Increase In Optical Band Gap Research Articles

Influence of magnesium doping on microstructure, optical and photocatalytic activity of zinc oxide thin films synthesis by sol–gel route

The article deals with the effect of Mg dopant on the properties and the photocatalytic of ZnO films synthesized by the sol–gel technique onto glass substrates. It is found that Mg dopant has a strong influence on the microstructure and functional properties. The EDX analysis revealed that Mg had been incorporated into the ZnO. Structural studies through XRD have shown that the deposited films are of hexagonal structure with a preferential growth along the c-axis and nanometer crystal size. According to AFM analysis; it is found that the roughness of Mg-doped ZnO films increases with the Mg dopant. The film surface depicted wrinkles morphology as observed by ESEM. Optical investigations by spectrophotometry and photoluminescence revealed that as the Mg dopant is increased, the optical band-gap increases. Moreover, near band edge and visible emissions as probed by Photoluminescence can be manipulated by the Mg dopant, as their intensity increases and decreases, respectively. Finally, the photocatalytic activity for degradation of methylene blue is strongly improved all the more as the Mg content is increased.

Structural, optical and magnetic properties of vacuum annealed Fe, Mn doped NiO nanoparticles

Iron (Fe) substituted nickel oxide (Ni1−xFexO) and manganese (Mn) substituted (Ni1−xMnxO) nanoparticles at x = 0.05 were prepared using solid-state reaction. The synthesized Ni1−xFexO and Ni1−xMnxO nanoparticles were annealed in vacuum at a pressure of 1 × 0–3 mbar at two different temperatures of 473 K and 673 K for 1 h. The influence of vacuum annealing on the physical properties of Ni1−xFexO and Ni1−xMnxO nanoparticles were studied. The vacuum annealed nanoparticles were characterized by XRD, SEM, EDS, UV–Vis-NIR and VSM instruments to study their structural, surface, chemical, optical and magnetic properties, respectively. From the XRD results it was found that Ni1−xFexO nanoparticles were in cubic structure with Fe impurity phases whereas the Ni1−xMnxO nanoparticles exhibited cubic structure without any impurity phases. The crystallite sizes of the nanoparticles were in the range of 25–30 nm. From the EDS spectra, it was found that the elements such as Fe, Ni, Mn and O were in almost stoichiometric ratio. An increase in optical band gap for Ni1−xFexO and Ni1−xMnxO nanoparticles were observed with an increase of annealing temperature. The pure NiO and doped NiO nanoparticles exhibited ferromagnetism at room temperature. The strength of magnetization decreased in NiO with a rise in annealing temperature. The Ni1−xFexO and Ni1−xMnxO nanoparticles were ferromagnetic at room temperature and the magnetization increased with increase in vacuum annealing temperature. The highest magnetization of 1.4 emu/g, 0.85 emu/g and 0.76 emu/g were observed for NiO, Ni1−xFexO and Ni1−xMnxO nanoparticles, respectively at 673 K. The nanoparticles will be suitable for storage device applications.

Sol-gel synthesis of SnO2 nanoparticles doped with Zr+4/Cd+2 and Co-doped with F−: Their structural, optical and electrical properties

Abstract Some nanoscale particles of SnO2 doped with Zr+4 (1), Zr+4 and co-doped with F− (2), Cd+2 (3) and with Cd+2 and co-doped with F− (4) have been prepared by sol–gel technology in basic medium using SnCl2·2H2O as precursor in isopropanol as solvent. Structural analysis by XRD patterns have shown formation of particles at nanoscale and retention of tetragonal rutile structure in SnO2 network. This fact was further confirmed by 119Sn MAS NMR spectroscopy. SEM images have shown formation of various geometrical patterns. In the IR spectra, O-Sn-O absorption bands appeared at their expected positions. UV–Vis spectroscopy has shown an increase in optical band gap. Photoluminescence spectra of all these derivatives are found to be almost similar, again indicated retention of tetragonal rutile SnO2 framework. I-V curves are non-linear showing schottky contacts in the material.

