DFT study of adsorption properties of the ammonia on both pristine and Si-doped graphene nanoflakes

Investigation of the interactions between nanomaterials and molecules at the molecular level is a crucial factor in the design of novel materials for nanosensor applications. In this study, we used the chemical calculations based on density functional theory calculations to evaluate the adsorption properties for the NH3 molecule (ammonia) over the surface of the pristine graphene nanoflakes (PGNFs) and Si-doped graphene nanoflakes (Si-GNFs). The results show that NH3 molecules are physically adsorbed onto the surface of PGNFs, while it is significantly chemisorbed onto the surface of Si-GNFs, with an adsorption energy of -1.561 eV. The recovery time for NH3/PGNF after adsorption process is very small, so the detection of the NH3 molecule is practically impossible even it has high electronic sensitivity of PGNF to the NH3 molecule. When a Si atom was substituted for a carbon atom, the adsorption characteristics of GNF improved. This, in turn, reduced the stability of the Si-GNF cluster, increasing its activity significantly relative to that of PGNF. When the Si-GNF cluster interacted with the NH3 molecule, its electrical conductivity increased significantly, and there was a large change in the energy gap. It follows that the Si-GNF cluster is an excellent candidate for use as a nanosensor for NH3 molecule detection due to its high electrical sensitivity to the above molecules. Therefore, the presence of silicon considerably promotes the NH3 chemisorption onto the GNFs and therefore significantly increases their sensitivity performance. In conclusion, the Si-GNF clusters could be employed as effective nanosensors for NH3 molecule detection.