The enhancement of heat conduction across the metal/graphite interface treated with a focused ion beam†
In this work, we report a convenient and efficient approach to improve heat conduction across the metal/graphite interface. It is demonstrated that the interfacial thermal conductance between Al and graphite can be enhanced by a factor of ∼5 after milling the graphite with a focused ion beam. Such enhancement is attributed to the decreased Fermi level of the milled graphite compared with the pristine counterpart. Once graphite is milled with the focused ion beam, surface defects are formed that induce the redistribution of electrons at the interface between Al and graphite. The formation of enormous dipoles on the milled graphite/Al interface leads to the conversion of the interfacial interaction from physisorption to chemisorption, which is beneficial for phonon transmission across the interface. Based on the measured Fermi level difference, the non-equilibrium Green's function method predicts that the interfacial interaction strength in the Al/milled graphite is increased 4-fold compared with Al/pristine graphite, which causes the increase of the interfacial thermal conductance. Our theoretical model also predicts that the interfacial thermal conductance does not increase monotonically with the interaction strength. Once the interaction strength exceeds a critical value, the interface thermal conductance will decrease.