Fabrication of Vanadium Doped Zinc Oxide Thin Film to Enhance the Optical, Magnetic and Electrical Properties using Electrospray Technique

Vanadium doped zinc oxide was deposited using a homemade electrospray technique. The structural, optical, magnetic, surface morphology and electrical studies were carried out using XRD, UV-vis-NIR spectroscopy, HRSEM, AFM, photoluminescence, VSM and Hall effect, respectively. The XRD results revealed that the addition of vanadium(V) does not affect hexagonal wurtzite structure in the films. Photoluminescence study implies the increase of oxygen vacancy on surface of the samples and the hexagonal plates like grains are found on the film surface and formation of cluster as doping percentage increases. Hall effect shows the remarkable improvement in carrier concentration, resistivity and mobility. The sheet resistance decreases to 59.5 × 102 Ω/2 for 4 at% of vanadium. All the samples achieved the transmittance above 80% in the visible region and optical band gap increases. The magnetic study shows that the enhancement of paramagnetic property and the study on the performances of the samples over the light intensity shows, the enhancement in the rate of decreases in resistance, which is higher than the undoped sample ware discussed.

Electro spray technique to enhance the physical property of sulphur doped zinc oxide thin film

The Sulphur doped Zinc oxide was deposited using a homemade electro spray technique and the change in physical properties was investigated. This method is used to prepare thin films using insoluble substance with precursor. The structural, optical, magnetic, surface morphology, and electrical studies were carried out using XRD, UV–vis-NIR spectroscopy, HRSEM, AFM, Photoluminescence, VSM and Hall effect. XRD result reveals that the increase of Sulphur does not affect hexagonal wurtzite structure in the film and the compressive force inside the lattice creates the decreasing effect in crystallites size. The enhancement of paramagnetic property due to the addition of Sulphur in ZnO lattice, which increase of oxygen vacancy on surface. The hexagonal plate like grains and formation of cluster shows the remarkable improvement in the carrier concentration, resistivity, and mobility. The sheet resistance reaches a minimum of 25 × 102 Ω/□ at 8at% for S:ZnO than the undoped sample. All the samples achieved the transmittance above 87% in the visible region and optical band gap increases. The performance of the samples on light intensity effect shows interstitial Sulphur ions enhance the rate of decreases in resistance and increase the sensitivity to light than the undoped sample were discussed.

Transmittance, Absorbance and Emission of Ga related Defects in Ga-doped ZnO Nanocrystal Films

ZnO films grown by ultrasonic spray pyrolysis with different Ga contents in the range of 1.0-6.5 at% on quartz substrates have been studied. The ZnO:Ga films were annealed at 400°C for 4h in a nitrogen flow. Morphology, emission, transmittance, absorbance and electrical resistivity were controlled. It is revealed that with a small content of Ga ≤ 4.0 at%, the ZnO:Ga films maintain a flat morphology, their transmittance increases to 86% together with the increase of the ZnO optical bandgap to 3.28 eV and the intensity enlargement of the near band edge (NBE) emission band A (3.188 eV). Furthermore, the new NBE emission band B (3.072 eV) appears in photoluminescence (PL) spectra at Ga contents ≥ 1.5 at%. Simultaneously, the process of decreasing electrical resistivity becomes saturating. The last effect is attributed to the self-compensation effect in n-type ZnO:Ga films related to the generation of acceptor type complexes (VZn2- - GaZn+). The thermal quenching of the PL intensities of the A and B PL bands is studded at 18-290K, which allows assigning the PL band A to the LO-phonon replica of the free exciton emission and the band B to the emission in donor-acceptor pairs: shallow donors - acceptor complexes (VZn2- - GaZn+). The NBE emission intensity drops and the ZnO optical bandgap demonstrates the shift to a lower energy at Ga doping up to ≤ 6.5 at%. Optimal Ga concentrations have been estimated to produce ZnO:Ga films with flat morphology, high optical transmittance and bright NBE emission.

