Anodic vacuum arc developed nanocrystalline Cu–Ni and Fe–Ni thin film thermocouples

Abstract

This paper deals with the development of nanocrystalline Cu–Ni and Fe–Ni thin film thermocouples (TFTCs) by using ion-assisted anodic vacuum arc deposition technique. The crystallographic structure and surface morphology of individual layer films have been studied by x-ray diffraction and scanning electron microscopy, respectively. The resistivity, temperature coefficient of resistance, and thermoelectric power of as deposited and annealed films have been measured. The observed departure of these transport parameters from their respective bulk values can be understood in terms of intrinsic scattering due to enhanced crystallite boundaries. From the measured values of thermoelectric power and the corresponding temperature coefficient of resistance of annealed Cu, Ni, and Fe films, the calculated values of log derivative of the mean free path of conduction electrons at the Fermi surface with respect to energy (U) are found to be −0.51, 3.22, and −8.39, respectively. The thermoelectric response of annealed Cu–Ni and Fe–Ni TFTCs has been studied up to a maximum temperature difference of 300°C. Reproducibility of TFTCs has been examined in terms of the standard deviation in thermoelectric response of 16 test samples for each pair. Cu–Ni and Fe–Ni TFTCs agree well with their wire thermocouple equivalents. The thermoelectric power values of Cu–Ni and Fe–Ni TFTCs at 300°C are found to be 0.0178 and 0.0279mV∕°C, respectively.