Average Optical Band Gap Research Articles

Development in gelatin-matrix composite films: The incorporation of vitamin C adducts enhances the optical behaviors of gelatin films†

The chemical cross-linking method continues to be widely recognized as the most efficient and popular strategy for modifying gelatin. However, the exploration of enhancing the optical and electrical characteristics of gelatins through the use of organic molecules is still in its early stages. In this investigation, two stable dopants of ascorbic acid adducts were synthesized via the smooth and facile procedure, and their identities were validated through Fourier transform-infrared (FT-IR) and nuclear magnetic resonance spectroscopy techniques, including FT-1H NMR, and FT-13C NMR. The novel gelatin-matrix composite films were fabricated by blending vitamin C adducts with various gelatins including pork gelatin (PG), fish gelatin (FG), bovine gelatin (BG), and chicken gelatin (CG) using the casting method. The chemical and homogenous interactions between dopants and gelatin matrixes were verified through several spectroscopic techniques. The XRD spectra of the composite films show a significant elevation in their amorphous structures when compared to the pure gelatin host. The FT-IR spectra of both the gelatin matrix and their composites demonstrate strong chemical interactions among the functional groups within the gelatin composite films. The UV–vis spectra provided the primary optical information for the synthesized hybrid film. Remarkably, the index of refraction (n) and dielectric loss (ɛi) magnitudes are raised, while the average optical band gap energy (Eg) decreased from 4.9 (pure gelatin) to 3.4 eV. By applying Tauc's model, we successfully recognized the direct electronic transition occurring between the valence band (VB) and the conduction band (CB). The results of our research highlights that minor changes in the adduct composition significantly impact optical and textural properties in polymer composites, offering a plethora of potential technological opportunities. These applications include materials packaging, blocking of harmful light, and encapsulation purposes.

A holistic approach to optical characterizations of vacuum deposited Cu2ZnSnS4 thin film coatings for solar absorbing layers

This article aimed at making a good absorber layer of Cu2ZnSnS4 thin film coatings deposited onto glass substrates via spin coating technique with different rotational speeds. Three sets of Cu2ZnSnS4 thin film coatings were prepared at rotations of 3000, 3500, and 4000/min. The thickness of the thin film coatings was measured using a surface profilometer, and the coating thickness shows good rpm dependence i.e., the thickness of the coatings decreased with increasing rpm. The thicknesses of the coatings were in the nanometer (nm) range for all samples. The structural, morphological, and optical properties of the as coated thin films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and ultraviolet–visible (UV–Vis) absorption spectroscopy. The XRD pattern confirmed the body-centered tetragonal lattice structure with Kesterite Cu2ZnSnS4 phase having good crystallinity. The average crystallite size increases while lattice strain, dislocation density, and crystallite number are decreased with increasing thicknesses of the Cu2ZnSnS4 coatings. SEM micrographs represent the homogeneous, agglomerated surface without any cracks and pores. The average optical band-gap of the coatings was found to be 1.5 eV. Dielectric parameters such as refractive index, high-frequency dielectric constant, and static dielectric constant were declined with increasing thickness of Cu2ZnSnS4 thin film coatings. These characteristics would allow the Cu2ZnSnS4 thin film coatings to be suitable for an absorber layer used in photovoltaic devices.

Double doping synergy to improve structural, morphological, optical, and electrical properties of solution-based Cd and M (M: Pb, Sn, Bi) double doped nanocrystalline copper oxide films

In this study, nanostructured CuO, Cd0.01Cu0.99O and Cu0.98Cd0.01M0.01O (M: Pb, Bi, Sn) films were synthesized using the successive ionic layer adsorption and reaction technique. The effects of Cd-doping, Sn, Pb, and Bi double doping on the structural, morphological, optical, and electrical properties were systematically investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis spectroscopy, and current–voltage (I–V) measurements, respectively. XRD results show that the peak intensity, crystallite size, and texture coefficient of the films changed intensely with double doping. SEM images reveal that the surface morphology of the nanostructures changed with the kind of dopant materials due to the differences in ionic radius. Energy dispersive X-ray spectroscopy studies confirmed the presence of Cd2+, Sn4+, Pb2+, and Bi+5 in the doped films. The estimated average optical band gap energies of the CuO samples varied from 1.366 to 1.480 eV with double doping. The lowest average electrical resistivity of 1.21 × 106 Ω cm was found for the Bi0.01 Cd0.01Cu0.98O sample.

