Graphene Layer Number-Dependent Heat Transport across Nickel/Graphene/Nickel Interfaces

Abstract

As a typical two-dimensional material, graphene (Gr) has shown great potential to be used in thermal management applications due to its ultrahigh in-plane thermal conductivity (k). However, low interface thermal conductance (ITC) between Gr and metals to a large extent limits the effective heat dissipation in Gr-based devices. Therefore, having a deep understanding on heat transport at Gr–metal interfaces is essential. Because of the semimetallic nature of Gr, electrons would possibly play a role in the heat transport across Gr–metal interfaces as heat carriers, whereas, However, how much the electron can participate in this process and how to optimize the total ITC considering both electron and phonon transportations have not yet been revealed yet. Therefore, in this work, hydrogenation-treated Gr (H-Gr) was sandwiched by nickel (Ni) nanofilms to compare with the samples containing pure Gr for investigating the interfacial electron behaviors. Moreover, both Gr and H-Gr sets of the samples were prepared with different layer numbers (N) ranging from 1 to 7, and the corresponding ITC was systematically studied based on both time-domain thermoreflectance measurements and theoretical calculations. We found that a larger ITC can be obtained when N is low, and the ITC may reach a peak value when N is 2 in certain circumstances. The present findings not only provide a comprehensive understanding on heat transport across Gr-metal interfaces byconsidering a combined effect of the interfacial interaction strength, phonon mode mismatch, and electron contributions, but also shed new lights on interface strucure optimiazations of Gr-based devices.

Quantifying Interfacial Bonding Using Thermal Boundary Conductance at Cubic Boron Nitride/Copper Interfaces with a Large Mismatch of Phonon Density of States

“…Time-domain thermoreflectance (TDTR), a technique with ultrahigh temporal and spatial resolutions, has been widely applied to measure the thermal properties of both bulk materials and nanostructured materials. , Meanwhile, TDTR is a nondestructive and noncontact pump–probe technique to study heat transport across heterogeneous interfaces, merely by depositing a metal transducer layer on the target material surface. Particularly, assisted by the equipped high-resolution optical microscopy, TDTR can ensure precise testing locations. , In addition, by combining the interface microstructure and measured thermal boundary conductance ( G ), the single effect of interface characteristics on electron and phonon scattering as well as their coupling behaviors can be analyzed. − For instance, for widely studied heat transport across metal/nonmetal interfaces, a large number of studies have demonstrated that electron–phonon coupling at the metal side (the first heat transport pathway) is closely related to the metal orientation and defects near the interface, , and thermal resistance generated in this pathway ( R 1 ) intrinsically is determined by relaxation time (τ) of electrons and phonons. Following this process, the phonon–phonon coupling (the second heat transport pathway) between metal and nonmetal happens, and this coupling process is mainly influenced by defects at the interface, interface orientation, interface compositions, and interfacial bonding .…”