Thermopower in thin-film copper-Constantan couples

Abstract

The thickness dependence of the thermal emf of thin-film copper-constantan thermocouples at room temperature and above shows nearly bulklike behavior when the thickness of both elements comprising the thermocouple is greater than ∼1200 Å. The thermal response time of the thermocouples as measured with a pulsed laser beam heating source is less than 10^-6 sec. The thickness-dependent contribution to the thermopower of copper films is deduced from the thermal emf data on thermocouples formed with a thick constantan film and compared with the size-effect theory based on the free-electron model. The marked thickness dependence observed yields anomalously high dependence (an order-of-magnitude higher) of the mean free path on the energy of electrons. This result is tentatively ascribed to the thermopower behavior of a transition layer formed by diffusion of the two components of the thermocouples.