Change In Optical Band Gap Research Articles

Structural, optical and electrical properties of chemically derived nickel substituted zinc ferrite nanocrystals

Single phase spinel Ni substituted nanocrystalline Zn ferrites have been synthesized using a soft chemical route. Effect of Ni substitution on structure, electrical and optical properties has been investigated. X-ray diffraction study confirms the growth of single phase nanocrystalline Ni substituted Zn ferrites. FTIR and UV–Visible studies delineate the change in structure and optical band gap due to inclusion of Ni ions. Substitution of Ni ion has been manifested on lattice parameter which systematically decreases from 8.448 Å to 8.280 Å. An initial increase followed by subsequent decrease in optical band gap with the increase in Ni content is observed. In addition, both ac and dc electrical studies shows anomalous behavior in conductivity and dielectric properties for the samples having Ni content in the range 0.2–0.6 mol fraction which can be attributed to the normal to inverse spinel structural changes.

Studies of dense electronic excitation-induced modification in crystalline Fe-doped SnO2 thin films

Dense electronic excitation-induced modification in thin films of Fe-doped tin oxide (SnO2) grown by RF sputtering technique was done by irradiating swift heavy ion (SHI) beams of 100MeV Au8+ with varying ion fluencies from 5×1011 to 1×1013 ions/cm2. While the AFM results exhibit grain size dependence on irradiation fluence, MFM images show uniformly distributed magnetized nanoparticles over the entire surface after irradiation. GAXRD pattern indicates particle size variation (from 5 to 26nm) due to irradiation and higher stability of (101) other planes against irradiation. Our reported results show that the surface energies of ESurf(101)>ESurf(110) in rutile structure of SnO2. Change in optical band gap between 3.78 and 5.08eV due to variation fluence was observed. This is attributed to variation in particle size, scattering due to surface roughness and modification in local electronic structure. RT magnetic studies done by SQUID shows that coercivity increases up to the fluence of 5×1012ions/cm2 (157.71Oe). The increase in coercivity is due to oxygen vacancies created and change in local electronic structure of Sn due to recoil implantation. Resonance RBS results confirm the presence of Fe in the samples with a new observation where increase in peak intensity of Sn after irradiation occurred. The presence of X-ray absorption near-edge structure spectra at O K-edge around 532.63eV in pristine and irradiated samples confirms the doping of Fe at the lattice site of Sn in SnO2. Evolution of new spectral features at 486.09, 486.75, 491.40, 492.85 and 499.14eV for XANES at Sn M-edge was obtained after irradiation.

Optical Behaviour Of CdS Nanorods Dispersed In Liquid Crystal

The optical properties of CdS nanorods have been modified in presence of antiferroelectric liquid crystals (AFLC). The effective refractive index of the CdS nanorods has been increased from 2.468 to 2.499 due to presence of AFLC molecules. The change in optical band gap of the CdS nanorods dispersed in AFLC causes the increment of refractive index of the CdS nanorods. The optical band gap of the CdS nanorods has been shifted from 2.61 eV to 2.52 eV due to presence of AFLC. We have also observed the enhanced photoluminescence (PL) intensity and red shift in emissive energy band of CdS nanorods dispersed in AFLC. Copyright © 2015 VBRI Press.

Influence of Bi2O3 on physical, electrical and thermal properties of Li2O·ZnO·Bi2O3·SiO2 glasses

