Issues

Journal & Issues

AHEAD OF PRINT

Volume 40 (2022): Issue 2 (August 2022)

Volume 40 (2022): Issue 1 (March 2022)

Volume 39 (2021): Issue 4 (December 2021)

Volume 39 (2021): Issue 3 (September 2021)

Volume 39 (2021): Issue 2 (June 2021)

Volume 39 (2021): Issue 1 (March 2021)

Volume 38 (2020): Issue 4 (December 2020)

Volume 38 (2020): Issue 3 (September 2020)

Volume 38 (2020): Issue 2 (June 2020)

Volume 38 (2020): Issue 1 (March 2020)

Volume 37 (2019): Issue 4 (December 2019)

Volume 37 (2019): Issue 3 (September 2019)

Volume 37 (2019): Issue 2 (June 2019)

Volume 37 (2019): Issue 1 (March 2019)

Volume 36 (2018): Issue 4 (December 2018)

Volume 36 (2018): Issue 3 (September 2018)

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

Volume 36 (2018): Issue 1 (March 2018)

Volume 35 (2017): Issue 4 (December 2017)

Volume 35 (2017): Issue 3 (October 2017)

Volume 35 (2017): Issue 2 (July 2017)

Volume 35 (2017): Issue 1 (March 2017)

Volume 34 (2016): Issue 4 (December 2016)

Volume 34 (2016): Issue 3 (September 2016)

Volume 34 (2016): Issue 2 (June 2016)

Volume 34 (2016): Issue 1 (March 2016)

Volume 33 (2015): Issue 4 (December 2015)

Volume 33 (2015): Issue 3 (September 2015)

Volume 33 (2015): Issue 2 (June 2015)

Volume 33 (2015): Issue 1 (March 2015)

Volume 32 (2014): Issue 4 (December 2014)

Volume 32 (2014): Issue 3 (September 2014)

Volume 32 (2014): Issue 2 (June 2014)

Volume 32 (2014): Issue 1 (January 2014)

Volume 31 (2013): Issue 4 (October 2013)

Volume 31 (2013): Issue 3 (August 2013)

Volume 31 (2013): Issue 2 (April 2013)

Volume 31 (2013): Issue 1 (January 2013)

Volume 30 (2012): Issue 4 (December 2012)

Volume 30 (2012): Issue 3 (September 2012)

Volume 30 (2012): Issue 2 (June 2012)

Volume 30 (2012): Issue 1 (March 2012)

Volume 29 (2011): Issue 4 (December 2011)

Volume 29 (2011): Issue 3 (September 2011)

Volume 29 (2011): Issue 2 (June 2011)

Volume 29 (2011): Issue 1 (March 2011)

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

Search

Volume 38 (2020): Issue 1 (March 2020)

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

Search

27 Articles
Open Access

Research on the influence of the filtrating electrode on the structure and optical properties of TiO2 thin films prepared by the energy filtering magnetron sputtering technique

Published Online: 08 May 2020
Page range: 1 - 7

Abstract

Abstract

TiO2 thin films were deposited by the energy filtrating magnetron sputtering (EFMS) technique and the traditional direct current magnetron sputtering (DMS) technique. The influence of the filtering electrode mesh number on the structure and optical properties of TiO2 thin films was investigated. The structure, surface morphology and optical properties were characterized by XRD, SEM and ellipsometric spectroscopy, respectively. Results show that the TiO2 thin films deposited by the DMS and EFMS techniques at the same deposition parameters are composed of the anatase phase exclusively. TiO2 thin films deposited at lower deposition rate by the EFMS technique have lower crystallinity, smaller particle size and smoother surface. With increasing the mesh number, the refractive index, extinction coefficient and optical band gap are larger.

Keywords

  • energy filtering magnetron sputtering
  • TiO thin film
  • optical property
Open Access

Nanocharacterization of metallic thin films deposited on different substrates

Published Online: 08 May 2020
Page range: 8 - 16

Abstract

Abstract

The purpose of this study was to determine the influence of different substrates (C45 steel, polycarbonate, glass) on the topography as well as tribological and mechanical properties (nanohardness, modulus of elasticity and friction force) of aluminum, gold and silver thin films. The 3D image analysis showed a strong influence of the substrate material on the topography of the studied thin films with no certain variation rule. Using the Oliver and Pharr method for determining nanohardness it was observed that, the smallest values were obtained for the thin films deposited on plastic substrate, followed by glass and C45 steel, regardless of the deposited material. The determination of the modulus of elasticity was done using the Hertzian method. The obtained results showed that the highest values of this parameter were obtained for the films deposited on plastic substrate, while the lowest values depended on both the deposited material and substrate. Friction force analysis for aluminum and gold showed a significant impact of the substrate material, with more constant values for gold. As a consequence, one must pay a particular attention when choosing the material for the substrate on which the thin films are deposited.

Keywords

  • metallic thin films
  • topography
  • nanohardness
  • friction force
  • modulus of elasticity
Open Access

Structural and optical properties of ZnO thin film prepared by sol-gel spin coating

Published Online: 08 May 2020
Page range: 17 - 22

Abstract

Abstract

Zinc oxide (ZnO) thin films were deposited on Si (1 0 0) and glass substrates by sol-gel spin coating technique. Zinc acetate dihydrate, monoethanolamine and isopropanol were used as the sources for precursor solution and the resulting gel was used for the preparation of ZnO thin films. The films were annealed at different temperatures (100 °C to 500 °C) and the effect of annealing on the structural and optical properties was investigated. X-ray diffraction (XRD) and UV-Vis spectroscopy were used for the analysis of the films. The XRD results indicated the polycrystalline hexagonal structure of the ZnO films with (0 0 2) orientation. The optical properties of the films were studied using UV-Vis spectrophotometer in the wavelength range of 190 – 1100 nm. The optical characterization of the ZnO thin films showed the high transmittance of ~90 % for the films annealed at 400 °C. The films showed the absorbance ~360 – 390 nm and bandgap values of 3.40 – 3.10 eV, depending on the annealing temperature of the films.

Keywords

  • ZnO thin films
  • sol-gel
  • spin coating
  • X-ray diffraction
  • optical properties
Open Access

Synthesis and optical properties of uranium-doped cadmium oxide synthesized by sol-gel method

Published Online: 08 May 2020
Page range: 23 - 27

Abstract

Abstract

Optical properties of cadmium oxide and uranium-doped CdO thin films synthesized by the sol-gel technique were investigated. The structural properties of the films were investigated using X-ray diffraction patterns of U-doped CdO. It was found that CdO-based films have a cubic NaCl structure. Structural properties of the films were investigated with atomic force microscopy (AFM). Reflectance, transmittance and absorption spectra of the films were measured with UV-Vis-NIR spectrophotometer. The photoluminescence (PL) behavior of the films was recorded using a fluorescence spectrophotometer. It was found that the nanostructure of the cadmium oxide film is controlled by U doping.

Keywords

  • cadmium oxide
  • sol gel
  • nanoparticles
Open Access

Preparation of ternary (35 – x)Sb2O3–xBi2O3–65P2O5 glasses for lead-free glass application

Published Online: 08 May 2020
Page range: 28 - 33

Abstract

Abstract

Glasses composed of ternary components (35 – x)Sb2O3–xBi2O3–65P2O5 (0 ⩽ x ⩽ 20 mol%) have been prepared and investigated as a potential alternative to lead-free glass for low temperature applications. Their structural properties were studied by Infrared Spectroscopy IR and Differential Thermal Analysis DTA. Results from the IR showed that Sb3+ and Bi3+ were responsible for glass network structure, which was supported by the diversification of density ρ and molar volume Vm with an increasing amount of Bi2O3. Glass transition temperature Tg, thermal stability, and coefficient of thermal expansion increased after substitution of Bi2O3 for Sb2O3 within the range of 0 mol% to 20 mol%. The water durability decreased and then increased; it could be attributed to the corrosion resistant P–O–Sb bonds. A typical sample of 25Sb2O3–10Bi2O3–65P2O5 possesses excellent properties and can be a promising candidate for further applications.

Keywords

  • structure
  • chemical properties
  • bismuth phosphates
Open Access

Microstructure and mechanical properties of Sn-9Zn-xAl and Sn-9Zn-xCu lead-free solder alloys

Published Online: 08 May 2020
Page range: 34 - 40

Abstract

Abstract

This study investigates microstructures and mechanical properties of the alloys obtained by adding Cu (0.7 % and 0.9 %) and Al (0.7 % and 0.9 %) to lead-free Sn-9Zn eutectic soldering alloy produced by investment casting method. The results show that Cu5Zn8 phase has formed in the structure of Cu added alloys and the Al2O3 phase has formed due to addition of Al. It was found that small and round-shaped Al2O3 phase increased the tensile strength of the new alloy compared to the eutectic alloy. In addition, it was observed that the microhardness of Cu added alloys was lower than that of Sn-9Zn eutectic alloy, but the microhardness of alloys containing Al was higher compared to the other eutectic Sn-9Zn alloy.

