Determining thermal expansion coefficient of stressed thin films at low temperature

The coefficient of thermal expansion (CTE) is one of the critical design parameters for the application of materials in cryogenic engineering and study of available results demonstrates that thin films have different properties from their bulk counterparts. However, few universal techniques have been developed to measure the CTE of thin films at cryogenic temperatures. Furthermore, the possible effect of the applied stress levels on CTE testing results has not received enough attention. In this study, two novel testing methods, one direct and the other indirect, for determining the CTE of thin films under different applied stress levels at cryogenic temperatures are proposed. The test temperature is from room temperature to 77 K and a lower temperature could be reached. Advantages of the two methods are also discussed.