Helium-dilution effects on thermophysical properties of hydrogenated amorphous carbon thin-films

Thermophysical properties of hydrogenated amorphous carbon thin-films were characterized in the present investigation. Samples were deposited in a direct current plasma enhanced chemical vapor deposition (DC PECVD) system from the discharge of methane (CH4) mixed with helium (He). 5 different films were fabricated with He-to-CH4 flow-rate ratios of 1:1, 2:1, 3:1, 4:1 and 5:1 in order to clarify the dependence of thermal diffusivity (α) on the microstructural changes due to the He-dilution effect. Using an ultrafast optical pump-probe technique, time-domain thermoreflectance signals were collected and the thermal property was extracted using the Paddock and Eesley model (1986). Results show strong correlation of α to the changes of sp2 carbon cluster determined by spectroscopic measurements.

► Measurements of thermal diffusivity α of hydrogenated amorphous carbon thin films using the optical pump-probe method ► Variations of thermal diffusivity α with helium-dilution of pure CH4 discharge ► Strong relations between the thermal diffusivity α and the microstructural changes in the sp2 C cluster