Keywords

  • Sn-Zn lead-free alloys
  • investment casting
  • mechanical properties
Open Access

Sputtering pressure influenced structural, electrical and optical properties of RF magnetron sputtered MoO3 films

Published Online: 08 May 2020
Page range: 41 - 47

Abstract

Abstract

MoO3 films were deposited by RF magnetron sputtering technique on glass and silicon substrates held at 473 K by sputtering of metallic molybdenum target at an oxygen partial pressure of 4 × 10−2 Pa and at different sputtering pressures in the range of 2 Pa to 6 Pa. The influence of sputtering pressure on the structure and surface morphology, electrical and optical properties of the MoO3 thin films was studied. X-ray diffraction studies suggest that the films deposited at a sputtering pressure of 2 Pa were polycrystalline in nature with mixed phase of α- and β-phase MoO3, while those formed at sputtering pressure of 4 Pa and above were of α-phase MoO3. Scanning electron micrographs showed a decrement in the size of the particles and their shapes changed from needle like structure to dense films with the increase of sputtering pressure. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic vibration modes of Mo=O, Mo–O and Mo–O–Mo related to MoO3. Electrical resistivity of the MoO3 films decreased from 6.0 × 104 Ω cm to 2 × 104 Ω cm with an increase of sputtering pressure from 2 Pa to 6 Pa, respectively. Optical band gap of the films decreased from 3.12 eV to 2.86 eV with the increase of sputtering pressure from 2 Pa to 6 Pa, respectively.

Keywords

  • MoO thin films
  • RF magnetron sputtering
  • sputtering pressure
  • structural properties
  • optical properties
Open Access

Effect of L-asparagine as dopant on the growth and characteristics of ammonium tetroxalate dihydrate single crystal

Published Online: 08 May 2020
Page range: 48 - 61

Abstract

Abstract

Single crystals of L-asparagine doped ammonium tetroxalate dihydrate were grown using slow evaporation solution growth technique with deionized water as a solvent. The shift and intensity of the peaks in the single crystal X-ray diffraction and Fourier transform infrared analyses confirmed the inclusion of L-asparagine in the ammonium tetroxalate dihydrate crystal structure. The optical transmission characteristics viz. optical band gap, optical conductivity, etc., were determined. Thermal studies revealed the occurrence of anomalies at 135.3 °C and 221.7 °C leading to the possibility of phase transitions and thereby, ferroelectric behavior. Vickers microhardness studies enabled determination of various microhardness parameters. Dielectric behavior was analyzed by varying the temperature and frequency. Anomalies were observed at 135 °C and 221 °C suggesting the existence of ferroelectric nature of the compound. Self-defocusing effect was observed. The polarization-electric field hysteresis loops showed a pinched effect due to defects induced by inclusion of dopant. The crystals were characterized by single crystal XRD, FT-IR, DRS, UV-Vis-NIR, Vickers microhardness test as well as thermal and dielectric techniques. In brief, L-asparagine as a dopant in ammonium tetroxalate dihydrate altered various physical properties of the crystals. They were highly transparent in the visible region with a wider optical band gap, softer material than the parent, higher phase transition temperature of 135 °C, negative nonlinearity and self-defocusing ability.

Keywords

  • Z-scan
  • dielectric properties
  • thermal characteristics
  • organic crystal
Open Access

Plasmonic nanostructures of SnO2:Sb thin film under gamma radiation response

Published Online: 08 May 2020
Page range: 62 - 72

Abstract

Abstract

This paper is a part of a natural dye solar cell project. Conductive transparent oxide (CTO) films have been deposited onto preheated glass substrates using a spray pyrolysis technique. The optical, electrical, structural properties as well as thermal annealing and gamma radiation response were studied. The average optical energy gap of doped films for direct allowed and direct forbidden transitions were found to be 3.92 and 3.68 eV, respectively. The plasmon frequency and plasmon energy after doping were found to be 3.48 × 1014 s −1 and 0.23 eV. The negative absorbance of the doped film was observed in UV-Vis range after applying both thermal annealing and γ-dose irradiation with 22 kGy. The negative refractive index of the doped film in UV range (220 – 300 nm) is promising for optical applications. The electron mobility μe reached a maximum of 27.4 cm2 V−1 s−1 for Sb concentration of 10 %. The corresponding resistivity ρ, and sheet resistance Rs reached their minimum values of 1.1 × 10−3 Ω cm and 35 Ω sq−1, respectively. The dopant concentration has been increased from 4.13 × 1019 to 2.1 × 1020cm−3. The doped film was found to exhibit three diffraction peaks associated with (2 2 2), (2 0 0), and (2 1 1) reflection planes, of which the peak of (2 2 2) of Sb2O3 and the peak of (2 0 0) were very close.

Keywords

  • CTO
  • doping
  • optical properties
  • electrical properties
  • structure
  • radiation
Open Access

Ca4−xLa2+xTi5−xBxO17 (B = Al, Ga) dielectric ceramics for microwave applications

Published Online: 08 May 2020
Page range: 73 - 78

Abstract

Abstract

In this study, Ca4−xLa2+xTi5−xBxO17 (B = Al, Ga; x = 0, 1) ceramics were processed via a mixed oxide solid state sintering route and characterized using XRD, SEM, EDS and Vector Network Analyzer. Phase analysis of the samples showed single phase formation for the sample x = 0 while secondary phases formed for Ca4−xLa2+xTi5−xBxO17 (B = Al, Ga; x = 1) ceramics. Ca4La2Ti5O17 exhibited ∈r = 74, Q×fo = 14,116 GHz and τf = 157 ppm/°C. The substitution of Ga or Al for Ti at the B-site of Ca4La2Ti5O17 ceramics significantly improved the microwave dielectric properties i.e. Ca3La3Ti4GaO17 and Ca3La3Ti4AlO17 have ∈r = 44, Q×fo = 16,128 GHz and τf = 7.3 ppm/°C and ∈r = 46, Q×fo = 13,754 GHz and τf = −2 ppm/°C, respectively. The microwave dielectric properties of these materials are suitable for high frequency microwave applications.

Keywords

  • ceramics
  • perovskite
  • microwave dielectric properties
Open Access

Thin films of copper phthalocyanine deposited by solution processing methods

Published Online: 08 May 2020
Page range: 79 - 90

Abstract

Abstract

In this work, we show and discuss the surface structure picture of copper phthalocyanine (CuPc) thin films deposited from trifluoroacetic acid (TFA) solvent onto silicon substrates at ambient conditions by four solution processing methods, namely drop-casting, dip-coating, spin-casting and spray-coating. The CuPc films were studied by AFM, as the main technique, and complemented by micro-Raman spectroscopy. Essentially, such thin films consist of CuPc molecular nanoribbons of a fixed ~1 nm thickness. CuPc molecules are arranged in an in-plane direction and formed in stacks under a defined tilt angle with respect to the substrate surface (monolayer) or underlying CuPc layer (multilayer). The film morphology takes various forms depending on the solution concentration, number of layers, and the deposition method. For instance, the morphology varies from very wide (~600 nm) but flat (~1 nm) ribbons for films prepared by dip-coating to crystallized rod-like features (multi-layered ribbons) when obtained by spray-coating. The factors studied in this paper should be taken into consideration in designing and controlling the criteria for rigorous CuPc film architecture.

Keywords

  • molecular structure
  • growth
  • copper phthalocyanine
  • solution processing methods
  • atomic force microscopy
Open Access

Direct formation of ZnO nanorods by hydrothermal process: study on its optical properties and electron transport

Published Online: 08 May 2020
Page range: 91 - 96

Abstract

Abstract

We report a new direct fabrication of the ZnO nanorods (NR) by hydrothermal method, in which the preparation of seed layer is eliminated. We show that the tuning of initial temperature rate during the hydrothermal process plays a key role in the structural modification of the ZnO NR. A highly oriented ZnO NR is successfully fabricated by using a low rate of initial temperature. The increase of optical absorption and electron transport was obtained by reducing the diameter and increasing distribution of the ZnO NR on the substrate. Interestingly, an additional absorption from the defects is obtained in the system, which plays an important role in expanding the optical absorption. Our system will provide a favourable characteristic for developing the high-performance optoelectronic devices with high optical absorption and high electron transport.

