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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.

The electronic properties of the T-Greaphene nanosheet (T-GNS) are developed by using different concentrations of the Al and Si impurities. The results demonstrated the electronic band gap is reduced and the shape of the DOS is altered via utilizing various concentrations of Al and Si impurities, excepted the Al4Si4-doped T-GNS has an opposie thing. For the stability, we detected that the T-GNS became more stable and lower reactive due to the total energy is increased with these impurities. Moreover, the results have shown that the AlSi-doped T-GNS, Al2Si2-doped T-GNS, and Al4Si4-doped T-GNS have the anti-ferromagnetic properties. Also, the pristine T-GNS and AlSi-doped T-GNS have an open shell systems, which means there are spin up and spin down, respectively. Moreover, the nature bond is dictated by adding any impurity of Al and Si impurities. By using these impurities, the T-GNS become more solid due to it has a higher hardness, which required higher excitation energy to transfer electrons. For optical properties this study has discovered that all structures out of the visible light region. Moreover the λmax takes values from 1146.507 nm for Al2Si2-doped T-GNS in site (1)(s3) to 16,845.562 nm for Al4Si4-doped T-GNS (s1). Also, the excitation energy increased compared with T-GNS. In brief, the electronic and optical properties depend on the site and concentrations of Al and Si impurities.

Electronic and optical properties of the graphene nanoflakes (GNFs) are investigated with and without various concentrations of S impurities in different locations via a time-dependent density-functional theory (TDDFT) calculation. Results showed very fascinating results. Results showed up that the pristine GNFs have a semiconductor behavior. S-doped GNFs also have a semiconductor behavior with reducing electronic band gap value. The band gap of the GNFs is reduced by altering the location of the S impurity. Correspondingly, it is decreased by increasing the concentration of the S impurity. Also, when the concentration of S goes up, the total and formation energies are increased with negative sign, which means the structures became more stable and exothermic process. Our findings show λ max also depends on the site and concentrations of S impurity, which is taken value from 474.54 to 12514.22 nm for pristine and 3S-PNG (a) cases, respectively. Correspondingly, we observed that the sturdy absorption peaks (pristine, 1S-PNG (a), 4S-PNG (b)) cases are in the visible light and near-infrared region. In brief, the optoelectronics properties of the GNFs are dependent on the position and concentrations of S impurities.