Thermal conductivity measurements of ultrananocrystalline diamond thin films by time domain thermo reflectance techniques
Hao-Yu Cheng1,2*, Chi-Yuan Yang1, I-Nan Lin3, Shiu-Jen Liu2, Chih-Ta Chia2, Kung-Hsuan Lin1
1Institute of Physics, Academia Sinica, Taipei, Taiwan
2Department of Physics, National Taiwan Normal University, Taipei, Taiwan
3Department of Physics, Tamkang University, Taipei, Taiwan
* presenting author:鄭皓宇,
Crystalline diamond possesses several fascinating properties such as high mechanical hardness, high thermal conductivity, low friction, and bio-compatibility. However, diamond thin films do not always possess the same properties of crystalline diamond. It was demonstrated that the properties of diamond thin films vary a lot depending on the growth techniques and parameters. It is thus possible to optimize the properties of diamond thin films for particular applications. In this poster, we present the thermal properties of ultrananocrystalline diamond (UNCD) thin films with different deposition parameters. The UNCD thin films were engineered at nanoscale by introducing H2 in the commonly used Ar/CH4 deposition plasma in a microwave plasma enhanced chemical vapor deposition (MPECVD) system [I-Nan Lin 2013 paper]. The presence of H2 influenced the granular structure of diamond films, resulting in different thermal properties. We utilized time domain thermoreflectance (TDTR) techniques to measure the thermal conductivities of UNCD thin films deposited with different growth conditions. The thicknesses of the UNCD films were measured by scanning electron microscope. For TDTR measurement, all of the UNCD films were coated with an Al thin film. After the optical pump pulses generated heat in the Al thin film, we monitored the time evolution of temperature near the surface of the Al film up to a few nanoseconds. We used a heat flow model to fit the TDTR traces and obtained the thermal conductivities of UNCD thin films with different granular structures. The longitudinal acoustic velocities of the UNCD films were also obtained.

Keywords: ultrananocrystalline diamond, time domain thermoreflectance, thermal conductivity