Keywords

  • optical properties
  • ZnO nanorods
  • hydrothermal process
  • semiconductor materials
Open Access

Density functional study of structures, stabilities and electronic properties of AgAunλ(λ=0,±1;n=1-12){\rm{AgAu}}_n^\lambda \left( {\lambda = 0, \pm 1;n = 1 - 12} \right) clusters: comparison with pure gold clusters

Published Online: 08 May 2020
Page range: 97 - 107

Abstract

Abstract

Geometrical structures, relative stabilities and electronic properties of neutral, cationic and anionic pure gold Aun+1λ{\rm{A}}u_{n + 1}^\lambda and Ag-doped bimetallic AgAunλ(λ=0,±1;n=1-12){\rm{AgAu}}_n^\lambda \left( {\lambda = 0, \pm 1;n = 1 - 12} \right) clusters have been systematically investigated by using density functional theory methodology. The optimized structures show that planar to three-dimensional structural transition occurs at n = 5 for cationic clusters. Due to strong relativistic effect of Au clusters, the ground state configurations of neutral and anionic bimetallic clusters favor planar geometry till n = 12. Silver atoms tend to occupy the most highly coordinated position and form the maximum number of bonds with Au atoms. The computed HOMO-LUMO energy gaps, fragmentation energies and second-order difference of energies show interesting odd-even oscillation behavior. The result indicates that AgAu5, AgAu2+{\rm{AgAu}}_2^ + and AgAu2-{\rm{AgAu}}_2^ - are the most stable clusters in this molecular system. The DFT based descriptors of bimetallic clusters are also discussed and compared with pure gold clusters. The high value of correlation coefficient between HOMO-LUMO energy gaps and DFT based descriptors supports our analysis. A good agreement between experimental and theoretical data has been obtained in this study.

Keywords

  • density functional theory
  • bimetallic cluster
  • AgAu
  • structures
  • properties
Open Access

Optical characterization of thin Al2O3 layers deposited by magnetron sputtering technique at industrial conditions for applications in glazing

Published Online: 08 May 2020
Page range: 108 - 115

Abstract

Abstract

In this study, thin Al2O3 films (11 nm – 82 nm) were deposited by means of a recently developed pulse gas injection magnetron sputtering method and investigated by means of atomic force microscopy, spectroscopic ellipsometry and spectrophotometry. Quite low values of optical constants (1.581 to 1.648 at λ = 550 nm) of the alumina films are directly associated with specific growth conditions (pulse injection of the reactive or reactive + inert gas) in the pulse gas injection magnetron sputtering process. The light transmittance of Al2O3/glass systems (86 % to 90 %) is only a few percent lower than that calculated for glass (93 %).

Keywords

  • AlO
  • GIMS
  • refractive index
  • light transmittance
  • glazing
Open Access

Synthesis of α-Fe2O3 nanoparticles and analyzing the effect of annealing temperature on its properties

Published Online: 08 May 2020
Page range: 116 - 121

Abstract

Abstract

α-Fe2O3 nanoparticles were synthesized via co-precipitation technique using ferric and ferrous salts and potassium hydroxide as precipitation agents. The samples were calcined at 350 °C, 550 °C and 750 °C for 3 hours. The obtained iron oxide was characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dynamic light scattering (DLS). Crystallinity of the sample was studied by X-ray diffraction. SEM micrographs showed nonuniform size distribution of the particles forming agglomerates. TGA analysis revealed trace amount of weight loss and material stability for the samples calcined at temperatures above 500 °C. DLS results indicated that increasing of annealing temperature resulted in reduction of the particle size and more uniform size distribution. At the maximum annealing temperature of 750 °C, the mean diameter of the particles of 100 nm was observed.

Keywords

  • magnetic nanoparticles
  • α-FeO
  • co-precipitation
  • annealing temperature
Open Access

Micro-structural and bonding structure analysis of TiAlN thin films deposited with varying N2 flow rate via ion beam sputtering technique

Published Online: 08 May 2020
Page range: 122 - 131

Abstract

Abstract

Titanium aluminum nitride (TiAlN) thin films were deposited on Si(1 0 0 ) substrate using titanium and aluminum targets in 1:1 ratio at various N2 flow rates using ion beam sputtering (IBS) technique. The morphology, particle and crystallite size of TiAlN thin films were estimated by field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), and grazing incidence X-ray diffraction (GIXRD) technique, respectively. The SEM images of the TiAlN thin films revealed smooth and uniform coating, whereas AFM images confirmed the particle size varying from 2.5 nm to 8.8 nm, respectively. The crystallite size and lattice strain were observed to vary from 4.79 nm to 5.5 nm and 0.0916 and 0.0844, respectively, with an increase in N2 flow rate in the TiAlN thin films. The X-ray absorption near edge structure (XANES) results showed Ti L, N K and O K-edges of TiAlN coating within a range of 450 eV to 470 eV, 395 eV to 410 eV and 480 eV to 580 eV photon energy, respectively. The electronic structure and chemical bonding of state of c-TiAlN thin film of Ti L, N K and O K-edges were analyzed through semi-empirical curve fitting technique.

Keywords

  • TiAlN
  • GIXRD
  • FE-SEM
  • XANES
Open Access

Bismuth and lead based metal organic frameworks: morphological, luminescence and Brunauer-Emmett-Teller (BET) studies

Published Online: 08 May 2020
Page range: 132 - 137

Abstract

Abstract

Biphenyl-4,4′-dicarboxylic acid (H2BDA) was used as an organic linker to synthesize bismuth and lead based organic frameworks (1 and 2). The structural/morphological studies of these metal organic frameworks (MOFs) were done using UV-Vis, Fourier transform infrared spectroscopy (FT-IR), 1H NMR, energy dispersive spectroscopy (EDXS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and powder X-ray diffraction method. Surface area as determined by Brunauer-Emmett-Teller (BET) studies revealed better N2 gas adsorption for MOF (1) compared to MOF (2). Both these MOFs exhibited good luminescence activity which was attributed to ligand-to-metal charge transfer transitions (LMCT).

Keywords

  • bismuth
  • lead
  • metal organic framework
  • luminescence
Open Access

Developing of buffer-precipitation method for lead metaborate (Pb(BO2)2 H2O) nanostructures

Published Online: 08 May 2020
Page range: 138 - 142

Abstract

Abstract

Amorphous lead metaborate (Pb(BO2)2 H2O) nanostructures were synthesized by a simpl and cost-effective synthesis method which is based on precipitation of lead ions using boric acid/sodium hydroxide buffer (pH 9.2) in the presence of polyethylene glycol (PEG). Scanning electron microscopy images showed that the average particle size is 30±9 nm and the particle shape is mostly spherical. The chemical formulation of Pb(BO2)2 H2O was confirmed by infrared spectroscopy, inductively coupled plasma and thermal gravimetric analysis (TGA). The percentage of PEG molecules on the particle surface equal to 2.5 % was determined by TGA. Optical reflectance measurement was performed by UV-Vis spectroscopy. Based on the Kubelka-Munk function, it was calculated that the Pb(BO2)2 H2O nanostructures have a direct band gap of 4.6 eV.

Keywords

  • lead metaborate
  • nanomaterials
  • chemical synthesis
Open Access

Synthesis of PMMA-HoVO4 nanocomposites by emulsifier-free emulsion polymerization: radical effects

Published Online: 08 May 2020
Page range: 143 - 150

Abstract

Abstract

Poly(methyl methacrylate)-holmium orthovanadate (PMMA-HoVO4) nanocomposites were synthesized using emulsifierfree emulsion polymerization system in two ways. In the first one, the HoVO4 nanoparticle dispersion was added to the emulsion system before or after polymerization start (in situ polymerization). In the other one, nanoparticle dispersion and polymeric latex were mixed together at room temperature (blending). Crystalline HoVO4 nanoparticles (about 60 nm) were synthesized by coprecipitation method. Three different composite latexes were synthesized by varying the potassium persulfate concentration and the time of HoVO4 nanoparticles addition. According to the dynamic light scattering analysis, the size of the polymer beads in the latexes is between 244.8 nm and 502.5 nm and the PDI values are in the range of 0.005 to 0.206. Infrared spectral analysis showed that HoVO4 caused some changes in the structure of the polymer. Luminescence measurements attempted to determine optical properties of the nanocomposites. The results have shown that HoVO4 nanoparticles do not protect their structure due to the reaction with persulfate radicals but that they enter the polymer beads and change the luminescence properties of the polymer forming a new material with different properties.

Keywords

  • PMMA
  • nanocomposite
  • holmium orthovanadate
  • emulsion polymerization
Open Access

Synthesis, photophysical properties and electrochemical polymerization of a new blue fluorescent compound based on 3,4-ethylenedioxythiophene moiety

Published Online: 08 May 2020
Page range: 151 - 158

Abstract

Abstract

New monomer, 4,4’-[(2,3-dihydrothieno[3,4-b][1,4]diorin-5-yl)vinyl]-1,1’-biphenyl (BPE), was synthesized, characterized and polymerized electrochemically via a potentiostatic method. The corresponding polymer poly(4,4’-[(2,3-dihydrothieno[3,4-b][1,4] diorin-5-yl)vinyl]-1,1’-biphenyl) (PBPE) obtained as a thin-layer film, was characterized by cyclic voltammetry, X-ray photoelectron spectroscopy, infrared spectroscopy and UV-Vis spectroscopy. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the obtained polymer were determined from cyclic voltammograms as –4.89 eV and –3.81 eV, respectively. Its optical and electrochemical band gaps were calculated, and found to be 1.08 eV and 1.49 eV, respectively. PBPE can be used as a donor material in bilayer organic photovoltaic solar cells having PCBM as acceptor material.

