This study investigates the dimensional crossover of thermal transport in few-layer graphene (FLG) materials, revealing how thermal conductivity changes as the number of atomic layers increases from 2 to 4. The thermal conductivity of FLG decreases from ~3000 W/mK to ~1500 W/mK, indicating a transition from 2-D to 3-D behavior. This change is attributed to the cross-plane coupling of low-energy phonons and corresponding changes in phonon Umklapp scattering. The results highlight the unique thermal properties of low-dimensional materials and suggest potential applications in thermal management for nanoelectronics. The study addresses the fundamental question of how thermal conductivity changes in 2-D and 1-D materials. Thermal transport in solids is described by Fourier's law, which states that heat flux is proportional to the temperature gradient. Recent theoretical studies suggest that the intrinsic thermal conductivity of 2-D and 1-D anharmonic crystals exhibits divergence with system size. In 2-D, K diverges as ln(N), while in 1-D, K scales with N^α (0 < α < 1). This divergence is a universal property and not confused with the length dependence of thermal conductivity in the ballistic transport regime. Experimental investigation of heat conduction in strictly 2-D or 1-D materials has been challenging due to the lack of suitable material systems. However, the emergence of mechanically exfoliated graphene, an ideal 2-D system, has enabled such studies. The thermal conductivity of suspended single-layer graphene (SLG) is significantly higher than that of bulk graphite, indicating the unique properties of 2-D materials. The study measured the thermal conductivity of FLG as the number of atomic layers changes from 2 to ~10. The results show that the thermal conductivity decreases with increasing number of layers, primarily due to changes in Umklapp scattering. The thermal transport in the experiment is in the diffusive regime, as the length of the sample is larger than the phonon mean free path. The study also examines the phonon dispersion in FLG and the role of different phonon modes in thermal conductivity. The results show that the thermal conductivity of FLG decreases with increasing thickness, primarily due to changes in Umklapp scattering. The study provides insights into the physical mechanisms behind the evolution of heat conduction in few-atomic-thick crystals and highlights the importance of understanding thermal transport in low-dimensional materials.This study investigates the dimensional crossover of thermal transport in few-layer graphene (FLG) materials, revealing how thermal conductivity changes as the number of atomic layers increases from 2 to 4. The thermal conductivity of FLG decreases from ~3000 W/mK to ~1500 W/mK, indicating a transition from 2-D to 3-D behavior. This change is attributed to the cross-plane coupling of low-energy phonons and corresponding changes in phonon Umklapp scattering. The results highlight the unique thermal properties of low-dimensional materials and suggest potential applications in thermal management for nanoelectronics. The study addresses the fundamental question of how thermal conductivity changes in 2-D and 1-D materials. Thermal transport in solids is described by Fourier's law, which states that heat flux is proportional to the temperature gradient. Recent theoretical studies suggest that the intrinsic thermal conductivity of 2-D and 1-D anharmonic crystals exhibits divergence with system size. In 2-D, K diverges as ln(N), while in 1-D, K scales with N^α (0 < α < 1). This divergence is a universal property and not confused with the length dependence of thermal conductivity in the ballistic transport regime. Experimental investigation of heat conduction in strictly 2-D or 1-D materials has been challenging due to the lack of suitable material systems. However, the emergence of mechanically exfoliated graphene, an ideal 2-D system, has enabled such studies. The thermal conductivity of suspended single-layer graphene (SLG) is significantly higher than that of bulk graphite, indicating the unique properties of 2-D materials. The study measured the thermal conductivity of FLG as the number of atomic layers changes from 2 to ~10. The results show that the thermal conductivity decreases with increasing number of layers, primarily due to changes in Umklapp scattering. The thermal transport in the experiment is in the diffusive regime, as the length of the sample is larger than the phonon mean free path. The study also examines the phonon dispersion in FLG and the role of different phonon modes in thermal conductivity. The results show that the thermal conductivity of FLG decreases with increasing thickness, primarily due to changes in Umklapp scattering. The study provides insights into the physical mechanisms behind the evolution of heat conduction in few-atomic-thick crystals and highlights the importance of understanding thermal transport in low-dimensional materials.