Search

Using first principle calculations based on the density functional theory (DFT), the structural, elastic, electronic, and thermoelectric properties, and thermodynamic stability of the LiMgZ (Z = P,...

The purpose of this research is to explore the properties of CoSe nanostructured thin films on glass substrates prepared by a chemical solution deposition method. Special attention is given to study the effects of precursor concentrations (Cobalt(II) acetate, Ammonia and Sodium Selenosulphite), fixing the Co:Se concentration ratio, on the grainy structure and optical properties of the resulting thin films. The structural, chemical composition and morphological characteristics were investigated by X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX) and scanning electron microscopy (SEM), respectively. The optical properties were determined by UV–visible spectroscopy determining the optical band gap energy (Eg). According to these results, the average particle diameter was decreased from 119 to 42 nm as the precursor salt concentration was decreased from 0.3 to 0.1 M, being the bigger nanoparticles more spherical. With the reduction of the particle size, a blue shift in the absorption peaks of the UV–visible spectra and an increment of their optical band gap energy (from 1.8 to 3.6 eV) occurred due to confinement effects.

Electronic and optical properties of pure and V-doped AlN nanosheet have been investigated using density functional theory, and the dielectric tensor is calculated using the random phase approximation (RPA). The results of structural calculations show that the V atoms tend to replace instead of aluminum atoms with the lowest formation energy. In addition, study of the electronic properties shows that pure AlN nanosheet is a p-type semiconductor that by increasing one V atom, it possesses the metallic properties and magnetic moment becomes Zero. Moreover, by replacing two V atoms, the half-metallic behavior with 100% spin polarization can be found, and each supercell gains a net magnetic moment of 3.99 µB. Optical properties like the dielectric function, the energy loss function, the absorption coefficients, the refractive index are calculated for both parallel and perpendicular electric field polarizations, and the results show that the optical spectra are anisotropic.

The aim of this research is to fabricate Ag nanoparticle assemblies forming nanolayers with different thicknesses in order to evaluate their physical properties and their 3-D (three-dimensional) surface micromorphology. Such Ag nanolayers were deposited by physical vapor deposition methods under ion-beam irradiation in argon atmosphere at room temperature. X-ray diffraction (XRD) characterizations confirmed the formation of silver nanocrystals. Using surface field parameters, which were derived from atomic force microscopy (AFM) analysis, the surface morphology of the nanolayers were described according ISO 25178-2:2012. The height and slope distribution functions, together with the autocorrelation (ACF), the height–height correlation (HHCF) and the power spectral density (PSDF) functions were determined for the different analyzed samples using linear interpolation in the horizontal direction. All samples had a fractal character with a fractal dimension of 2.54 ± 0.01 independent of the film thickness.

Theoretical study of triplet half-Heusler compound RbBaB shows that this compound is a ferromagnetic half-metal with a gap of about 1.2 eV in the bulk state. The structural, electronic, optical properties, and thermodynamic stability of all possible terminations of the (001) thin film of this compound are calculated with the full-potential linear augmented plane waves method. According to the phase diagram, it was found that the Ba-B termination is the most stable one among all terminations. The electronic study reveals the half-metallic behavior with a spin polarization of less than 100 for the two Ba-B and Rb-B terminations and the metallic property for the Rb–Ba termination. The main optical response to incident light of two Rb-B and Ba-B terminations occurred in the visible area, similar to the bulk state. Excessive amounts of e1(ω) imply the metal behavior of the Rb-B and Ba-B terminations. The e2(ω) peaks in the infrared and visible area imply the intra-band transitions. Also, the energy loss function peaks are presented at the higher ultraviolet range, indicating good optical response on the surface of these compounds at IR and visible areas.

In this study nickel–carbon (Ni–C) nanocomposite thin films composed of Ni nanoparticles with different average sizes embedded in amorphous hydrogenated carbon, were prepared through the combination of radio frequency sputtering and plasma enhanced chemical vapor deposition techniques. Such samples were used as experimental models to study the three dimensional surface morphology properties in thin films by atomic force microscopy imaging and fractal analysis over square areas of 1 μm × 1 μm. The deposition time was varied at 7, 10 and 13 min, respectively, to study changes in the properties of the obtained films. The studied samples exhibited fractal properties characterized by fractal dimensions dependent on the deposition time with values between 2.43 ± 0.01 and 2.71 ± 0.01.

We conducted extensive density functional theory calculations within GGA + U approach to explore the geometry, electronic structure and optical properties of armchair and zigzag zinc oxide nanoribbons as a function of width. Our results show that single layered armchair ZnONRs are semiconductors, whereas the zigzag counterparts are metallic. However, the electronic energy gap in armchair configurations decreases considerably when the width of the ribbon increase. The first absorption peak of the armchair NRs is placed along the in-plane polarization and inside the visible spectral range; while it occurs at energies less than 1.2 eV for zigzag NRs. Moreover, the first absorption peak of both zigzag and armchair configurations is located in the ultraviolet region along the out-of-plane polarization. In addition, for all cases, the optical spectra are highly anisotropic along the in-plane and out-of-plane directions. These diverse electronic and optical properties might open ZnONR materials great possibility in future optoelectronic applications.

