Band Gap Of Oxide Research Articles

Prediction of nature of band gap of perovskite oxides (ABO3) using a machine learning approach

A material's electronic properties and technological utility depend on its band gap value and the nature of band gap (i.e. direct or indirect). This nature of band gaps is notoriously difficult to compute from first principles. In fact it is computationally intense to approximate and also rather time consuming. Hence its prediction represents a challenging problem. Machine learning based approach offers a promising and computationally efficient means to address this problem. Here we predict the nature of band gap for perovskite oxides (ABO3) with elemental composition, ionic radius, ionic character and electronegativity. We do this by training machine learning models on computationally generated datasets. Knowing the nature of the band gap of the perovskite oxides (whether direct or indirect) plays a pivotal role in determining whether the perovskite can be used for photovoltaic or photocatalytic applications. A total of 5329 perovskite oxides are considered in this study. Here, we determine the correlation between the nature of band gap and the composition of the perovskite oxide. A Random Forest algorithm is used for predicting the same since it yielded higher accuracy (∼91%) compared to the other Machine Learning models. The approach suggested here can be used to predict the nature of bandgap and can also aid in novel materials discovery within the family of perovskites. This is a robust, quick, and low-cost strategy to find novel materials for light harvesting applications in particular. Also we present feature ranking as it pertains to prediction of nature of bandgap and also discuss correlation between the features. We also show feature importance graphs and SHapley Additive exPlanations (SHAP) as is relevant for prediction of nature of band gaps. Using the approach reported, NaPuO3 and VPbO3 are discovered to be good candidates for solar cell materials (direct band gap∼1.5 eV). Novel composition predictions for targeted applications are the future and our model is a step ahead in this direction.

Structural, and optical characterizations of Cu/Fe@Na2B4O7 oxide glass: For shielding and optical applications

This work has been set up to estimate how the structural, and optical properties of the copper sodium borate-based glass change when the low bandgap oxide Cu2O3 is replaced by the one of the highest bandgap of Fe2O3. Where the value of the optical band gap of Cu2O3 (1.25–1.33 eV) is one half that of Fe2O3 (2.2 eV), approximately. Using the traditional fast quenching method, three categories of solid samples have been obtained, copper-free (one sample), iron-free (one sample), and copper-iron-doped (three samples). X-ray diffraction (XRD), Transmission electron microscopes (TEM), Fourier transform infrared (FTIR), and ultraviolet-visible (UV–Vis.) spectra have been used for structural and optical characterization. XED exhibited an amorphous nature for all the prepared samples, while the FTIR showed an increase in the number of the nonbridging oxygen atoms as a result of conversion from BO4 into BO3. Also, FTIR showed that Fe- cations occupied the interstitial spaces as FeO6. The Photoluminescence PL emission showed two emission peaks due to Fe2+, 3+ and Cu2+, 3+ multi-valence cations. The metallization factor, bulk density, and the optical band gaps increased when Cu2O3 was replaced by Fe2O3, with an increase in the values of the molar volume and the linear refractive index. Shielding parameter Zeff referred that the Fe-Free sample is more suitable for shielding applications than the Cu-Free sample, at low energies.

Optical measurements and Burstein Moss effect in optical properties of Nb-doped BaSnO3 perovskite

The research for novel transparent electrodes has gained popularity due to the low abundance and the high cost of Indium. In this paper, we used first-principles calculations employing density functional theory with the exchange-correlation energy functional approximation Generalized Gradient Approximation to analyze the optical, structural, and electronic properties of Niobium doped Barium tin oxide with 12.5%, 6.25%, and 3.125% of doping. The electronic structure calculations show an indirect bandgap of Barium tin oxide. Niobium induces extrinsic donor energy states around the bottom of the conduction band giving rise to an improvement in the electrical conductivity in the system. The Fermi level shifts upward to the conduction band, a typical characteristic of an n-type semiconductor. Burstein Moss effect was found in the optical measurements for the dope systems, leading to an increase in the apparent bandgap. A diminution in the absorption coefficient in the UV–visible range of the light was presented. These characteristics suggest that Nb-doped BaSnO3 is a promising transparent conducting oxide and can be useful for optoelectronic applications.

