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Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

Volume 36 (2018): Issue 2 (June 2018)

Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

24 Articles
Open Access

Synthesis and Luminescence Properties of ZrO2:Gd3+, RE3+(RE = Sm3+ ,Er3+) Phosphors

Published Online: 25 Jun 2018
Page range: 162 - 166

Abstract

Abstract

In the present study, ZrO2co-doped with Gd3+/Sm3+and Gd3+/Er3+ions have been synthesized using Pechini method. Phase composition, morphology and photoluminescence properties of the synthesized phosphors were investigated by using X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and photoluminescence spectrofluorometer (PL). After heating at 1200 °C, XRD revealed that the phosphors were crystallized as monoclinic and tetragonal multiphases. SEM images indicated that the phosphors consist of fine and spherical grains with a size around 200 nm to 250 nm. Luminescence studies of these phosphors have been carried out on the emission and excitation, along with lifetime measurements

Keywords

  • ZrO2
  • Sm3+
  • Er3+
  • luminescence
Open Access

Quinoxaline-Based Small Molecules: Synthesis and Investigation on Their Optoelectronic Properties

Published Online: 25 Jun 2018
Page range: 167 - 176

Abstract

Abstract

Small molecules of ThQuTh, CzQuTh, CzQuCz and TPAQuCz were designed and synthesized, based on quinoxaline acceptor, and electron donating groups, i.e. alkyl-thioephene, carbazole and triphenylamine on both side chains and molecular backbones. Their thermal, optical and electrochemical properties were systematically compared and studied. The absorption spectra of the small molecules were strongly affected by the donor units attached to quinoxaline. Strong electron donating groups, such as carbazole on the molecular backbone would lower optical band gap, resulting in a wide absorption and the strong donor on the side chain would enhance the absorption intensity in short wavelength region. The highest occupied molecular orbital (HOMO) energy levels of the four molecules were up-shifted with increasing the electron donating properties of donor units. The bulk-heterojunction organic solar cells with a device structure of ITO/PEDOT:PSS/SMs:PC61BM/LiF/Al were fabricated, in which the small molecules functioned as donors while PC61BM as acceptor. Because the electron-donating ability of carbazole (Cz), triphenylamine (TPA) is higher than that of thiophene (Th), CzQuTh, CzQuCz and TPAQuCz show higher power conversion efficiency (PCE) than that of ThQuTh. Furthermore, being the strongest in absorption intensity and widest in absorption spectrum, TPAQuCz has the highest power conversion efficiency. Further improvement of the device efficiency by optimizing the device structure is currently under investigation

Keywords

  • quinoxaline
  • acceptor materials
  • optoelectronic properties
  • solar cells
Open Access

Growth, spectral, density functional theory (DFT) and Hirshfeld surface analysis on 4-aminopyridinium adipate monohydrate nonlinear optical single crystal

Published Online: 25 Jun 2018
Page range: 177 - 184

Abstract

Abstract

4-aminopyridinium adipate monohydrate (4APA) was grown by slow evaporation solution growth technique. The functional groups in the grown crystal were identified from FT-IR spectral evaluation. The optical properties together with transmittance of the grown crystal were obtained from UV-Vis spectroscopic study. The mechanical and thermal properties of the grown crystal were studied using Vickers microhardness and TGA/DTA analyses, respectively. Microhardness test revealed that 4-aminopyridinium adipate monohydrate crystal is a soft category material. The density functional method (DFT) was performed using B3LYP with the 6-311G (d,p) basis set. The electronic charge distribution, reactivity of the molecules and the molecular electrostatic potential (MEP) of the grown crystal were analyzed using the B3LYP method. The intermolecular interactions that exist in the crystal structure of the 4APA have also been investigated by Hirshfeld surface analysis. The nonlinear optical properties of the 4APA crystal were confirmed by Kurtz-Perry technique.

Keywords

  • crystal growth
  • growth from solution
  • Hirshfeld
  • DFT
  • organic material
  • nonlinear optical material
Open Access

Preparation and characterization of PEO-based composite gel-polymer electrolytes complexed with lithium trifluoro methane sulfonate

Published Online: 25 Jun 2018
Page range: 185 - 192

Abstract

Abstract

Chitosan has been successfully incorporated as a filler in a polyethylene oxide (PEO) and lithium trifluoromethanesulfonate (LiCF3SO3) matrix with a combination of plasticizers, namely 1,3-dioxolane (DIOX) and tetraethylene glycol dimethylether (TEGDME). The composite gel-polymer electrolyte (CGPE) membranes were prepared by solution casting technique in an argon atmosphere. The prepared membranes were subjected to SEM, TG/DTA and FT-IR analyses. A Li/CGPE/Li symmetric cell was assembled and the variation of interfacial resistance was measured as a function of time. The lithium transference number (Li+t) was measured and the value was calculated as 0.6 which is sufficient for battery applications. The electrochemical stability window of the sample was studied by linear sweep voltammetry and the polymer electrolyte was found to be stable up to 5.2 V.

Keywords

  • polyethylene oxide
  • ionic conductivity
  • FT-IR
  • transport number
  • interfacial properties
Open Access

Structural and optical characterization of annealed As30Te60Ga10 thin films prepared by thermal evaporation technique

Published Online: 25 Jun 2018
Page range: 193 - 202

Abstract

Abstract

Effect of annealing temperature on the structural and optical properties of As30Te60Ga10 thin film was studied using various techniques such as differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The DSC analysis revealed that the As30Te60Ga10 glass has a single glass transition and crystallization peak while XRD results confirmed that the as-prepared and annealed films have crystalline nature. The coexistence of the crystalline phases in the investigated films could be attributed to the formation of orthorhombic As, hexagonal Ga7Te10, and monoclinic As2Te3 phases. It was found that the average crystallite size and optical parameters of the studied films depend on the annealing temperature. For example, the optical band gap decreased from 1.54 eV to 1.11 eV as the annealing temperature increased from 300 K to 433 K.

Keywords

  • chalcogenide
  • As-Te-Ga
  • thin films
  • structural properties
  • optical properties
  • thermal evaporation
Open Access

High Pressure Raman Study of Layered Semiconductor Tlgase2

Published Online: 25 Jun 2018
Page range: 203 - 208

Abstract

Abstract

Raman spectroscopy measurements of a monoclinic layered semiconductor TlGaSe2were performed in a pressure range up to 10.24 GPa. The pressure-induced first-order phase transition accompanied by reconstruction of the layer structure was observed at the pressure P ~ 0.9 GPa. The mode-Grüneisen parameters of intralayer bonds were calculated for TlGaSe2. The contribution of thermal expansion to temperature changes of phonon frequencies was defined. The type of intralayer bonds and their pressure transformation were analyzed in layered TlGaSe2. It was shown that the nature of intramolecular forces in molecular crystals and intralayer forces in layered GaS, GaSe and TlGaSe2is similar