In this work, the optical absorption spectra of carbon–nickel films annealed at different temperatures (300–1000 °C) with a special emphasis on the surface plasmon resonance (SPR) were investigated. The films were grown on quartz substrates by radio-frequency (RF) magnetron co-sputtering at room temperature with a deposition time of 600 s. The optical absorption peaks due to the SPR of Ni particle are observed in the wavelength range of 300–330 nm. With annealing temperature increasing up to 500 °C due to the increase in Ni particle size, the intensity of the SPR peaks increases, but weakens with annealing temperature increasing over 500 °C. The Ni nanoparticle size, the dielectric function of carbon matrix (e m) and the plasma frequency of the free electrons (ω p) at 500 °C have the maximum values of 21.63 nm, 0.471 and 5.26 × 1015 s−1, respectively. The absorption peak shows a redshift trend up to 500 °C and then turn to blueshift with annealing temperature increasing over 500 °C. These observations are in a good agreement with the electrical measurements in temperature range of 15–520 K and the Maxwell–Garnett (M–G) effective medium theory (EMT).

Thin films of Ag/Cu were deposited by reactive DC magnetron sputtering on (001)-oriented Si and glass substrates for various deposition times (4–24 min). These films were characterized by atomic force microscopy (AFM), and a power law scaling was performed on the obtained micrographs to investigate the self-affine nature of the sample morphology, which is indicative of a fractal structure. We applied the Higuchi’s algorithm to the AFM data to determine the fractal dimension of each sample, and the Hurst exponents were computed. The deposition time dependences of these parameters and the grain size distributions estimated from the UV–visible spectra using the Mie theory, allowed us to describe a particle formation mechanism during the deposition process, in which the length of continuous paths of conductive particles increases as the deposition time is increased. In agreement with this explanation, the electrical resistance decreased with the increment of the deposition time.

The electronic and the linear optical properties of a monolayer B2C graphene sheet are investigated through the density functional theory. The dielectric tensor is derived within the random phase approximation (RPA). Specifically, the dielectric function, absorption coefficient, optical conductivity, extinction index, loss function, reflectivity, and the refraction index of the monolayer B2C graphene sheet are calculated for both parallel and perpendicular electric field polarizations. The results show that the optical spectra are anisotropic along these two polarizations. For the electric field parallel to monolayer B2C graphene E ∥ x , adding the intraband transitions contribution, will change the optical spectra of a monolayer B2C graphene sheet significantly, while in the electric field perpendicular to monolayer B2C graphene E ∥ z did not change. Adding the intraband transitions contribution shows that the dielectric function has singularity at zero frequency because of the metallic behavior of a monolayer B2C graphene sheet. Also by considering the intraband transitions contribution for energy loss function in the electric field parallel to monolayer B2C graphene, the first plasmon frequency peak has been shifted from 2.76 eV to 4 eV.

Cobalt/carbon nanocomposite coating (Co NPs @ a-C: H), which consist of cobalt nanoparticles buried in hydrogenated amorphous carbon are prepared by RF-sputtering and RF-plasma enhanced chemical vapor deposition on silicon substrates. In these processes, the coatings are produced from a cobalt sputtered target and acetylene reactant gas. The crystalline structure and surface topography of the deposited films are characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. The AFM shows that the average size distribution depends on the deposition conditions and RMS varies from 3.5 up to 6 nm. The XRD analyses indicate the presence of cobalt nanostructure as centered face cubic phase and its oxide, but with no evidence of carbide structure. The energy-dispersive X-ray spectroscopy analysis was used to identify the elements composition in the films and the ultraviolet–visible spectrophotometry is used to study surface plasmon resonance bands of Co nanoparticles.

Optical and electronic properties of ZB, RS and WZ structures of gallium nitride (GaN) are studied in equilibrium and under pressure using the first-principles calculation in the density functional theory (DFT) framework to obtain quantities like dielectric function, loss function, reflectance and absorption spectra, refractive index and their relation parameters. The electronic properties are studied using EV-GGA and GGA approximations and the results calculated by EV-GGA approximation were found to be much closer to the experimental results. The interband electron transitions are studied using the band structure and electron transition peaks in the imaginary part of the dielectric function; these transitions occur in three structures from N-2p orbital to Ga-4s and Ga-4p orbitals in the conduction band. Different optical properties of WZ structure were calculated in two polarization directions of (100) and (001) and the results were close to each other. Plasmon energy corresponding to the main peak of the energy-loss function in RS with the value of 26 eV was the highest one, which increased under pressure. In general, RS shows more different properties than WZ and ZB.