EFFECT OF DOPING CONCENTRATION ON THE OPTICAL PROPERTIES OF NANOCRYSTALLINE Zn DOPED PbS THIN FILMS DEPOSITED BY CBD METHOD

Nanocrystalline PbS and Zn doped PbS thin films have been deposited on glass substrates by chemical bath deposition (CBD) method. The as deposited thin films were found to be crystalline having cubic phase structure. The optical properties of the undoped and Zn doped PbS thin film have been studied. The chemically prepared Zn doped and undoped nanocrystalline PbS films have high absorbance in the UV-visible region. The linear nature of (αhν)2 vs (hν) plots of PbS thin films confirmed that the transition is direct and the optical band gap energy of PbS films is found to increase from 1.90 eV to 2.28 eV with decreasing crystallite size from 29 nm to 15 nm and these obtained band gap values are higher than the bulk value (0.40 eV). The increase in optical band gap supports the quantum confinement effect in the PbS thin films prepared by CBD technique. The optical band gap of Zn doped PbS films are found to increase with increase in dopant concentrations.

Ferromagnetic transition metal-doped CdS nanoparticles: a comparative study

In the present work, series of ferromagnetic transition metal-doped (Fe, Co) CdS nanoparticles were synthesized via hydrothermal technique. The particles were characterized for structural, morphological, optical and magnetic properties. The X-ray diffraction confirmed the single wurtzite phase for all compositions. The relatively smaller crystallite size (~ 11.50 nm) was obtained with Fe (x = 0.15) compared to Co doping (~ 13.88 nm). The HR-TEM micrographs revealed spherical morphology of nanoparticles with decrease in average particle size. The increase in optical band gap was observed with doping. In photoluminescence spectra, the main emission peak at 529 nm corresponds to green emission due to d-d intra ion transition. The magnetic analysis confirmed room temperature ferromagnetism in all the compositions and highest value of saturation magnetization has been observed for Fe-doped nanoparticles.

Simulation, Analysis, and Characterization of Calcium-Doped ZnO Nanostructures for Dye-Sensitized Solar Cells

In this research article, the authors have discussed the simulation, analysis, and characterization of calcium-doped zinc oxide (Ca-doped-ZnO) nanostructures for advanced generation solar cells. A comparative study has been performed to envisage the effect of Ca-doped ZnO nanoparticles (NP), seeded Ca-doped ZnO nanorods (NR), and unseeded Ca-doped ZnO NR as photoanodes in dye-sensitized solar cells. Simulations were performed in MATLAB fuzzy logic controller to study the effect of various structures on the overall solar cell efficiency. The simulation results show an error of less than 1% in between the simulated and calculated values. This work shows that the diameter of the seeded Ca-doped ZnO NR is greater than that of the unseeded Ca-doped ZnO NR. The incorporation of Ca in the ZnO nanostructure is confirmed using XRD graphs and an EDX spectrum. The optical band gap of the seeded substrate is 3.18 eV, which is higher compared to those of unseeded Ca-doped ZnO NR and Ca-doped ZnO NP, which are 3.16 eV and 3.13 ev, respectively. The increase in optical band gap results in the improvement of the overall solar cell efficiency of the seeded Ca-doped ZnO NR to 1.55%. The incorporation of a seed layer with Ca-doped ZnO NR increases the fill factor and the overall efficiency of dye-sensitized solar cells (DSSC).

Cu/(Co+Sn) ratio effects on physical and photodetective properties for visible light absorbing Cu2CoSnS4 nanoparticles via a one-pot hydrothermal process

