Two-dimensional (2D) material research is rapidly evolving to broaden the spectrum of emergent 2D systems. Here, we review recent advances in the theory, synthesis, characterization, device, and quantum physics of 2D materials and their heterostructures. First, we shed insight into modeling of defects and intercalants, focusing on their formation pathways and strategic functionalities. We also review machine learning for synthesis and sensing applications of 2D materials. In addition, we highlight important development in the synthesis, processing, and characterization of various 2D materials (e.g., MXnenes, magnetic compounds, epitaxial layers, low-symmetry crystals, etc.) and discuss oxidation and strain gradient engineering in 2D materials. Next, we discuss the optical and phonon properties of 2D materials controlled by material inhomogeneity and give examples of multidimensional imaging and biosensing equipped with machine learning analysis based on 2D platforms. We then provide updates on mix-dimensional heterostructures using 2D building blocks for next-generation logic/memory devices and the quantum anomalous Hall devices of high-quality magnetic topological insulators, followed by advances in small twist-angle homojunctions and their exciting quantum transport. Finally, we provide the perspectives and future work on several topics mentioned in this review.

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The low-temperature growth of materials that support high-performance devices is crucial for advanced semiconductor technologies such as integrated circuits built using monolithic three-dimensional (3D) integration and flexible electronics. However, low growth temperature prohibits sufficient atomic diffusion and directly leads to poor material quality, imposing severe challenges that limit device performance. Here, we demonstrate superior quality growth of 3D semiconductors at growth temperatures reduced by >200 °C by using two-dimensional (2D) materials as intermediate layers to optimize the potential energy barrier for adatom diffusion. We reveal the benefits of maintaining, but reducing, the potential field through the 2D layer, which coupled with the inert surface of the 2D material lowers the kinetic barriers, enabling long-distance atomic diffusion and enhanced material quality at lower growth temperatures. As model systems, GaN and ZnSe, grown using WSe2 and graphene intermediate layers, exhibit larger grains, preferred orientation, reduced strain, and improved carrier mobility, all at temperatures lower by >200 °C compared to direct growth as characterized by diffraction, X-ray photoelectron spectroscopy, Raman, and Hall measurements. The realization of high-performance materials using 2D intermediate layers can enable transformative technologies under thermal budget restrictions, and the 2D/3D heterostructures could enable promising heterostructures for future device designs.