ZnO nano-structured based devices for chemical and optical sensing applications

Zinc oxide (ZnO), a direct, wide band gap and n-type metal oxide semiconductor, is being anticipated as the next generation functional nano-material towards remarkably diversified sensing applications. ZnO and its composites have revealed a new era in the fabrication of sensors owing to their excellent opto-electronic, physicochemical, electrical properties such as low dielectric constant, plentiful Zn-O bonds, high luminous transmittance, good physicochemical stability, huge excitation binding energy, non-toxicity, biocompatibility, large surface area to volume ratio and so on. This comprehensive review summarizes the applications of ZnO nano-structures in the areas of environmental monitoring, biomedical, and optical sensing. Fundamental sensing mechanisms of the ZnO based sensors are examined to provide a better insight into the role of ZnO in each of these sensors. Wherever relevant, limitations of the existing approaches and future outlook have also been discussed.

Фотокаталитический нанореактор на основе низкоразмерных структур оксидов титана

Synthesized titanium oxide nanotubes from titanium raw materials are efficient nanoreactors for photocatalysis in comparison with macroanalogues. The dependence of the geometry of titanium oxide structures on the redistribution of the density of electronic states was studied. The presence of natural iron ligands leads to the appearance of midgap states inside the bandgap of titanium oxide.

Room‐Temperature Processed Lateral Trench‐Metal–Insulator–Semiconductor Schottky Barrier Diodes with Amorphous Gallium Oxide (a‐Ga2O3) Thin Films on Single‐Crystal Silicon <100>

This article proposes a novel design approach for the fabrication of lateral Schottky barrier diodes (SBD) using a wide bandgap oxide semiconductor on silicon. Structural and electrical properties of the fabricated device are reported and compared with published data. The metal–insulator–semiconductor (MIS) Schottky barrier is realized between the room‐temperature sputtered Al/a‐Ga2O3 on single‐crystal <100> boron‐doped silicon substrate (p‐type). The device fabrication process is implemented entirely at room temperature. The proposed trench diode yields an ideality factor of 1.65 and a rectification ratio of ≈1 × 106 at ±5.0 V. The extracted specific ON resistance is 78 mΩ cm2, and the breakdown voltage is not observed for 180 V for a 200‐nm‐thin layer of a‐Ga2O3. Due to such low‐temperature process, simple fabrication steps, and notably high Baliga's figure‐of‐merit (BFOM), the proposed diode is, therefore, promising for power electronics applications.

Quick screening stable double perovskite oxides for photovoltaic applications by machine learning

Rapid discovery of functional materials remains a public challenge because traditional trial and error methods are general inefficient, especially when thousands of candidates are treated. Machine learning (ML) is essential to deal with a large number of data sets, predict unknown material properties and reveal the relationship between structures and properties. Herein, in order to find double perovskite oxide (DPO) materials for solar cells, we design a framework and develop a robust ML model to predict band gaps of DPOs based on a dataset containing band gap values of 236 experimentally studied perovskite oxides. Successfully, 236 promising stable ferroelectric photovoltaic DPOs with suitable band gaps are screened out from 4,058,905 candidate compositions. The developed ML model provides an excellent predictive performance (R2:0.932,RMSE:0.196eV) based on only three component features. Moreover, our statistical graph confirms the previous studies that tuning the electronegativity difference between oxygen and B site cation via doping foreign cations could change the band gaps of perovskite oxides. These findings show that ML is very promising not only for predicting the properties, but also for investigation on the physical law.

The characterization of amorphous AZO-n/Si-p hetrojunction diode for solar cell application

The aim of the present study is to verify the effect of annealing temperature variation on zinc oxide doped with aluminum thin films deposited on p-type silicon substrates. Here, all thin films were annealed in nitrogen environment and its structural, electrical, and optical characterizations were investigated. The results of X ray diffraction patterns showed the amorphous structure of zinc oxide doped with aluminum thin films. Field Emission Scanning Electron Microscopes images illustrated the increase of grain size by increasing annealing temperature up to 500 °C. The reflectance analysis showed that for this annealing temperature, that the energy band gap of zinc oxide doped with aluminum thin film was moved to higher energy level. The electrical properties were investigated by Current–Voltage measurement carried out in the light at room temperatures. The short circuit current, ideality factor, saturation current, and open circuit voltage of the zinc oxide doped with aluminum on silicon heterojunction strongly depended on annealing conditions due to charge carrier trapping and density of defect on interface. By considering reverse current and forward current, the ratio of forward current to reverse current had the maximum value at 1 V which was belonged to n type zinc oxide doped with aluminum on p type silicon heterojunction at 500 °C annealing temperature.

