Forbidden Energy Band Gap Research Articles

Heterogeneous single-atom doped 2D-layered graphitic carbon nitride electrocatalyst for oxygen evolution reaction and removal of toxic heavy metal ion Cr from Wastewater

The 2D-layered graphitic carbon nitride (gCN) has been a well-known electro-photocatalyst to have wide applications in energy storage, energy evolution, and environmental remediation. The physicochemical properties of the bulk, O-doped (O-gCN), and hetero atom are compared, which is further utilized as an electrocatalyst for the oxygen evolution reactions (OER) process. The prepared nanosheets exhibited a layered structure with a uniform porous nature. Moreover, the forbidden energy bandgap (Eg) of 1.7 eV is observed, which is lower than bulk and O-doped gCN. The heteroatom BO-gCN nanosheets have higher OER activity compared to other samples and benchmark catalysts. The BO-gCN nanosheets exhibit a lower overpotential and Tafel potential of 240 mV and 207 mV/dec, respectively. Effects of various operating parameters such as photocatalyst dosage and solution pH are investigated. The photocatalytic removal results exhibited BO-gCN can be a robust and effective catalyst for the removal of Cr ions in environmental remediation.

Synthesis, characterization, and tailoring variations in the linear optical of erbium‐ions doped (PVA/PVP) polymeric composites for optical devices: Improvement of the dielectric characteristics

AbstractThe simple solution casting method was utilized for preparing composite films (PVA‐30 wt% PVP) incorporated with various content of erbium ions (Er3+) (0.11, 0.37, 1.85, 3.7, 9.25, and 18.5) wt%. The composite films' properties were investigated using XRD, UV–Vis, and dielectric spectrometers. The XRD patterns showed a noticeable decline in structural elements, including crystallinity level. The transmittances of the investigated samples decrease as Er3+ increases. Studies on UV–Vis absorption have revealed that the UV–Vis absorption spectra are shifting to the higher wavelengths, causing a decrease in the optical energy bandgap values from 4.66 to 3.48 eV for an indirect transition and from 5 to 4.84 eV for a direct transition, which suggests that the filler interacts with the blend matrix. As the number of localized states in the forbidden energy bandgap rises, it has been shown that with increasing Er3+‐ the estimated Urbach's energy increases from 1.95 to 32 meV. The addition of erbium ions raises the refractive index of the blend film. The optical limits of the samples are investigated using a He‐Ne laser beam with a wavelength of 632.8 nm and a solid‐state green diode laser beam with a wavelength of 532 nm. The prospect of greater charge carrier concentration and mobility was confirmed by increased AC conductivity with increasing frequency. Dielectric permittivity and dielectric loss tangent were utilized to analyze dielectric behavior. The analysis of the electric modulus (M′ and M′′) of as‐prepared samples has been completed. These findings are anticipated to notably impact a broad spectrum of applications, including organic semiconductors, optoelectronic devices, polymer solar cells, and polymer waveguides.

AlInN/AlN HEMT’in Detaylı Optik Özellikleri

In this study, the optical properties of AlInN/AlN high electron mobility transistor (HEMT) structure, grown on c-oriented sapphire with Metal-Organic Chemical Vapor Deposition (MOCVD) technique, being investigated. Optical characterization is made Kubelka- Munk method. Transmittance, absorbance, and reflectance are investigated in detail. Also, the Kubelka-Munk theory is employed to determine the forbidden energy band gap of InN by using special functions. The energy band gap obtained by this method was compared.

