Transient thermoreflectance from graphene composites with matrix of indium and copper

Transient thermoreflectance was measured from In and In-graphene composite films pressed on to different substrates that include Si, GaAs, Cu and Cu-graphene composite. Measurements were also made from Al film deposited on substrates of Cu and Cu-graphene composite. The experimental results were modeled using solution to the thermal diffusion equation to determine the thermal conductivity of the phases and thermal conductance of the interface. The In-graphene and Cu-graphene composites are found to spread the heat more rapidly than In and Cu, respectively. The interface thermal conductance of In or In-graphene film pressed on to Cu was found to be smaller than the observed values for metal-metal contacts reported in the literature although higher than the value observed for the interface between Pb-Sn eutectic solder alloy bonded to Cu. The interface thermal conductance between Al film deposited on mechanically polished Cu or Cu-graphene composite is also found to be much lower than the value observed previously. The smaller value of interface thermal conductance of either In or In-gr or Al film on different substrates is explained by absence of atomic level bonding, presence of rough surfaces with incomplete contact and oxygen or water vapor at the interface.