Keywords

  • conducting polymer
  • 3,4-ethylenedioxythiophene
  • poly(p-phenylenevinylene)
  • electropolymerization
  • cyclic voltammetry
  • band gap
Open Access

Microstructure, transmittance and upconversion luminescence of Y2O3:Er3+ translucent ceramics

Published Online: 08 May 2020
Page range: 159 - 164

Abstract

Abstract

Y2O3:Er3+ translucent ceramics was fabricated with addition of La(OH)3 nanopowder as a sintering aid. The influence of La(OH)3 addition on the microstructure, transmittance and upconversion luminescence of Y2O3:Er3+ ceramics was investigated in detail. The results show that the ceramics sample with 5 mol % La(OH)3 additives exhibits finer microstructure with fewer pores and higher optical transmittance than others. It was proved that La(OH)3 additives could greatly reduce the porosity and improve the transparency of Y2O3:Er3+ ceramics. By using a 980 nm diode laser as a pumping source, the Y2O3:Er3+ ceramics gave bright visible upconversion luminescence, which was ascribed to the radiative transitions of 2H11/2,4S3/24I15/2 and 4F9/24I15/2 of Er3+ ions, respectively. The possible upconversion mechanism has been proposed accordingly.

Keywords

  • ceramics
  • YO
  • microstructure
  • upconversion luminescence
Open Access

Hafnium dioxide effect on the electrical properties of M/n-GaN structure

Published Online: 08 May 2020
Page range: 165 - 173

Abstract

Abstract

In the present paper, using of SILVACO-TCAD numerical simulator for studying the enhancement in Pt/n-GaN Schottky diode current–voltage (I-V) characteristics by introduction of a layer of hafnium dioxide (HfO2) (with a thickness e = 5 nm) between the Pt contact and semiconductor interface of GaN is reported. The simulation of I-V characteristics of Pt/n-GaN was done at a temperature of 300 K. However, the simulation of Pt/HfO2/n-GaN structure was performed in a temperature range of 270 – 390 K at steps of 30 K. The electrical parameters: barrier height (Φb), ideality factor and series resistance have been calculated using different methods: conventional I-V, Norde, Cheung, Chattopadhyay and Mikhelashvili. Statistical analysis showed that the metal-insulator-semiconductor (Pt/HfO2/n-GaN) structure has a barrier height of 0.79 eV which is higher compared with the (Pt/n-GaN) structure (0.56 eV). The parameters of modified Richardson ((ln(I0T2)-(q2σs022kT2)=ln(AA*)-qB0kT)(\left( {\ln \left( {{{{{\rm{I}}_0}} \over {{{\rm{T}}^{\rm{2}}}}}} \right) - \left( {{{{{\rm{q}}^2}\sigma _{{\rm{s}}0}^2} \over {2{\rm{k}}{{\rm{T}}^2}}}} \right) = \ln \left( {{\rm{AA*}}} \right) - {{{\rm{q}}{\emptyset _{{\rm{B}}0}}} \over {{\rm{kT}}}}} \right) equation versus (1kT{1 \over {{\rm{kT}}}}) have been extracted using the mentioned methods. The following values: ASimul*=22.65A/cm2K2{\rm{A}}_{{\rm{Simul}}}^* = 22.65\,{\rm{A/c}}{{\rm{m}}^{\rm{2}}} \cdot {{\rm{K}}^2}, 14.29 A/cm2 K2, 25.53 A/cm2 K2 and 21.75 A/cm2 K2 were found. The Chattopadhyay method occurred the best method for estimation the theoretical values of Richardson constant.

Keywords

  • Schottky diode
  • Pt/n-GaN
  • Pt/HfO/n-GaN
  • (I-V)
  • Norde
  • Cheung
  • Mikhelashvili and Chattopadhyay methods
  • modified Richardson equation
Open Access

Enhancement of electrical performance of ZnSe thin films via Au nanosandwiching

Published Online: 08 May 2020
Page range: 174 - 180

Abstract

Abstract

In this work, we report the effect of sandwiching of Au nanosheets on the structural and electrical properties of ZnSe thin films. The ZnSe films which are grown by the thermal evaporation technique onto glass and yttrium thin film substrates exhibit lattice deformation accompanied with lattice constant extension, grain size reduction and increased defect density upon Au nanosandwiching. The temperature dependent direct current conductivity analysis has shown that the 70 nm thick Au layers successfully increased the electrical conductivity by three orders of magnitude without causing degeneracy. On the other hand, the alternating current conductivity studies in the frequency domain of 10 MHz to 1800 MHz have shown that the alternating current conduction in ZnSe is dominated by both of quantum mechanical tunneling and correlated barrier hopping of electrons over the energy barriers formed at the grain boundaries. The Au nanosheets are observed to increase the density of localized states near Fermi level and reduce the average hopping energy by ~5 times. The conductivity, capacitance, impedance and reflection coefficient spectral analyses have shown that the nanosandwiching of Au between two layers of ZnSe makes the zinc selenide more appropriate for electronic applications and for applications which need microwave cavities.

Keywords

  • ZnSe
  • Au
  • nanosandwiching
  • conductivity
  • defects
Open Access

Effect of vacuum conditions on stability and crystallization of cobalt based amorphous alloy

Published Online: 08 May 2020
Page range: 181 - 188

Abstract

Abstract

The aim of this work was to investigate the effects of moderate vacuum conditions (10 Pa, 1 × 103 Pa and 2 × 104 Pa) on glass forming ability, thermal stability and aging behavior of Co42Cu1Fe20Ta5:5B26:5Si5 amorphous samples in terms of size and distribution of crystalline precipitates. The thinnest parts (300 μm) of the wedge-shaped samples were amorphous for all vacuum conditions, and they had similar compositional, structural and thermal characteristics. However, they represented different microstructural features after heat treatments at 950 K and 1100 K. The same phases precipitated in all samples but the amount and the size of the precipitates increased as the pressure was raised to the normal atmospheric value. The differences in the glass forming ability and the microstructure due to aging are considered to originate from lower thermal characteristics, such as relaxation and reduced glass temperature as well as γ parameter, resulting from the poor vacuum pressure used in the production process. The differences in the microstructures and hardness values caused by heat treatments have been observed.

Keywords

  • metallic glass
  • glass forming ability
  • crystallization behavior
  • thermal stability
  • casting atmosphere
Open Access

Impact of firing temperature on insulating properties of Low Temperature Co-fired Ceramics

Published Online: 08 May 2020
Page range: 189 - 196

Abstract

Abstract

In this paper, results of investigation on the impact of firing temperature on insulating properties of Low Temperature Cofired Ceramics are presented. Dissipation factor, volume resistivity and breakdown electric field intensity were determined for firing peak temperature in the range from 800 °C to 900 °C. The tests were performed for two commercial LTCC materials: 951 Green Tape (DuPont, USA) and SK47 (Keko, Slovenia). The results showed that the firing temperature had a significant effect on the dielectric loss factor, volume resistivity and lifetime at applied high voltage. No clear tendency was observed for dielectric strength in the analyzed firing temperature range.

Keywords

  • LTCC
  • ceramics
  • breakdown
  • volume resistivity
  • high voltage
Open Access

The impacts of Ba2Li2Si2O7:Sn2+,Mn2+ and CaMgSi2O6:Eu2+,Mn2+ particles on the optical properties of remote phosphor LED

Published Online: 08 May 2020
Page range: 197 - 205

Abstract

Abstract

As implied in the title, the triple-layer remote phosphor (TRP), constructed with the yellow YAG:Ce3+ layer at the bottom, the red CaMgSi2O6:Eu2+,Mn2+ phosphor layer on the top, and the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer between these two layers, is suggested in this paper to improve the color and luminescence of white LEDs (WLEDs). In order to control the red light for the purpose of increasing the color rendering index (CRI), it is suggested that the red CaMgSi2O6:Eu2+,Mn2+ phosphor should be applied in the TRP structure. Simultaneously, the structure uses the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer to control the green light, which increases the luminous efficacy (LE) of WLEDs. In addition, when the concentration of these two phosphors increases, the yellow YAG:Ce3+ concentration must be reduced to keep the average correlated color temperatures (ACCTs) stable at 6000 K to 8500 K. Besides, appropriate adjusting of CRI, LE, and color quality scale (CQS) is also analyzed by modifying the concentration of the green phosphor and red phosphor. The results show that the CRI can get better values if CaMgSi2O6:Eu2+,Mn2+ concentration is higher. In contrast, the CRI decreases dramatically when the concentration of Ba2Li2Si2O7:Sn2+,Mn2+ increases. Meanwhile, CQS can be significantly increased in the range of 10 % to 14 % CaMgSi2O6:Eu2+,Mn2+, regardless of the concentration of Ba2Li2Si2O7:Sn2+,Mn2+. In particular, along with the improvement of CRI and CQS, LE can also be increased by more than 40 % by reducing the scattered light and adding the green light. Obtained results are a valuable reference for manufacturers for improving WLEDs color and luminescence quality to produce a broader range of WLEDs with better quality fulfilling social needs.

