Black phosphorus (BP) is a rapidly up and coming star in two‐dimensional (2D) materials. The unique characteristic of BP is its in‐plane anisotropy. This characteristic of BP ignites a new type of 2D materials that have low‐symmetry structures and in‐plane anisotropic properties. On this basis, they offer richer and more unique low‐dimensional physics compared to isotropic 2D materials, thus providing a fertile ground for novel applications including electronics, optoelectronics, molecular detection, thermoelectric, piezoelectric, and ferroelectric with respect to in‐plane anisotropy. This article reviews the recent advance in characterization and applications of in‐plane anisotropic 2D materials.

Two-dimensional molecular crystals, consisting of zero-dimensional molecules, are very appealing due to their novel physical properties. However, they are mostly limited to organic molecules. The synthesis of inorganic version of two-dimensional molecular crystals is still a challenge due to the difficulties in controlling the crystal phase and growth plane. Here, we design a passivator-assisted vapor deposition method for the growth of two-dimensional Sb₂O₃ inorganic molecular crystals as thin as monolayer. The passivator can prevent the heterophase nucleation and suppress the growth of low-energy planes, and enable the molecule-by-molecule lateral growth along high-energy planes. Using Raman spectroscopy and in situ transmission electron microscopy, we show that the insulating α-phase of Sb₂O₃ flakes can be transformed into semiconducting β-phase under heat and electron-beam irradiation. Our findings can be extended to the controlled growth of other two-dimensional inorganic molecular crystals and open up opportunities for potential molecular electronic devices.