Structural and electronic properties of layered nanoporous organic nanocrystals

In this work, we present the optimized geometric stacking of several layered nanoporous organic nanocrystals (NONs) and the stacking effect on their electronic structure. Hexagonal layered structures, C(12)H(6)-h2D, B(6)N(6)H(6)-h2D and C(6)N(6)-h2D are built from aromatic organic molecular units benzene, borazine and 1,3,5-triazine, respectively while oblique structures, C(10)N(2)H(4)-o2D, C(8)N(4)H(2)-o2D, C(10)P(2)H(4)-o2D and C(10)As(2)H(4)-o2D, are built from pyridine, 1,3-diazine, phosphinine and arsinine, respectively. Our density functional theory calculations show stacking energy profiles of NONs that are similar to graphene in both the stand-alone and bulk C(12)H(6)-h2D and B(6)N(6)H(6)-h2D structures while the rest of the studied layered materials deviate from the perfect AB stacking. The number of layers as well as the stacking configuration significantly influence the electronic properties of these materials. Indirect to direct band gap crossovers from the bulk to monolayers are observed in all of the NONs except in C(6)N(6)-h2D which exhibits a direct band gap in both the monolayer, isolated few-layers, and bulk. Furthermore, it is observed that the electronic nature of C(10)As(2)H(4)-o2D changes from a semiconducting character in the isolated monolayer to a metallic character in the bulk. The porous nature and the stability of these layered NONs combined with the electronic properties observed in this work point at them as valuable materials for potential applications in nanoelectronics and gas separation membranes, as well as deep ultraviolet optoelectronics and laser devices.