Ga2O3 and Related Ultra-Wide Bandgap Power Semiconductor Oxides: New Energy Electronics Solutions for CO2 Emission Mitigation.

Currently, a significant portion (~50%) of global warming emissions, such as CO2, are related to energy production and transportation. As most energy usage will be electrical (as well as transportation), the efficient management of electrical power is thus central to achieve the XXI century climatic goals. Ultra-wide bandgap (UWBG) semiconductors are at the very frontier of electronics for energy management or energy electronics. A new generation of UWBG semiconductors will open new territories for higher power rated power electronics and solar-blind deeper ultraviolet optoelectronics. Gallium oxide—Ga2O3 (4.5–4.9 eV), has recently emerged pushing the limits set by more conventional WBG (~3 eV) materials, such as SiC and GaN, as well as for transparent conducting oxides (TCO), such asIn2O3, ZnO and SnO2, to name a few. Indeed, Ga2O3 as the first oxide used as a semiconductor for power electronics, has sparked an interest in oxide semiconductors to be investigated (oxides represent the largest family of UWBG). Among these new power electronic materials, AlxGa1-xO3 may provide high-power heterostructure electronic and photonic devices at bandgaps far beyond all materials available today (~8 eV) or ZnGa2O4 (~5 eV), enabling spinel bipolar energy electronics for the first time ever. Here, we review the state-of-the-art and prospects of some ultra-wide bandgap oxide semiconductor arising technologies as promising innovative material solutions towards a sustainable zero emission society.

Pathways for Electron Transfer at MgO-Water Interfaces from Ab Initio Molecular Dynamics.

The nature of electron transfer across metal oxide-water interfaces depends significantly on the band gap of the oxide and its band edge energies relative to the potentials of relevant aqueous redox couples. Here we focus on the water interface with MgO, a prototypical wide band gap oxide whose conduction band edge is close in energy to that of water. We investigate the behavior of an excess electron at and out of equilibrium near the interface using ab initio molecular dynamics based on hybrid density functional theory. Our simulations show that under equilibrium conditions the excess electron (donated by an Al impurity in MgO) localizes to a midgap defect state comparable in energy and shape to a hydrated electron in bulk water. To characterize the electron transfer from the conduction band of MgO to interfacial product states, we dope near-equilibrium configurations of the pristine MgO-water system with Al and run short trajectories of these instantaneously out-of-equilibrium systems. We observe two distinct products associated with the excess electron: a surface-localized electron (esurf-) and an aqueous hydrogen radical (H•). The H• pathway exhibits a much higher activation barrier despite being more exoergic, making esurf- the kinetic product. Our characterization of the pathways on the basis of Marcus theory is consistent with the poor observed utility of MgO for water radiolysis. Moreover, we anticipate that the computational framework employed here will be broadly applicable to assessing electron transfer mechanisms at aqueous, photocatalytic interfaces.

High-sensitivity measurements of the nonlinear absorption coefficient of wide bandgap oxide thin films with the Z-scan method

The nonlinear response of wide bandgap oxide thin films gradually emerges and attracts attention with the development of an ultra-short and ultra-intense laser. In Z-scan technique, due to the extremely lower nonlinear response of thin film compared with the common substrate, it isn’t easy to measure the multiphoton absorption coefficient of wide bandgap oxide thin films. In this study, a method is proposed to suppress the substrate impact and improve the thin film measurement sensitivity. To make the thin film nonlinear intensity dominate the total intensity, including unwanted substrate impact, material and thickness of the substrate are analyzed. Considering the nonlinear effects of different substrates and the adhesion between the substrate and the thin film, 50 μm MgF2 and quartz glass are selected as the substrate for deposition. The nonlinear intensity of substrate is suppressed to at least 80% of the whole element or can even be ignored so that the normalized transmittance of the thin film can be obtained effectively. The two-photon and three-photon absorption coefficients of HfO2, Al2O3, and SiO2 thin film are measured at different wavelengths. The nonlinear absorption response measurements of wide bandgap oxide thin films can advance the design and fabrication of low-loss photonic devices in ultra-fast lasers.

