In-plane thermal conductivity measurements of Si thin films under a uniaxial tensile strain

At the atomic level, heat is viewed as energy for lattice vibrational waves, i.e., a mechanical wave. Correspondingly, the strain as atomic displacement can have a profound impact on the thermal transport. Despite numerous atomistic simulations, fewer experimental efforts can be found for strain-dependent thermal properties of individual nanostructures and thin films. In this work, suspended 2 μm-thick Si films were stretched to reveal the influence of the uniaxial tensile strain on in-plane thermal conductivity along the stretching direction. In a high vacuum, the room-temperature thermal conductivity of a 2 μm-thick Si film decreased from 135.5 ± 6.9 to 127.2 ± 6.5 W/m K under a ∼0.44% tensile strain. This thermal conductivity decrease followed the predicted trend for Si films. In addition, the heat transfer coefficient of representative thin films in the air was also measured to reveal the impact of the heat loss along the sample sidewall on previous in-air thermal measurements.