Keywords

  • layered semiconductor
  • high pressure
  • Raman study
Open Access

Fabrication of Cu2O Nanostructured Thin Film by Anodizing

Published Online: 25 Jun 2018
Page range: 209 - 216

Abstract

Abstract

Cuprous oxide, a narrow bandgap p-type semiconductor, has been known as a potential material for applications in supercapacitors, hydrogen production, sensors, and energy conversion due to its properties such as non-toxicity, easy availability, cost effectiveness, high absorption coefficient in the visible region and large minority carriers diffusion length. In this study, Cu2O nanostructured thin film was fabricated by anodizing of Cu plates in ethylene glycol containing 0.15 M KOH, 0.1 M NH4F and 3 wt.% deionized water. The effects of anodizing voltage and temperature of electrolyte were investigated and reported. It was found that nanoporous Cu2O thin film was formed when anodizing voltages of 50 V and 70 V were used while a dense Cu2O thin film was formed due to the aggregation of smaller nanoparticles when 30 V anodizing voltage was used. Nanoplatelets thin film was formed when the temperature of electrolyte was reduced to 15 °C and 5 °C. X-ray diffraction confirmed the presence of Cu2O phase in thin film formed during anodizing of Cu plates, regardless of the anodizing voltage and temperature of electrolyte. Photoluminescence spectroscopy showed the presence of Cu2O peak at 630 nm corresponding to band gap of 1.97 eV. A mechanism of the formation of Cu2O thin film was proposed. This study reported the ease of tailoring Cu2O nanostructures of different morphologies using anodizing that may help widen the applications of this material

Keywords

  • anodizing
  • cuprous oxide
  • nanopores
  • nanoplatelets
  • thin film
Open Access

Noncontact Method of Conducting Elements “Writing” on Insulating Ge–Sb–Te Matrix Using a Laser Beam

Published Online: 25 Jun 2018
Page range: 217 - 224

Abstract

Abstract

Direct writing of low resistance wires on an amorphous Ge-Sb-Te matrix is reported. A 1342 nm continuous wave laser was used for local heating of the sample to form these wires. Mechanical contact was not needed for making the conducting elements. The properties of the samples were investigated down to 1.4 K and the laser conditions required for the writing of low resistance GST wires were found. The results are discussed with a view to possible applications, such as connectors and electrical wires made only via remote light exposure of the samples to make different resistors and non-linear elements

Keywords

  • GST
  • laser
  • conductor
  • noncontact method
Open Access

Electron Work Functions of (H K L)-Surfaces of W, Re, and Cu Crystals

Published Online: 25 Jun 2018
Page range: 225 - 234

Abstract

Abstract

Work function (WF) and some physicochemical data for several most prominent crystal planes of three metals of typical structures are calculated within the linear approximation employing the surface dipole and 2D gas models. “Composite” crystal of a homogeneous bulk phase and a thick surface composed of eight (h k l)-oriented facets with different unsaturated bonds is treated as a nine-phase nine-component system with two degrees of freedom. It contains the two-dimensional metal-lattice plasma of free electrons and the immobile atom-core network. For twenty four (h k l) surfaces, the WF and dipole barrier term, chemical and electrostatic potential levels, electron charge densities, surface dipole fields, and other parameters are calculated and tabularized. WF values obtained from the thermodynamics based formula are compared to the ones obtained from the quantum mechanics based formula, which shows good agreement with experiment and also reveals a specific deviation in the case of field emission method for the most packed plane. A set of accurate face dependent data can be of interest to electronics and materials science workers

Keywords

  • surface
  • interface
  • electron emission
  • work function
  • 2D plasma density
  • local Fermi levels
Open Access

Sol-Gel Derived Cds Nanocrystalline Thin Films: Optical and Photoconduction Properties

Published Online: 25 Jun 2018
Page range: 235 - 241

Abstract

Abstract

High-quality CdS nanocrystalline thin films were grown by sol-gel spin coating method at different solution temperatures on glass substrates. As-deposited films exhibited nanocrystalline phase with hexagonal wurtzite structure and showed good adhesion and smooth surface morphology. It was clearly observed that the crystallinity of the thin films improved with the increase in solution temperature. Crystallites sizes of the films also increased and were found to be in the range of 10 mm to 17 nm. The influence of the growth mechanism on the band and sub-band gap absorption of the films was investigated using UV-Vis and photothermal deflection spectroscopy (PDS). The band gap values were calculated in the range of 2.52 eV to 2.75 eV. The band gap decreased up to 9 % with the increase in solution temperature from 45 °C to 75 °C. Absorption coefficients estimated by PDS signal showed the significant absorption in low photon energy region of 1.5 eV to 2.0 eV. The dark and illuminated I-V characteristics revealed that the films were highly photosensitive. The results demonstrated the potential applications of sol-gel grown CdS nanocrystalline thin films as photoconductors and optical switches.

Keywords

  • CdS
  • sol-gel
  • optical properties
  • photothermal deflection spectroscopy
  • photoconductivity
Open Access

Analysis of glass forming ability using percolation concept and tunability of physical parameters of a-Ge12Se76 - xAs12Bix glassy semiconductors

Published Online: 25 Jun 2018
Page range: 242 - 254

Abstract

Abstract

Glass forming ability of lone-pair semiconductors was analyzed for (x = 0, 2, 4, 6, 8, 10) system. Values of lone pair electrons L were calculated using average coordination number of valence electrons. These values were found to decrease, as the system was moving towards the rigid region. L > 3 values showed vitreous state. Deviation of the stoichiometry confirmed the chalcogen-rich region. A linear correlation was found between the mean bond energy and glass transition temperature. Chemical Bond Approach model was applied to calculate the cohesive energy of the system. A linear relationship was found to exist between the cohesive energy and the theoretical band gap, calculated using Shimakawa relation. A decrease in both parameters was explained on the basis of average stabilization energy and electronegativity of the system. The density values were found to increase and may account for higher refractive index of the system. Large Bohr radius of the Bi atom accounted for an increase in the polarizability. Other parameters viz. degree of covalency, packing density, compactness, molar volume, free volume percentage, excess volume and polaron radius were also calculated. An effort was made to correlate the effect of Bi addition to Ge12Se76 - xAs12Bixlone-pair semiconductor on the basis of the structure of the glassy matrix or the connectedness of the material.

Keywords

  • constraints
  • glass transition temperature
  • band gap
  • cohesive energy
Open Access

Substitutional effect of copper on the cation distribution in cobalt chromium ferrites and their structural and magnetic properties

Published Online: 25 Jun 2018
Page range: 255 - 263

Abstract

Abstract

A series of copper substituted cobalt chromium ferrites, CuxCo1 - xCr0.5Fe1.5O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) has been synthesized, by employing powder metallurgy method. Calcination of the samples has been carried out for 24 hours at 1100 °C. The resultant materials have been investigated by using a variety of techniques, including X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM)), scanning electron microscopy (SEM), and ultraviolet visible spectroscopy (UV-Vis). The XRD patterns confirmed that all compositions had a cubic spinel structure with a single phase and the lattice parameter was found to increase with increasing copper concentration. FT-IR spectroscopy has been used for studying the chemical bonds in the spinel ferrite. Shifting of the bands ν1 and ν2 has been observed. It has been revealed from VSM analysis that saturation magnetization and coercivity decrease with rising the Cu+2 doping. Magnetic properties have been explained on the basis of cation distribution. Scanning electron microscopy (SEM) has been used to study the surface morphology of prepared samples. UV-Vis analysis revealed the optical absorption of the samples. An increase in band gaps has been observed with increasing copper concentration in the sample.