Directional solidification and characterization of InBi1−xSbx crystals

Homogeneous and stoichiometric samples of InBi1−xSbx (x = 0, 0.1) crystals have been directionally solidified to explore their suitability for optoelectronic applications. Prior to the growth, the temperature distribution of an indigenously fabricated horizontal furnace has been analysed and optimized to conduct the growth experiments on the basis of phase diagram of the material. Systematic trials have been carried out for several growth runs (48, 60 and 72 h) by maintaining an axial temperature gradient of 4, 6 and 8 °C/cm with the aid of a temperature controller mechanism. The key parameters governing the growth mechanism, composition, phase, and structure of the grown InBi1−xSbx crystals were investigated via X-ray diffraction, scanning electron and atomic force microscopy, Raman and Fourier transform infrared spectroscopy. The presence of secondary phases was ruled out and the average congruent melting points of InBi and InBi0.9Sb0.1 samples were confirmed as 109.43 and 121.13 °C respectively, by employing differential scanning calorimetric analysis. Investigations on the optical, electrical and mechanical properties of these materials were carried out. Vickers microhardness was found to increase with the Sb incorporation. The average optical band gap computed from the IR transmission spectra was found to be 0.165 eV. The results obtained promise that InBi1−xSbx crystals grown by directional solidification are favourable candidates than those grown by other melt methods.

PAH structure analysis of soot in a non-premixed flame using high-resolution transmission electron microscopy and optical band gap analysis

Soot particles formed in a system of non-premixed liquid fuel flames supported on a wick-fed, smoke point test burner (ASTM D1322-08) were characterized by in-situ visible light extinction and thermophoretically-sampled high-resolution transmission electron microscopy measurements, HRTEM. The fuels studied were heptane, toluene and their iso-volumetric mixture (H50T50), given their relevance as surrogate fuels. Extinction measurements were used to calculate the soot volume fraction, Fv, and determine the optical band gap (OBG) as a function of flame position. The OBG was derived from the near-edge absorption feature using Tauc/Davis-Mott analysis. A direct band gap (r = 0.5) was selected for this analysis assuming that the electronic properties of soot are dominated by the molecular structure of the PAHs. For the HRTEM analysis, soot samples were collected at different locations in the flame using thermophoretic sampling and a fast-insertion technique. The images were then analyzed using a ‘lattice-fringe’ algorithm, to determine important parameters such as the fringe length. Polycyclic aromatic hydrocarbon (PAH) sizes were estimated from conjugation lengths obtained from OBG measurements and fringe lengths from HRTEM measurements. Across all studied flames, the peak Fv ranged from 3.4 ppm in the heptane flame to 17.6 ppm in the toluene flame. Despite this wide range, the average OBG across the different flames only varied from 2.05 eV in the H50T50 to 2.10 eV in the toluene flames, which is consistent with molecule lengths of between 0.96 nm and 0.99 nm. Lattice fringe analysis yielded slightly lower average fringe lengths between 0.91 and 0.99 nm throughout the different flames. Results of in-situ and ex-situ characterization of soot suggests that flames of different fuel nature and sooting stage undergo the transition from chemical to physical growth at a similar size, about the size of circumpyrene.

