Wide Band Gap Energy Research Articles

One-step electrodeposition of ZnO/graphene composites with enhanced capability for photocatalytic degradation of organic dyes.

Zinc oxide is a popular semiconductor used in catalysts due to its wide bandgap and high exciton binding energy. However, the photocatalytic performance of ZnO was compromised by its insufficient electron-hole separation efficiency and electron transfer rate. Herein, ZnO-reduced graphene oxide (rGO) composite solid catalyst was synthesized by one-step electrodeposition method on FTO substrate using lithium perchlorate (LiClO4) as the supporting electrolyte. Scanning electron microscopy, Raman, Fourier Transform Infrared, and XRD characterizations confirmed the deposition of ZnO and the reduction of graphene oxide Owing to the cooperative effect between rGO and ZnO, the as-prepared ZnO-rGO composites show much enhanced photocatalytic degradation ability compared with pure ZnO nanorods. By optimizing the conditions of electrodeposition of ZnO-rGO composites, the degradation rate of methylene blue can reach 99.1% within 120min. Thus, the simple preparation and the excellent performance could endow the ZnO-rGO composites with promising application in practical dye-polluted water treatment.

Precursor Molarity Influence on Sprayed Mo-doped ZnO Films for solar cells

Objectives: Current research focuses on the role of precursor molarity effect on sprayed Mo-doped ZnO films and their suitability as window layers in solar cells. Methods: Molybdenum (Mo) doped zinc oxide (MZO) thin films were deposited by the technique of spray pyrolysis, varying the Zn molarity in the range, of 0.01 M to 0.20 M at a constant substrate temperature of 400 ◦C. The Mo doping concentration was constant at 2 at. %. Findings: The XPS studies witnessed the presence of Mo and Zn in +6 and +2 state respectively. The XRD pattern showed both (111) and (002) as strong peaks, confirming the hexagonal wurtzite crystal structure. The optical investigations showed that the MZO films with Zn molarity 0.10 M exhibited high optical transmittance having a wide energy band gap. Films with zinc molarity of 0.10 M showed low resistivity and high mobility. The prepared CTS/MZO hetero junction solar cells performance was studied by evaluating parameters such as open circuit voltage (Voc) of 0.14 V, short circuit current density (Jsc) of 6.46 mA cm-2, a fill factor (FF) of 0.27, and a conversion efficiency of 0.25 %. Novelty: Studies on the physical properties of Mo:ZnO layers such as Ritveld refinement analysis and Haze were reported first time. CTS/MZO hetero junction solar cells have not yet been published. The observed results are analogous to improve the efficiency of solar cells using environmentally benign materials. Keywords: Spray pyrolysis; Thin films; XRD; Optical properties; Haze; Hall measurements

PbBi(SeO3)2F and Pb2Bi(SeO3)2Cl3: Coexistence of Three Kinds of Stereochemically Active Lone-Pair Cations Exhibiting Excellent Nonlinear Optical Properties.

Stereochemically active lone-pair (SCALP) cations are one attractive type of nonlinear optical (NLO)-active units because of their large microcosmic polarizability and anisotropy. Currently, the single and/or dual lone-pair cation-based noncentrosymmetric (NCS) oxides have been extensively investigated and verified to be one class of outstanding NLO materials. From the perspective of function optimization, the integration of three kinds of SCALP cations into one crystal may synergistically improve the NLO properties, which is greatly expected but unexplored to date. Herein, by introducing flexible metal halide bonds to guarantee the stereochemical activity and overcome the energetically favorable antiparallel arrangements of lone-pair cations, the first type of three lone-pair-cation (Pb2+, Bi3+, and Se4+)-coexisting NCS oxides PbBi(SeO3)2F (I) and Pb2Bi(SeO3)2Cl3 (II) was obtained. As expected, both compounds show outstanding NLO properties, such as the strong second-harmonic-generation signal (10.5× and 13.5 × KDP), large birefringence (0.103 and 0.186), relatively wide energy band gaps (3.75 and 3.45 eV), and good physicochemical stability. Theoretical calculations demonstrated the effect of three lone-pair-cation-based polyhedra and the halide anion on NLO properties.

