Electrical, optical and structural properties of e-beam deposited manganese dioxide (MnO2) thin films for selective surface application

Abstract

MnO2 thin films of thickness ranging from 55 to 250 nm have been prepared bye-beam deposition technique onto glass substrate at two pressures, namely at about 2x10·5 torr and at about 6xl 0 -6 torr, respectively and the deposition rate was about 3 nm/sec. MnOz thin films were characterized through X-ray diffraction technique. These studies hint that the films are amorphous in nature. Electrical conductivity was measured as a function of temperature ranging from 303 to 403K and exhibits an anomaly in conductivity at a temperature 323 K. The films deposited at about 2xl 0·5 torr show the electrical conductivity metallic in character by indicating positive Temperature Coefficient of Resistance (TCR), whereas a negative Temperature Coefficient of Resistance (fCR) indicating semiconducting behaviour exhibits on the films deposited at a pressure of about 6x10-6 torr. This result, therefore, suggests that preparation and properties of MnO2 films are very much dependent on ambient pressure. It is seen that the activation energy for the samples are fairly low. It is also observed that the activation energy was inversely proportional with the film thickness above the anomaly and was directly proportional below the anomaly temperature. Thickness-dependent electrical conductivity study was done in semiconducting MnO2 films and it was seen that below 200nm thickness, the film shows thickness-dependent property and above this range the film has thickness-independent behaviour which is in good agreement with Fuchs-Sondheimer theory