Limited thermal conductance of metal-carbon interfaces

The thermal conductance for a series of metal-graphite interfaces has been experimentally measured with time-domain thermoreflectance (TDTR). For metals with Debye temperatures up to ∼400 K, a linear relationship exists with the thermal conductance values. For metals with Debye temperatures in excess of ∼400 K, the measured metal-graphite thermal conductance values remain constant near 60 MW m⁻² K⁻¹. Titanium showed slightly higher conductance than aluminum, despite the closeness of atomic mass and Debye temperature for the two metals. Surface analysis was used to identify the presence of titanium carbide at the interface in contrast to the aluminum and gold-carbon interfaces (with no detectable carbide phases). It was also observed that air-cleaved graphite surfaces in contact with metals yielded slightly higher thermal conductance than graphite surfaces cleaved in vacuo. Examination of samples with scanning electron microscopy revealed that the lack of absorbed molecules on the graphite surface resulted in differences in transducer film morphology, thereby altering the interface conductance. Classical molecular dynamic simulations of metal-carbon nanotube thermal conductance values were calculated and compared to the TDTR results. The upper limit of metal-graphite thermal conductance is attributed to the decreased coupling at higher frequencies of the lighter metals studied, and to the decreased heat capacity for higher vibrational frequency modes.