Lithium zinc bismuth silicate glasses having composition 30Li2O·20ZnO·xBi2O3·(50−x)SiO2, (10⩽x⩽40mol%) were prepared by using normal melt quenching technique. Physical, optical, electrical and thermal properties have been investigated in order to understand mixed former effect because of the presence of Bi2O3 and SiO2 in these glasses. The compositional variations of density (Dg) and molar volume (Vg) have been examined. From the optical absorption spectra, the cut-off wavelength (λg), optical band gap (Eg) and Urbach’s energy (ΔE) have been determined and are related with the structural changes occurring in these glasses with increase in bismuth oxide content. The electronic polarizability of the oxide ion and optical basicity has also been obtained from the calculated values of the optical band gap. The ac and dc conductivities, activation energy for dc conduction (Edc) and for relaxation frequency (EM″) were calculated from the impedance spectra. The results obtained from dc conductivity depicted that the lithium ions are mainly responsible for the conduction mechanism and it also confirmed the network forming role of zinc oxide in these glasses. The temperature dependence of the relaxation dynamics in these glasses has been interpreted by using the scaling of the conductivity spectra. The observed conductivity spectra follows power law with exponent ‘s’ which decreases with temperature and satisfies the correlated barrier hopping (CBH) model. The exact overlying of normalized plots of electrical modulus on a single ‘master curve’ indicates temperature independent dynamical process at various frequencies. The non-linear compositional change in optical band gap, activation energies as well as glass transition temperature reveals the mixed glass former effect. The increase in the values of thermal parameters such as glass stability factor and Hruby’s parameter, suggests large stability of glasses.

Solution- Processed Alkali Metals-Doped Amorphous Zinc Tin Oxide Thin-Film Transistors and Analysis of Alkali Metal Doping Mechanism through the UV-Visible Spectroscopic

Recently, alkali metal doped ZnO has received much positive attention owing to its high performance and good electrical stability. In particular, since alkali metals such as Li and Na are general elements and show good potential as doping elements in ZnO semiconductors, several researchers have been interested in alkali metal doping process of polycrystalline zinc oxide semiconductors. However, only a few studies have been reported the doping mechanism to enhance the mobility. In addition, there have been few studies on alkali metal doping mechanism in amorphous metal oxide semiconductors. Most studies about alkali metal doped oxide semiconductor have been inquired in term of crystallinity, oxygen vacancy, and surface morphology properties. For these reasons, we also studied the mechanism of alkali metal doping in view of oxygen vacancy by spectroscopic study using XPS and surface morphology using AFM. However, although we observed that oxygen vacancy contents are reduced slightly with a correlation by interstitial or substitutional mechanism, it seems to be difficult to identify the correlation between the enhancement of electrical properties induced by interstitial doping and the changes of oxygen vacancy contents, because the difference of XPS spectra in doped ZTO films is too small. Also, as the decrease of oxygen vacancy contents means the decrease of electron mobility in metal oxide semiconductors, the tendency of oxygen vacancy spectra in XPS is inconsistence with general phenomena. It means that other mechanisms are required to precisely explain the electrical properties of the doped amorphous ZTO TFTs related to alkali metal doping mechanism. Otherwise, the change in the optical band gap supported by the Burstein-moss theory showed successfully that the enhancement of mobility was related to the interstitial doping of alkali metals. This result shows that the change of the optical band gap clearly applied to the study of the relationship between the change in mobility and interstitial doping concentrations.Here in, we introduce alkali metals doped and solution processed amorphous zinc tin oxide (ZTO) semiconductor TFTs, which show better electrical properties, such as field effect mobility and conductivity, than that of intrinsic amorphous ZTO based TFTs. We also analyze that the doping mechanism of alkali metals in the amorphous ZTO based TFTs using various techniques such as, atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS), Hall mobility. Furthermore, through the UV-visible spectroscopy, we suggest a comprehensive technique for investigating the enhanced electrical performance induced by alkali metal doping in terms of the change in optical band gap. Specially, we showed that UV-visible spectroscopic analysis for investigating the electrical performance of alkali metal doped metal oxide semiconductor TFTs has good potential as a fast and non-destructive analytical technique.

Tuning of optical bandgap and magnetization of CoFe2O4 thin films

Single phase CoFe2O4 thin films are deposited on quartz substrates at 400 °C using ultrasonic assisted chemical vapor deposition, and the tuning of optical bandgap and saturation magnetization of films is demonstrated by varying the post deposition annealing temperature. The optical band gap varies from 1.58 to 1.41 eV and saturation magnetization increases from 4 to 46 emu/g as the post deposition annealing temperature is increased from 500 °C to 700 °C. The observed change in optical bandgap and the magnetic properties is attributed of the shifting of Co2+ from the octahedral to the tetrahedral site with the increase in the annealing temperature. Raman studies of the films support the redistribution of Co2+ among the octahedral and tetrahedral sites in CoFe2O4 films with the increase in the annealing temperature.