Keywords

  • crystal structure
  • ferromagnetic properties
  • optical band gap
Open Access

The influence of Kanthal wire surface defects on the formation of Si nanolayer deposited by PVD method

Published Online: 25 Jun 2018
Page range: 264 - 269

Abstract

Abstract

The subject of this research is the structure of a Si nanolayer deposited on a FeCrAl wire surface by means of magnetron sputtering method. Si layer was selected as one of possible protections of the wire surface against excessive corrosive-erosive wear. In order to increase the power necessary for the DC discharge of the magnetron with Si cathode, a second magnetron with an aluminum disc as a cathode was used. The wire was attached to a carousel holder to ensure its rotation around the magnetron. The thickness of the deposited layers was about 150 nm. A wire surface examination indicated the presence of defects such as gaps between grains, cavities as well as severely deformed grains of surface layer. The research was conducted on the sample sections which had been prepared by focused ion beam method (FIB). The technique of transmission microscopy, which was used for observation, allowed us to obtain images in bright field (BF), dark field (DF), as well as in high resolution (HREM). The studies were also performed on the wire surface after the cutting process of the expanded polystyrene blocks. A metallographic optical microscope Nikon MA200 with a large depth of field was used for the examination which showed the presence of carbon deposit products. Additionally, a composition microanalysis was carried out along the line within selected areas of samples, with the use of energy dispersive spectroscopy (EDS). A large impact of wire surface defects on Si layer forming was found as well as a high direct homogeneous growth. The examination of the sections indicated the existence of a mechanism of defects sealed by Si layer, where directionality of grains growth in these areas revealed the tendency for vertical location relative to defects surface. Consequently, closed nanopores, i.e. spaces not covered with Si layer, were created. It is a characteristic feature of areas with defects covered with an oxide film created in a natural way.

Keywords

  • PVD
  • nanolayers
  • microwire
  • corrosion
  • EPS
Open Access

Structural, thermal and optical investigation of tin sulfide nanoparticles for next-generation photovoltaic applications

Published Online: 25 Jun 2018
Page range: 270 - 275

Abstract

Abstract

We report a simple approach for synthesizing monodispersed, crystalline and size-tunable tin sulfide nanoparticles for environment friendly next generation solar cell applications. Both SnS and SnS2 nanoparticles could be a potential nanomaterial for solar cells. The structural, morphological, thermal and optical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FT-IR). The XRD spectra revealed hexagonal and orthorhombic phases of SnS and SnS2 nanoparticles, respectively, where the grains size ranged from 11 nm to 30 nm. The weight percentage as a function of temperature was determined using TGA analysis. Functional groups were observed by FT-IR. The energy bandgap was determined as 1.41 eV showing usefulness of the nanoparticles in next generation environmental friendly solar energy applications.

Keywords

  • SnS nanoparticles
  • energy bandgap
  • next generation photovoltaics
Open Access

Exploration of donor effect on electron injection and photovoltaic properties of chalcone derivatives

Published Online: 25 Jun 2018
Page range: 276 - 282

Abstract

Abstract

Various photovoltaic parameters, i.e., electron injection (ΔGinject.), electronic coupling constants (|VRP|), light harvesting efficiencies (LHE), band alignment and electronic properties of five chalcone derivatives were studied by density functional theory (DFT) and time domain. The light was also shed on the effect of different electron donating groups and their strength intensity on the electronic and charge transfer properties. The balanced hole and electron reorganization energies for Comp 4 showed that it might have better ambipolar charge transfer in nature. The strong electron donating group(s) usually enhance(s) the ΔGinject. and |VRP| of chalcones as -N(CH3)2 > OCH3 > OH. Additionally, ΔGinject. and |VRP| of various substituted chalcone derivatives have been observed as trimethoxy > dimethoxy > monomethoxy. The greater electron donating ability of substituents is also favorable for the staggered band alignment. The superior ΔGinject. of all the studied chalcones than of the referenced compounds disclosed that the prior compounds would be proficient photovoltaic materials.

Keywords

  • renewable energy
  • photovoltaic properties
  • density functional theory (DFT)
  • band alignment
  • charge transfer properties
  • electron injection
Open Access

Thermal and electrical properties of polyimide/PANI nanofiber composites prepared via in situ polymerization

Published Online: 25 Jun 2018
Page range: 283 - 287

Abstract

Abstract

Polyimide/polyaniline nanofiber composites were prepared by in situ polymerization with various weight percentages of polyaniline (PANI) nanofibers. X-ray diffraction (XRD) and Fourier transform infrared spectra (FT-IR), proved the successful preparation of PANI nanofiber composite films. In addition, thermal stability of PI/PANI nanofiber composites was superior relative to PI, having 10 % gravimetric loss in the range of 623 °C to 671 °C and glass transition temperature of 289 °C to 297 °C. Furthermore, the values of the loss tangent tanδ and AC conductivity σAC of the nanocomposite films were notably higher than those of pure polyimide. The addition of 5 wt.% to 15 wt.% PANI nanofiber filler enhanced the activation energy of PI composites from 0.37 eV to 0.34 eV.

Keywords

  • polyimide
  • polyaniline nanofiber
  • in situ polymerization
  • PI/PANI nanofiber composite films
Open Access

Gas Composition Influence on the Properties of Boron-Doped Diamond Films Deposited on the Fused Silica

Published Online: 25 Jun 2018
Page range: 288 - 296

Abstract

Abstract

The main subject of this study are molecular structures and optical properties of boron-doped diamond films with [B]/[C]ppm ratio between 1000 and 10 000, fabricated in two molar ratios of CH4-H2mixture (1 % and 4 %). Boron-doped diamond (BDD) film on the fused silica was presented as a conductive coating for optical and electronic purposes. The scanning electron microscopy images showed homogenous and polycrystalline surface morphology. The Raman spectroscopy confirmed the growth of sp3diamond phase and sp2carbon phase, both regular and amorphous, on the grain boundaries, as well as the efficiency of boron doping. The sp3/sp2ratio was calculated using the Raman spectra deconvolution method. A high refractive index (in a range of 2.0 to 2.4 at λ= 550 nm) was achieved for BDD films deposited at 700 °C. The values of extinction coefficient were below 1.4 at λ= 550 nm, indicating low absorption of the film

Keywords

  • microwave plasma chemical vapor deposition
  • boron-doped diamond
  • optical constants
  • fused silica
Open Access

Diethylenetriamine-assisted one-step hydrothermal synthesis of cotton-like CoS cluster for high-performance supercapacitor

Published Online: 25 Jun 2018
Page range: 297 - 303

Abstract

Abstract

Cotton-like CoS cluster has been successfully synthesized via a simple one-step hydrothermal route assisted by diethylenetriamine (DETA) as a ligand and structure-directing agent. The structure and morphology of the product were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and N2 adsorption-desorption isotherm. The CoS sample which has a hexagonal phase without any impurities possesses a microscopic morphology made by cotton-like clusters. The as-fabricated CoS as a supercapacitor electrode presents desirable supercapacitive performance with a high specific capacitance (664 F∙g-1 at 0.5 A∙g-1), remarkable rate capability and excellent cycling stability (85.7 % specific capacitance retention after 1000 cycles), making it applicable as an electrode for high-performance supercapacitors.

