Surface structure of linear nanopores in amorphous silica: Comparison of properties for different pore generation algorithms.

Abstract

We compare the surface structure of linear nanopores in amorphous silica (a-SiO2) for different versions of "pore drilling" algorithms (where the pores are generated by the removal of atoms from the preformed bulk a-SiO2) and for "cylindrical resist" algorithms (where a-SiO2 is formed around a cylindrical exclusion region). After adding H to non-bridging O, the former often results in a moderate to high density of surface silanol groups, whereas the latter produces a low density. The silanol surface density for pore drilling can be lowered by a final dehydroxylation step, and that for the cylindrical resist approach can be increased by a final hydroxylation step. In this respect, the two classes of algorithms are complementary. We focus on the characterization of the chemical structure of the pore surface, decomposing the total silanol density into components corresponding to isolated and vicinal mono silanols and geminal silanols. The final dehyroxylation and hydroxylation steps can also be tuned to better align some of these populations with the target experimental values.