Heat transfer and thermoelectric voltage at metallic point contacts

Metallic point contacts have been extensively studied from the viewpoint of their interesting, and often nonlinear, electrical properties. Their thermal characteristics, however, have largely been ignored, even though they show great potential as microscale temperature sensors. It has been previously demonstrated that when a temperature drop exists across a point contact consisting of two identical metals, a thermoelectric voltage can be generated, provided the mean contact radius is comparable in size to the electron mean free path. In the present experimental study, a point contact is formed by pressing a sharply etched Ag whisker against either a Ag or a Cu flat plate. In addition to confirming the previous results, the feasibility of using such a point contact is demonstrated by calibrating the voltage output against the nondimensionalized plate temperature. Furthermore, the thermoelectric voltage at a Ag-Cu point contact is also presented, showing that a point contact made from dissimilar metals is even more promising than one made from identical materials. Finally, the point-contact thermal resistance is demonstrated to depend nonlinearly on the electrical resistance, or contact area, and on the temperature drop.