for UV and gas sensing properties based on the change in resistance in UV light when exposed to CH4 gas. The gas sensing response was recorded for temperature ranging from 50 to 200 °C for 400 ppm concentration of methane gas. The sensing response of Mg-doped ZnO nanobelts was found as high as 54%. The Mg-doped ZnO nanobelts showed significant, stable and enhanced sensing properties (54%) towards 400 ppm of CH4 gas at optimal temperature of 200 °C. The observations revealed that Mg doping in ZnO nanostructures would help to improve the CH4 and UV sensing of these materials.