New technologies are emerging which allow us to manipulate and assemble 2-dimensional (2D) building blocks, such as graphene, into synthetic van der Waals (vdW) solids. Assembly of such vdW solids has enabled novel electronic devices and could lead to control over anisotropic thermal properties through tuning of inter-layer coupling and phonon scattering. Here we report the systematic control of heat flow in graphene-based vdW solids assembled in a layer-by-layer (LBL) fashion. In-plane thermal measurements (between 100 K and 400 K) reveal substrate and grain boundary scattering limit thermal transport in vdW solids composed of one to four transferred layers of graphene grown by chemical vapor deposition (CVD). Such films have room temperature in-plane thermal conductivity of ~400 Wm⁻¹ K⁻¹. Cross-plane thermal conductance approaches 15 MWm⁻² K⁻¹ for graphene-based vdW solids composed of seven layers of graphene films grown by CVD, likely limited by rotational mismatch between layers and trapped particulates remnant from graphene transfer processes. Our results provide fundamental insight into the in-plane and cross-plane heat carrying properties of substrate-supported synthetic vdW solids, with important implications for emerging devices made from artificially stacked 2D materials.

新技术的出现使我们能够将二维（2D）构建基块（例如石墨烯）操纵并组装到合成范德华（vdW）固体中。这种vdW固体的组装已实现了新颖的电子设备，并可能通过调整层间耦合和声子散射来控制各向异性的热性能。在这里，我们报告了以逐层（LBL）方式组装的基于石墨烯的vdW固体中的热流的系统控制。平面内热测量（介于100 K和400 K之间）揭示了衬底和晶界散射限制了vdW固体中的热传输，该固体由一到四个通过化学气相沉积（CVD）生长的石墨烯转移层组成。此类薄膜的室温面内热导率为〜400 Wm ^-1  K ^-1。对于由通过CVD生长的七层石墨烯薄膜组成的石墨烯基vdW固体，跨平面热导率接近15 MWm ^-2  K ^-1，这很可能受到层间旋转失配和石墨烯转移过程中残留的捕集颗粒的限制。我们的结果提供了对衬底支撑的合成vdW固体的面内和平面内传热特性的基本见识，并对由人工堆叠的2D材料制成的新兴设备具有重要意义。