Applied Surface Science, Vol.423, 1012-1018, 2017
A study on the electrical properties of Mn-Co-Ni-O thin films grown by radio frequency magnetron sputtering with different thicknesses
This study provides an insight to understanding the role of thickness on the hopping frequency (v(0)) of electrons between Mn3+ and Mn4+, the temperature coefficient of resistance (alpha(T)) and the characteristic temperature (T-0) in Mn-Co-Ni-O spinel films. A remarkable decrease in the Mn3+/Mn4+ ratio of films from 265 to 693 nm and an increase in the range of 693-887 nm can be probed by x-ray photoelectron spectroscopy. From the analysis of the Hall measurements, it is found that both the 1/v(0) and alpha(T) = 303K increase with the thickness below 693 nm, and then decrease above 693 nm. Such a feature is attributed to the change in the distribution of Mn cation. The T-0 are 3675, 3352, 3087, 3366 and 3816 K for films with thicknesses from 265 to 887 nm. It reveals that the ratio of Mn3+/Mn4+ should also be responsible for T-0, which can result in significantly different electrical properties of Mn-Co-Ni-O films with increasing thickness. The present result will open a way to design a desired negative temperature coefficient thermistor by adjusting the thickness of films. (C) 2017 Elsevier B.V. All rights reserved.