Ce and F Comodification on the Crystal Structure and Enhanced Photocatalytic Activity of Bi2WO6 Photocatalyst under Visible Light Irradiation

The novel Ce and F codoped Bi2WO6 samples have been successfully obtained by a facile one-step hydrothermal reaction for the first time. They were characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra. The presence of Ce3+, Ce4+, and F– dopants in Bi2WO6 was confirmed by XPS. The change of microstructure and optical band gap has also been observed after the doping of Ce and F. Under visible light, the as-synthesized plate-like F–Ce–Bi2WO6 sample exhibits a much better visible-light-responsive photocatalytic performance than pure Bi2WO6 for the degradation of RhB and photocurrent (PC) generation. The mechanism of high photcatalytic activity was also suggested on the basis of the PL spectra, electrochemical impedance spectra (EIS), and active species trapping measurements. The results indi...

High-energy ion treatments of amorphous As40Se60 thin films for optical applications

The treatment of 100MeV Ag swift-heavy ion (SHI) irradiation with five different fluences (3×1010, 1×1011, 3×1011, 1×1012, and 3×1012ions/cm2) was used to design optical and structural properties of amorphous (a-) As40Se60 chalcogenide thin films. Swanepoel method was applied on transmission measurements to determine the changes in optical bandgap, Tauc parameter and linear optical parameters, i.e., linear optical absorption, extinction coefficient and linear refractive index. Dispersion of the material was determined by Wemple–DiDomenico relation. Changes in nonlinear optical parameters of third-order optical susceptibility and nonlinear refractive index were determined using semi-empirical relations. Changes in surface morphology of the films were investigated using SEM observation, which indicated that fluence 3×1012ions/cm2 was upper threshold limit for these films for ion treatment. It is observed that optical bandgap reduces from 1.76eV to 1.64eV, and nonlinear refractive index increases from 1.31×10−10 [esu] to 1.74×10−10 [esu]. Linear refractive index initially increases from 2.80 to 3.52 (for fluence 3×1010ions/cm2) and then keeps decreasing. The observed changes in optical properties upon irradiation were explained in terms of structural rearrangements by Raman measurement. The study was compiled with the previous literature to propose SHI as an effective optical engineering technique to achieve desired changes according to the need of optical/photonic applications.

The effect of post-annealing on Indium Tin Oxide thin films by magnetron sputtering method

Abstract We report effects of post-annealing on Indium Tin Oxide (ITO) thin films by their physical, electrical, optical, and electronic properties. Carrier concentrations increase up to annealing temperatures of 400 °C, and then decrease at higher annealing temperatures. Burstein–Moss effect occurs as a function of annealing temperature with the highest optical bandgap of 4.17 eV achieved at 400 °C. X-ray photoelectron spectroscopy revealed a ∼0.3 eV shift in the Fermi level of the annealed ITO films at 400 °C, and the shift was reduced for temperatures higher than 400 °C. In addition, the results of curve-fitting for the core levels showed a change of ratios of SnO2 and oxygen in the oxygen deficient regions after annealing. This is correlated to the change of carrier concentration and optical bandgap in the ultraviolet and near-infrared regions at different annealing temperatures.

The Optical and Chemical Response of Thermal Neutron-Irradiated CR-39 Polymeric Track Detector after Annealing

In the present work, the aliphatic polycarbonate CR-39 with average thickness 260µm was irradiated with different neutron fluences from the Cirus reactor, Bhabha Atomic Research Center, Mumbai. For all samples, the isochronal annealing was done in the temperature zone 130°–150°C, each for 45 min. The effect of annealing on irradiated samples was studied using UV-Visible and FTIR spectroscopic techniques. With UV-Vis analysis, the change in optical band gap and Urbach's energy with annealing for a particular dose have been revealed. The FTIR analysis of irradiated annealed samples indicates the partial repair of bonds on annealing at high temperatures.

