International Journal of Nanoscience

The stabilities and reactivities of two transition metal ($X=\mathrm{\text{Cu}}$, Zn)-doped structures of C${}_{20}$ fullerene have been investigated by density functional theory approach. We have observed a noticeable structural change in pristine C${}_{20}$ due to the substitution of one of its carbon atom by Cu or Zn atom. From our findings, it is found that the energy gap of C${}_{19}$Cu and C${}_{19}$Zn increases with respect to pristine C${}_{20}$, thus making the two doped fullerenes more stable than their pristine counterpart. The reactivity parameters such as chemical hardness, chemical potential and electrophilicity index for these structures are also studied. Interestingly, our calculations reveal that both the doped fullerenes obey the maximum hardness principle and minimum electrophilicity principle. Also, from the electronic absorption spectra analysis, it can be inferred that the maximum absorption peak of the two heteroatom-substituted fullerenes C${}_{19}$Cu and C${}_{19}$Zn are shifted towards the longer wavelength region as compared to the pure C${}_{20}$ fullerene, which clearly indicates that a red shift is introduced on account of doping.

We report here the theoretical model study of antiferromagnetic ordering in graphene. We propose a tight-binding model Hamiltonian describing electron hopping up to third-nearest neighbors in graphene. The Hamiltonian describing inequivalence of $A$ and $B$ sublattices in graphene-on-substrate is incorporated. The Hubbard-type repulsive Coulomb interaction is considered for both the sublattices with same Coulomb energy. The electron–electron interaction is considered within mean-field approximation with mean electron occupancies $n_{\sigma }^a=1∕2(n+m_a\sigma )$ at $A$ sublattice and $n_{\sigma }^b=1∕2(n-m_b\sigma )$ at $B$ site with $m_a$ and $m_b$ being the antiferromagnetic magnetizations at $A$ and $B$ sublattices, respectively. The total Hamiltonian is solved by Zubarev’s techniques of double time single particle Green’s functions. The magnetizations are calculated from the correlation functions corresponding to the respective Green’s functions. The temperature-dependent magnetizations are solved self-consistently taking suitable grid points for the electron momentum. Finally, the electron density of states (DOS) which is proportional to imaginary part of the electron Green’s functions is calculated and computed numerically at a given temperature varying different model parameters for the system. The conductance spectra show a gap near the Dirac point due to substrate-induced gap and magnetic gap, while the van Hove singularities split into eight peaks due to two different sublattice magnetizations and two different spin orientations of the electron in graphene-on-substrate.

In the last few years, plasmonics has attracted much attention and has been included in the principal domains of nanophotonics that can manage optical fields at the nanodimension level. Its exquisite characteristic is to increase the electromagnetic fields at the nanometer scale particularly in the solar cell. In the plasmonic discipline, noble metals used as nanoparticles in which the density of the electron gas which oscillates at surface plasmon frequency at that time also enhances absorption via scattering. So the usage of plasmonics in solar cells offers better possibility of improving the performance through absorption, because the optical spectrum loss is principal as a part of the overall loss for the solar photovoltaic cell. So we investigated the impact of the nanoparticle size for the enhancement of extinction in terms of absorption and scattering by using surface plasmon resonance, and additionally studied the finite-difference time domain (FDTD)-based proposed model and found various plasmonic fields components and characterized optical enhancement in the plasmonic thin film solar cell.

In this present work, an attempt is made to compare the microstructural, mechanical and tribological properties of Al 5083-5% and 10% Gr, Al 5083-5% and 10% ZrSiO₄ composite with Al 5083-5, 10% Gr-5 and 10% ZrSiO₄ hybrid composite. The samples were prepared by using the stir casting technique, and the characterizations of composites and hybrid composite were observed by using SEM, EDAX and X-ray diffraction (XRD). The mechanical properties such as hardness, tensile, compressive strength of hybrid composite were found to be better than those of composites. The wear test was carried out by using a pin-on-disc wear tribometer by varying parameters like normal load (5, 10N), sliding speed (1, 1.5, 2m/s) with constant sliding distance (2000m). The worn surface of the samples is examined by using SEM, and the wear properties of the hybrid composite are found to exhibit superior wear resistance properties than composites.

