Zheling Li

Diamond offers exceptional thermal conductivity for high-power and wide-bandgap devices, but poor wettability limits its application in liquid-cooling environments. In this work, femtosecond laser irradiation was used to modify the near-surface structure of single-crystal diamond, and the resulting effects on bonding configuration, lattice integrity, thermal response, and wetting behavior were systematically examined. Laser processing roughens the surface, produces an amorphous carbon layer, and introduces shock-related stress into the substrate. As the fluence increases from 3.77 to 19.39 J/cm2, the amorphous layer becomes thinner and less ordered, the amorphous–diamond interface becomes progressively more corrugated, and the underlying crystal evolves from exhibiting residual strain to containing dense stacking faults and point defects. The roughened surfaces and laser-induced sp2-bonded amorphous carbon improve wettability and facilitate bubble nucleation during boiling, while ultrafast reflectivity measurements show that defect accumulation suppresses carrier excitation and slows thermal relaxation. In line with these trends, the droplet evaporation time decreases from 8.357 s on the pristine surface to 6.745 s after irradiation at 3.77 J/cm2, whereas the times for the 7.97 and 19.39 J/cm2 surfaces increase to 6.935 and 7.890 s, respectively. These results demonstrate how laser-induced carbon structural modifications govern thermal transport and identify processing conditions that enhance wettability without severely degrading thermal transport performance, offering a promising route for engineering diamond interfaces for liquid-cooling applications.

Van der Waals' heterostructures of 2D materials have great potential in developing electronic and optoelectronic devices. Understanding heat transfer in these heterostructures is essential for effective thermal management. However, studying heat transfer in the few‐atom‐thick 2D heterostructure remains challenging. In this work, the first measurement of in‐plane thermal conductivities of suspended graphene/MoS ₂ heterostructures using optothermal Raman spectroscopy is reported. The thermal conductivity of the suspended graphene/MoS ₂ heterostructure is extracted from the dependencies of the MoS ₂ A _1g Raman peak frequency on temperature and excitation laser power. The average thermal conductivity of graphene/MoS ₂ heterostructures at room temperature is found at 172 W m ⁻¹ K ⁻¹ , which is 5.4 times higher than that of the suspended monolayer MoS ₂ (32 ± 5 W m ⁻¹ K ⁻¹ ). This superior heat transfer in the graphene/MoS ₂ heterostructure is attributed to the high thermal conductivity (700 ± 58 W m ⁻¹ K ⁻¹ ) of monolayer graphene prepared by chemical vapor deposition. This work not only demonstrates the measurement of in‐plane thermal conductivities of van der Waals heterostructures of 2D materials but also shows the great potential of using monolayer graphene to significantly enhance heat dissipation in ultrathin materials.

Artificially stacking 2D materials (2DMs) into vdW heterostructures creates materials with properties not present in nature that offer great potential for various applications such as flexible electronics. Properties of such stacked structures are controlled largely by the interfacial interactions and the structural integrity of the 2DMs. In spite of their crucial roles, interfacial stress transfer and the failure mechanisms of the vdW heterostructures, particularly during deformation, have not been well addressed so far. In this work, the interfacial stress transfer and failure mechanisms of a MoS₂/graphene vdW heterostructure are studied, through the strain distributions both laterally in individual 2DMs and vertically across different 2DMs revealed in‐situ. The fracture of the MoS₂ and the associated states of stress and strain are monitored experimentally. This enables various interfacial properties, such as the interfacial shear strength and interfacial fracture energy, to be estimated. Based only on the measured strength and interfacial properties of a single vdW heterostructure, a failure criterion is proposed to predict the failure mechanisms of similar vdW heterostructures with any lateral dimensions. This work provides an insight to the deformation micromechanics of vdW heterostructures that are of great value for their miniaturization and applications, especially in flexible electronics.