Thermal conductivity measurements on suspended diamond membranes using picosecond and femtosecond time-domain thermoreflectance

We report on the room temperature in-plane thermal conductivity measurements on a 1-micrometer thick suspended diamond membrane grown by chemical vapor deposition using two different time domain thermoreflectance (TDTR) setups. The first setup is at Stanford University and the second is at Georgia Institute of Technology. Despite the differences between the two setups and the difficulty associated with diamond membranes thermal measurements, we demonstrate excellent repeatability from each setup and a very good agreement between the two setups. The paper outlines steps considered by both groups to minimize the measurement uncertainty and achieve such agreement. The measurement results show that the thermal conductivity displays a large variability across the membrane. The sensitivity and uncertainty analyses suggest that this variability could be a result of the nonuniformity in the diamond and aluminum coating thicknesses across the sample.