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Journal of Alloys and Compounds, Volume 511, Issue 1, 15 January 2012, Pages 14-21
S.K. Mukherjee, P.K. Barhai
Department of Applied Physics, Birla Institute of Technology Mesra, Ranchi 835215, Jharkhand, India
Abstract
Inductively coupled plasma optical emission spectrometry (ICP-OES) was applied for the analysis of major and minor elements of thermoelectric alloys (Constantan, Chromel and Alumel) and their thin films deposited using anodic vacuum arc (AVA) plasma deposition technique. Digestion of samples was done in aqua regia. The minor and trace elements were determined without matrix separation. The precision for all the constituents was <3%. The changes in the composition of these alloy films were studied as a function of number of deposition cycles and also with various positions of the samples on the substrate holder. Due to the difference in the evaporation rates of the alloy constituents and the interaction of Ni with the refractory basket, the AVA deposited films showed varying compositions in the initial cycles of deposition. However, a good agreement was obtained among the samples deposited on various positions of the substrate holder, suggesting a uniform plasma flux in the system. Films deposited using Constantan wires were much enriched with Cu. By depositing bilayers of Cu and Ni, followed by post annealing, we were able to produce films in which the Cu and Ni concentrations were similar to that of Constantan. A deviation of ∼15% was observed among 10 Cu films of thickness ∼300 nm deposited using this technique. AVA deposited films of Chromel and Alumel having Ni (≥90%) could be developed without much alteration in their composition.
Additional Information
Thin film thermocouples (TFTCs) are the prototypes of wire thermocouples. They are commonly preferred where measurement of surface temperature with minimal intrusion is a dire necessity such as, for temperature measurements inside jet aircraft engines, combustion chambers, etc. Their remarkable properties include very fast response to temperature changes, very high spatial resolution and ability to form an integral part of the component whose temperature is being measured. The work was conducted by Sanat Kumar Mukherjee in Plasma and Thin Film Laboratory of Birla Institute of Technology, Ranchi, INDIA under the supervision of Prof. P. K. Barhai with an aim to develop TFTC prototypes of conventional thermocouples.