The composition ratio plays a vital role in modulating the thermal, magnetic, and optoelectronic properties of earth-abundant quaternary chalcogenides. Here we report on an impact of Cu/(Co + Sn) ratio on secondary phase formation, size, and shape of Cu2CoSnS4 (CCTS) nanoparticles synthesized via monoethanolamine (MEA) promoted the hydrothermal process. The CCTS phase formation mechanism is experimentally elucidated by a time-dependent synthesis study during a one-pot facile hydrothermal reaction, and it is confirmed by using X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) analysis. The morphology, particle size distribution, and shape of synthesized nanoparticles are examined by field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) analysis. The N-Methyl-2-pyrrolidone (NMP) solvent-based CCTS paste was drop-casted on a thermally oxidized silicon wafer (∼100 nm SiO2) to form films. The increase in optical bandgap from 1.48 eV to 2.00 eV is observed for an increase in Cu/(Co + Sn)) ratio of prepared CCTS films. The electrical, photodetection properties of the prepared films with respect to the (Cu/(Co + Sn)) ratio under dark and light illumination are studied. The lowest sheet resistance (Rsh= (13.56 ± 0.9) × 103 Ω/cm) and contact resistance (Rc= (108.31 ± 3.43) × 103 Ω) is obtained for devices made with a higher value of Cu/(Co + Sn) ratio = 1.17. On the other hand, the highest photosensitivity (Sph = 32%), photoresponsivity (Rph = 75.58 mA/W), and detectivity (Dph = 1.44 × 108 Jones) are demonstrated for device assembled with the lowest ratio (∼0.86) of Cu/(Co + Sn). The present study reveals that Cu/(Co + Sn) ratio affects a significant impact on such as a phase, morphology, chemical compositional ratio of nanoparticles, optical, electrical, and photoresponsive properties of prepared films.

Arsenic modified (Ge11.5Te12.5Se67.5)100-x compound for IR application

Multi-component selenium rich glasses with various arsenic content have been prepared using conventional melt-quenching technique. XRD, SEM and EDX were carried out to study the structure of the prepared samples. From XRD it is found that studied samples are amorphous. DSC has been recorded which confirms that the prepared material is of glassy nature. FTIR spectra give information regarding presence of impurities in the glass. Optical parameters like α, Eg, Eu and n have been determined from the UV–Vis transmittance spectra. It has been noticed that the film transparency and optical bandgap have been increased whereas the absorption coefficient and extinction coefficient k decreased with increasing As concentration. It was found that the prepared samples obey the allowed indirect transition process. The increase in optical bandgap with As concentration has been described by Mott and Davis model. The refractive index shows ordinary dispersion behavior while it increases with As concentration.

Physical Investigations of Niobium Oxide Nanorod Imploring Laser Radiation

In this work, the Nb2O5 nanostructure has been deposited using Q-switched Nd: YAG laser in the vacuum pressure of 0 bar pressure on quartz substrates. Physical properties of the prepared films at different substrate temperatures (300, 400, and 500) °C were characterized. The obtained results reflect the formation of good quality monoclinic Nb2O5 thin film. A clear blow shift was also obtained where the optical band gap increase from (to) with temperature. Finally, AFM results revealed the increase the surface roughness with substrate temperatures.

Effect of the microwave-assisted thermal annealing on structural and optical properties of the sol–gel-derived ZnO thin films

ZnO thin films were prepared by sol–gel spin coating technique, and the effect of microwave-assisted thermal annealing on structural and optical properties was investigated. Structural features, microstructural morphology and optoelectronic properties were studied using XRD, FE-SEM, UV–visible spectrophotometry and four-point probes measurement system. During microwave-assisted annealing, rapid volumetric heating preserved nanostructure along with pore-free dense morphology. Also, this annealing technique induced larger tensile strain and increased preferential orientation along (002). Power consumption for sintering was reduced as obvious from the decreased annealing time. An increase in optical band gap with a decrease in electric resistivity by one order of magnitude can be attributed to its nanostructured pore-free structure, and the induced strain resulted from microwave-assisted annealing.

Structural Stabilization and Piezoelectric Enhancement in Epitaxial (Ti1−xMgx)0.25Al0.75N(0001) Layers

