Thermal contact conductance of adhered microcantilevers

The thermal contact conductance $G$ for polycrystalline silicon cantilever beams that are adhered to an underlying substrate is examined using two different optical techniques. Using time-domain thermoreflectance, we measure $\text{G=9±2\hspace{0.17em}}{\mathrm{MW m}}^{\text{−2}} {\mathrm{K}}^{\text{−1}}$ at $\text{25\hspace{0.05em}°}\mathrm{C}$ and $\text{G=4±1\hspace{0.17em}}{\mathrm{MW m}}^{\text{−2}} {\mathrm{K}}^{\text{−1}}$ at $\text{150\hspace{0.05em}°}\mathrm{C}.$ The room temperature value is confirmed using a modified Ångström method, which establishes a lower limit of $\text{G>5\hspace{0.17em}}{\mathrm{MW m}}^{\text{−2}} {\mathrm{K}}^{\text{−1}}.$ This contact conductance is a factor of ${\text{10–10}}^5$ greater than values reported for metal–metal and ceramic–ceramic interfaces. The large interfacial conductance is consistent with the presence of a thin layer of water trapped between the cantilever and the substrate. The thermal conductivity Λ of the phosphorus doped polysilicon cantilever is nearly isotropic with ${\Lambda }_{\mathrm{cross\hspace{0.17em}plane}}\text{=65\hspace{0.17em}}{\mathrm{W m}}^{\text{−1}} {\mathrm{K}}^{\text{−1}},$ and ${\Lambda }_{\mathrm{in\hspace{0.17em}plane}}\text{=70\hspace{0.17em}}{\mathrm{W m}}^{\text{−1}} {\mathrm{K}}^{\text{−1}}$ at room temperature.