Nanocomposite silica thin films made using the sol-gel method were studied. The nano-silica films were prepared using a mixture of tetraethyl orthosilicate (TEOS), deionized water, ethanol, and ammonia solution. To control the growth of the particles inside the film, the nanocomposite silica film was prepared using a mixture of the nano-silica sol and the silica sol. The change in the particle size with the heat treatment temperature ranging from 450 °C to 1100 °C was investigated. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), NKD (refractive index-N, extinction coefficient-K, and thickness-D) and ultraviolet-visible (UV-Vis) spectrophotometry were used for characterization purposes. The XRD studies showed that the nano-silica thin films were amorphous at all annealing temperatures except for 1100 °C. The_-cristobalite crystal structure formed at the annealing temperature of 1100 °C. Optical parameters, such as refractive indices and extinction coefficients, were obtained using the NKD analyzer with respect to the annealing temperature of the films. The activation energy and enthalpy of the nanocomposite silica film were evaluated as 22.3 kJ/mol and 14.7 kJ/mol, respectively. The cut-off wavelength values were calculated by means of extrapolation of the absorbance spectra estimated using the UV-Vis spectroscopy measurements. A red shift in the absorption threshold of the nanocomposite silica films indicated that the size of the silica nanoparticles increased with an increase of the annealing temperatures from 450 °C to 900 °C, and this confirms the quantum confinement effect in the nanoparticles.
Structural, electronic, intrinsic magnetic, anisotropic elastic properties, sound velocities and Debye temperature of Fe1−xMnx B (x = 0, 0.25, 0.5, 0.75, 1) transition metal monoborides have been studied by first-principles calculations within the method of virtual crystal approximation (VCA) based on density-functional theory (DFT) through generalized gradient approximation (GGA). The average magnetic moment per cell increased with increasing of Mn content, which could be associated with the relationship between the composition and magnetic properties. The observed magnetic behavior of Fe1−xMnx B compounds can be explained by Stoner model. Lattice parameters and Debye temperature agree well with the experimental values. Furthermore, we have plotted three-dimensional (3D) surfaces and planar contours of the directional dependent Young and bulk moduli of the compounds on several crystallographic planes, to reveal their elastic anisotropy versus Mn content (x) in Fe1−xMnx B.
Nuray Ucar, Ilkay Ozsev Yuksek, Mervin Olmez, Elif Can and Ayşen Onen
Graphene, a carbon allotrope, became a significant area of research with its superior electrical, mechanical, optical properties, etc. There are several methods to obtain graphene oxide from graphite, one of which is the Hummers method. In this study, several modifications and pre-treatments preceding the Hummers method have been employed. Three different graphene oxide fibers have been produced by three different procedures, i.e. fibers obtained by Hummers method with pre-oxidation step, modified Hummers method and modified Hummers method with pre-oxidation step. It has been observed that pre-oxidation has a significant effect on graphene oxide fiber properties produced by wet spinning process (coagulation). Modified Hummers method without pre-oxidation leads to the highest breaking strength and breaking elongation. Reduced fiber linear density, breaking strength and breaking elongation together with increased crimp were observed in graphene fiber due to the addition of pre-oxidation step.
Fillali Cherif, Ilyes Baba Ahmed, Abdelkader Abderrahmane and Saad Hamzaoui
Silicon as a raw material for solar cells can be produced by numerous methods. The carbothermic reduction of silica using electric arc furnace is the most widely used process in silicon industry. This paper presents a new approach to produce solar grade silicon using microwave furnace. Pellets of different sizes were prepared from a mixture of silica and carbon using water and polyvinyl alcohol as binder agents. Raman spectra indicated a peak at about 515 cm−1 attributed to silicon in the pellets prepared with polyvinyl alcohol, and peaks at about 523 cm−1 and 794 cm−1 attributed to silicon and silicon carbide, in the pellets prepared with water. The pellet size affects the absorption of microwave energy emitted from the magnetrons. Polyvinyl alcohol as a binder agent is promising for the production of silicon using microwave furnace.
K.K. Pathak, Mimi Akash Pateria, Kusumanjali Deshmukh and Piyush Jha
Present paper reports optical and electrical properties of samarium doped CdSe nanocrystalline thin film which was grown on a glass substrate by chemical bath deposition method (CBD). X-ray diffraction (XRD) analysis revealed that the deposited films were nanocrystalline with sphalerite cubic structure. The average crystallite size calculated from FWHM of XRD peaks was found to be 10.11 nm. The bandgap of the Sm doped CdSe nanocrystalline thin films was calculated to be 1.91 eV to 2.22 eV. The optical absorption edge of undoped (pure) and Sm doped CdSe films was obtained between 650 nm to 640 nm showing blue shift as compared to bulk CdSe. Sm doping further enhanced the photoconductivity of these films. The I-V characteristic confirmed the suitability of prepared films for photosensor applications.
