1-D thermoreflectance measurement technique for freestanding micro/nano cantilever beams

Pump-probe thermoreflectance is a well-known noncontact optical measurement technique for thermal property analysis of thin film materials on a semi-infinite substrate. Two laser lines are commonly used, one of which is used to heat the structure (the pump) and the other is used to measure the change in reflectivity (the probe) to infer thermal properties of the material/structure. This work extends the technique to freestanding cantilever beams. The pump beam applies a constant flux to the free end of the cantilever thereby inducing a thermal gradient along its length which is measured by the probe beam. Measurement of the thermal gradient allows for determination of the thermal conductivity of the material. Convective and radiative heat losses are minimized by performing the experiment at high vacuum and removing the substrate underneath the beam. We demonstrate the technique by measuring the thermal conductivity for four Si cantilever beams that are 1.29 μm thick. The average thermal conductivity for the beams was measured to be 96.9 ± 1.76 Wm^-1K^-1.