Keywords

  • cobalt sulfide
  • diethylenetriamine
  • hydrothermal synthesis
  • supercapacitor
  • pseudocapacitance
Open Access

Optical investigations of microwave induced synthesis of zinc oxide thin-film

Published Online: 25 Jun 2018
Page range: 304 - 309

Abstract

Abstract

In this article, ZnO thin-film deposition on a glass substrate was done using microwave induced oxygen plasma based CVD system. The prepared thin-films were tested in terms of crystallinity and optical properties by varying the microwave power. The effect of power variation on the morphology and size of final products was carefully investigated. The crystal structure, chemical composition and morphology of the final products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, Raman spectroscopy and photoluminescence (PL). This technique confirmed the presence of hexagonal ZnO nanocrystals in all the thin-films. The minimum crystallite grain size as obtained from the XRD measurements was ~9.7 nm and the average diameter was ~18 nm.

Keywords

  • ZnO
  • thin film
  • microwave CVD
  • XRD
  • SEM
  • UV
  • PL
  • Raman spectroscopy
Open Access

Correlation between Structural, Magnetic and Spectroscopic Properties of Mg Substituted CoFe2O4

Published Online: 25 Jun 2018
Page range: 310 - 319

Abstract

Abstract

Mg substituted cobalt ferrite spinel powder samples with the general formula MgxCO1-xFe2O4(x = 0 to 0.25) were synthesized chemically through sol-gel method and annealed at 1100 °C for 2 h. They were initially screened for the structural and morphological properties by X-ray diffraction and field emission scanning electron microscopy, respectively. Vibrational properties of the samples were studied by Raman and infrared spectroscopies. X-ray diffraction confirmed the formation of single pure or near-pure phase with cubic spinel structure for all the samples with expected occupancy values. The field emission scanning electron microscopy revealed a decrease in the particle size with an increase in Mg concentration. Both structural and magnetic properties of the samples were characterized using Mössbauer spectroscopy while the magnetic properties were studied using vibrating sample magnetometry. The changes in magnetic moment of ions, their coupling with neighboring ions and cation exchange interactions were confirmed from the Mössbauer spectroscopy analysis. Saturation magnetization and coercivity values can be explained based on the Slater-Pauling curve. The magnetometry results showed a decrease in saturation magnetization of the samples with increase in Mg concentration

Keywords

  • Mg substituted cobalt ferrite
  • sol-gel method
  • Rietveld refinement
  • vibrational properties
  • spectroscopic techniques
Open Access

Facile microwave-assisted synthesis of Al:Mn co-doped PbI2 nanosheets: structural, vibrational, morphological, dielectric and radiation activity studies

Published Online: 25 Jun 2018
Page range: 320 - 326

Abstract

Abstract

Herein, we report a successful development of nano-scale pure and Al and Mn co-doped PbI2 using facile microwaveassisted route. Structural study was done through X-ray diffraction analysis of grain size, dislocation density and lattice strain. The crystallite size was found to vary from 28 nm to 40 nm due to Al:Mn co-doping in PbI2. The presence of various vibrational modes was confirmed by FT-IR spectroscopy and red shifting was observed in peak positions compared to the bulk. Surface morphology, examined using a scanning electron microscope, confirmed the formation of single crystal nanosheets of a thickness in the range of 10 nm to 30 nm. The single crystal nanosheets were found to be transformed to large area nanosheets due to the doping. Enhancement in dielectric constant from ~7.5 to 11 was observed with increasing Al doping concentration. Linear attenuation coefficient was calculated and showed the enhancement of blocking gamma rays with increasing doping concentration. Its value was found to increase from 7.5 to 12.8 with the doping. The results suggest that the synthesized nanostructures can be used for detection and absorption of gamma rays emitted by 137Cs and 241Am sources.

Keywords

  • semiconductor
  • scanning electron microscopy (SEM)
  • Raman spectroscopy
  • dielectric properties
  • radiation effects
Open Access

A novel photoelectrode of NiO@ZnO nanocomposite prepared by Pechini method coupled with PLD for efficiency enhancement in DSSCs

Published Online: 25 Jun 2018
Page range: 327 - 336

Abstract

Abstract

The dye-sensitized solar cells made of NiO@ZnO nanoparticles were synthesized by a novel Pechini route using different NiO molar concentration ratios. The thermal, structural morphological, optical and electrical properties of the prepared samples were investigated using thermal gravimetric analysis and differential scanning calorimetery (TGA/DSC), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), FT-IR and Raman spectroscopy, UV-diffuse reflectance (UV-DRS), photoluminescence (PL) and current-voltage (I-V) measurements. The success of doping process was confirmed by the XRD patterns, which revealed the existence of new peak at 43.2° corresponding to secondary phase NiO. UV spectra exhibited red shifts in NiO doped ZnO NCs and PL spectra showed strong emission band at 355 nm. The doping of ZnO with NiO was intended to enhance the surface defects of ZnO. The current-voltage measurements showed an improvement of the short circuit photocurrent (Jsc) and fill factor (FF) and a decrease in the open circuit voltage (VOC) for dye-sensitized solar cell (DSSC) based on NiO-ZnO NCs. A clear enhancement in efficiency of DSSC from 1.26±0.10 % for pure ZnO to 3.01±0.25 % for NiO-ZnO NCs at the optimum doping with 1.5 mol% of NiO to ZnO (ZN1.5) was observed. The obtained material can be a suitable candidate for photovoltaic applications.

Keywords

  • ZnO nanoparticles
  • NiO/ZnO nanocomposite
  • dye-sensitized solar cell (DSSC)
  • efficiency
Open Access

Photovoltage Formation Across Si P-N Junction Exposed to Laser Radiation

Published Online: 25 Jun 2018
Page range: 337 - 340

Abstract

Abstract

Photovoltage formation across Si p-n junction exposed to laser radiation is experimentally investigated. Illumination of the junction with 1.06 μm wavelength laser radiation leads to formation of classical photovoltage Uphdue to intense electronhole pair generation. When the photon energy is lower than the semiconductor forbidden energy gap, the photovoltage U is found to consist of two components, U = Uf+ Uph. The first Uf is a fast one having polarity of thermoelectromotive force of hot carriers. The second Uphis classical photovoltage with polarity opposite to Uf. It is found that Ufis linearly dependent on laser intensity. The classical photovoltage is established to decrease with the rise of radiation wavelength due to decrease in two-photon absorption coefficient with wavelength. Predominance of each separate component in the formation of the net photovoltage depends on both laser wavelength and intensity

Keywords

  • silicon
  • laser radiation
  • p-n junction
  • solar cell
  • hot carriers
Open Access

Morphological, optical and electrochromic properties of dry-lithiated nanostructured WO3 thin films

Published Online: 25 Jun 2018
Page range: 341 - 347

Abstract

Abstract

Tungsten trioxide (WO3) thin films were prepared by thermal evaporation technique on thoroughly cleaned glass substrates at high pressure of 133.322 mPa in presence of argon. The substrate temperature was maintained from 6 °C to 8 °C with the help of a cold jar. The deposited films were annealed at 400 °C in air for about 2 hours. The films were characterized in terms of their composition by X-ray photoelectron spectroscopy. Subsequently, the laboratory developed dry lithiation method was used to intercalate lithium atoms into as-deposited films in various proportions. With the amount of lithium content inserted into the film, the films showed coloration in visible and near infrared regions. The morphology, coloration efficiency and optical constants of annealed and lithiated films were calculated.