Keywords

  • WLEDs
  • triple-layer structure
  • remote phosphor package
  • color quality
  • luminous flux
Open Access

Study of Ho doped Ag2S thin films prepared by CBD method

Published Online: 08 May 2020
Page range: 206 - 213

Abstract

Abstract

Ho doped Ag2S thin films were grown on the glass substrate by chemical bath deposition (CBD) method at room temperature. The bath contained aqueous solution of silver nitrate, thiourea, EDTA, ammonia and holmium nitrate. Silver nitrate was used as a silver (Ag+) ion source; thiourea as sulfur (S) ion source, EDTA was a complexing agent while ammonia was used to maintain pH, Ho(NO3)3 was taken as a source of Ho ions. The optical absorption edge of undoped (pure) and Ho doped silver sulfide films was determined between 324 nm and 298 nm showing blue shift as compared to bulk Ag2S. Band gaps calculated from Tauc plot also showed an increase in values for doped samples. The increase in band gap indicates reduced particle size in the prepared Ho doped films. The photoluminescence emission peaks were observed at around 578 nm to 601 nm wavelength and excitation peaks were found at 351 nm to 294 nm for undoped and doped films. The SEM micrograph consists of globular ball type and flower type structures observed in the prepared films of Ho doped Ag2S.

Keywords

  • CBD
  • thin films
  • photoluminescence
  • silver nitrate
27 Articles
Open Access

Research on the influence of the filtrating electrode on the structure and optical properties of TiO2 thin films prepared by the energy filtering magnetron sputtering technique

Published Online: 08 May 2020
Page range: 1 - 7

Abstract

Abstract

TiO2 thin films were deposited by the energy filtrating magnetron sputtering (EFMS) technique and the traditional direct current magnetron sputtering (DMS) technique. The influence of the filtering electrode mesh number on the structure and optical properties of TiO2 thin films was investigated. The structure, surface morphology and optical properties were characterized by XRD, SEM and ellipsometric spectroscopy, respectively. Results show that the TiO2 thin films deposited by the DMS and EFMS techniques at the same deposition parameters are composed of the anatase phase exclusively. TiO2 thin films deposited at lower deposition rate by the EFMS technique have lower crystallinity, smaller particle size and smoother surface. With increasing the mesh number, the refractive index, extinction coefficient and optical band gap are larger.

Keywords

  • energy filtering magnetron sputtering
  • TiO thin film
  • optical property
Open Access

Nanocharacterization of metallic thin films deposited on different substrates

Published Online: 08 May 2020
Page range: 8 - 16

Abstract

Abstract

The purpose of this study was to determine the influence of different substrates (C45 steel, polycarbonate, glass) on the topography as well as tribological and mechanical properties (nanohardness, modulus of elasticity and friction force) of aluminum, gold and silver thin films. The 3D image analysis showed a strong influence of the substrate material on the topography of the studied thin films with no certain variation rule. Using the Oliver and Pharr method for determining nanohardness it was observed that, the smallest values were obtained for the thin films deposited on plastic substrate, followed by glass and C45 steel, regardless of the deposited material. The determination of the modulus of elasticity was done using the Hertzian method. The obtained results showed that the highest values of this parameter were obtained for the films deposited on plastic substrate, while the lowest values depended on both the deposited material and substrate. Friction force analysis for aluminum and gold showed a significant impact of the substrate material, with more constant values for gold. As a consequence, one must pay a particular attention when choosing the material for the substrate on which the thin films are deposited.

Keywords

  • metallic thin films
  • topography
  • nanohardness
  • friction force
  • modulus of elasticity
Open Access

Structural and optical properties of ZnO thin film prepared by sol-gel spin coating

Published Online: 08 May 2020
Page range: 17 - 22

Abstract

Abstract

Zinc oxide (ZnO) thin films were deposited on Si (1 0 0) and glass substrates by sol-gel spin coating technique. Zinc acetate dihydrate, monoethanolamine and isopropanol were used as the sources for precursor solution and the resulting gel was used for the preparation of ZnO thin films. The films were annealed at different temperatures (100 °C to 500 °C) and the effect of annealing on the structural and optical properties was investigated. X-ray diffraction (XRD) and UV-Vis spectroscopy were used for the analysis of the films. The XRD results indicated the polycrystalline hexagonal structure of the ZnO films with (0 0 2) orientation. The optical properties of the films were studied using UV-Vis spectrophotometer in the wavelength range of 190 – 1100 nm. The optical characterization of the ZnO thin films showed the high transmittance of ~90 % for the films annealed at 400 °C. The films showed the absorbance ~360 – 390 nm and bandgap values of 3.40 – 3.10 eV, depending on the annealing temperature of the films.

Keywords

  • ZnO thin films
  • sol-gel
  • spin coating
  • X-ray diffraction
  • optical properties
Open Access

Synthesis and optical properties of uranium-doped cadmium oxide synthesized by sol-gel method

Published Online: 08 May 2020
Page range: 23 - 27

Abstract

Abstract

Optical properties of cadmium oxide and uranium-doped CdO thin films synthesized by the sol-gel technique were investigated. The structural properties of the films were investigated using X-ray diffraction patterns of U-doped CdO. It was found that CdO-based films have a cubic NaCl structure. Structural properties of the films were investigated with atomic force microscopy (AFM). Reflectance, transmittance and absorption spectra of the films were measured with UV-Vis-NIR spectrophotometer. The photoluminescence (PL) behavior of the films was recorded using a fluorescence spectrophotometer. It was found that the nanostructure of the cadmium oxide film is controlled by U doping.

Keywords

  • cadmium oxide
  • sol gel
  • nanoparticles
Open Access

Preparation of ternary (35 – x)Sb2O3–xBi2O3–65P2O5 glasses for lead-free glass application

Published Online: 08 May 2020
Page range: 28 - 33

Abstract

Abstract

Glasses composed of ternary components (35 – x)Sb2O3–xBi2O3–65P2O5 (0 ⩽ x ⩽ 20 mol%) have been prepared and investigated as a potential alternative to lead-free glass for low temperature applications. Their structural properties were studied by Infrared Spectroscopy IR and Differential Thermal Analysis DTA. Results from the IR showed that Sb3+ and Bi3+ were responsible for glass network structure, which was supported by the diversification of density ρ and molar volume Vm with an increasing amount of Bi2O3. Glass transition temperature Tg, thermal stability, and coefficient of thermal expansion increased after substitution of Bi2O3 for Sb2O3 within the range of 0 mol% to 20 mol%. The water durability decreased and then increased; it could be attributed to the corrosion resistant P–O–Sb bonds. A typical sample of 25Sb2O3–10Bi2O3–65P2O5 possesses excellent properties and can be a promising candidate for further applications.

Keywords

  • structure
  • chemical properties
  • bismuth phosphates
Open Access

Microstructure and mechanical properties of Sn-9Zn-xAl and Sn-9Zn-xCu lead-free solder alloys

Published Online: 08 May 2020
Page range: 34 - 40

Abstract

Abstract

This study investigates microstructures and mechanical properties of the alloys obtained by adding Cu (0.7 % and 0.9 %) and Al (0.7 % and 0.9 %) to lead-free Sn-9Zn eutectic soldering alloy produced by investment casting method. The results show that Cu5Zn8 phase has formed in the structure of Cu added alloys and the Al2O3 phase has formed due to addition of Al. It was found that small and round-shaped Al2O3 phase increased the tensile strength of the new alloy compared to the eutectic alloy. In addition, it was observed that the microhardness of Cu added alloys was lower than that of Sn-9Zn eutectic alloy, but the microhardness of alloys containing Al was higher compared to the other eutectic Sn-9Zn alloy.

Keywords

  • Sn-Zn lead-free alloys
  • investment casting
  • mechanical properties
Open Access

Sputtering pressure influenced structural, electrical and optical properties of RF magnetron sputtered MoO3 films

Published Online: 08 May 2020
Page range: 41 - 47

Abstract

Abstract

MoO3 films were deposited by RF magnetron sputtering technique on glass and silicon substrates held at 473 K by sputtering of metallic molybdenum target at an oxygen partial pressure of 4 × 10−2 Pa and at different sputtering pressures in the range of 2 Pa to 6 Pa. The influence of sputtering pressure on the structure and surface morphology, electrical and optical properties of the MoO3 thin films was studied. X-ray diffraction studies suggest that the films deposited at a sputtering pressure of 2 Pa were polycrystalline in nature with mixed phase of α- and β-phase MoO3, while those formed at sputtering pressure of 4 Pa and above were of α-phase MoO3. Scanning electron micrographs showed a decrement in the size of the particles and their shapes changed from needle like structure to dense films with the increase of sputtering pressure. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic vibration modes of Mo=O, Mo–O and Mo–O–Mo related to MoO3. Electrical resistivity of the MoO3 films decreased from 6.0 × 104 Ω cm to 2 × 104 Ω cm with an increase of sputtering pressure from 2 Pa to 6 Pa, respectively. Optical band gap of the films decreased from 3.12 eV to 2.86 eV with the increase of sputtering pressure from 2 Pa to 6 Pa, respectively.