AbstractEpitaxial (Ti1−xMgx)0.25Al0.75N(0001)/Al2O3(0001) layers are used as a model system to explore how Fermi‐level engineering facilitates structural stabilization of a host matrix despite the intentional introduction of local bonding instabilities that enhance the piezoelectric response. The destabilizing octahedral bonding preference of Ti dopants and the preferred 0.67 nitrogen‐to‐Mg ratio for Mg dopants deteriorate the wurtzite AlN matrix for both Ti‐rich (x < 0.2) and Mg‐rich (x ≥ 0.9) alloys. Conversely, x = 0.5 leads to a stability peak with a minimum in the lattice constant ratio c/a, which is caused by a Fermi‐level shift into the bandgap and a trend toward nondirectional ionic bonding, leading to a maximum in the expected piezoelectric stress constant e33. The refractive index and the subgap absorption decrease with x, the optical bandgap increases, and the elastic constant along the hexagonal axis C33 = 270 ± 14 GPa remains composition independent, leading to an expected piezoelectric constant d33 = 6.4 pC N−1 at x = 0.5, which is 50% larger than for the pure AlN matrix. Thus, contrary to the typical anticorrelation between stability and electromechanical coupling, the (Ti1−xMgx)0.25Al0.75N system exhibits simultaneous maxima in the structural stability and the piezoelectric response at x = 0.5.

Effect of thickness on characteristics of ZnSe thin film synthesized by vacuum thermal evaporation

Zinc selenide (ZnSe) thin films with various thicknesses were grown on ultrasonically clean glass substrates using vacuum evaporation of 99.99% pure ZnSe powder. Thickness dependence of the structural, optical and electrical properties was thoroughly investigated. X-ray diffraction (XRD) analyses revealed that (110) ZnSe plane is the dominant crystal plane for all the fabricated films. Both dislocation density and micro-strain go down with the increase in film thickness, indicating lower lattice defects and improvement in crystallinity at higher film thickness. Transmittance spectra show that all the films have almost linear upward tendency of transmittance in near-infrared region and small fluctuations in visible region for higher-thickness films. With the increase in film thickness, the optical bandgap increases and also an increasing tendency of dielectric constant was observed. Studies of electrical properties showed a sharp increase in carrier mobility and concentration with film thickness. As the film thickness increases from 30 to 90 nm, the carrier mobility goes up from 255 to 1250 cm2/VS and the carrier concentration increases from 2.14 × 1018 to 9.37 × 1018 cm−3. The electrical transport properties of the deposited thin films were explained in terms of scattering of the charge carrier.

Structural, morphological and optical properties of barium doped bismuth ferrite thin films deposited by spray pyrolysis

In the area of material science and technology, fabrication and characterization of nano-materials play an important role since it leads to the development of devices with interesting performance and potential applications in electronics, magnetics, optics, and photonics. Among the materials perovskite materials are gaining prominence. In this investigation, thin films of bismuth ferrite have been prepared and the impact of co–substitution of barium on their structural, morphological and optical properties have been studied. The spray pyrolysis procedure was used to prepare the thin films of bismuth ferrite with medium thickness by doping barium with concentrations of 1%, 3%, 5% and 10%. Various characterization techniques were employed to study the films. The presence of barium, bismuth and iron in the samples was confirmed by EDAX spectra. X-Ray diffraction studies confirmed the polycrystalline nature of the films having a rhombohedrally distorted pervoskite crystal structure fitting to space group R3c. The Scherrer rule was applied to obtain the crystallite size which was found to be small. Surface morphology studies carried out using field emission scanning electron microscopy revealed that the grain size and roughness of the films are modified with increase in doping concentration. The measurement results of optical absorption showed an increase in optical band gap with doping with barium. The results of structural, morphological and optical parameters with the increasing doping concentration indicate that these films are promising candidate for applications in opto-electronics, photovoltaics and gas sensors.

Structural transformation of Ag3PO4 and Ag3PO4/TiO2 induced by visible light and Cl− ions: its impact on their photocatalytic, antimicrobial, and antifungal performance