Keywords

  • WO3 thin films
  • thermal evaporation
  • XPS
  • atomic force microscopy
  • optical and electrochromic properties
24 Articles
Open Access

Synthesis and Luminescence Properties of ZrO2:Gd3+, RE3+(RE = Sm3+ ,Er3+) Phosphors

Published Online: 25 Jun 2018
Page range: 162 - 166

Abstract

Abstract

In the present study, ZrO2co-doped with Gd3+/Sm3+and Gd3+/Er3+ions have been synthesized using Pechini method. Phase composition, morphology and photoluminescence properties of the synthesized phosphors were investigated by using X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and photoluminescence spectrofluorometer (PL). After heating at 1200 °C, XRD revealed that the phosphors were crystallized as monoclinic and tetragonal multiphases. SEM images indicated that the phosphors consist of fine and spherical grains with a size around 200 nm to 250 nm. Luminescence studies of these phosphors have been carried out on the emission and excitation, along with lifetime measurements

Keywords

  • ZrO2
  • Sm3+
  • Er3+
  • luminescence
Open Access

Quinoxaline-Based Small Molecules: Synthesis and Investigation on Their Optoelectronic Properties

Published Online: 25 Jun 2018
Page range: 167 - 176

Abstract

Abstract

Small molecules of ThQuTh, CzQuTh, CzQuCz and TPAQuCz were designed and synthesized, based on quinoxaline acceptor, and electron donating groups, i.e. alkyl-thioephene, carbazole and triphenylamine on both side chains and molecular backbones. Their thermal, optical and electrochemical properties were systematically compared and studied. The absorption spectra of the small molecules were strongly affected by the donor units attached to quinoxaline. Strong electron donating groups, such as carbazole on the molecular backbone would lower optical band gap, resulting in a wide absorption and the strong donor on the side chain would enhance the absorption intensity in short wavelength region. The highest occupied molecular orbital (HOMO) energy levels of the four molecules were up-shifted with increasing the electron donating properties of donor units. The bulk-heterojunction organic solar cells with a device structure of ITO/PEDOT:PSS/SMs:PC61BM/LiF/Al were fabricated, in which the small molecules functioned as donors while PC61BM as acceptor. Because the electron-donating ability of carbazole (Cz), triphenylamine (TPA) is higher than that of thiophene (Th), CzQuTh, CzQuCz and TPAQuCz show higher power conversion efficiency (PCE) than that of ThQuTh. Furthermore, being the strongest in absorption intensity and widest in absorption spectrum, TPAQuCz has the highest power conversion efficiency. Further improvement of the device efficiency by optimizing the device structure is currently under investigation

Keywords

  • quinoxaline
  • acceptor materials
  • optoelectronic properties
  • solar cells
Open Access

Growth, spectral, density functional theory (DFT) and Hirshfeld surface analysis on 4-aminopyridinium adipate monohydrate nonlinear optical single crystal

Published Online: 25 Jun 2018
Page range: 177 - 184

Abstract

Abstract

4-aminopyridinium adipate monohydrate (4APA) was grown by slow evaporation solution growth technique. The functional groups in the grown crystal were identified from FT-IR spectral evaluation. The optical properties together with transmittance of the grown crystal were obtained from UV-Vis spectroscopic study. The mechanical and thermal properties of the grown crystal were studied using Vickers microhardness and TGA/DTA analyses, respectively. Microhardness test revealed that 4-aminopyridinium adipate monohydrate crystal is a soft category material. The density functional method (DFT) was performed using B3LYP with the 6-311G (d,p) basis set. The electronic charge distribution, reactivity of the molecules and the molecular electrostatic potential (MEP) of the grown crystal were analyzed using the B3LYP method. The intermolecular interactions that exist in the crystal structure of the 4APA have also been investigated by Hirshfeld surface analysis. The nonlinear optical properties of the 4APA crystal were confirmed by Kurtz-Perry technique.

Keywords

  • crystal growth
  • growth from solution
  • Hirshfeld
  • DFT
  • organic material
  • nonlinear optical material
Open Access

Preparation and characterization of PEO-based composite gel-polymer electrolytes complexed with lithium trifluoro methane sulfonate

Published Online: 25 Jun 2018
Page range: 185 - 192

Abstract

Abstract

Chitosan has been successfully incorporated as a filler in a polyethylene oxide (PEO) and lithium trifluoromethanesulfonate (LiCF3SO3) matrix with a combination of plasticizers, namely 1,3-dioxolane (DIOX) and tetraethylene glycol dimethylether (TEGDME). The composite gel-polymer electrolyte (CGPE) membranes were prepared by solution casting technique in an argon atmosphere. The prepared membranes were subjected to SEM, TG/DTA and FT-IR analyses. A Li/CGPE/Li symmetric cell was assembled and the variation of interfacial resistance was measured as a function of time. The lithium transference number (Li+t) was measured and the value was calculated as 0.6 which is sufficient for battery applications. The electrochemical stability window of the sample was studied by linear sweep voltammetry and the polymer electrolyte was found to be stable up to 5.2 V.

Keywords

  • polyethylene oxide
  • ionic conductivity
  • FT-IR
  • transport number
  • interfacial properties
Open Access

Structural and optical characterization of annealed As30Te60Ga10 thin films prepared by thermal evaporation technique

Published Online: 25 Jun 2018
Page range: 193 - 202

Abstract

Abstract

Effect of annealing temperature on the structural and optical properties of As30Te60Ga10 thin film was studied using various techniques such as differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The DSC analysis revealed that the As30Te60Ga10 glass has a single glass transition and crystallization peak while XRD results confirmed that the as-prepared and annealed films have crystalline nature. The coexistence of the crystalline phases in the investigated films could be attributed to the formation of orthorhombic As, hexagonal Ga7Te10, and monoclinic As2Te3 phases. It was found that the average crystallite size and optical parameters of the studied films depend on the annealing temperature. For example, the optical band gap decreased from 1.54 eV to 1.11 eV as the annealing temperature increased from 300 K to 433 K.

Keywords

  • chalcogenide
  • As-Te-Ga
  • thin films
  • structural properties
  • optical properties
  • thermal evaporation
Open Access

High Pressure Raman Study of Layered Semiconductor Tlgase2

Published Online: 25 Jun 2018
Page range: 203 - 208

Abstract

Abstract

Raman spectroscopy measurements of a monoclinic layered semiconductor TlGaSe2were performed in a pressure range up to 10.24 GPa. The pressure-induced first-order phase transition accompanied by reconstruction of the layer structure was observed at the pressure P ~ 0.9 GPa. The mode-Grüneisen parameters of intralayer bonds were calculated for TlGaSe2. The contribution of thermal expansion to temperature changes of phonon frequencies was defined. The type of intralayer bonds and their pressure transformation were analyzed in layered TlGaSe2. It was shown that the nature of intramolecular forces in molecular crystals and intralayer forces in layered GaS, GaSe and TlGaSe2is similar