Investigation of Cobalt Substitution on the Structural, Optical Band Gap, and Photocatalytic Dye Degradation Properties of Spray Deposited SnO2Thin Films

Pure and cobalt substituted tin oxide thin films are successfully formed on a glass substrate using the simple spray pyrolysis technique. XRD patterns reveal the polycrystalline nature of the samples with tetragonal rutile structure. The shift in X-ray diffraction peak to a higher 2θ value and its subsequent contraction of the SnO2 rutile lattice along the c-axis manifests the infusion of the guest cobalt ions. Crystallite size and microstrain values are found to vary with cobalt substitution. SEM analysis shows the uniform dispersion of the nanoparticles in the prepared thin films. The optical band gap values are found to narrow down with cobalt substitution from 4.04 eV–3.93 eV. Photoluminescence study hints at the presence of intermediate states within the forbidden energy band gap of SnO2. Photocatalytic dye degradation of Methylene blue (MB) highlights the role of cobalt with a high photocatalytic activity of 86 % compared to other investigated thin films.

Insight into structural, electronic, and chemical bonding properties of PEO-PEG-LiI polymer electrolyte: A first-principles investigation

Quantum chemistry-based codes and methods provide valuable computational tools to study the atomic and molecular structure of any system. This paper provides insights into the electronic and structural properties of polyethylene oxide (PEO) and polyethylene glycol (PEG) based solid polymer electrolyte incorporated with lithium iodide as ion-conducting species using first principle method. PEO shows insulator characteristics with a broad bandgap of 5.2 eV which decreased significantly to 3.19 eV in PEO-PEG-LiI. The wide forbidden energy band gap of PEO-PEG-LiI concludes that conductivity in polymer electrolytes is predominantly ionic rather than electronic. The presence of hydrogen bonding between PEG and PEO shows their amazing compatibility. Hirschfield population analysis (HPA) quantify the interactions involved within the structure and explains the interaction of Li-ion with ether group of PEO. Overlapping of wavefunctions of C, O and H atoms in polymers proves the existence of partial ionic and partial covalent bonding among them.

Synthesis and optical properties of Er/Yb/Ag modified bismuth – tellurite based glasses

The Er2O3-Yb2O3 codoped TeO2-Bi2O3-Na2O-Glasses along with addition of AgNO3 in basic compositions glasses have been prepared by traditional melt quench method. Investigation of the synthesized glasses is done by DSC, XRD, and UV-Vis. spectroscopy. The glass transition temperature is observed by differential scanning calorimetry. The amorphous nature of the synthesized glasses is confirmed by X-ray diffractogram taken at room temperature. The fluid displacement method on the basis of the Archimedes principle was used to calculated density of prepared samples. The UV-Visible absorption characterizations have been done in the range of 200–1100 nm of synthesized glasses having different percentage of doping of Er2O/Yb2O3/AgNO3. The study of optical properties of the glasses such as the absorption coefficient (α), cut-off wavelength, forbidden energy band gap (Eopt), refractive index and Urbach Energy (Eu) have been done. The effect of Er2O/Yb2O3/AgNO3 on optical properties is observed.

Synthesis and optical properties of ternary TeO2-Bi2O3-Na2O glass system

The glasses with composition TBN: 80TeO2-10Bi2O3-10Na2O in mol% have been prepared by using a conventional melt-quench and pressing technique. Investigation of the prepared sample is done by XRD, EDS and UV–Visible spectroscopy. The glassy nature of prepared sample is confirmed by X-ray diffraction at room temperature and composition is verified by EDS. The density was calculated using the fluid displacement method on the basis of the Archimedes principle. UV–Visible absorption measurements have been taken in the range of 200–1100 nm of TBN glasses having different thickness for the study of optical properties. For the evaluation of optical properties of the samples such as the absorption coefficient (α), cut-off wavelength, forbidden energy band gap (Eopt), refractive index and Urbach Energy (Eu) have been done. The effect of thickness on optical properties is observed.

