Atomic-Level Controlled Synthesis and Emergent Physical Properties of 2D Metal Nitrides and Janus Sulfurnitrides

Designing and engineering new material structures at reduced dimensions lay the foundation for discovering emergent physical phenomena. Over the past decades, two-dimensional (2D) materials have provided a unique platform to reveal remarkable properties such as unconventional superconductivity, quantum anomalous Hall effects, spin–valley locking, and sliding ferroelectricity. While extensive progress has been achieved in van der Waals (vdW) 2D materials such as graphene, transition metal dichalcogenides (TMDs), and hexagonal boron nitride (hBN), little attention has been devoted to non-vdW materials, which represent the vast majority of known compounds. A central challenge lies in the absence of effective synthesis routes to access these materials in the ultrathin limit. In this talk, I will introduce an atomic substitution approach that we have developed to transform vdW layered materials (e.g. MoS₂) into nanometer-thin non-vdW structures (e.g. MoN) via chemical reactions in 2D lattices. This universal strategy enables atomic-level control of nucleation, composition, and thickness, facilitating the synthesis of diverse non-vdW 2D materials with tunable properties for both fundamental studies and device applications. I will highlight the electronic properties of nanometer-thin transition-metal nitrides (TMNs) and their potential as robust electrical contacts for nanoelectronic devices. Furthermore, I will present our recent achievement in realizing 2D Janus molybdenum sulfurnitride (SMoN) through atomic-level substitution of the top sulfur layer in MoS₂ with nitrogen. This approach can be extended to other 2D Janus systems such as SWN. The resulting asymmetric structure exhibits a large intrinsic out-of-plane dipole, confirmed by both theoretical calculations and experimental measurements of work functions and nonlinear optical responses. These findings open a promising avenue for exploring emergent phenomena in symmetry-broken 2D structures.