Keywords

  • layered semiconductor
  • high pressure
  • Raman study
Open Access

Fabrication of Cu2O Nanostructured Thin Film by Anodizing

Published Online: 25 Jun 2018
Page range: 209 - 216

Abstract

Abstract

Cuprous oxide, a narrow bandgap p-type semiconductor, has been known as a potential material for applications in supercapacitors, hydrogen production, sensors, and energy conversion due to its properties such as non-toxicity, easy availability, cost effectiveness, high absorption coefficient in the visible region and large minority carriers diffusion length. In this study, Cu2O nanostructured thin film was fabricated by anodizing of Cu plates in ethylene glycol containing 0.15 M KOH, 0.1 M NH4F and 3 wt.% deionized water. The effects of anodizing voltage and temperature of electrolyte were investigated and reported. It was found that nanoporous Cu2O thin film was formed when anodizing voltages of 50 V and 70 V were used while a dense Cu2O thin film was formed due to the aggregation of smaller nanoparticles when 30 V anodizing voltage was used. Nanoplatelets thin film was formed when the temperature of electrolyte was reduced to 15 °C and 5 °C. X-ray diffraction confirmed the presence of Cu2O phase in thin film formed during anodizing of Cu plates, regardless of the anodizing voltage and temperature of electrolyte. Photoluminescence spectroscopy showed the presence of Cu2O peak at 630 nm corresponding to band gap of 1.97 eV. A mechanism of the formation of Cu2O thin film was proposed. This study reported the ease of tailoring Cu2O nanostructures of different morphologies using anodizing that may help widen the applications of this material

Keywords

  • anodizing
  • cuprous oxide
  • nanopores
  • nanoplatelets
  • thin film
Open Access

Noncontact Method of Conducting Elements “Writing” on Insulating Ge–Sb–Te Matrix Using a Laser Beam

Published Online: 25 Jun 2018
Page range: 217 - 224

Abstract

Abstract

Direct writing of low resistance wires on an amorphous Ge-Sb-Te matrix is reported. A 1342 nm continuous wave laser was used for local heating of the sample to form these wires. Mechanical contact was not needed for making the conducting elements. The properties of the samples were investigated down to 1.4 K and the laser conditions required for the writing of low resistance GST wires were found. The results are discussed with a view to possible applications, such as connectors and electrical wires made only via remote light exposure of the samples to make different resistors and non-linear elements

Keywords

  • GST
  • laser
  • conductor
  • noncontact method
Open Access

Electron Work Functions of (H K L)-Surfaces of W, Re, and Cu Crystals

Published Online: 25 Jun 2018
Page range: 225 - 234

Abstract

Abstract

Work function (WF) and some physicochemical data for several most prominent crystal planes of three metals of typical structures are calculated within the linear approximation employing the surface dipole and 2D gas models. “Composite” crystal of a homogeneous bulk phase and a thick surface composed of eight (h k l)-oriented facets with different unsaturated bonds is treated as a nine-phase nine-component system with two degrees of freedom. It contains the two-dimensional metal-lattice plasma of free electrons and the immobile atom-core network. For twenty four (h k l) surfaces, the WF and dipole barrier term, chemical and electrostatic potential levels, electron charge densities, surface dipole fields, and other parameters are calculated and tabularized. WF values obtained from the thermodynamics based formula are compared to the ones obtained from the quantum mechanics based formula, which shows good agreement with experiment and also reveals a specific deviation in the case of field emission method for the most packed plane. A set of accurate face dependent data can be of interest to electronics and materials science workers

Keywords

  • surface
  • interface
  • electron emission
  • work function
  • 2D plasma density
  • local Fermi levels
Open Access

Sol-Gel Derived Cds Nanocrystalline Thin Films: Optical and Photoconduction Properties

Published Online: 25 Jun 2018
Page range: 235 - 241

Abstract

Abstract

High-quality CdS nanocrystalline thin films were grown by sol-gel spin coating method at different solution temperatures on glass substrates. As-deposited films exhibited nanocrystalline phase with hexagonal wurtzite structure and showed good adhesion and smooth surface morphology. It was clearly observed that the crystallinity of the thin films improved with the increase in solution temperature. Crystallites sizes of the films also increased and were found to be in the range of 10 mm to 17 nm. The influence of the growth mechanism on the band and sub-band gap absorption of the films was investigated using UV-Vis and photothermal deflection spectroscopy (PDS). The band gap values were calculated in the range of 2.52 eV to 2.75 eV. The band gap decreased up to 9 % with the increase in solution temperature from 45 °C to 75 °C. Absorption coefficients estimated by PDS signal showed the significant absorption in low photon energy region of 1.5 eV to 2.0 eV. The dark and illuminated I-V characteristics revealed that the films were highly photosensitive. The results demonstrated the potential applications of sol-gel grown CdS nanocrystalline thin films as photoconductors and optical switches.

Keywords

  • CdS
  • sol-gel
  • optical properties
  • photothermal deflection spectroscopy
  • photoconductivity
Open Access

Analysis of glass forming ability using percolation concept and tunability of physical parameters of a-Ge12Se76 - xAs12Bix glassy semiconductors

Published Online: 25 Jun 2018
Page range: 242 - 254

Abstract

Abstract

Glass forming ability of lone-pair semiconductors was analyzed for (x = 0, 2, 4, 6, 8, 10) system. Values of lone pair electrons L were calculated using average coordination number of valence electrons. These values were found to decrease, as the system was moving towards the rigid region. L > 3 values showed vitreous state. Deviation of the stoichiometry confirmed the chalcogen-rich region. A linear correlation was found between the mean bond energy and glass transition temperature. Chemical Bond Approach model was applied to calculate the cohesive energy of the system. A linear relationship was found to exist between the cohesive energy and the theoretical band gap, calculated using Shimakawa relation. A decrease in both parameters was explained on the basis of average stabilization energy and electronegativity of the system. The density values were found to increase and may account for higher refractive index of the system. Large Bohr radius of the Bi atom accounted for an increase in the polarizability. Other parameters viz. degree of covalency, packing density, compactness, molar volume, free volume percentage, excess volume and polaron radius were also calculated. An effort was made to correlate the effect of Bi addition to Ge12Se76 - xAs12Bixlone-pair semiconductor on the basis of the structure of the glassy matrix or the connectedness of the material.

Keywords

  • constraints
  • glass transition temperature
  • band gap
  • cohesive energy
Open Access

Substitutional effect of copper on the cation distribution in cobalt chromium ferrites and their structural and magnetic properties

Published Online: 25 Jun 2018
Page range: 255 - 263

Abstract

Abstract

A series of copper substituted cobalt chromium ferrites, CuxCo1 - xCr0.5Fe1.5O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) has been synthesized, by employing powder metallurgy method. Calcination of the samples has been carried out for 24 hours at 1100 °C. The resultant materials have been investigated by using a variety of techniques, including X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM)), scanning electron microscopy (SEM), and ultraviolet visible spectroscopy (UV-Vis). The XRD patterns confirmed that all compositions had a cubic spinel structure with a single phase and the lattice parameter was found to increase with increasing copper concentration. FT-IR spectroscopy has been used for studying the chemical bonds in the spinel ferrite. Shifting of the bands ν1 and ν2 has been observed. It has been revealed from VSM analysis that saturation magnetization and coercivity decrease with rising the Cu+2 doping. Magnetic properties have been explained on the basis of cation distribution. Scanning electron microscopy (SEM) has been used to study the surface morphology of prepared samples. UV-Vis analysis revealed the optical absorption of the samples. An increase in band gaps has been observed with increasing copper concentration in the sample.