DFT Study of Effect of Hydrostatic Pressure on Structural, Electronic and Magnetic Properties of In0.875Cr0.125P

In this paper, the effect of hydrostatic pressure on structural, electronic and magnetic properties of In0.875Cr0.125P Diluted Magnetic Semiconductor (DMS) in Zinc Blende (B3) phase has been studied at 0 GPa to 26 GPa. The calculations have been performed using Density Functional Theory as implemented in the Spanish Initiative for Electronic Simulations with Thousands of Atoms code (SIESTA) using LDA+U (U=3) as exchange-correlation (XC) potential. The study of electronic structures and magnetic properties show that In0.875Cr0.125P is half metallic in nature and this behaviour is maintained at given pressure range. It is found that forbidden energy band gap increases with increase in pressure due to shifting of valence band maximum and conduction band minimum of energy levels. The investigation of structural properties shows that lattice constant and volume of compound decreases along with increase in total energy of compound with applied pressure. The study of induced local magnetic moment values show their continuous increase on non-magnetic indium and phosphorus atoms with increasing pressure.

Swanepoel method for AlInN/AlN HEMTs

In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriented sapphire substrate using metal organic chemical vapor deposition method. Optical properties of the structure are investigated by photoluminescence (PL) and ultraviolet (UV–Vis.) spectras. According to PL results, direct bandgap of AlN is determined around 2.80 eV. In UV–Vis. spectra it is seen that conduction of AlInN layer starts at 360 nm. Swanepoel envelope method is applied on transmission spectra and some optical properties such as refractive index (n), film thickness (t), absorption coefficient (α), and extinction coefficient (k) are determined. Forbidden energy bandgap is determined again from Tau method and it is compared with the value gained from PL spectra. This study is a rare one that presents optical properties of HEMTs using Swanepoel and Tau methods. In addition to this, it helps estimating how optical properties of HEMTs effect electrical properties.

Study of effect of hydrostatic pressure on structural, electronic and magnetic properties of In0.75Mn0.25P using density functional theory

In this paper, the investigation of effect of hydrostatic pressure on the structural, electronic and magnetic properties of In0.75Mn0.25P Diluted Magnetic Semiconductor in Zinc Blende (B3) phase at 0 GPa–26 GPa pressure range is done using first principal calculations as implemented in Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code.The theoretical investigation of electronic and magnetic properties of this compound represents that the compound is half-metallic ferromagnet and show 100% spin polarization at different values of pressure. It is found that forbidden energy band gap increases with increase in pressure as spin polarized band structures experience changes with applied pressure. The calculated results show that lattice constant and volume of compound decreases along-with increase in induced local magnetic moments values of non-magnetic indium and phosphorus atoms with applied pressure.

Pseudodielectric Dispersion in As2Se3 Thin Films

Herein, X‐ray diffraction, energy dispersive X‐ray spectroscopy, and spectral ellipsometry techniques are used to investigate the structural, pseudo‐optical, and pseudodielectric properties of arsenic selenide thin films. The stoichiometric films which are prepared by the thermal evaporation technique are found to prefer the amorphous nature of growth. While the pseudoabsorption coefficient spectra display strong absorption bands at 1.84, 1.81, 1.41, and 1.13 eV, the preferred pseudo‐optical transitions happen within a direct forbidden energy bandgap of 1.80 eV. In addition, the real part of the pseudodielectric spectra displays three strong resonance peaks at critical energy values of 2.33, 1.90, and 1.29 eV. Modeling of the imaginary part of the pseudodielectric constant spectra in accordance with the Drude–Lorentz approach results in the existence of six linear oscillators. The response of arsenic selenide to elliptically polarized light signals shows that the films exhibit drift mobility, free electron concentration, and plasmon frequency values in the ranges of 0.21–43.96 cm2 V−1s−1, 1.90–58.0 × 1019 cm−3, and 5.8–32.0 GHz, respectively. The optical conductivity parameters for As2Se3 film nominate it as a promising candidate for the fabrication of tunneling diodes suitable for microwaves filtering up to 32.0 GHz and as thin‐film transistors.

Ab initio study of Li2 CaTa2 O7 compound: electronic and optical properties forthree phases

The Li2 CaTa2 O7 compound belongs to the Ruddlesden-Popper family of layered perovskites. First principle approximation was used to investigate the electronic band structure and optical properties of the compound for three phases. Independent of the studied compound's structural type, Li2 CaTa2 O7 has semiconductor behavior and direct transition. In addition, the forbidden energy band gap of the compound decreases with rising temperature, as expected. Furthermore, the 3d orbital of Ca contributes to the conduction band due to the crystal field effect. Moreover, the optical response of the chosen axes of the compound to incoming electromagnetic rays varies with phase transition.

