Department of Mechanical Engineering and Texas Materials Institute, The University of Texas at Austin, Austin, TX 78712.
Proc Natl Acad Sci U S A. 2013 Oct 8;110(41):16321-6. doi: 10.1073/pnas.1306175110. Epub 2013 Sep 25.
The recent studies of thermal transport in suspended, supported, and encased graphene just began to uncover the richness of two-dimensional phonon physics, which is relevant to the performance and reliability of graphene-based functional materials and devices. Among the outstanding questions are the exact causes of the suppressed basal-plane thermal conductivity measured in graphene in contact with an amorphous material, and the layer thickness needed for supported or embedded multilayer graphene (MLG) to recover the high thermal conductivity of graphite. Here we use sensitive in-plane thermal transport measurements of graphene samples on amorphous silicon dioxide to show that full recovery to the thermal conductivity of the natural graphite source has yet to occur even after the MLG thickness is increased to 34 layers, considerably thicker than previously thought. This seemingly surprising finding is explained by long intrinsic scattering mean free paths of phonons in graphite along both basal-plane and cross-plane directions, as well as partially diffuse scattering of MLG phonons by the MLG-amorphous support interface, which is treated by an interface scattering model developed for highly anisotropic materials. Based on the phonon transmission coefficient calculated from reported experimental thermal interface conductance results, phonons emerging from the interface consist of a large component that is scattered across the interface, making rational choice of the support materials a potential approach to increasing the thermal conductivity of supported MLG.
最近对悬浮、支撑和封装石墨烯中的热传输的研究刚刚开始揭示二维声子物理的丰富性，这与基于石墨烯的功能材料和器件的性能和可靠性有关。悬而未决的问题包括：与非晶材料接触的石墨烯中测量到的基面热导率被抑制的确切原因，以及支撑或嵌入多层石墨烯（MLG）恢复石墨高热导率所需的层厚度。在这里，我们使用对非晶硅二氧化硅上石墨烯样品的灵敏面内热传输测量表明，即使在 MLG 厚度增加到 34 层之后，仍未完全恢复到天然石墨源的热导率，这比之前认为的要厚得多。这一看似令人惊讶的发现可以通过石墨中声子在基面和横向上的固有长散射平均自由程以及 MLG-非晶支撑界面处的 MLG 声子部分漫散射来解释，该界面散射由针对各向异性材料开发的界面散射模型进行处理。基于从报告的实验热界面电导结果计算的声子透射系数，从界面出现的声子包含大量在界面上散射的分量，因此合理选择支撑材料是提高支撑 MLG 热导率的一种潜在方法。
