Band Structure Engineering For Graphynes Bychemical Doping:A Computational Study

It is challenging to design two-dimensional semiconducting materials that simultaneously have sizable band gaps and high carrier mobilities.This work utilizes boron(B)atoms with transition-metal-like properties as the building blocks to design new two dimensional materials.It is found that the doping of carbon-based two dimensional materials with such peculiar B atoms can open their band gaps and to the largest extent maintain their high carrier mobilities.It is usually considered that the p_z orbitals of sp~2 hybridized B atoms are empty and thus are electron deficient when bonding with other atoms.Recent experimental and computational studies have demonstrated that the p_z orbitals of B can accommodate one or two electrons when they make bonds with strong?donating ligands L.When ligands L have ?~* antibonding orbitals,the p_z electrons of B can even back donate to the?~*antibonding orbitals,namely,the B atoms behave like transition metals.Although the transition metal like properties of B atoms have been been widely used for the design and synthesis of molecules,their use in designing materials have been scarcely reported.This work applies density functional theory calculations to study the?conjugated systems of graphynes that are co-doped with B and N heteroatoms.Attention has been paid to the specific BN co-doping pattern,in which C and N form the isocyanide ligand(-N?C,denoted as L)and further form the?donation(L?B?L)and?back donation(L?B?L)bonds with B.This co-doping pattern does not introduce empty or doubly filled p_z orbitals into the?conjugated systems of graphynes.Therefore,the hybrid materials have identical?electron configuration with the pristine graphynes and thus can open their band gaps and retain their excellent carrier mobilities.The results pay a new way to the rational design of two dimensional semiconducting materials with high electron conductivities.