Keywords

  • crystal structure
  • ferromagnetic properties
  • optical band gap
Open Access

The influence of Kanthal wire surface defects on the formation of Si nanolayer deposited by PVD method

Published Online: 25 Jun 2018
Page range: 264 - 269

Abstract

Abstract

The subject of this research is the structure of a Si nanolayer deposited on a FeCrAl wire surface by means of magnetron sputtering method. Si layer was selected as one of possible protections of the wire surface against excessive corrosive-erosive wear. In order to increase the power necessary for the DC discharge of the magnetron with Si cathode, a second magnetron with an aluminum disc as a cathode was used. The wire was attached to a carousel holder to ensure its rotation around the magnetron. The thickness of the deposited layers was about 150 nm. A wire surface examination indicated the presence of defects such as gaps between grains, cavities as well as severely deformed grains of surface layer. The research was conducted on the sample sections which had been prepared by focused ion beam method (FIB). The technique of transmission microscopy, which was used for observation, allowed us to obtain images in bright field (BF), dark field (DF), as well as in high resolution (HREM). The studies were also performed on the wire surface after the cutting process of the expanded polystyrene blocks. A metallographic optical microscope Nikon MA200 with a large depth of field was used for the examination which showed the presence of carbon deposit products. Additionally, a composition microanalysis was carried out along the line within selected areas of samples, with the use of energy dispersive spectroscopy (EDS). A large impact of wire surface defects on Si layer forming was found as well as a high direct homogeneous growth. The examination of the sections indicated the existence of a mechanism of defects sealed by Si layer, where directionality of grains growth in these areas revealed the tendency for vertical location relative to defects surface. Consequently, closed nanopores, i.e. spaces not covered with Si layer, were created. It is a characteristic feature of areas with defects covered with an oxide film created in a natural way.

Keywords

  • PVD
  • nanolayers
  • microwire
  • corrosion
  • EPS
Open Access

Structural, thermal and optical investigation of tin sulfide nanoparticles for next-generation photovoltaic applications

Published Online: 25 Jun 2018
Page range: 270 - 275

Abstract

Abstract

We report a simple approach for synthesizing monodispersed, crystalline and size-tunable tin sulfide nanoparticles for environment friendly next generation solar cell applications. Both SnS and SnS2 nanoparticles could be a potential nanomaterial for solar cells. The structural, morphological, thermal and optical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FT-IR). The XRD spectra revealed hexagonal and orthorhombic phases of SnS and SnS2 nanoparticles, respectively, where the grains size ranged from 11 nm to 30 nm. The weight percentage as a function of temperature was determined using TGA analysis. Functional groups were observed by FT-IR. The energy bandgap was determined as 1.41 eV showing usefulness of the nanoparticles in next generation environmental friendly solar energy applications.

Keywords

  • SnS nanoparticles
  • energy bandgap
  • next generation photovoltaics
Open Access

Exploration of donor effect on electron injection and photovoltaic properties of chalcone derivatives

Published Online: 25 Jun 2018
Page range: 276 - 282

Abstract

Abstract

Various photovoltaic parameters, i.e., electron injection (ΔGinject.), electronic coupling constants (|VRP|), light harvesting efficiencies (LHE), band alignment and electronic properties of five chalcone derivatives were studied by density functional theory (DFT) and time domain. The light was also shed on the effect of different electron donating groups and their strength intensity on the electronic and charge transfer properties. The balanced hole and electron reorganization energies for Comp 4 showed that it might have better ambipolar charge transfer in nature. The strong electron donating group(s) usually enhance(s) the ΔGinject. and |VRP| of chalcones as -N(CH3)2 > OCH3 > OH. Additionally, ΔGinject. and |VRP| of various substituted chalcone derivatives have been observed as trimethoxy > dimethoxy > monomethoxy. The greater electron donating ability of substituents is also favorable for the staggered band alignment. The superior ΔGinject. of all the studied chalcones than of the referenced compounds disclosed that the prior compounds would be proficient photovoltaic materials.

Keywords

  • renewable energy
  • photovoltaic properties
  • density functional theory (DFT)
  • band alignment
  • charge transfer properties
  • electron injection
Open Access

Thermal and electrical properties of polyimide/PANI nanofiber composites prepared via in situ polymerization

Published Online: 25 Jun 2018
Page range: 283 - 287

Abstract

Abstract

Polyimide/polyaniline nanofiber composites were prepared by in situ polymerization with various weight percentages of polyaniline (PANI) nanofibers. X-ray diffraction (XRD) and Fourier transform infrared spectra (FT-IR), proved the successful preparation of PANI nanofiber composite films. In addition, thermal stability of PI/PANI nanofiber composites was superior relative to PI, having 10 % gravimetric loss in the range of 623 °C to 671 °C and glass transition temperature of 289 °C to 297 °C. Furthermore, the values of the loss tangent tanδ and AC conductivity σAC of the nanocomposite films were notably higher than those of pure polyimide. The addition of 5 wt.% to 15 wt.% PANI nanofiber filler enhanced the activation energy of PI composites from 0.37 eV to 0.34 eV.

Keywords

  • polyimide
  • polyaniline nanofiber
  • in situ polymerization
  • PI/PANI nanofiber composite films
Open Access

Gas Composition Influence on the Properties of Boron-Doped Diamond Films Deposited on the Fused Silica

Published Online: 25 Jun 2018
Page range: 288 - 296

Abstract

Abstract

The main subject of this study are molecular structures and optical properties of boron-doped diamond films with [B]/[C]ppm ratio between 1000 and 10 000, fabricated in two molar ratios of CH4-H2mixture (1 % and 4 %). Boron-doped diamond (BDD) film on the fused silica was presented as a conductive coating for optical and electronic purposes. The scanning electron microscopy images showed homogenous and polycrystalline surface morphology. The Raman spectroscopy confirmed the growth of sp3diamond phase and sp2carbon phase, both regular and amorphous, on the grain boundaries, as well as the efficiency of boron doping. The sp3/sp2ratio was calculated using the Raman spectra deconvolution method. A high refractive index (in a range of 2.0 to 2.4 at λ= 550 nm) was achieved for BDD films deposited at 700 °C. The values of extinction coefficient were below 1.4 at λ= 550 nm, indicating low absorption of the film

Keywords

  • microwave plasma chemical vapor deposition
  • boron-doped diamond
  • optical constants
  • fused silica
Open Access

Diethylenetriamine-assisted one-step hydrothermal synthesis of cotton-like CoS cluster for high-performance supercapacitor

Published Online: 25 Jun 2018
Page range: 297 - 303

Abstract

Abstract

Cotton-like CoS cluster has been successfully synthesized via a simple one-step hydrothermal route assisted by diethylenetriamine (DETA) as a ligand and structure-directing agent. The structure and morphology of the product were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and N2 adsorption-desorption isotherm. The CoS sample which has a hexagonal phase without any impurities possesses a microscopic morphology made by cotton-like clusters. The as-fabricated CoS as a supercapacitor electrode presents desirable supercapacitive performance with a high specific capacitance (664 F∙g-1 at 0.5 A∙g-1), remarkable rate capability and excellent cycling stability (85.7 % specific capacitance retention after 1000 cycles), making it applicable as an electrode for high-performance supercapacitors.