In this work, synthesis of Ag3PO4 and its composite with TiO2 (Ag3PO4/TiO2) toward study of two phenomena naturally occurring in Ag3PO4 is reported, specifically a visible light-driven (i.e., photocorrosion) and chloride ion-driven transformation of Ag3PO4 to AgCl in chloride-free and chloride-present aqueous solution. A deeper insight on this transformation via study of their structural and morphological changes using X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) is performed. Substantial amount of AgCl is detected in both Ag3PO4-based materials after visible light irradiation in chloride-present environment. This led to an increase in optical band gap of Ag3PO4 and Ag3PO4/TiO2 from 2.52 to 2.99 eV and 2.48 to 3.02 eV, respectively. Impact of these structural changes in Ag3PO4 and Ag3PO4/TiO2 on their photocatalytic activity is evaluated from the photoinduced catalytic, antibacterial, and antifungal performance under visible light irradiation. The photocatalytic activity of pristine and photocorroded Ag3PO4 is increased by ~ 10 times compared to that of pristine and photocorroded Ag3PO4/TiO2. Photocorroded Ag3PO4 and Ag3PO4/TiO2 possess minor antibacterial and antifungal activities (cell survival ~ 90%), whereas using pristine Ag3PO4 and Ag3PO4/TiO2 the cell survival is reduced by 100% after 60 and 120 min, respectively.

Exploration of organic additives-assisted vanadium pentoxide (V2O5) nanoparticles for Cu/n-V2O5/p-Si Schottky diode applications

The organic additives-assisted vanadium pentoxide (OA:V2O5) nanoparticles (NPs) were prepared by a facile co-precipitation method and their structural, optical, and electrical properties have been analyzed. The orthorhombic crystal structure was observed in the X-ray diffraction pattern of pure vanadium pentoxide (V2O5) NPs. The XRD patterns of OA: V2O5 NPs reveals that the crystallite size of the V2O5 NPs reduced without any change in the crystal structure. The SEM images showed that organic additives strongly influence on the surface morphology of the V2O5 NPs. The TEM analysis revealed that the acid-treated V2O5 NPs are relatively smaller in size compared to without acid-treated V2O5 NPs. From the optical measurements, an increase in optical band gap was observed for OA:V2O5 NPs. The dc electrical analysis revealed that the increased dc electrical conductivity is due to the incorporation of various organic additives (OA) in the V2O5 NPs. The electrical parameters such as ideality factor (n), barrier height (ФB), series resistance (Rs), and interface properties have been analyzed for the Cu/n-V2O5/p-Si Schottky diodes (SBDs) by the J–V, Cheung’s and Norde method. The barrier height value is increased for Cu/OA:V2O5/p-Si SBDs.

Dominant role of trioctylphosphine on the particle size and various properties of CoO nanoparticles

The dominant role of trioctylphosphine (TOP) on the particle size and various properties of CoO nanoparticle (NP) samples having Scherrer size in the range 9.4–42.8 nm is reported here; samples have been characterized in detail systematically. Remarkably, while nanosized CoO or CoO/Co nanocomposites with monoclinic or face-centered cubic (fcc) phase can be prepared depending on the synthesis conditions and particle size systematically decreases with increase in concentration of TOP, there is an increase in optical band gap and electrical resistivity with decrease in particle size. The highly semiconducting electrical resistivity is explained with the variable range hopping and small polaron hopping models that indicate in turn enhanced localized density of states, but decrease in Debye temperature (θD) as the particle size decreases. Curiously, 25.9 nm sample shows anomalous behaviour. Moreover, the silica-coated 9.4 nm CoO NP and bare 10.8 nm CoO NP samples exhibit ferromagnetism at 300 K even though their bulk counterpart is antiferromagnetic, with attractive indications of possible potential biomedical applications of the former.

Influence of Germanium Addition on Optical Properties of As–Se Glasses

Present paper focus on the optical properties of Se62.5As37.5 and Se62.5As22 5Ge15 chalcogenide thin films prepared by vacuum evaporation method. The structural and stoichiometric properties of prepared glassy alloys were investigated by X-ray diffraction and energy dispersive X-ray spectroscopy. Addition of Ge at the cost of As increases the absorption and optical band-gap while the value of extinction coefficient decreases. The transmission spectrum (300–1100 nm) obtained by UV-Vis spectrophotometer were used to find the different optical constants. The increase of optical bandgap is explained based on Mott-Davis model assuming that there is decrease of localized states in prepared samples after addition of Ge in As–Se alloy which results in increase of optical bandgap.