Synthesis and characterization of Cu3SbS3 nanocrystallites: Effect of reaction time

Cu3SbS3 nanocrystallites were successfully obtained through a facile solvothermal route at 165°C for 8, 12, 16, 20 and 24h, based on reactions between CuCl2, SbCl3 and thioglycolic acid in glycol. The effect of reaction time on structural, morphology and optical properties was investigated. It can be seen from the TEM images that the products grew from spherical to rhombus. The UV–visible absorption indicates a significant change in optical band gap (0.75–1.2eV) with extending the reaction time. In addition, the proposed solvothermal method with thioglycolic acid as both sulfur source and complexing reagent provides an alternative approach to prepare other ternary semiconductor nanomaterials.

Structural, optical and electrical properties of Ti doped amorphous silicon prepared by co-sputtering

Titanium-doped unhydrogenated amorphous silicon (a-Si: Ti) films were prepared by rf co-sputtering. Structural, optical and electrical properties of a-Si: Ti as a function of Ti content were investigated by RBS(Rutherford Backscattering Spectrometry), XPS(X-ray Photoelectron Spectroscopy), Raman, ESR (Electron Spin Resonance), Spectroscopic Ellipsometry, thermoelectric tests and temperature dependent I–V tests. Introducing Ti impurity in amorphous Si results in n-type material, room temperature conductivity increases more than three orders of magnitude and activation energy decreases obviously. When Ti content is lower than 2 at.%, the degree of short-range order and defect state density of amorphous Si network improve while the optical bandgap changes little. However, with Ti content higher than 2 at.%, the degree of short-range order decreases and the optical gap of a-Si shrinks. The role of Ti atoms in amorphous Si network is discussed. ESR results confirm that introducing low content of Ti can compensate the dangling bonds of amorphous Si, while with Ti content higher than 2%, most Ti atoms compensate the unpaired electrons in the conduction band tail.

Influence of Surface Passivation on Optical Properties of Spray Pyrolysis Deposited Pd-F:SnO2

Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution consisting of stannic chloride (SnCl4.5H20), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters has been done in order to obtain high quality thin films. The effect of varying the fluorine content on the optical properties of Pd-F:SnO2 thin films were studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was measured using the solid spec 3700DUV spectrophotometer. The calculated optical band gap of the as prepared thin films has been found to range from 3.8eV to 4.11eV. Fluorine incorporation for Pd-F:SnO2 has been found to have a narrowing effect on the band gap, but at its higher concentration the band gap has been seen to increase. The band gap narrowing is due to the incorporation of F- ions in the crystal lattice therefore giving rise to donor levels in the SnO2 band gap which is an essential characteristic for the gas sensor applications. Both annealing and passivation have been found to have very insignificant change in optical band gap of Pd-F:SnO2.

Composition and Optical Dispersion Characterization of Nanoparticles ZnO-NiO Thin Films: Effect of Annealing Temperature

Thin films of ZnO0.7NiO0.3 have deposited on glass substrates at room temperature by using thermal evaporation technique under vacuum 10-5 mbar. The optical properties and dispersion parameters of the films have been studied. Changes in direct optical energy band gap of films were confirmed before and after annealing. The optical energy gap Eg decreased from 3.11 to 2.86 eV with increasing of annealing temperature to 200 °C. Some of the optical absorption parameters, such as optical dispersion energies Eo and Ed, Urbach tails EU , dielectric constant ε, the average values of oscillator strength So, and wavelength of single oscillator λo have been reported. An increase in the annealing temperature causes an increase in the average oscillator strength from 62.02 to 87.71 eV.