Keywords

  • cobalt sulfide
  • diethylenetriamine
  • hydrothermal synthesis
  • supercapacitor
  • pseudocapacitance
Open Access

Optical investigations of microwave induced synthesis of zinc oxide thin-film

Published Online: 25 Jun 2018
Page range: 304 - 309

Abstract

Abstract

In this article, ZnO thin-film deposition on a glass substrate was done using microwave induced oxygen plasma based CVD system. The prepared thin-films were tested in terms of crystallinity and optical properties by varying the microwave power. The effect of power variation on the morphology and size of final products was carefully investigated. The crystal structure, chemical composition and morphology of the final products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, Raman spectroscopy and photoluminescence (PL). This technique confirmed the presence of hexagonal ZnO nanocrystals in all the thin-films. The minimum crystallite grain size as obtained from the XRD measurements was ~9.7 nm and the average diameter was ~18 nm.

Keywords

  • ZnO
  • thin film
  • microwave CVD
  • XRD
  • SEM
  • UV
  • PL
  • Raman spectroscopy
Open Access

Correlation between Structural, Magnetic and Spectroscopic Properties of Mg Substituted CoFe2O4

Published Online: 25 Jun 2018
Page range: 310 - 319

Abstract

Abstract

Mg substituted cobalt ferrite spinel powder samples with the general formula MgxCO1-xFe2O4(x = 0 to 0.25) were synthesized chemically through sol-gel method and annealed at 1100 °C for 2 h. They were initially screened for the structural and morphological properties by X-ray diffraction and field emission scanning electron microscopy, respectively. Vibrational properties of the samples were studied by Raman and infrared spectroscopies. X-ray diffraction confirmed the formation of single pure or near-pure phase with cubic spinel structure for all the samples with expected occupancy values. The field emission scanning electron microscopy revealed a decrease in the particle size with an increase in Mg concentration. Both structural and magnetic properties of the samples were characterized using Mössbauer spectroscopy while the magnetic properties were studied using vibrating sample magnetometry. The changes in magnetic moment of ions, their coupling with neighboring ions and cation exchange interactions were confirmed from the Mössbauer spectroscopy analysis. Saturation magnetization and coercivity values can be explained based on the Slater-Pauling curve. The magnetometry results showed a decrease in saturation magnetization of the samples with increase in Mg concentration

Keywords

  • Mg substituted cobalt ferrite
  • sol-gel method
  • Rietveld refinement
  • vibrational properties
  • spectroscopic techniques
Open Access

Facile microwave-assisted synthesis of Al:Mn co-doped PbI2 nanosheets: structural, vibrational, morphological, dielectric and radiation activity studies

Published Online: 25 Jun 2018
Page range: 320 - 326

Abstract

Abstract

Herein, we report a successful development of nano-scale pure and Al and Mn co-doped PbI2 using facile microwaveassisted route. Structural study was done through X-ray diffraction analysis of grain size, dislocation density and lattice strain. The crystallite size was found to vary from 28 nm to 40 nm due to Al:Mn co-doping in PbI2. The presence of various vibrational modes was confirmed by FT-IR spectroscopy and red shifting was observed in peak positions compared to the bulk. Surface morphology, examined using a scanning electron microscope, confirmed the formation of single crystal nanosheets of a thickness in the range of 10 nm to 30 nm. The single crystal nanosheets were found to be transformed to large area nanosheets due to the doping. Enhancement in dielectric constant from ~7.5 to 11 was observed with increasing Al doping concentration. Linear attenuation coefficient was calculated and showed the enhancement of blocking gamma rays with increasing doping concentration. Its value was found to increase from 7.5 to 12.8 with the doping. The results suggest that the synthesized nanostructures can be used for detection and absorption of gamma rays emitted by 137Cs and 241Am sources.

Keywords

  • semiconductor
  • scanning electron microscopy (SEM)
  • Raman spectroscopy
  • dielectric properties
  • radiation effects
Open Access

A novel photoelectrode of NiO@ZnO nanocomposite prepared by Pechini method coupled with PLD for efficiency enhancement in DSSCs

Published Online: 25 Jun 2018
Page range: 327 - 336

Abstract

Abstract

The dye-sensitized solar cells made of NiO@ZnO nanoparticles were synthesized by a novel Pechini route using different NiO molar concentration ratios. The thermal, structural morphological, optical and electrical properties of the prepared samples were investigated using thermal gravimetric analysis and differential scanning calorimetery (TGA/DSC), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), FT-IR and Raman spectroscopy, UV-diffuse reflectance (UV-DRS), photoluminescence (PL) and current-voltage (I-V) measurements. The success of doping process was confirmed by the XRD patterns, which revealed the existence of new peak at 43.2° corresponding to secondary phase NiO. UV spectra exhibited red shifts in NiO doped ZnO NCs and PL spectra showed strong emission band at 355 nm. The doping of ZnO with NiO was intended to enhance the surface defects of ZnO. The current-voltage measurements showed an improvement of the short circuit photocurrent (Jsc) and fill factor (FF) and a decrease in the open circuit voltage (VOC) for dye-sensitized solar cell (DSSC) based on NiO-ZnO NCs. A clear enhancement in efficiency of DSSC from 1.26±0.10 % for pure ZnO to 3.01±0.25 % for NiO-ZnO NCs at the optimum doping with 1.5 mol% of NiO to ZnO (ZN1.5) was observed. The obtained material can be a suitable candidate for photovoltaic applications.

Keywords

  • ZnO nanoparticles
  • NiO/ZnO nanocomposite
  • dye-sensitized solar cell (DSSC)
  • efficiency
Open Access

Photovoltage Formation Across Si P-N Junction Exposed to Laser Radiation

Published Online: 25 Jun 2018
Page range: 337 - 340

Abstract

Abstract

Photovoltage formation across Si p-n junction exposed to laser radiation is experimentally investigated. Illumination of the junction with 1.06 μm wavelength laser radiation leads to formation of classical photovoltage Uphdue to intense electronhole pair generation. When the photon energy is lower than the semiconductor forbidden energy gap, the photovoltage U is found to consist of two components, U = Uf+ Uph. The first Uf is a fast one having polarity of thermoelectromotive force of hot carriers. The second Uphis classical photovoltage with polarity opposite to Uf. It is found that Ufis linearly dependent on laser intensity. The classical photovoltage is established to decrease with the rise of radiation wavelength due to decrease in two-photon absorption coefficient with wavelength. Predominance of each separate component in the formation of the net photovoltage depends on both laser wavelength and intensity

Keywords

  • silicon
  • laser radiation
  • p-n junction
  • solar cell
  • hot carriers
Open Access

Morphological, optical and electrochromic properties of dry-lithiated nanostructured WO3 thin films

Published Online: 25 Jun 2018
Page range: 341 - 347

Abstract

Abstract

Tungsten trioxide (WO3) thin films were prepared by thermal evaporation technique on thoroughly cleaned glass substrates at high pressure of 133.322 mPa in presence of argon. The substrate temperature was maintained from 6 °C to 8 °C with the help of a cold jar. The deposited films were annealed at 400 °C in air for about 2 hours. The films were characterized in terms of their composition by X-ray photoelectron spectroscopy. Subsequently, the laboratory developed dry lithiation method was used to intercalate lithium atoms into as-deposited films in various proportions. With the amount of lithium content inserted into the film, the films showed coloration in visible and near infrared regions. The morphology, coloration efficiency and optical constants of annealed and lithiated films were calculated.

Keywords

  • WO3 thin films
  • thermal evaporation
  • XPS
  • atomic force microscopy
  • optical and electrochromic properties

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