Black phosphorus is the thermodynamically stable form of phosphorus at room temperature and pressure. In 2014, researchers were able to exfoliate the material to thin films just 10 to 20 atoms thick. Not only does it have an inherent bandgap unlike graphene, but that bandgap is also highly tunable, depending on the number of layers used. However, the property that really sets black phosphorus apart from graphene and nearly all two-dimensional materials is its intrinsically strong, in-plane anisotropy. That means its properties are directionally dependent, like the grain of a piece of wood.