With the advances of the electronics industry, the continuing trend of miniaturization and integration imposes challenges of efficient heat removal in nanoelectronic devices. Two-dimensional (2D) materials, especially graphene and hexagonal boron nitride (h-BN), are widely accepted as ideal candidates for thermal management materials due to their high intrinsic thermal conductivity and good mechanical flexibility. In this review, we introduce phonon dynamics of solid materials and thermal measurement methods at nanoscale, and highlight the unique thermal properties of 2D materials in relation to sample thickness, domain size, and interfaces. In addition, we discuss recent achievements of thermal management applications in which 2D materials act as heat spreader and thermal interface materials based on their controlled growth and selfassembly. Finally, critical consideration on the challenges and opportunities in thermal management applications of 2D materials is presented.

Heat conduction mechanisms in superlattices could be different across different types of interfaces. Van der Waals superlattices are structures physically assembled through weak van der Waals interactions by design and may host properties beyond the traditional superlattices limited by lattice matching and processing compatibility, offering a different type of interface. In this work, natural van der Waals (SnS)1.17(NbS2)n superlattices are synthesized, and their thermal conductivities are measured by time-domain thermoreflectance as a function of interface density. Our results show that heat conduction of (SnS)1.17(NbS2)n superlattices is dominated by interface scattering when the coherent length of phonons is larger than the superlattice period, indicating that incoherent phonon transport dominates through-plane heat conduction in van der Waals superlattices even when the period is atomically thin and abrupt, in contrast to conventional superlattices. Our findings provide valuable insights into the understanding of the thermal behavior of van der Waals superlattices and devise approaches for effective thermal management of superlattices depending on the distinct types of interfaces.

With the irreversible trend of miniaturization and the pursuit of a high power density in electronic devices, heat dissipation has become crucial for designing nextgeneration electronic products. Graphene, which has the highest thermal conductivity among all discovered solid materials, has attracted attention from both academia and the industry. As a two-dimensional material with atom-scale thickness, graphene is suitable for investigating the phonon transport behavior at reduced dimensions. The mass production technique of graphene makes it a promising material for thermal management in consumer electronics, information technology, medical devices, and new energy automobiles. In this review, we summarize the recent progress on the thermal conduction of graphene. In the first part, we introduce the thermal conductivity measurement methods for graphene, including the optothermal Raman method, suspended-pad method, and time-domain thermoreflectance (TDTR) method. The thermal measurement of graphene with high accuracy is key to understanding the heat transfer mechanism of graphene; however, it is still a significant challenge. Despite the development of measurement methods, the thermal measurement of suspended single-layer graphene is limited by the graphene transfer technique, estimation of the thermal contact resistance, sensitivity to the in-plane thermal conductivity in the thermal model, and other factors. In the second part, we discuss the theoretical study of the thermal conductivity of graphene via first principle calculations and molecular dynamics simulation. The "selection rule" of phonon scattering explains the thickness-dependent thermal conductivity of few-layer graphene, and the understanding of the contribution of phonon modes to the thermal conductivity of graphene has been updated recently by taking multiple-phonon scattering into consideration. The size effect on the thermal conductivity of graphene is discussed in this section for a better understanding of the phonon transport behavior of graphene. In the third part, we conclude with the thermal management applications of graphene, including a highly thermally conductive graphene film, graphene fiber, and graphene-enhanced thermal interface materials. For graphene films, which are the pioneering thermal management applications in industrial use, we focus on the challenge of fabricating highly thermally conductive graphene films with large thicknesses and propose possible technical methods. For graphene-enhanced thermal interface materials, we summarize the main factors affecting the thermal properties and discuss the tradeoff between the high thermal conductivity of graphene flakes and the dispersibility of graphene in the polymer matrix. It was demonstrated that a 3D thermal conductive network is essential for efficient heat dissipation in graphene-based composites. Finally, a summary of opportunities and challenges in the thermal study of graphene is presented at the end of the review. Research on the thermal properties of graphene has made imm...