Performance enhancement of humidity sensors made from oxide heterostructure nanorods via microstructural modifications

Abstract

We reported the fabrication of a highly sensitive and fast switchable humidity sensor based on ZnO-TiO 2 core-shell nanorods that were synthesized using hydrothermal solution and atomic layer deposition. These nanorods were thermally treated under various physical conditions to improve their sensing performance.The structural investigation revealed that the crystal and microstructure changed with the thermal treatment. Notably, the amorphous TiO 2 shell layer transformed into various degrees of crystalline phase after annealing in air and a vacuum at 400 C. Furthermore, the responses of the sensors fabricated from the ZnO-TiO 2 nanorods, with and without thermal annealing, to relative humidity (RH) changes were proportional with the increase in humidity. Among various samples, ZnO-TiO 2 nanorods thermally treated in a vacuum exhibited the highest humidity selectivity in response to the cyclic changes in humidity from 11% RH to 33-95% RH at room temperature. Possible mechanisms for the enhancement of sensor performance have been discussed based on structural modifications caused by the thermal treatments.

High-temperature solid-state reaction induced structure modifications and associated photoactivity and gas-sensing performance of binary oxide one-dimensional composite system

“…The detailed preparation procedures for the hydrothermal growth of the ZnO nanorods have been reported elsewhere. 17 During growth of the SnO 2 shell layers onto the surfaces of the ZnO rods, the DC sputtering power of Sn metallic target was xed at 30 W. The thin-lm growth temperature was maintained at 325 C with an Ar/O 2 ratio of 25 : 15. The gas pressure during sputtering thin-lm deposition was xed at 2.67 Pa. For preparation of ZnO-ZTO composite nanorods, the as-synthesized ZnO-SnO 2 core-shell nanorods were subsequently annealed in ambient air for 1 hour at the high temperature of 900 C to induce a high-temperature solid-state reaction between the ZnO core and SnO 2 shell and formed the ZnO-ZTO core-sell nanorods.…”

Improvement of Ethanol Gas-Sensing Responses of ZnO–WO3 Composite Nanorods through Annealing Induced Local Phase Transformation

“…Although various ZnO-based composite systems have been proposed to improve the gas-sensing responses to target gases, the reports on construction of one-dimensional ZnO–WO 3 composite system are still limited in number. Moreover, thermal annealing of solid materials is an efficient method to modulate their microstructures and to control their physical and chemical properties [13,14]. The past research works show that conducting proper thermal annealing procedures causes the possible solid-state reaction between the constituent oxides in a nanoscale in low-dimensional oxide systems [15,16].…”

Structure-dependent gas detection ability of clustered ZnS crystallites with heterostructure and tube-like architecture

“…The synthesis of vertically aligned ZnO rods consisted of two steps corresponding to the formation of ZnO seed layer and the growth of rods. The detailed experiment on the synthesis of hydrothermally synthesized ZnO rods has been described elsewhere [20]. The as-synthesized ZnO rods were immersed in a Teflon autoclave containing 0.05 M Thioacetamide (TAA) aqueous solution.…”