Abstract
Room-temperature time-domain thermoreflectance technique (TDTR) measurements of cross-plane heat conduction across gold-graphene-silicon interfaces are presented. The graphene layers are originally grown on a copper substrate by chemical vapor deposition and later transferred to a silicon substrate in layer-by-layer fashion. We estimate the thermal boundary conductance (TBC) as a function of number of graphene layers, by fitting a layered heat conduction model that accounts for heat accumulation in the gold layer to the TDTR data, using the TBC as a free fitting parameter. The estimated TBC was found to decrease with number of graphene layers at the interface, as observed in previous TDTR measurements reported in the literature. The decrease in TBC with number of graphene layers matches the trends in the transmission coefficient of low frequency (25 GHz) coherent acoustic phonons across the interface, indicating that the interface elastic stiffness decreases with the number of graphene layers due to poor bonding between the gold film and silicon substrate.
Highlights
Other factors such as, the acoustic impedance mismatch of layers and the nature of the bonding between graphene, metal film, and silica substrate may limit the cross-plane heat conductance, especially where majority of the heat carriers are thermal phonons
We report the cross-plane thermal boundary conductance (TBC) for chemical vapor deposition (CVD)-grown fewlayered (1-7) graphene sandwiched between a gold thin film and a silicon substrate measured by the time-domain thermoreflectance (TDTR) technique at room temperature
The coherent acoustic wave transmission coefficient depends on the acoustic impedance mismatch between the gold film and silicon substrate and the interface stiffness between the two materials
Summary
Other factors such as, the acoustic impedance mismatch of layers and the nature of the bonding between graphene, metal film, and silica substrate may limit the cross-plane heat conductance, especially where majority of the heat carriers are thermal phonons. We report the cross-plane TBC for CVD-grown fewlayered (1-7) graphene sandwiched between a gold thin film and a silicon substrate measured by the TDTR technique at room temperature. We observed that the decrease in TBC with number of graphene layers agree qualitatively with measured coherent acoustic wave transmission coefficient across the layered system, obtained using the picosecond ultrasonic technique.
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