First-principles study of elastic, electronic and optical properties of full-Heusler Co2V(Al, Ge, Ga and Si) compounds are calculated through density functional theory (DFT) to obtain and compare the mentioned properties. Equilibrium lattice constants of these compounds are in good agreement with other works. Electronic calculations are shown full spin polarization at Fermi level for all compounds, so in the down spin, indirect bandgap is calculated as 0.33, 0.6, 0.2 and 0.8 eV for Co2V(Al, Ge, Ga and Si), respectively. The integer amounts of the magnetic moments are compatible with Slater–Pauling role. The optical treatment of Co2VGa is different from three other compounds. All mentioned compounds have metallic behavior by 22 eV plasmonic frequency. The imaginary part of the dielectric function for the up spin indicates that the main optical transitions occurred in this spin mode. Moreover, the elastic results show that the Co2VGa does not have elastic stability, but the other three compounds have fully elastic stability and the Co2V(Al, Ge and Si) belong to the hardness of materials.

Structural, elastic, optical, and electronic properties of wurtzite (WZ), zinc-blende (ZB), and rocksalt (RS) structures of AlN are investigated using the first-principles method and within the framework of density functional theory (DFT). Lattice parameters, bulk modulus, shear modulus, Young’s modulus, and elastic constants are calculated at zero pressure and compared with other experimental and theoretical results. The wurtzite and zinc-blende structures have a transition to rocksalt phase at the pressures of 12.7 GPa and 14 GPa, respectively. The electronic properties are calculated using both GGA and EV-GGA approximations; the obtained results by EV-GGA approximation are in much better agreement with the available experimental data. The RS phase has the largest bandgap with an amount of 4.98 eV; by increasing pressure, this amount is also increased. The optical properties like dielectric function, energy loss function, refractive index, and extinction coefficient are calculated under pressure using GGA approximation. Inter-band transitions are investigated using the peaks of imaginary part of the dielectric function and these transitions mainly occur from N-2[Formula: see text] to Al-3[Formula: see text] levels. The results show that the RS structure has more different properties than the WZ and ZB structures.

In this paper, some optical properties of pure and transition metal-doped (TM = Co and V) single-walled ZnO nanotubes (8,0) (SWZnONT(8,0)) such as, real and imaginary parts of the dielectric function, optical conductivity, refractive index and optical reflectivity, were investigated. The calculations have been performed within framework of the density functional theory (DFT) using the full potential linearized augmented plane wave (FP-LAPW) and the generalized gradient approximation (GGA). The results show that, optical properties of SWZnONT(8,0) are anisotropic, especially at low energies and this anisotropy at low energies increases with doping of V in SWZnONT(8,0) while the Co-doped SWZnONT(8,0) behaves like pure SWZnONT(8,0). Doping of ZnO nanotubes has a significant impact on the value of the dielectric constant, so that due to the presence of V atom, the dielectric constant is increased up to three times. Study of the imaginary part of the dielectric function and optical conductivity showed that the important energy range for absorption processes and optical transitions is low energy range to 15 eV. The optical transitions have been studied based on band structure and density of states. The results of the optical reflectivity showed that these nanotubes are transparent in a wide energy ranges which provide them for using in transparent coatings. In addition, due to the reported magnetic properties for V- and Co-doped ZnO nanotubes, these nanotubes are suitable for using in spintronics and magneto-optic devices.

The structural, electronic and magnetic properties of transition metal TM (TM = Fe and Co) monatomic nanochains encapsulated inside and between (6,6) boron nitride nanotube (BNNT) bundle have been investigated by the first-principles calculations in the framework of the density functional theory. Our results show that intercalation of TM chains leads to the significant changes in the geometrical structure. All TM chains TM-Chs@BNNT bundle systems have negative formation energy so they are stable and exothermic. It is found that all these TM-Chs@BNNTs bundle systems are ferromagnetic and a spin splitting between spin up and down is observed. The spin polarization and the magnetic moment of the systems depend on the position and the type of the transition metal atomic chains.

In this paper, colloidal silver nanoparticles were prepared by chemical reduction of AgNO 3 and pure Sn in a new and simple method. The type of crystallite lattice and the size of nanopowders were estimated by X-Ray Diffraction (XRD) analysis. The geometric, heterogeneous and mixing structure of synthesized nanopowders were studied by Scanning Electron Microscopy (SEM). Optical properties such as plasmon absorption and frequency of soluble colloidal nanopowders in two solutions of distilled water and oil were investigated by UV-Visible spectroscopy, which was developed to calculate the absorbance spectra of nanoparticles solution containing a size distribution of particles using the Mie theory. Dipole and quadrupole plasmons related to molecular structure of water and oil were found by absorbance spectra. Also, Differential Scanning Calorimetry (DSC) analysis was used for determining the thermal behavior, endothermic and exothermic peaks of Ag nanopowder.