**3.3 Two-dimensional nanostructures**

Two-dimensional nanostructures have two dimensions outside of the nanometric size range. In recent years, a synthesis of two-dimensional nanostructures with certain geometries exhibits unique shape-dependent characteristics and their subsequent utilization as building blocks for the key components of nano-devices. In **Figure 3c**, two-dimensional nanostructures, such as junctions (continuous islands), branched structures, nano-prisms, nano-plates, nano-sheets, nano-walls, nanodisks, etc., are confirmed in the literature. Round disks, hexagonal/triangular/ quadrangular plates or sheets, belts, mesoporous hollow nanospheres, hollow rings, etc. are also forms of two-dimensional nanostructures [20].