Dependence of O2, N2 flow rate and deposition time on the structural, electrical and optical properties of SnO2 thin films deposited by atmospheric pressure chemical vapor deposition (APCVD)

In this research, SnO2 films were prepared by atmospheric pressure chemical vapor deposition technique on a glass substrate. Then, the effects of oxygen and nitrogen flow rates and deposition time on the structural, optical and electrical properties of the thin films were studied. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, atomic force microscopy, electrical resistance measurements using two-point probe technique, Hall Effect, photo-conductivity effect and optical absorption (UV–Vis). The films had uniform polycrystalline structure. The average optical band gap of the films was 3.8 eV. The results of Hall Effect showed that majority carriers were n-type and carrier concentration varies in the range of 5.84 × 1018–1.89 × 1019 cm−3. Increasing oxygen flow rate led to increasing the specific resistance, photosensitivity and Seebeck coefficient (at 350 K), and also decreasing optical band gap, mean grain size and surface roughness plus higher XRD peaks. Increasing nitrogen flow rate led to decreasing optical band gap, specific resistance, and photosensitivity and Seebeck coefficient (at 350 K). Increasing the deposition time led to an increase–decrease trend in the optical band gap, a decrease–increase trend in specific resistance and an increase in photosensitivity and Seebeck coefficient (at 350 K). The average transmittance and optical band gap of films were 82 % and 3.8 eV, respectively. Hall Effect studies revealed that the films exhibit n-type conductivity.

Structural, Electrical, and Optical Properties of the Tetragonal, Fluorite-Related Zn0.456In1.084Ge0.460O3

We report the discovery of Zn0.456In1.084Ge0.460O3, a material closely related to bixbyite. In contrast, however, the oxygen atoms in this new phase occupy 4 Wyckoff positions, which result in 4 four-coordinate, 24 six-coordinate (2 different Wyckoff positions), and 4 eight-coordinate sites as compared to the 32 six-coordinate (also 2 different Wyckoff positions) sites of bixbyite. This highly ordered material is related to fluorite, Ag6GeSO8, and γ-UO3 and is n-type with a bulk carrier concentration of 4.772 × 1014 cm–3. The reduced form displays an average room temperature conductivity of 99(11) S·cm–1 and an average optical band gap of 2.88(1) eV. These properties are comparable to those of In2O3, which is the host material for the current leading transparent conducting oxides. The structure of Zn0.456In1.084Ge0.460O3 is solved from a combined refinement of synchrotron X-ray powder diffraction and time-of-flight neutron powder diffraction and confirmed with electron diffraction. The solution is a new, ...

Electrical and optical properties of mixed phase tungsten trioxide films grown by laser pyrolysis

AbstractLaser pyrolysis was chosen to synthesize tungsten trioxide starting with tungsten ethoxide precursor. The film was found to have a thickness that varied from 205 nm to 1 µm. X‐ray diffraction and Raman spectroscopy confirmed the presence of a mixture of hexagonal and tetragonal phase WO3 in the synthesized film, as well as tungsten bronzes. It was evident that annealing greatly influenced the phases and types of structures formed, and EDXS was carried out in an attempt to quantify the tungstate bronzes to tungsten oxide. I‐V curves of the films showed n‐type semiconducting behaviour, but the mixed phase appeared to cause a similar behaviour of dopants in a semiconductor. The refractive index decreased with increasing wavelength and gave values of up to 21 at low wavelengths. The average optical band gap was found to be 3.6 eV from UV/Vis spectroscopy. Scanning Electron Microscopy (SEM) showed a mixture of nano‐ and microstructures after annealing. Nanorod structures were isolated and Pt‐contacted using FIB for possible applications such as an active sensing medium in gas sensors. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical and dielectric properties of nano BaNbO3prepared by a combustion technique