Optical properties of Si single crystals with different orientations (1 0 0) and (1 1 1) were investigated using spectrophotometric measurements in a spectral range of 200 nm to 2500 nm. The data of optical absorption revealed an indirect allowed transition with energy gap of 1.1 ± 0.025 eV. An anomalous dispersion in refractive index. The normal dispersion of the refractive index was discussed according to Wemple-DiDomenico single oscillator model. The oscillator energy Eo, dispersion energy Ed, high frequency dielectric constant ∈∞, lattice dielectric constant ∈L and electronic polarizability αe were estimated. The real ∈1 and imaginary ∈2 parts of dielectric constant were also determined.
A.K. Sharma, S.S. Potdar, M.A. Yewale, Deepak B. Shirgaonkar, K.S. Pakhare, B.M. Sargar, M.V. Rokade and U.M. Patil
Cadmium oxide (CdO) thin films were synthesized using chemical bath deposition (CBD) method from aqueous cadmium nitrate solution. The bath temperatures were maintained at room temperature (25 °C) and at higher temperature (80 °C). The structural studies revealed that the films showed mixed phases of CdO and Cd(OH)2 with hexagonal/monoclinic crystal structure. Annealing treatment removed the hydroxide phase and the films converted into pure CdO with cubic, face centered crystal structure. SEM micrographs of as-deposited films revealed nanowire-like morphology for room temperature deposited films while nanorod-like morphology for high temperature deposited films. However, cube-like morphology was observed after air annealing. Elemental composition was confirmed by EDAX analysis. Band gap energies of the as-deposited films varied over the range of 3 eV to 3.5 eV, whereas the annealed films showed band gap energy variation in the range of 2.2 eV to 2.4 eV. The annealed films were successfully investigated for NH3 sensing at different operating temperatures and at different gas concentrations. The room temperature synthesized film showed a response of 17.3 %, whereas high temperature synthesized film showed a response of 13.5 % at 623 K upon exposure to 24 ppm of NH3.
Copper tin sulfide (Cu2SnS3) is a unique semiconductor, whose nanocrystals have attracted researchers’ attention for its tunable energy bandgap and wavelength in visible and near infrared range. Quantum dots which are fabricated from this material are highly suitable for optoelectronics and solar cell applications. This paper discusses the tunable energy bandgap, exciton Bohr radius and wavelength range of wurtzite structure of Cu2SnS3 quantum dots to assess the opportunity to use them in optoelectronics applications. The considerations show that the mole fraction of copper increases as energy bandgap decreases and tunable energy bandgap of this quantum dot material is inversely proportional to the wavelength.
An aqueous colloidal solution was prepared at 80 °C and pH = 9 from suitable chemical compounds to produce zinc oxide (ZnO) crystals and thin films. The ZnO crystals were grown in the colloidal solution under special conditions. Their micrographs showed ZnO rods with hexagonal structure. The number of the rods, increased over time. The ZnO thin films were produced on glass substrates in the same colloidal solution using the chemical bath deposition (CBD) method in different deposition times. The produced films were post-annealed for about one hour at 400 °C. Crystalline structure, phase transitions and nanostructure of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). ZnO wurtzite structure was dominant, and by increasing the deposition time, the films became more crystalline. Nanostructure of the films changed from rod to wire and transformed into pyramid-like structures. Also, morphology of the films changed and re-nucleation ocurred. Optical reflectance was measured in the wavelength of 300 nm to 800 nm with a spectrophotometer. Other optical properties and optical band gaps were calculated using Kramers-Kronig relation on reflectivity curves. Second harmonic generation was calculated by Z-scan technique. Nonlinear refraction and real part of susceptibilities were obtained. Both positive and negative nonlinear refractions appeared in the ZnO films. It is important for the use in optoelectronic devices. Electronic properties were assessed by the full potential linearized augmented plane wave (FP-LAPW) method, within density functional theory (DFT). In this approach, the generalized gradient approximation (GGA) was used for the exchange-correlation potential calculation. The band gap structure and density of states were calculated.
Jian Chen, Xiongfei Li, Wei Li, Cong Li, Baoshan Xie, Shuowei Dai, Jian-Jun He and Yanjie Ren
Quasi-static uniaxial compressive tests of open-cell copper (Cu) foams (OCCF) were carried out on an in-situ bi-direction tension/compress testing machine (IBTC 2000). The effects of strain rate, porosity and pore size on the energy absorption of open-cell copper foams were investigated to reveal the energy absorption mechanism. The results show that three performance parameters of open-cell copper foams (OCCF), involving compressive strength, Young modulus and yield stress, increase simultaneously with an increase of strain rate and reduce with increasing porosity and pore size. Furthermore, the energy absorption capacity of OCCF increases with an increase of porosity and pore size. However, energy absorption efficiency increases with increasing porosity and decreasing pore size. The finite element simulation results show that the two-dimensional stochastic model can predict the energy absorption performance of the foam during the compressive process. The large permanent plastic deformation at the weak edge hole is the main factor that affects the energy absorption.