Visible-light responsive PVDF/carbon sphere@TiO2 membrane for dye scavenging and bacteria inactivation

Titanium dioxide (TiO2) is wildly used for dye scavenging and bacteria inactivation in wastewater treatment. However, its photocatalytic efficiency is significantly limited by two inherent limitations including quick electron-hole pair recombination and wide bandgap energy (∼3.2 eV). In this work, we present a composite membrane that shows superior photocatalytic properties under visible light in dye scavenging and bacteria inactivation. The carbon sphere@TiO2 (CST) was manufactured via a two-step hydrothermal progress as a visible-light activated nano-photocatalyst and then electrospun with poly(vinylidene fluoride) (PVDF) to fabricate PVDF/CST composite membrane. When exposed to visible light, the PVDF/CST composite membrane performs well in terms of organic dye degradation. Furthermore, antibacterial activity assays show that the composite membrane has excellent sterilizing characteristics. Overall, this composite membrane appears to be a potential material for dye scavenging and bacterial inactivation in wastewater treatment.

Optical absorption from boron-containing quantum dot structures

This work studies optical absorption in the zinc-blende boron-containing quantum dot (QD) structures. Eight structures are studied; two of them are the ternary BInP/GaP and BInP/BP. The others are BGaAsP/BP, BAlAsP/BAs, BInAsP/InP, BGaInAs/GaAs, BGaInP/BP, and BInAsP/GaP. The emission wavelengths of the structures cover a broad spectrum range from UV to near-infrared. The structures with BAs and BP barriers emit at 227,292nm. The structures BInAsP/InP and BGaInAs/GaAs have peak absorptions at 870nm and 920nm wavelengths, while ternary and quaternary structures with GaP barrier are at 720 and 1200nm. The structures with GaP barrier have importance in silicon device technology. The absorption peaks are arranged where the smallest energy difference between the transition subbands correspond to a higher absorption peak and are associated with a wide bandgap energy difference between the barrier and QD. For boron increment by 0.005 in the QD region, the peak absorption of BInP/GaP and BInP/BP in the TE mode have a wider red-shift (170 nm) in the peak wavelength. BGaAsP/BP has an absorption peak four orders higher than BAlAsP/BP. For of BInAsP/InP QD structure, the absorption spectrum is increased by more than four times under 0.0001-mole fraction increment of boron.

Triphenylethene-carbazole-based molecules for the realization of blue and white aggregation-induced emission OLEDs with high luminance

Molecules that use triphenylethene-carbazole moieties decorated with different substitutions were designed and synthesized, harvesting wide energy bandgaps and aggregation-induced emission (AIE) characteristics. The photophysical, thermal, and electroluminescence (EL) characteristics of the designed emitters were investigated to clarify the molecular structure-property-performance relationship. The photoluminescence spectra of the synthesized molecules measured using tetrahydrofuran-water solution presented strong blue emissions, confirming their AIE property. The doped blue-emitting organic light-emitting diodes (OLEDs) with compound 2 exhibited satisfactory peak efficiency of 8.7 cd/A and high maximum luminance of 18474 cd/m2. In comparison, the peak efficiency of the 2-based sky-blue OLEDs with a non-doped emitting layer was 10.2 cd/A with an even superior peak luminance of 39661 cd/m2. Blue-emitting AIE OLEDs have rarely presented such high luminance values, and this improvement can facilitate the development of white-emitting OLEDs (WOLEDs) for lighting applications. The fabricated WOLEDs with 2 achieved a maximum efficiency of 5.6% (8.0 cd/A and 7.5 lm/W), stable EL spectra, and high luminance of 29319 cd/m2. These results indicate that the triphenylethene-carbazole structure designs for AIE molecules could simultaneously harvest wide energy bandgap and high luminance, demonstrating their high potential for EL applications.

Preparation and modification methods of defective titanium dioxide-based nanoparticles for photocatalytic wastewater treatment-a comprehensive review.

The rapid population growth and industrial expansion worldwidehave created serious water contamination concerns. To curb the pollution issue, it has become imperative to use a versatile material for the treatment. Titanium dioxide (TiO2) has been recognized as the most-studied nanoparticle in various fields of science and engineering due to its availability, low cost, efficiency, and other fascinating properties with a wide range of applications in modern technology. Recent studies revealed the photocatalytic activity of the material for the treatment of industrial effluents to promote environmental sustainability. With the wide band gap energy of 3.2eV, TiO2 can be activated under UV light; thus, many strategies have been proposed to extend its photoabsorption to the visible light region. In what follows, this has generated increasing attention to study its characteristics and structural modifications in different forms for photocatalytic applications. The present review provides an insight into the understanding of the synthesis methods of TiO2, the current progress in the treatment techniques for the degradation of wide environmental pollutants employing modified TiO2 nanoparticles, and the factors affecting its photocatalytic activities. Further, recent developments in using titania for practical applications, the approach for designing novel nanomaterials, and the prospects and opportunities in this exciting area have been discussed.