Keywords

  • MoO thin films
  • RF magnetron sputtering
  • sputtering pressure
  • structural properties
  • optical properties
Open Access

Effect of L-asparagine as dopant on the growth and characteristics of ammonium tetroxalate dihydrate single crystal

Published Online: 08 May 2020
Page range: 48 - 61

Abstract

Abstract

Single crystals of L-asparagine doped ammonium tetroxalate dihydrate were grown using slow evaporation solution growth technique with deionized water as a solvent. The shift and intensity of the peaks in the single crystal X-ray diffraction and Fourier transform infrared analyses confirmed the inclusion of L-asparagine in the ammonium tetroxalate dihydrate crystal structure. The optical transmission characteristics viz. optical band gap, optical conductivity, etc., were determined. Thermal studies revealed the occurrence of anomalies at 135.3 °C and 221.7 °C leading to the possibility of phase transitions and thereby, ferroelectric behavior. Vickers microhardness studies enabled determination of various microhardness parameters. Dielectric behavior was analyzed by varying the temperature and frequency. Anomalies were observed at 135 °C and 221 °C suggesting the existence of ferroelectric nature of the compound. Self-defocusing effect was observed. The polarization-electric field hysteresis loops showed a pinched effect due to defects induced by inclusion of dopant. The crystals were characterized by single crystal XRD, FT-IR, DRS, UV-Vis-NIR, Vickers microhardness test as well as thermal and dielectric techniques. In brief, L-asparagine as a dopant in ammonium tetroxalate dihydrate altered various physical properties of the crystals. They were highly transparent in the visible region with a wider optical band gap, softer material than the parent, higher phase transition temperature of 135 °C, negative nonlinearity and self-defocusing ability.

Keywords

  • Z-scan
  • dielectric properties
  • thermal characteristics
  • organic crystal
Open Access

Plasmonic nanostructures of SnO2:Sb thin film under gamma radiation response

Published Online: 08 May 2020
Page range: 62 - 72

Abstract

Abstract

This paper is a part of a natural dye solar cell project. Conductive transparent oxide (CTO) films have been deposited onto preheated glass substrates using a spray pyrolysis technique. The optical, electrical, structural properties as well as thermal annealing and gamma radiation response were studied. The average optical energy gap of doped films for direct allowed and direct forbidden transitions were found to be 3.92 and 3.68 eV, respectively. The plasmon frequency and plasmon energy after doping were found to be 3.48 × 1014 s −1 and 0.23 eV. The negative absorbance of the doped film was observed in UV-Vis range after applying both thermal annealing and γ-dose irradiation with 22 kGy. The negative refractive index of the doped film in UV range (220 – 300 nm) is promising for optical applications. The electron mobility μe reached a maximum of 27.4 cm2 V−1 s−1 for Sb concentration of 10 %. The corresponding resistivity ρ, and sheet resistance Rs reached their minimum values of 1.1 × 10−3 Ω cm and 35 Ω sq−1, respectively. The dopant concentration has been increased from 4.13 × 1019 to 2.1 × 1020cm−3. The doped film was found to exhibit three diffraction peaks associated with (2 2 2), (2 0 0), and (2 1 1) reflection planes, of which the peak of (2 2 2) of Sb2O3 and the peak of (2 0 0) were very close.

Keywords

  • CTO
  • doping
  • optical properties
  • electrical properties
  • structure
  • radiation
Open Access

Ca4−xLa2+xTi5−xBxO17 (B = Al, Ga) dielectric ceramics for microwave applications

Published Online: 08 May 2020
Page range: 73 - 78

Abstract

Abstract

In this study, Ca4−xLa2+xTi5−xBxO17 (B = Al, Ga; x = 0, 1) ceramics were processed via a mixed oxide solid state sintering route and characterized using XRD, SEM, EDS and Vector Network Analyzer. Phase analysis of the samples showed single phase formation for the sample x = 0 while secondary phases formed for Ca4−xLa2+xTi5−xBxO17 (B = Al, Ga; x = 1) ceramics. Ca4La2Ti5O17 exhibited ∈r = 74, Q×fo = 14,116 GHz and τf = 157 ppm/°C. The substitution of Ga or Al for Ti at the B-site of Ca4La2Ti5O17 ceramics significantly improved the microwave dielectric properties i.e. Ca3La3Ti4GaO17 and Ca3La3Ti4AlO17 have ∈r = 44, Q×fo = 16,128 GHz and τf = 7.3 ppm/°C and ∈r = 46, Q×fo = 13,754 GHz and τf = −2 ppm/°C, respectively. The microwave dielectric properties of these materials are suitable for high frequency microwave applications.

Keywords

  • ceramics
  • perovskite
  • microwave dielectric properties
Open Access

Thin films of copper phthalocyanine deposited by solution processing methods

Published Online: 08 May 2020
Page range: 79 - 90

Abstract

Abstract

In this work, we show and discuss the surface structure picture of copper phthalocyanine (CuPc) thin films deposited from trifluoroacetic acid (TFA) solvent onto silicon substrates at ambient conditions by four solution processing methods, namely drop-casting, dip-coating, spin-casting and spray-coating. The CuPc films were studied by AFM, as the main technique, and complemented by micro-Raman spectroscopy. Essentially, such thin films consist of CuPc molecular nanoribbons of a fixed ~1 nm thickness. CuPc molecules are arranged in an in-plane direction and formed in stacks under a defined tilt angle with respect to the substrate surface (monolayer) or underlying CuPc layer (multilayer). The film morphology takes various forms depending on the solution concentration, number of layers, and the deposition method. For instance, the morphology varies from very wide (~600 nm) but flat (~1 nm) ribbons for films prepared by dip-coating to crystallized rod-like features (multi-layered ribbons) when obtained by spray-coating. The factors studied in this paper should be taken into consideration in designing and controlling the criteria for rigorous CuPc film architecture.

Keywords

  • molecular structure
  • growth
  • copper phthalocyanine
  • solution processing methods
  • atomic force microscopy
Open Access

Direct formation of ZnO nanorods by hydrothermal process: study on its optical properties and electron transport

Published Online: 08 May 2020
Page range: 91 - 96

Abstract

Abstract

We report a new direct fabrication of the ZnO nanorods (NR) by hydrothermal method, in which the preparation of seed layer is eliminated. We show that the tuning of initial temperature rate during the hydrothermal process plays a key role in the structural modification of the ZnO NR. A highly oriented ZnO NR is successfully fabricated by using a low rate of initial temperature. The increase of optical absorption and electron transport was obtained by reducing the diameter and increasing distribution of the ZnO NR on the substrate. Interestingly, an additional absorption from the defects is obtained in the system, which plays an important role in expanding the optical absorption. Our system will provide a favourable characteristic for developing the high-performance optoelectronic devices with high optical absorption and high electron transport.

Keywords

  • optical properties
  • ZnO nanorods
  • hydrothermal process
  • semiconductor materials
Open Access

Density functional study of structures, stabilities and electronic properties of AgAunλ(λ=0,±1;n=1-12){\rm{AgAu}}_n^\lambda \left( {\lambda = 0, \pm 1;n = 1 - 12} \right) clusters: comparison with pure gold clusters

Published Online: 08 May 2020
Page range: 97 - 107

Abstract

Abstract

Geometrical structures, relative stabilities and electronic properties of neutral, cationic and anionic pure gold Aun+1λ{\rm{A}}u_{n + 1}^\lambda and Ag-doped bimetallic AgAunλ(λ=0,±1;n=1-12){\rm{AgAu}}_n^\lambda \left( {\lambda = 0, \pm 1;n = 1 - 12} \right) clusters have been systematically investigated by using density functional theory methodology. The optimized structures show that planar to three-dimensional structural transition occurs at n = 5 for cationic clusters. Due to strong relativistic effect of Au clusters, the ground state configurations of neutral and anionic bimetallic clusters favor planar geometry till n = 12. Silver atoms tend to occupy the most highly coordinated position and form the maximum number of bonds with Au atoms. The computed HOMO-LUMO energy gaps, fragmentation energies and second-order difference of energies show interesting odd-even oscillation behavior. The result indicates that AgAu5, AgAu2+{\rm{AgAu}}_2^ + and AgAu2-{\rm{AgAu}}_2^ - are the most stable clusters in this molecular system. The DFT based descriptors of bimetallic clusters are also discussed and compared with pure gold clusters. The high value of correlation coefficient between HOMO-LUMO energy gaps and DFT based descriptors supports our analysis. A good agreement between experimental and theoretical data has been obtained in this study.

