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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.

Controlled chemical doping with oxygen impurities is a promising approach for the electronic band engineering of graphene nanoflakes (GNFs). Based on the first-principles of the density functional theory (DFT) calculations, we investigated the effect of various consternations of substitutional impurities from oxygen atoms on the electronic properties of GNFs. Our results show that the electronic properties of GNFs do not only depend on the oxygen impurity concentrations, but also depend on the geometrical pattern of oxygen impurities in the GNFs. Additionally, we also found interesting electronic properties of GNFs structure, which significantly contribute to that oxygen dopants cause a decreased energy gap. So, our results suggest that substitutional impurities are the best viable option for enhancement of desired electronic properties of GNFs. [ABSTRACT FROM AUTHOR]

There are many applications in the polymer chemistry, pharmaceutical, agricultural and industrial fields of the thiadiazole molecule and their derivatives. Allowance of the energy gap of the polymer conjugated is an object of great interesting debit for the possible removal of a doping in the preparation of highly conductivity polymers. Thiadiazoles derivatives are structural foundation of the polymer materials. In this present work, the electronic properties of graphene nanoflakes (GNFs)-phenanthrene-1,3,4-thiadiazoles oligomers are studied and discussed. Where thiadiazoles is expanded from one to 9 unit's molecules at the structure. The energy gap, HOMO, LUMO distribution, total energy, Fermi level energy, work function, maximum wavelength absorption, vertical absorption energies, and oscillator strengths are calculated for each molecule. All calculations are carry out by usage density function theory (DFT) and depended time density function theory (TD-DFT) with the B3LYP/6-31G model in the Gaussian 09W software packages. Results show that increasing the number of monomeric units lead to great enhance in the electronic properties, which caused it decreased the band gap from 3.17 eV in the system with one unit of thiadiazole just to 1.35 eV in the system with 9 units of thiadiazole. This case is raised the value of maximum absorption wavelengths to >500 nm to give the better performance in optoelectronic and solar cell, as these structures have prime absorption bands within the solar spectrum. [ABSTRACT FROM AUTHOR]

The Special Number Field Sieve factoring algorithm has a large number of parametric choices, each of which can affect its run time. We give guidelines for these choices along with a discussion of useful coding optimizations. We also give a theoretical argument which proves that the choice of sieving region that has been used so far in successful factorizations is not optimal and show how to obtain an improved sieve region. The improvement has yielded a 15% speed increase in practice.

Abstract: In this work, silver (Ag) nanoparticles were deposited onto graphite nanofibers (GNFs) by chemical reduction while polyaniline-coated Ag-GNFs (Ag-GNFs/PANI) were prepared by in situ polymerization. The effect of the Ag nanoparticles intercalated in composite interface on the electrochemical performances, such as CV curve, charge–discharge behaviors, and specific capacitance of the GNFs/PANI was investigated. It was found that nano-sized Ag particles could be uniformly deposited onto the GNFs and that Ag-GNFs were successfully coated by PANI via in situ polymerization. According to the charge–discharge curves, the highest specific capacitance (212F/g) of the Ag-GNFs/PANI was obtained at a scan rate of 0.1A/g, as compared to 153F/g for GNFs/PANI and 80F/g for PANI. This indicated that the Ag nanoparticles that were deposited onto the GNFs led to a bridge effect between GNFs and PANI to improve the charge transfer, which resulted in the enhanced electrochemical performances of the composites due to a synergistic effect. [Copyright &y& Elsevier]

Abstract: Graphite nanofibers (GNFs) treated at various temperatures were used as carbon supports to improve the efficiency of PtRu catalysts. The electrochemical properties of the PtRu/GNFs catalysts were then investigated to evaluate their potential for application in DMFCs. The results indicated that the particle size and dispersibility of PtRu in the catalysts were changed by heat treatment, and the electrochemical activity of the catalysts was improved. Consequently, it was found that heat treatments could have an influence on the surface and structural properties of GNFs, resulting in enhancing an electrocatalytic activity of the catalysts for DMFCs. [Copyright &y& Elsevier]