First principle study of 0.75AgI:0.25AgCl: A density functional approach

The first principles calculations based on norm-conserving pseudo potentials and density functional theory are performed for zincblende structured new host 0.75AgI:0.25AgCl. For comparison point of view zincblende structured β-AgI is considered. The structural analysis provides the higher cationic concentration in new host. Density of state analysis explains a weak p-d hybridization in β-AgI and strong in new host. There is decrease in forbidden energy band gap by 0.05eV and hence large ionic concentration and conductivity is found in new host.

On the studies of capacitance-voltage-temperature and deep level characteristics of an Au/p-GaTe Schottky diode

This paper deals with the capacitive properties of an unintentionally doped Au/p-GaTe/In Schottky junction. The capacitance-voltage (C-V) measurements are realized at 120–300 K temperature range and also, the deep level characteristics at bulk of p-GaTe are investigated by thermally stimulated capacitance measurement technique (TSC). The C-V measurements yield the C−2 − Vr curves with fairly high correlation at high temperatures. However, the anomaly decreasing of the capacitance values with the temperature is attributed to the ionization of the deep levels which are electrically active at closely 100–270 K temperature ranges. In addition, due to the effect on the measured capacitance curves of the series resistance, the true capacitance characteristics are obtained. The values of barrier height are calculated to be 0.639 eV at 300 K and 1.556 eV at 140 K and it does not follow to the variation of forbidden energy band gap of p-GaTe. In addition, it is seen that the barrier height values from true capacitance curves are the more resolute from the barrier heights of measured capacitance curves. Moreover, the rapid increasing of the barrier height values at low temperatures is only attributed to the effect of the deep levels.

Nanometric structures of highly oriented zinc blende ZnO thin films

Zinc oxide thin films in cubic zinc blende (ZB) crystalline phase on glass substrates by means of the spray pyrolysis technique were deposited. X-ray diffraction spectra revealed that the ZB–ZnO films grow highly oriented along the (004) crystalline direction with no epitaxial influence. Optical absorbance measurements indicated that the forbidden energy band gap is 3.18±0.02eV in accordance with reports on the experimental value of the band gap of ZB–ZnO structures. Atomic Force Microscopy images exhibit nanometric structures of the surface with the approximated aspect of circular nanodiscs. The thickness of the thin films is 350±20nm, which suggests a good stability of the films.

Dielectric dispersion and energy band gap of Bi1.5−xSmxZn0.92Nb1.5O6.92 solid solution

The optical transmittance and reflectance spectra of samarium doped bismuth–zinc–niobium-oxide (BZN) pyrochlore ceramics are investigated in the wavelength range of 200–1050nm (200–1500THz). The Sm content in the Bi1.5−xSmxZn0.92Nb1.5O6.92 solid solution significantly alters the optical properties. Therefore, increasing the Sm doping ratio from x=0.10 to x=0.13 decreased the indirect forbidden energy band gap from 3.60 to 3.05eV. In addition, above 350THz, increasing the Sm content decreases the dielectric constant values and alters the dielectric dispersion parameters. The dielectric spectra which were evaluated in the frequency range of 200–1500THz reflected a sharp decrease in the dielectric constant with increasing frequency down to 358THz. The spectra reflected a resonance peak at this frequency. Such resonance spectrum is promising for technological applications as it is close to the illumination of 870nm IR lasers that are used in optical communications. The calculated oscillator (Eo) and dispersion (Ed) energies near that critical range (375–425THz) reflected an increase in both Eo and Ed with increasing Sm content.