Keywords

  • density functional theory
  • bimetallic cluster
  • AgAu
  • structures
  • properties
Open Access

Optical characterization of thin Al2O3 layers deposited by magnetron sputtering technique at industrial conditions for applications in glazing

Published Online: 08 May 2020
Page range: 108 - 115

Abstract

Abstract

In this study, thin Al2O3 films (11 nm – 82 nm) were deposited by means of a recently developed pulse gas injection magnetron sputtering method and investigated by means of atomic force microscopy, spectroscopic ellipsometry and spectrophotometry. Quite low values of optical constants (1.581 to 1.648 at λ = 550 nm) of the alumina films are directly associated with specific growth conditions (pulse injection of the reactive or reactive + inert gas) in the pulse gas injection magnetron sputtering process. The light transmittance of Al2O3/glass systems (86 % to 90 %) is only a few percent lower than that calculated for glass (93 %).

Keywords

  • AlO
  • GIMS
  • refractive index
  • light transmittance
  • glazing
Open Access

Synthesis of α-Fe2O3 nanoparticles and analyzing the effect of annealing temperature on its properties

Published Online: 08 May 2020
Page range: 116 - 121

Abstract

Abstract

α-Fe2O3 nanoparticles were synthesized via co-precipitation technique using ferric and ferrous salts and potassium hydroxide as precipitation agents. The samples were calcined at 350 °C, 550 °C and 750 °C for 3 hours. The obtained iron oxide was characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dynamic light scattering (DLS). Crystallinity of the sample was studied by X-ray diffraction. SEM micrographs showed nonuniform size distribution of the particles forming agglomerates. TGA analysis revealed trace amount of weight loss and material stability for the samples calcined at temperatures above 500 °C. DLS results indicated that increasing of annealing temperature resulted in reduction of the particle size and more uniform size distribution. At the maximum annealing temperature of 750 °C, the mean diameter of the particles of 100 nm was observed.

Keywords

  • magnetic nanoparticles
  • α-FeO
  • co-precipitation
  • annealing temperature
Open Access

Micro-structural and bonding structure analysis of TiAlN thin films deposited with varying N2 flow rate via ion beam sputtering technique

Published Online: 08 May 2020
Page range: 122 - 131

Abstract

Abstract

Titanium aluminum nitride (TiAlN) thin films were deposited on Si(1 0 0 ) substrate using titanium and aluminum targets in 1:1 ratio at various N2 flow rates using ion beam sputtering (IBS) technique. The morphology, particle and crystallite size of TiAlN thin films were estimated by field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), and grazing incidence X-ray diffraction (GIXRD) technique, respectively. The SEM images of the TiAlN thin films revealed smooth and uniform coating, whereas AFM images confirmed the particle size varying from 2.5 nm to 8.8 nm, respectively. The crystallite size and lattice strain were observed to vary from 4.79 nm to 5.5 nm and 0.0916 and 0.0844, respectively, with an increase in N2 flow rate in the TiAlN thin films. The X-ray absorption near edge structure (XANES) results showed Ti L, N K and O K-edges of TiAlN coating within a range of 450 eV to 470 eV, 395 eV to 410 eV and 480 eV to 580 eV photon energy, respectively. The electronic structure and chemical bonding of state of c-TiAlN thin film of Ti L, N K and O K-edges were analyzed through semi-empirical curve fitting technique.

Keywords

  • TiAlN
  • GIXRD
  • FE-SEM
  • XANES
Open Access

Bismuth and lead based metal organic frameworks: morphological, luminescence and Brunauer-Emmett-Teller (BET) studies

Published Online: 08 May 2020
Page range: 132 - 137

Abstract

Abstract

Biphenyl-4,4′-dicarboxylic acid (H2BDA) was used as an organic linker to synthesize bismuth and lead based organic frameworks (1 and 2). The structural/morphological studies of these metal organic frameworks (MOFs) were done using UV-Vis, Fourier transform infrared spectroscopy (FT-IR), 1H NMR, energy dispersive spectroscopy (EDXS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and powder X-ray diffraction method. Surface area as determined by Brunauer-Emmett-Teller (BET) studies revealed better N2 gas adsorption for MOF (1) compared to MOF (2). Both these MOFs exhibited good luminescence activity which was attributed to ligand-to-metal charge transfer transitions (LMCT).

Keywords

  • bismuth
  • lead
  • metal organic framework
  • luminescence
Open Access

Developing of buffer-precipitation method for lead metaborate (Pb(BO2)2 H2O) nanostructures

Published Online: 08 May 2020
Page range: 138 - 142

Abstract

Abstract

Amorphous lead metaborate (Pb(BO2)2 H2O) nanostructures were synthesized by a simpl and cost-effective synthesis method which is based on precipitation of lead ions using boric acid/sodium hydroxide buffer (pH 9.2) in the presence of polyethylene glycol (PEG). Scanning electron microscopy images showed that the average particle size is 30±9 nm and the particle shape is mostly spherical. The chemical formulation of Pb(BO2)2 H2O was confirmed by infrared spectroscopy, inductively coupled plasma and thermal gravimetric analysis (TGA). The percentage of PEG molecules on the particle surface equal to 2.5 % was determined by TGA. Optical reflectance measurement was performed by UV-Vis spectroscopy. Based on the Kubelka-Munk function, it was calculated that the Pb(BO2)2 H2O nanostructures have a direct band gap of 4.6 eV.

Keywords

  • lead metaborate
  • nanomaterials
  • chemical synthesis
Open Access

Synthesis of PMMA-HoVO4 nanocomposites by emulsifier-free emulsion polymerization: radical effects

Published Online: 08 May 2020
Page range: 143 - 150

Abstract

Abstract

Poly(methyl methacrylate)-holmium orthovanadate (PMMA-HoVO4) nanocomposites were synthesized using emulsifierfree emulsion polymerization system in two ways. In the first one, the HoVO4 nanoparticle dispersion was added to the emulsion system before or after polymerization start (in situ polymerization). In the other one, nanoparticle dispersion and polymeric latex were mixed together at room temperature (blending). Crystalline HoVO4 nanoparticles (about 60 nm) were synthesized by coprecipitation method. Three different composite latexes were synthesized by varying the potassium persulfate concentration and the time of HoVO4 nanoparticles addition. According to the dynamic light scattering analysis, the size of the polymer beads in the latexes is between 244.8 nm and 502.5 nm and the PDI values are in the range of 0.005 to 0.206. Infrared spectral analysis showed that HoVO4 caused some changes in the structure of the polymer. Luminescence measurements attempted to determine optical properties of the nanocomposites. The results have shown that HoVO4 nanoparticles do not protect their structure due to the reaction with persulfate radicals but that they enter the polymer beads and change the luminescence properties of the polymer forming a new material with different properties.

Keywords

  • PMMA
  • nanocomposite
  • holmium orthovanadate
  • emulsion polymerization
Open Access

Synthesis, photophysical properties and electrochemical polymerization of a new blue fluorescent compound based on 3,4-ethylenedioxythiophene moiety

Published Online: 08 May 2020
Page range: 151 - 158

Abstract

Abstract

New monomer, 4,4’-[(2,3-dihydrothieno[3,4-b][1,4]diorin-5-yl)vinyl]-1,1’-biphenyl (BPE), was synthesized, characterized and polymerized electrochemically via a potentiostatic method. The corresponding polymer poly(4,4’-[(2,3-dihydrothieno[3,4-b][1,4] diorin-5-yl)vinyl]-1,1’-biphenyl) (PBPE) obtained as a thin-layer film, was characterized by cyclic voltammetry, X-ray photoelectron spectroscopy, infrared spectroscopy and UV-Vis spectroscopy. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the obtained polymer were determined from cyclic voltammograms as –4.89 eV and –3.81 eV, respectively. Its optical and electrochemical band gaps were calculated, and found to be 1.08 eV and 1.49 eV, respectively. PBPE can be used as a donor material in bilayer organic photovoltaic solar cells having PCBM as acceptor material.

Keywords

  • conducting polymer
  • 3,4-ethylenedioxythiophene
  • poly(p-phenylenevinylene)
  • electropolymerization
  • cyclic voltammetry
  • band gap
Open Access

Microstructure, transmittance and upconversion luminescence of Y2O3:Er3+ translucent ceramics

Published Online: 08 May 2020
Page range: 159 - 164

Abstract

Abstract

Y2O3:Er3+ translucent ceramics was fabricated with addition of La(OH)3 nanopowder as a sintering aid. The influence of La(OH)3 addition on the microstructure, transmittance and upconversion luminescence of Y2O3:Er3+ ceramics was investigated in detail. The results show that the ceramics sample with 5 mol % La(OH)3 additives exhibits finer microstructure with fewer pores and higher optical transmittance than others. It was proved that La(OH)3 additives could greatly reduce the porosity and improve the transparency of Y2O3:Er3+ ceramics. By using a 980 nm diode laser as a pumping source, the Y2O3:Er3+ ceramics gave bright visible upconversion luminescence, which was ascribed to the radiative transitions of 2H11/2,4S3/24I15/2 and 4F9/24I15/2 of Er3+ ions, respectively. The possible upconversion mechanism has been proposed accordingly.

