Growth of Noncentrosymmetric Two-Dimensional Single Crystals.

Among the various two-dimensional (2D) materials, more than 99% of them are noncentrosymmetric. However, since the commonly used substrates are generally centrosymmetric, antiparallel islands are usually inevitable in the growth of noncentrosymmetric 2D materials because of the energetic equivalency of these two kinds of antiparallel islands on centrosymmetric substrates. Therefore, achieving the growth of noncentrosymmetric 2D single crystals has long been a great challenge compared with the centrosymmetric ones like graphene. In this review, we presented the remarkable efforts and progress in the past decade, through precise chemical processes. We first discussed the great challenge and possible strategies in the growth of noncentrosymmetric 2D single crystals. Then, we focused on the advancements made in producing representative noncentrosymmetric 2D single crystals, including hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDs), and other noncentrosymmetric 2D materials. At last, we summarized and looked forward to future research on the growth of layer-, stacking-, and twist-controlled noncentrosymmetric 2D single crystals and their heterostructures.