Heat Capacity of Copper Thin Films Measured by Micro Pulse Calorimeter

Abstract

Thermal properties of thin films may differ from the bulk value due to the differences in microstructure, such as the grain size, impurities and defects. Heat capacity is one of the thermophysical properties and it is measured by calorimetry. However, traditional calorimeters can’t measure heat capacity of thin films which are quasi-2D and has small heat capacity. Recently, micro calorimeters with suspending membrane structure have been developed to measure the heat capacity of ultra thin films with thickness of sub-micrometer to nanometer scale. Efforts are focused on reducing heat capacitance of the addenda and minimizing the thermal link so as to permit an adiabatic measurement of the heat capacity of thin film. In this paper, a micro pulse calorimeter was developed and heat capacities of the copper thin films were measured by the micro pulse calorimetry. The heating rate of the micro calorimeter is up to 200K/ms with heating power of 4.5mW, and the heat capacity of the calorimeter is about 23.4nJ/K at 300K. Heat capacities of polycrystalline copper thin films with thickness from 20nm to 340nm were measured in the temperature range from 300K to 420K in vacuum of 1mPa. In order to extract the specific heat of the Cu films, mass of the films was calculated with volume and density of the sample film. The specific heat of the Cu films was compared with the literature values of bulk Cu. The specific heat of the 340nm Cu film is close to the literature data of bulk Cu. For the thinner films, enhanced specific heat was observed, and the data shows that the specific heat increases with the decreasing of crystalline size and film thickness.