Nanocrystalline Barium niobate (<TEX>$BaNbO_3$</TEX>) has been synthesized by a novel auto-igniting combustion technique. The X-Ray diffraction studies reveals that <TEX>$BaNbO_3$</TEX> posses a cubic structure with lattice constant <TEX>$a=4.071{\AA}$</TEX>. Phase purity and structure of the nano powder are further examined using Fourier-Transform Infrared and Raman spectroscopy. The average particle size of the as prepared nano particles from the Transmission Electron Microscopy is 20 nm. The UV-Vis absorption spectra of the samples are recorded and the calculated average optical band gap is 3.74eV. The sample is sintered at an optimized temperature of <TEX>$1425^{\circ}C$</TEX> for 2h and attained nearly 98% of the theoretical density. The morphology of the sintered pellet is studied with Scanning Electron Microscopy. The dielectric constant and loss factor of a well-sintered <TEX>$BaNbO_3$</TEX> at 5MHz sample is found to be 32.92 and <TEX>$8.09{\times}10^{-4}$</TEX> respectively, at room temperature. The temperature coefficient of dielectric constant was <TEX>$-179pp/^{\circ}C$</TEX>. The high dielectric constant, low loss and negative temperature coefficient of dielectric constant makes it a potential candidate for temperature sensitive dielectric applications.

ZnO thin films prepared by a modified water-based Pechini method

ZnO films were prepared by a modified water-based Pechini method where ethanol was added to avoid some disadvantages of solely water-based precursor solution. The ratio of ethanol to water (E/W) largely influences the quality of films, and the appropriate ratio is about 1.2. FT-IR spectra show that the addition of ethanol largely promotes the esterification reaction in the dried gel. XRD results show that all films are of wurtzite structure while the annealing temperature is not higher than 700 °C. The secondary phase Zn 2SiO 4 was found in the films annealed at 800 °C because of the reaction between SiO 2 substrate and ZnO film. SEM photographs show that all films consist of nanocrystalline grains with sizes in the range of 25–82 nm, and the addition of ethanol improves the growth of grains. Transmittance spectra reveal that all films have high average transmittance of about 90% in the range of 450–800 nm except those annealed at 800 °C. The average optical band gap of films is about 3.29 eV.

Preparation and characterisation of sprayed tin sulphide films grown at different precursor concentrations

Tin sulphide films have been grown by spray pyrolysis technique at different precursor concentrations varied in the range, 0.01–0.2 M keeping other deposition parameters constant. The physical properties of the deposited films were systematically studied in relation to the precursor concentration. The studies indicated that the films grown in the precursor concentration range, 0.09–0.13 M were nearly stoichiometric with the Sn, S ratio of 1.06 and exhibited only SnS phase with a strong (1 1 1) preferred orientation that belongs to the orthorhombic crystal structure. These single-phase films showed an average electrical resistivity of 32.9 Ω cm, Hall mobility of 139 cm 2 V −1 s −1 and carrier density of ∼10 15 cm −3. These films had an average optical band gap of 1.32 eV with an absorption coefficient greater than 10 4 cm −1. These properties demonstrated that single-phase SnS films could be used as an absorber layer in the fabrication of heterojunction solar cells.

High Quality Amorphous Silicon Germanium Alloy Solar Cells Made by Hot-wire CVD at 10 Å/s

ABSTRACTHigh quality amorphous silicon germanium (a-SiGe:H) alloys have been obtained using the hot wire chemical vapor deposition (HWCVD) from a gas mixture of SiH4, GeH4, and H2 at a deposition rate of ∼10 Å/s. Solar cells in a SS/n-i-p/ITO configuration are evaluated in which the n- and i-layers are deposited by HWCVD at NREL and the microcrystalline p-layer by conventional RF glow discharge in a separate reactor by United Solar. Effects of hydrogen dilution and step-wise bandgap profile have been studied and optimized. The best cell has an average optical bandgap of 1.6 eV and incorporates multi-bandgap steps where the narrow-most bandgap is near the p-i interface. J-V characteristics are measured under AM 1.5 illumination with a λ&gt;530 nm filter. The best initial power output obtained exceeds 4 mW/cm2, which is usually used as an indicator for a good quality middle-gap cell. Double-junction cells are made on textured Ag/ZnO back reflectors. The bottom cell uses the optimized a-SiGe:H alloy cell by HWCVD, and the top cell uses an optimized a-Si:H cell near the amorphous-to-microcrystalline transition by PECVD at ∼1 Å/s. The best double-junction cell made to date exhibits an initial AM 1.5 active-area efficiency of 11.7%, and a stable efficiency after 1000 hours of one sun light soaking of 9.6%.