Thermal conductivity of nano- and micro-crystalline diamond films studied by photothermal excitation of cantilever structures

Polycrystalline diamond films have unique structural and thermal properties that make them suitable for use in extreme environments. Recently, they have been utilized in accelerator beamlines for electron stripping due to their unique combination of mechanical and thermal properties. Thermal conductivities of nanocrystalline diamond (NCD) and microcrystalline diamond (μCD) films were characterized using photothermally actuated bimaterial cantilevers. Approximately one micrometer thick NCD and μCD cantilevers were fabricated from microwave plasma enhanced chemical vapor deposition grown polycrystalline diamond (PD) films. A layer of gold was sputtered on the diamond film surfaces to make bilayer cantilevers and the thermal response time was measured by photothermally exciting the bilayer cantilevers, causing them to deflect. Finite element thermomechanical modeling of the deflection dynamics in response to photothermal actuation was performed to determine the NCD and μCD thermal diffusivities and conductivities. By fitting the simulated and experimentally observed response times, thermal conductivities of 10 and 60 W/(m-K) were extracted for the NCD and μCD samples, respectively. Expected changes in thermal conductivity of PD in higher temperature regimes are also discussed. In addition to applications of PD films as electron stripping foils, these findings also have implication in fields such as micro/nano-electromechanical systems.