Keywords

  • ceramics
  • YO
  • microstructure
  • upconversion luminescence
Open Access

Hafnium dioxide effect on the electrical properties of M/n-GaN structure

Published Online: 08 May 2020
Page range: 165 - 173

Abstract

Abstract

In the present paper, using of SILVACO-TCAD numerical simulator for studying the enhancement in Pt/n-GaN Schottky diode current–voltage (I-V) characteristics by introduction of a layer of hafnium dioxide (HfO2) (with a thickness e = 5 nm) between the Pt contact and semiconductor interface of GaN is reported. The simulation of I-V characteristics of Pt/n-GaN was done at a temperature of 300 K. However, the simulation of Pt/HfO2/n-GaN structure was performed in a temperature range of 270 – 390 K at steps of 30 K. The electrical parameters: barrier height (Φb), ideality factor and series resistance have been calculated using different methods: conventional I-V, Norde, Cheung, Chattopadhyay and Mikhelashvili. Statistical analysis showed that the metal-insulator-semiconductor (Pt/HfO2/n-GaN) structure has a barrier height of 0.79 eV which is higher compared with the (Pt/n-GaN) structure (0.56 eV). The parameters of modified Richardson ((ln(I0T2)-(q2σs022kT2)=ln(AA*)-qB0kT)(\left( {\ln \left( {{{{{\rm{I}}_0}} \over {{{\rm{T}}^{\rm{2}}}}}} \right) - \left( {{{{{\rm{q}}^2}\sigma _{{\rm{s}}0}^2} \over {2{\rm{k}}{{\rm{T}}^2}}}} \right) = \ln \left( {{\rm{AA*}}} \right) - {{{\rm{q}}{\emptyset _{{\rm{B}}0}}} \over {{\rm{kT}}}}} \right) equation versus (1kT{1 \over {{\rm{kT}}}}) have been extracted using the mentioned methods. The following values: ASimul*=22.65A/cm2K2{\rm{A}}_{{\rm{Simul}}}^* = 22.65\,{\rm{A/c}}{{\rm{m}}^{\rm{2}}} \cdot {{\rm{K}}^2}, 14.29 A/cm2 K2, 25.53 A/cm2 K2 and 21.75 A/cm2 K2 were found. The Chattopadhyay method occurred the best method for estimation the theoretical values of Richardson constant.

Keywords

  • Schottky diode
  • Pt/n-GaN
  • Pt/HfO/n-GaN
  • (I-V)
  • Norde
  • Cheung
  • Mikhelashvili and Chattopadhyay methods
  • modified Richardson equation
Open Access

Enhancement of electrical performance of ZnSe thin films via Au nanosandwiching

Published Online: 08 May 2020
Page range: 174 - 180

Abstract

Abstract

In this work, we report the effect of sandwiching of Au nanosheets on the structural and electrical properties of ZnSe thin films. The ZnSe films which are grown by the thermal evaporation technique onto glass and yttrium thin film substrates exhibit lattice deformation accompanied with lattice constant extension, grain size reduction and increased defect density upon Au nanosandwiching. The temperature dependent direct current conductivity analysis has shown that the 70 nm thick Au layers successfully increased the electrical conductivity by three orders of magnitude without causing degeneracy. On the other hand, the alternating current conductivity studies in the frequency domain of 10 MHz to 1800 MHz have shown that the alternating current conduction in ZnSe is dominated by both of quantum mechanical tunneling and correlated barrier hopping of electrons over the energy barriers formed at the grain boundaries. The Au nanosheets are observed to increase the density of localized states near Fermi level and reduce the average hopping energy by ~5 times. The conductivity, capacitance, impedance and reflection coefficient spectral analyses have shown that the nanosandwiching of Au between two layers of ZnSe makes the zinc selenide more appropriate for electronic applications and for applications which need microwave cavities.

Keywords

  • ZnSe
  • Au
  • nanosandwiching
  • conductivity
  • defects
Open Access

Effect of vacuum conditions on stability and crystallization of cobalt based amorphous alloy

Published Online: 08 May 2020
Page range: 181 - 188

Abstract

Abstract

The aim of this work was to investigate the effects of moderate vacuum conditions (10 Pa, 1 × 103 Pa and 2 × 104 Pa) on glass forming ability, thermal stability and aging behavior of Co42Cu1Fe20Ta5:5B26:5Si5 amorphous samples in terms of size and distribution of crystalline precipitates. The thinnest parts (300 μm) of the wedge-shaped samples were amorphous for all vacuum conditions, and they had similar compositional, structural and thermal characteristics. However, they represented different microstructural features after heat treatments at 950 K and 1100 K. The same phases precipitated in all samples but the amount and the size of the precipitates increased as the pressure was raised to the normal atmospheric value. The differences in the glass forming ability and the microstructure due to aging are considered to originate from lower thermal characteristics, such as relaxation and reduced glass temperature as well as γ parameter, resulting from the poor vacuum pressure used in the production process. The differences in the microstructures and hardness values caused by heat treatments have been observed.

Keywords

  • metallic glass
  • glass forming ability
  • crystallization behavior
  • thermal stability
  • casting atmosphere
Open Access

Impact of firing temperature on insulating properties of Low Temperature Co-fired Ceramics

Published Online: 08 May 2020
Page range: 189 - 196

Abstract

Abstract

In this paper, results of investigation on the impact of firing temperature on insulating properties of Low Temperature Cofired Ceramics are presented. Dissipation factor, volume resistivity and breakdown electric field intensity were determined for firing peak temperature in the range from 800 °C to 900 °C. The tests were performed for two commercial LTCC materials: 951 Green Tape (DuPont, USA) and SK47 (Keko, Slovenia). The results showed that the firing temperature had a significant effect on the dielectric loss factor, volume resistivity and lifetime at applied high voltage. No clear tendency was observed for dielectric strength in the analyzed firing temperature range.

Keywords

  • LTCC
  • ceramics
  • breakdown
  • volume resistivity
  • high voltage
Open Access

The impacts of Ba2Li2Si2O7:Sn2+,Mn2+ and CaMgSi2O6:Eu2+,Mn2+ particles on the optical properties of remote phosphor LED

Published Online: 08 May 2020
Page range: 197 - 205

Abstract

Abstract

As implied in the title, the triple-layer remote phosphor (TRP), constructed with the yellow YAG:Ce3+ layer at the bottom, the red CaMgSi2O6:Eu2+,Mn2+ phosphor layer on the top, and the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer between these two layers, is suggested in this paper to improve the color and luminescence of white LEDs (WLEDs). In order to control the red light for the purpose of increasing the color rendering index (CRI), it is suggested that the red CaMgSi2O6:Eu2+,Mn2+ phosphor should be applied in the TRP structure. Simultaneously, the structure uses the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer to control the green light, which increases the luminous efficacy (LE) of WLEDs. In addition, when the concentration of these two phosphors increases, the yellow YAG:Ce3+ concentration must be reduced to keep the average correlated color temperatures (ACCTs) stable at 6000 K to 8500 K. Besides, appropriate adjusting of CRI, LE, and color quality scale (CQS) is also analyzed by modifying the concentration of the green phosphor and red phosphor. The results show that the CRI can get better values if CaMgSi2O6:Eu2+,Mn2+ concentration is higher. In contrast, the CRI decreases dramatically when the concentration of Ba2Li2Si2O7:Sn2+,Mn2+ increases. Meanwhile, CQS can be significantly increased in the range of 10 % to 14 % CaMgSi2O6:Eu2+,Mn2+, regardless of the concentration of Ba2Li2Si2O7:Sn2+,Mn2+. In particular, along with the improvement of CRI and CQS, LE can also be increased by more than 40 % by reducing the scattered light and adding the green light. Obtained results are a valuable reference for manufacturers for improving WLEDs color and luminescence quality to produce a broader range of WLEDs with better quality fulfilling social needs.

Keywords

  • WLEDs
  • triple-layer structure
  • remote phosphor package
  • color quality
  • luminous flux
Open Access

Study of Ho doped Ag2S thin films prepared by CBD method

Published Online: 08 May 2020
Page range: 206 - 213

Abstract

Abstract

Ho doped Ag2S thin films were grown on the glass substrate by chemical bath deposition (CBD) method at room temperature. The bath contained aqueous solution of silver nitrate, thiourea, EDTA, ammonia and holmium nitrate. Silver nitrate was used as a silver (Ag+) ion source; thiourea as sulfur (S) ion source, EDTA was a complexing agent while ammonia was used to maintain pH, Ho(NO3)3 was taken as a source of Ho ions. The optical absorption edge of undoped (pure) and Ho doped silver sulfide films was determined between 324 nm and 298 nm showing blue shift as compared to bulk Ag2S. Band gaps calculated from Tauc plot also showed an increase in values for doped samples. The increase in band gap indicates reduced particle size in the prepared Ho doped films. The photoluminescence emission peaks were observed at around 578 nm to 601 nm wavelength and excitation peaks were found at 351 nm to 294 nm for undoped and doped films. The SEM micrograph consists of globular ball type and flower type structures observed in the prepared films of Ho doped Ag2S.

Keywords

  • CBD
  • thin films
  • photoluminescence
  • silver nitrate

Plan your remote conference with Sciendo