Effect of incorporating graphene oxide in ZnS and study of the thermistor applications of ZnS-RGO film

Abstract

We report the effect of incorporating graphene oxide in ZnS and developed a ZnS-RGO hybrid film with negative temperature coefficient (NTC) for thermistor application towards temperature sensing in this study. The light sensing properties of the films were also investigated by exposing the film to light sources from mercury and tungsten lamp and recording the photo resistance. As the composition of ZnS in ZnS-RGO increased, sharper diffraction peaks were observed thus confirming improved crystallinity. The crystallite size of ZnS-RGO hybrid decreased from 4.02 to 1.87 nm while the lattice strain increased from 0.0086 to 0.0185 as the composition of ZnS in the hybrid increased. ZnS-RGO recorded a maximum sensor response of 1.91 which is approximately twice the maximum value obtained for pure ZnS in literature. The negative temperature coefficient (NTC) for ZnS-RGO (0.00174825/K) was higher than values obtained in literature for ZnS and Ag nanoparticles coated RGO. Furthermore, the sensitivity value of ZnS-RGO (0.00769 Ω/ K) was five times that of ZnS while the activation energy (0.0352 eV) was about seven times the value reported for ZnS. The increase in activation energy of ZnS-RGO compared to ZnS is responsible for the improved sensing response of the hybrid while the intercalation of ZnS in GO created reactive sites that resulted in activation energy, sensing response and an NTC much higher than in pure ZnS thus favoring utilization of ZnS-RGO as thermistors. This research has shown that ZnS, intercalated in the matrix of GO improved the thermal and photo sensing properties of ZnS and is thus suitable in thermistor applications. These properties can be used to suggest the application of ZnS-RGO in optoelectronic applications such as EM detectors, solar cells and temperature monitoring devices.