Influence of internal stress on the optical properties of CdS:Cu nanoparticles

Nanocrystalline CdS:Cu thin films were prepared by chemical synthesis on glass at 70°C. X-ray diffraction (XRD), optical absorption (OA) and Raman measurements were carried out in order to characterize the material. From the XRD patterns it is concluded that grains of Cu-doped CdS films grow mainly in the zincblende cubic phase. The average radius (R), calculated by employing the Scherrer’s formula, is located in the range 2.7–8.7nm. The forbidden energy band gap (Eg) was estimated from the optical absorbance spectra and by means of the maximum of their first derivative. As effect of the doping the unit cell volume of CdS:Cu undergoes a shrinkage due to the compressive stress introduced by Cu atoms. Two effects overlap to change the Eg values: (a) the quantum confinement and (b) the internal stress (IS). IS is that which does not come from forces out to the volume of the material like the stress produced by substrates. Raman spectra indicate that the stress decreases when R decreases. On the other hand, the (111) interplanar distance and the unit cell volume (UCV) increases when R decreases, following the relationship UCV∝R−1. In the CdS:Cu stressed lattices, UCV increases when R decreases because in smaller particles the relaxation of the induced IS is more effective than in larger particles.

Forbidden energy band gap in diluted a-Ge1 − xSix:N films

By means of electron gun evaporation Ge1−xSix:N thin films, in the entire range 0≤x≤1, were prepared on Si (100) and glass substrates. The initial vacuum reached was 6.6×10−4Pa, then a pressure of 2.7×10−2Pa of high purity N2 was introduced into the chamber. The deposition time was 4min. Crucible-substrate distance was 18cm. X-ray diffraction patterns indicate that all the films were amorphous (a-Ge1−xSix:N). The nitrogen concentration was of the order of 1at% for all the films. From optical absorption spectra data and by using the Tauc method the energy band gap (Eg) was calculated. The Raman spectra only reveal the presence of SiSi, GeGe, and SiGe bonds. Nevertheless, infrared spectra demonstrate the existence of SiN and GeN bonds. The forbidden energy band gap (Eg) as a function of x in the entire range 0≤x≤1 shows two well defined regions: 0≤x≤0.67 and 0.67≤x≤1, due to two different behaviors of the band gap, where for x>0.67 exists an abruptly change of Eg(x). In this case Eg(x) versus x is different to the variation of Eg in a-Ge1−xSix and a-Ge1−xSix:H. This fact can be related to the formation of Ge3N4 and GeSi2N4 when x≤0.67, and to the formation of Si3N4 and GeSi2N4 for 0.67≤x.

Trap-assisted conduction in Pt-gated Gd2O3/Si capacitors

The barrier height at the Pt/Gd2O3 interface is determined by current–voltage measurements. Current conduction is found to be governed by carrier injection from the electrode, with a barrier height of 0.6 ± 0.1 eV. This value, which was verified by the method suggested by Zafar et al. [Appl. Phys. Lett. 80, 4858 (2002)], is much smaller than the difference between the metal work function (5.6 eV) and the oxide electron affinity (1.95–2.05 eV). As Fermi-level pinning is not dominant at Pt/Gd2O3 interfaces, it is proposed that electrons are injected into a defect-related energy band in the oxide. The existence of such a defect, as well as its position in the oxide forbidden energy bandgap, agrees with results obtained by magnetic resonance measurements.

Sonochemical growth of antimony sulfoiodide in multiwalled carbon nanotube

This paper presents for the first time the nanocrystalline, semiconducting ferroelectrics antimony sulfoiodide (SbSI) grown in multiwalled carbon nanotubes (CNTs). It was prepared sonochemically using elemental Sb, S and I in the presence of methanol under ultrasonic irradiation (35 kHz, 2.6 W/cm 2) at 323 K for 3 h. The CNTs filled with SbSI were characterized by using techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction, and optical diffuse reflection spectroscopy. These investigations exhibit that the SbSI filling the CNTs is single crystalline in nature and in the form of nanowires. It has indirect forbidden energy band gap E gIf = 1.871(1) eV.