The graphene-on-substrate in the presence of impurity exhibits ferromagnetism. In the present paper, we propose a tight-binding Hamiltonian model which consists of electron hopping upto-third-nearest-neighbors. The graphene-on-substrate develops a gap of few meV. This Hamiltonian incorporates a gap of energy $+\mathrm{\Delta }$ at A sub-lattice and a gap of energy $-\mathrm{\Delta }$ at B sub-lattice. The Hamiltonian describes the impurity effect at A and B sub-lattices with the impurity potential describing hole and/or electron doping. The on-site Coulomb interaction at A and B sub-lattices is described by Hubbard type repulsive Coulomb interaction which is considered within the mean-field approximation having ferromagnetic magnetization of two different magnitudes at the sub-lattices. The total Hamiltonian is solved by Zubarev’s Green’s function technique. The temperature-dependent ferromagnetic magnetizations are solved self-consistently taking $100\times 100$ grid points of the electron momentum. The electron band dispersion splits into four for A site and four for B site and the combined band dispersion exhibits eight bands for up/down spin orientations. The evolution of the band dispersion is investigated by varying different model parameters of graphene.

The pristine graphene is a zero band gap semiconductor with valence and conduction bands touching each other at Dirac points. The graphene-on-substrate exhibits a small gap at the Dirac points. The microscopic Hamiltonian describes the nearest-neighbor $\pi$-electron hopping with tight-binding approach. Graphene-on-substrate exhibits a gap at the Dirac points where the energy at A sublattice is raised by $+\mathrm{\Delta }$ and the energy at B sublattice is lowered by energy $-\mathrm{\Delta }$ leading to asymmetry in the two sublattices. Further, we have introduced impurities at both the sublattices. The Coulomb interaction in graphene-on-substrate is described by Hubbard-type Coulomb interaction with energy U. The Coulomb interaction is treated in the calculation within the mean-field approximation in the paramagnetic limit. The temperature-dependent site-independent electron occupancies at both the sublattices are calculated and computed self-consistently. The difference between the electron occupancies of both the sublattices introduces a charge gap. The effect of charge gap on the electronic band dispersion in graphene-on-substrate is investigated by varying different model parameters of the system like Coulomb energy, substrate-induced gap, temperature, total band filling and impurity concentrations. It is observed that both the valence and conduction bands are shifted above the Fermi level exhibiting a charge gap between the bands. As a result, the partially filled valence band exhibits metallic behavior.

ZnS nanostructures are synthesized by a wet chemical route using starch as green capping agent under nitrogen environment. The as-prepared nanostructures are characterized structurally, optically and electrically. X-ray diffraction (XRD) spectra confirm that the zinc sulfide (ZnS) nanoparticles have cubic phase (zinc blende). UV–Vis spectrum of the sample clearly shows that the absorption peak exhibits blue shift compared to their bulk counterpart, which confirms the quantum confinement effect of the nanostructures. Its photoluminescence (PL) spectrum shows near band gap emission at 392nm and extrinsic emission at 467nm. The particle sizes calculated from XRD and UV studies are in fair agreement with high resolution transmission electron microscopy (HRTEM) results. Starch is found to be a noble capping agent in bringing quantum confinement. The synthesis under nitrogen environment has been observed to produce quality products by reducing the oxide traces. Moreover, the I–V characteristics under dark and illumination show that ZnS can be more suitable as photodetector.

Thin films of Sb₂S₃ and CdI₂ composites were deposited by thermal vapor deposition method on a glass substrate. The structural and optical properties have been investigated as a function of the film thickness. Three samples were deposited with thickness of 160nm, 210nm and 380nm. The samples were characterized by X-ray diffraction (XRD), UV–visible (UV–Vis) absorption spectroscopy and photoluminescence (PL) spectroscopy. The XRD result confirms the orthorhombic structure of Sb₂S₃ peaks. The bigger crystals are formed with the increase of the thickness of the film. The band gaps of the deposited composite thin films were found to be in range 2.17–1.48eV and suggest the possibility of band gap tunability in the visible region with the changing the thickness of the film. The PL study reveals the intense emission due to band to band recombination with emission in the red region corresponding to trap states.