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Directional Selective Thermal Diffusivity Jump by Temperature in High Purity Graphene Paper



The in-plane and out-of-plane thermal diffusivity () of high purity graphene paper (GP), partly reduced graphene paper (PRGP), and graphene oxide paper (GOP) is measured from room temperature (RT) down to 10 K. An in-plane jump phenomenon in GP induced by temperature reduction is reported. However, the outof- plane of GP does not show such jump behavior. In addition, PRGP and GOP have much lower and do not show jump in any direction. From phonon propagation analysis, the directional selective jump behavior of GP is attributed to the switchable substrate effect from neighboring flakes. Before jump, the interactions between pure graphene flakes and surrounding impurity-embedded flakes efficiently suppress phonon transport in GP. After switch-on, the structure separation frees the pure graphene flakes from the impurity-embedded neighbors, leading to 5-8- fold increase. Along the out-of-plane direction of GP, however, the strong interlayer interface scattering plays a much more significant role in controlling the phonon propagation. PRGP and GOP contain high density of structure defects and weak inter-flake connection, which provides large phonon scattering. These competing factors overshadow the effect of structure separation on , which makes the jump not observable in the out-of-plane direction of GP, or any direction in PRGP and GOP. This work shed light on a deep understanding of the relationship between phonon propagation and structure of two-dimensional graphene based materials.


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