van der Waals layered structures, notably the transitional metal dichalcogenides (TMDs) and TMD-based heterostructures, have recently attracted immense interest due to their unique physical properties and potential applications in electronics, optoelectronics, and energy harvesting. Despite the recent progress, it is still a challenge to perform comprehensive characterizations of critical properties of these layered structures, including crystal structures, chemical dynamics, and interlayer coupling, using a single characterization platform. In this study, we successfully developed a multimodal nonlinear optical imaging method to characterize these critical properties of molybdenum disulfide (MoS2) and MoS2-based heterostructures. Our results demonstrate that MoS2 layers exhibit strong four-wave mixing (FWM), sum-frequency generation (SFG), and second-harmonic generation (SHG) nonlinear optical characteristics. We believe this is the first observation of FWM and SFG from TMD layers. All three kinds of optical nonlinearities are sensitive to layer numbers, crystal orientation, and interlayer coupling. The combined and simultaneous SHG/SFG-FWM imaging not only is capable of rapid evaluation of crystal quality and precise determination of odd-even layers but also provides in situ monitoring of the chemical dynamics of thermal oxidation in MoS2 and interlayer coupling in MoS2-graphene heterostructures. This method has the advantages of versatility, high fidelity, easy operation, and fast imaging, enabling comprehensive characterization of van der Waals layered structures for fundamental research and practical applications.

A novel high‐entropy carbide ceramic, (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C, with a single‐phase rock salt structure, was synthesized by spark plasma sintering. X‐ray diffraction confirmed the formation of a single‐phase rock salt structure at 26‐1140°C in Argon atmosphere, in which the 5 metal elements may share a cation position while the C element occupies the anion position. (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C exhibits a much lower thermal diffusivity and conductivity than the binary carbides HfC, ZrC, TaC, and TiC, which may result from the significant phonon scattering at its distorted anion sublattice. (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C inherits the high elastic modulus and hardness of the binary carbide ceramics.

In this study, the degree of conversion (DC) of an acrylic-based resin (IP-L 780) in two-photon polymerization (TPP) is systematically investigated via Raman microspectroscopy. A quantitative relationship between TPP laser parameters and the DC of the resin is established. Nonlinear increase in DC with increased laser average power is observed. The resin DC is more sensitive to the laser average power than the laser writing speed. Nanoindentation was employed to correlate the results obtained from Raman microspectroscopy with the mechanical properties of microstructures fabricated by TPP. At constant writing speeds, microstructures fabricated with high laser average powers possess high hardness and high reduced Young's modulus (RYM), indicating high DCs. The results are in line with high DCs measured under the same TPP parameters in Raman microspectroscopy. Raman microspectroscopy is proved to be an effective, rapid, and nondestructive method characterizing microstructures fabrication by TPP.