Catherine Lozano

Major: Aerospace Engineering
Mentors: Yujie Quan, Professor Bolin Liao

Finding Materials with High Reflectivity and Thermal-Optic Coefficient for the use of Low-Temperature TDTR Measurement

Time-domain Thermoreflectance (TDTR) is a method that measures a materials thermal properties at different temperatures. A metal trans- ducer whose reflectivity changes linearly with the surface temperature is used in TDTR to indicate the time-dependent heat distribution. Due to the high reflectivity as well as the high thermo-optical coefficient, aluminum is utilized as a transducer in TDTR in room temperatures. However, the thermal-optical coefficient of aluminum decreases a lot at low temperatures, interfering with capture of the TDTR signal. To improve the signal magnitude and quality, metals with both high re- flectivity and thermal-optic coefficients at low temperatures are sought to advance TDTR signal capture in low-temperature TDTR. Out of selected metal samples, which exhibit a high reflectance, and thermal optic coefficient? To find the reflectance and the thermal optic coefficient we use a Ti- Sapphire laser which outputs onto the transducer above the metal sam- ple creating a reflected signal. Comparing the reflected signal to the reference signal which is our reflected signal but at room temperature, we can get reflectivity values at different temperatures and thus calculate the thermal-optic coefficient, which is the derivative of reflectivity as a function of temperature. Changes between signals is small, so to successfully measure, a balance detector compares the reflected and reference signal. Our preliminary results consist of running simulations based on the Drude model on various metals, as well as designing and optimizing the methods for measuring reflectivity as a function of temperatures. 34 Success in finding proper materials will enable the cryogenic TDTR measurement.