Experimental investigations on fast gold-tin metal film second-sound detectors and their application

Abstract

In order to optimize gold-tin metal film probes as bolometers for measurement of fast second-sound signals in He II, the influence of their composition and of annealing on their electrical properties at low temperatures was investigated systematically. Measurements of the dependence of the voltage-current characteristics on temperature were supplemented by electron microscopy of the film surfaces and by measurement of the resistivity of the composed films at room temperature as a function of the atomic percentage of tin. Fast interdiffusion, which took place after evaporating typically 1000 A of tin onto 200 A of gold, resulted in the development of different phases of the Au-Sn system in the layer. Due to proximity effects between grains of these phases the transition temperature of such a film is reduced to the temperature range of He II. Different types of weak-link behavior which may govern the current-induced breakdown of superconductivity are discussed. As an example of the application of the metal film probes, the circulation of a macroscopic vortex ring was measured using the flow-induced variation of the traveling times of second-sound shock waves. Values of up to several cm2/sec were thus obtained to an accuracy of some 10−2 cm2/sec.