Preparation and characterization of thin film thermistors of metal oxides of manganese and vanadium (Mn-V-O)

摘要

Thin films of mixed metal oxides of manganese and vanadium (Mn-V-O) have been prepared by electron beam evaporation technique for the first time. Chemical composition, surface morphology and electrical and optical properties of thin films have been studied using energy dispersive analysis of x-ray (EDAX), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-VIS-NIR spectrometer. It is observed by X-ray diffraction analysis that all the thin films of Mn-V-O are amorphous. The XPS analyses indicate the core level binding energies correspond to Mn (2p), V (2p) and O (1s). The study of electrical properties clearly show that all the thin films follow a typical characteristics of negative temperature coefficient (NTC) resistivity, with activation energy varying from 0.274 to 0.358 eV, which is attributed to small polaron hopping. The observed temperature of coefficient of resistivity (TCR) is found to be comparable with TCR of many of the known thermistor materials. All the thin film samples are found to have optical band gaps varying from 2.66 to 3.17 eV which are marginally different from the band gaps of MnO and V _2O_5. The optical absorption characteristics in near infrared region show enhanced absorption compared to visible region which are attributed to presence of defect states due to V~(4+), oxygen ion vacancies and energy states due to polarons.