Optical Dispersion Characterization of Sprayed Zn<sub>1-x</sub>Mn<sub>x</sub>O Thin Films

Uniform and adherent Zn1-xMnxO films have been deposited by using spray pyrolysis technique on glass substrates. The optical properties and dispersion parameters of zinc oxide have been studied as a function of doping concentration with Mn. Changes in direct optical energy band gap of cobalt oxide films were confirmed after doping, the optical energy gap Eg increased from 3.13 eV for the undoped ZnO to 3.39 eV with increasing the doping concentration of Mn to 4%. The changes in dispersion parameters and Urbach tails were investigated. An increase in the doping concentration causes a decrease in the average oscillator strength. The single-oscillator parameter has been reported.

Photosensitivity of pulsed laser deposited Ge20As20Se60 and Ge10As30Se60 amorphous thin films

Amorphous Ge20As20Se60 and Ge10As30Se60 thin films are fabricated by pulsed laser deposition. Prepared films are characterized in terms of their morphology, chemical composition, and optical properties. Special attention is given to the photosensitivity of the layers, which was studied by spectroscopic ellipsometry with as-deposited, annealed and exposed films by three different laser sources (593, 635, and 660nm). The results show better photostability for Ge20As20Se60 thin films, where photoinduced change of optical band gap was found to be equal or less than 0.04eV and these layers present almost zero photorefraction.

Composition and Optical Dispersion Characterization of Nanoparticles ZnO-NiO Thin Films: Effect of Annealing Temperature

Thin films of ZnO0.7NiO0.3 have deposited on glass substrates at room temperature by using thermal evaporation technique under vacuum 10-5 mbar. The optical properties and dispersion parameters of the films have been studied. Changes in direct optical energy band gap of films were confirmed before and after annealing. The optical energy gap Eg decreased from 3.11 to 2.86 eV with increasing of annealing temperature to 200 °C. Some of the optical absorption parameters, such as optical dispersion energies Eo and Ed, Urbach tails EU , dielectric constant ε, the average values of oscillator strength So, and wavelength of single oscillator λo have been reported. An increase in the annealing temperature causes an increase in the average oscillator strength from 62.02 to 87.71 eV.

Are the Temperature Sensors Based on Chalcogenide Glass Possible?

Principal possibility of the using of chalcogenide glasses (on the example of Ge18As18Se64) as active media for temperature sensors is considered in this work. Differential scanning calorimetry testing of the investigated glasses shown that 2 years of natural storage does not lead to the drift of their DSC-parameters (glass transition temperature and endothermic peak area). Investigation of the temperature dependence of optical transmission spectra shows the linear character of optical band-gap changes with a temperature. Temperature sensitivity index β for Ge18As18Se64 is estimated to be equal to the ~1.2·10-3 eV/°C.

Optical Dispersion Characterization of Sprayed Zn<sub>1-x</sub>Mn<sub>x</sub>O Thin Films

Uniform and adherent Zn1-xMnxO films have been deposited by using spray pyrolysis technique on glass substrates. The optical properties and dispersion parameters of zinc oxide have been studied as a function of doping concentration with Mn. Changes in direct optical energy band gap of cobalt oxide films were confirmed after doping, the optical energy gap Eg increased from 3.13 eV for the undoped ZnO to 3.39 eV with increasing the doping concentration of Mn to 4%. The changes in dispersion parameters and Urbach tails were investigated. An increase in the doping concentration causes a decrease in the average oscillator strength. The single-oscillator parameter has been reported.

Structural investigation of 2 MeV proton-irradiated fullerene nanorods

Self-assembled fullerene C60-nanorods on Si (111) substrates were irradiated by 2MeV protons with fluencies ranging from 5.0×1016 to 1.0×1017ions/cm2. Proton irradiation has induced optical band-gap changes and surface modification of the C60-nanorods making them insoluble in toluene specifically. Raman spectroscopy investigations indicate a change in the substantial Raman shift to lower values of the characteristic Ag modes of C60 after irradiation. X-rays diffraction results indicate that the fcc crystalline structure of the as-deposited nanorods has a tendency to amorphous after irradiation. High resolution transmission electron transmission microscopy confirmed such a modification in the planar spacing.