Effects of the Phase, Morphology, Band Gap and Hydrogen Evolution of Vanadium Oxide with Reduced Graphene Oxide

Effects of the Phase, Morphology, Band Gap and Hydrogen Evolution of Vanadium Oxide with Reduced Graphene Oxide

Anti-corrosion MgO nanoparticle-equipped graphene oxide nanosheet for efficient room-temperature H2S removal

Enhanced room-temperature H2S removal on homogenized metal oxide nanoparticle-loaded 2D carbon nanosheets is reported. Band gap of metal oxides and degree of their bands mixing with H2S orbitals are crucial for anti-corrosion oxidation of H2S.

Synthesis and photocatalytic activity of Ni doped SnO2 nanoparticles for removal of toxic industrial dyes

Metal oxide semiconducting material like SnO2 has novel features like wide band gap (3.6 eV) and large exciton binding energy (130 meV) which ensure its promising optoelectronic applications. In the present work, we have carried out a detailed study on the above materials i.e. SnO2 and Sn1-xNixO2 which were synthesized using sol–gel method with stannous chloride, nickel nitrate hexahydrate, ammonium hydroxide and isopropyl alcohol as the starting materials. XRD study confirms that SnO2 and Ni-SnO2 samples are of tetragonal structure with crystal size 32 nm and 28 nm respectively as estimated from Scherrer formula. The optical band gap of pure tin oxide is found to be 3.73 eV from UV–Vis absorption measurements which shifts to 3.70 eV for Ni-SnO2. The PL spectra show several emission bands at 418 nm, 437 nm, 463 nm, 487 nm and 530 nm in the visible region. These bands are ascribed to the defect emissions arising due to oxygen vacancies. With Ni doping, the intensity of these bands increases which may be due to the increase in the density of the above defects. The photocatalytic degradation of Congo red (CR) dye was studied by irradiating UV–Vis light source and found the degradation efficiency of 83% for Ni-SnO2 sample which was 74% for the pristine sample. Ni doping helps to enhance the light absorption ability of SnO2 leading to better degradation efficiency.

Tuning the bandgap and absorption behaviour of the newly-fabricated Ultrahigh Molecular weight Polyethylene Oxide- Polyvinyl Alcohol/ Graphene Oxide hybrid nanocomposites

Graphene nanosheets are promising nanofillers to the tunable structure, properties of materials, and optical bandgap. This search focuses on investigating the new nanocomposites of Ultra-high molecular weight polyethylene oxide (UHMWPEO) with different loading ratios of polyvinyl alcohol (PVA) reinforced with graphene oxide (GO) by applying the modified solution-sonication-casting method. Fourier-transform infrared spectroscopy (FTIR) shows strong interfacial interaction between the blended polymers and GO nanosheets in the nanocomposites. X-Ray diffraction (XRD) reveals a significant shifting in the PEO and reduction in the crystallinity. Optical microscopy (OM) images exhibit fine homogeneity of the polymer in the matrix with excellent dispersal of GO in nanocomposites as supported by scanning electron microscopy (SEM). Attractively, the samples with a higher ratio of UHMWPEO exhibit better optical behavior, and great improvements were presented after the contribution of GO. UV-visible spectroscopy has characterized the absorption, absorption coefficient, real and imaginary, bandgap, and other parameters. The allowed bandgap was significantly enhanced by reducing up to 80%, whereas the forbidden bandgap was improved by up to 160% of the nanocomposites. Additionally, nanocomposites exhibited significant adsorption of radiation-ray, especially after the contribution of GO. The findings are promising as various applications could come to the fore: radiation protection, spectroscopy devices, and other applications.

First principle investigation of Niobium (Nb) doped MgO

This paper presents the structural, electronic, and magnetic properties of pure and Nb doped MgO, in its zinc blende and rock salt phase for small concentration. In our work, the full potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method, implemented in the WIEN2K simulation package and the Local Density Approximation (LDA) were employed. The results obtained show that pure MgO has a gap of 4.97 eV and Mg0.875Nb0.125O has a metallic character. The modifications in the band gap and magnetic properties of magnesium oxide mainly originate from the 4 d-orbitals of the Nb atoms. In comparison with Mg and O atoms (0.007 and 0.054), the magnetic data shows that the Niobium magnetic moment (1.3528 µβ) is the dominant one. As a result, the total magnetic moment of our component is equals to 2.9091 µβ. We consider that MgO and Mg0.875Nb0.125O could be promising candidates for electronic systems and related fields.

Highly Transparent Bidirectional Transparent Photovoltaics for On-Site Power Generators.

