Thermal Conduction of Polycrystalline Diamond Thin Films and Crystalline Diamond Substrate Studied by Ultrafast Optical Spectroscopy
Hao-Yu Cheng1*, Chi-Yuan Yang1,2, I-Nan Lin3, Chih-Ta Chia4, Kun-Cheng Peng5, Kung-Hsuan Lin1
1Institute of Physics, Academia Sinica, Taipei, Taiwan
2Department of Physics, National Taiwan University, Taipei, Taiwan
3Department of Physics, Tamkang University, New Taipei City, Taiwan
4Department of Physics, National Taiwan Normal University, Taipei, Taiwan
5Department of materials Engineering, Ming Chi University of Technology, New Taipei City, Taiwan
* presenting author:Hao-Yu Cheng,
Crystalline diamond possesses several fascinating properties such as high hardness, electron-emitting surfaces, and low friction. The use of diamond thin films, instead of bulk diamond, enables further applications such as surface acoustic wave (SAW) devices, electrochemical electrodes, microelectromechanical systems (MEMS) and flat-panel displays. For electronic devices, thermal management is an important issue. We conducted ultrafast optical spectroscopy to study thermal conduction of polycrystalline diamond thin films and crystalline diamond substrate synthesized by plasma-enhanced chemical vapor deposition (PECVD). Optical pump beams were focused onto the Al thin films, which were coated on the studied samples, to generate heat. We measured the transient reflectivity of the probe beams and monitored the temporal variation of temperature in the top Al thin film up to 6 ns. This so-called time-domain thermolreflectance (TDTR) technique enabled us to obtain the thermal conductivities of polycrystalline diamond thin films and crystalline diamond substrate. The synthesized crystalline diamond substrate exhibited ultrahigh thermal conductivity, which is similar to the thermal properties of naturally crystalline diamond. In contrast, the thermal conductivities of polycrystalline diamond thin films highly depend on the grain sizes. In this work, we have studied the samples with grain size ranging from a few microns down to a few nanometers. Detailed results and discussions will be presented in the conference.

Keywords: Thermal conductivity, Polycrystalline diamond, Crystalline diamond, Time-domain thermolreflectance