Pressure dependence of the thermal contact resistance at the Si/He interface

For bulk solid-solid interfaces, the thermal contact resistance TCR) is generally attributed to a mismatch in the acoustic impedances (density x sound velocity) of each medium [1]. Here, we present a novel study of the TCR for a bulk Silicon crystal (111) in contact with superfluid helium, as a function of the acoustic impedance of the superfluid. The cell design and experimental technique are discussed in [2]. The acoustic impedance is varied by monitoring the pressure of the superfluid. Measurements are carried-out at T∼1.8 K, from a few torrs (vapor pressure) up to 25 bars, corresponding to approximately an 80% change in the acoustic impedance of the superfluid. The experiments show no change in TCR over the entire pressure range, indicating a negligible contribution due to the acoustic impedances. A comparison to the diffuse mismatch model [1] is discussed.