If we can transparently produce energy, we may apply invisible power generators to residential architectures to supply energy without losing visibility. Transparent photovoltaic cells (TPVs) are a transparent solar technology that transmits visible light while absorbing the invisible short wavelengths, such as ultraviolet. Installing TPVs in buildings provides an on-site energy supply platform as a window-embedded power generator or color-matched solar cell installation on a building surface. The record-high power generation (10.82 mW) and photocurrent value (68.25 mA) were achieved from large-scale TPVs (25 cm2). The metal oxide heterojunction is the fundamental TPV structure. The high-performance TPVs were achieved by adopting a thin Si film between ZnO and NiO as a functional light-absorbing layer. Based on the large energy band gap of metal oxides, TPVs have a clear transmittance (43%) and good color coordinates, which ensure degrees of freedom to adopt TPV power generators in various colored structures or transparent power windows. The bidirectional feature of TPVs is ultimately desirable to maximize light utilization. TPVs can generate electric power from sunlight during the day and can also work from artificial light sources at night. In the near future, humans will acquire electric power without losing visibility with on-site energy supply platforms.

Ferroelectric structural transition in hafnium oxide induced by charged oxygen vacancies

The discovery of ferroelectric ${\mathrm{HfO}}_{2}$ in thin films and more recently in bulk is an important breakthrough because of its silicon compatibility and unexpectedly persistent polarization at low dimensions, but the origin of its ferroelectricity is still under debate. The stabilization of the metastable polar orthorhombic phase was often considered as the cumulative result of various extrinsic factors such as stress, grain boundary, and oxygen vacancies as well as phase transition kinetics during the annealing process. We propose a mechanism to stabilize the polar orthorhombic phase over the nonpolar monoclinic phase that is the bulk ground state. Our first-principles calculations demonstrate that the doubly positively charged oxygen vacancy, an overlooked defect but commonly presenting in binary oxides, is critical for the stabilization of the ferroelectric phase. The charge state of the oxygen vacancy serves as a degree of freedom to control the thermodynamic stability of competing phases of wide band gap oxides.

Green Synthesis of Ni-Cu-Zn Based Nanosized Metal Oxides for Photocatalytic and Sensor Applications

The preparation, characterization, and application of Nickel oxide (NiO)–Copper oxide (CuO)–Zinc oxide (ZnO) transition nanometal oxides have significantly enhanced their tunable properties for superior multifunctional performances compared with well-known metal oxides. NiO–CuO–ZnO nano transition metal oxides were synthesized by a simple eco-friendly solution combustion method. X-ray diffraction studies revealed distinct phases such as monoclinic, cubic, and hexagonal wurtzite for CuO, NiO, and ZnO, respectively, with NiO having the highest composition. The particle sizes were found to be in the range between 25 and 60 nm, as determined by powder X-ray diffraction. The energy bandgap values were found to be 1.63, 3.4, and 4.2 eV for CuO, ZnO, and NiO, respectively. All metal oxides exhibited a moderate degradation efficiency for AR88 dye. The results of ultraviolet–visible absorption spectra helped identify the bandgap of metal oxides and a suitable wavelength for photocatalytic irradiation. Finally, we concluded that the electrochemical studies revealed that the synthesized materials are well suitable for sensor applications.

A photo-Fenton graphene oxide membrane with improved perm-selectivity and self-cleaning ability for efficient dye removal under visible light irradiation

Reactive membranes (RMs) have attracted worldwide attention for wastewater purification and treatment due to their unique characteristics. In this study, through manipulating the band gap of graphene oxide (GO), a photo-Fenton GO membrane with enlarged inner channels, great selectivity and permeability as well as excellent self-cleaning ability was prepared for the first time via vacuum filtration. Notably, increased permeability (~130.0 L m−2·h−1 bar−1) and enhanced dye removal efficiency (≥ 99%) of the GO membrane are observed in the synergistic photo-Fenton/filtration system. Additionally, the GO membrane maintained high flux and superior rejection properties after 10 repetitions, indicating its desirable stability and anti-fouling capabilities in photo-Fenton/filtration systems. The GO membrane can also be used as a photocatalyst and shows great removal efficiency for MB (90.1%) in the photo-Fenton system. Besides, the mechanism of the self-cleaning property of the GO membrane is explored and it is found that the highly reactive •OH and •O2− species contribute to membrane anti-fouling behavior. Based on our results, the GO membrane has potential for use as a self-cleaning membrane for advanced wastewater purification.