Polyoxometalate Accelerated Cationic Migration for Reservoir Computing

AbstractMemristor‐based reservoir computing systems represent an attractive approach in processing the time‐series information with a low training cost, in a range of fields from finance to engineering. Previous investigations have identified the charming potential of organic devices for next‐generation memory devices. However, the structural inhomogeneity and wide energy bandgap of most organic polymers usually lead to low‐yield and high operation power microelectronic devices, that permit their further application in neuromorphic computing. Herein, an organic‐inorganic hybrid memristor that can be conveniently processed into crossbar devices with tolerable yield via spin‐coating is shown. The doped inorganic polyoxometalate (POM) clusters via supramolecular assembly strategy not only act as the charge trapping modules but also assist the formation of conductive filaments due to their delocalized electrostatic adsorption property. With the dynamic short‐term memory property, the designed memristor devices can be used as a reservoir framework to process temporal information directly. A smaller reservoir with 100 memristors can be used for the recognition of emotion patterns efficiently. This strategy demonstrates the unique role of POM in developing low‐power and repeated memristors, which provides a new material platform to design advanced function memristors for neuromorphic computing.

Stability, elastic and electronic properties of the CsSrI3 halid perovskite

Due to the importance of halide perovskite in many applications, namely optical and electronic ones, it is a challenging task to determine the precise stable studied structure for a given overall use. In view of this point, we present in this work, for the first time, theoretical calculations carried out by means of the full-potential linearized augmented plane wave (FP−LAPW) method on the CsSrI3compound. Deep analysis of energetic and dynamical investigations shows that this compound adopts an orthorhombic Cmcm structure. Meanwhile, both bonding and mechanical properties reveal a strong ionic/anisotropic behavior of the studied materials. This trend drastically influences electronic properties, giving rise to a wide band gap energy of 4 eV. The analysis of band structure and effective mass predicts favorable properties for UV applications.

Recent Breakthrough in Layered Double Hydroxides and Their Applications in Petroleum, Green Energy, and Environmental Remediation

The fast development of the world civilization is continuously based on huge energy consumption. The extra-consumption of fossil fuel (petroleum, coal, and gas) in past decades has caused several political and environmental crises. Accordingly, the world, and especially the scientific community, should discover alternative energy sources to safe-guard our future from severe climate changes. Hydrogen is the ideal energy carrier, where nanomaterials, like layered double hydroxides (LDHs), play a great role in hydrogen production from clean/renewable sources. Here, we review the applications of LDHs in petroleum for the first time, as well as the recent breakthrough in the synthesis of 1D-LDHs and their applications in water splitting to H2. By 1D-LDHs, it is possible to overcome the drawbacks of commercial TiO2, such as its wide bandgap energy (3.2 eV) and working only in the UV-region. Now, we can use TiO2-modified structures for infrared (IR)-induced water splitting to hydrogen. Extending the performance of TiO2 into the IR-region, which includes 53% of sunlight by 1D-LDHs, guarantees high hydrogen evolution rates during the day and night and in cloudy conditions. This is a breakthrough for global hydrogen production and environmental remediation.

Graphene/porous GaN Schottky Betacell

Betavoltaic batteries have advantages over other batteries due to their high energy density, long life, insensitivity to the environment, and small size. This study aims to design a new structure for betavoltaic batteries using porous GaN with a wide energy bandgap. Many nanowires, coated with graphene, are formed on the surface of GaN. Graphene makes a Schottky junction with GaN and creates an internal electric field to separate electron-hole pairs in the depletion region. In our simulation, Ni63 with an activity of 1 mCi, radiant energy of 17 keV, and radiant flux of 6 Pa is used for beta radiation. The structure is simulated in a TCAD 3D simulator, and an auxiliary function written in C++ is employed to simulate the beta beam. This function provides the spatial distribution of the generated electron-hole pairs in GaN as the input data to our simulator to calculate the battery characteristics. The simulation results indicated that the open-circuit voltage, short-circuit current, fill factor (FF), output power, and efficiency were obtained as 1.22 V, 61.5 nA, 37%, 28.4 nW, and 28.4%, respectively. The effect of changes in the radioisotope source activity and temperature on the betavoltaic battery performance is also investigated. The use of porous GaN, along with the graphene as the semi-metal in Schottky junctions with GaN, has caused a good increase in the performance of our proposed betavoltaic cell in comparison with previously published works.

Synthesis, optical and dielectric properties of polyacryloyloxy imino fluorophenyl acetamide and polyacryloyloxy imino fluorophenyl acetamide-co-polystyrene sulfonate

Our scope is synthesis a new poly fluorobenzamide oxime ester and study its structural, optical, and dielectric properties. Consequently, ((E)-2-((acryloyloxy)imino)-N-(4-fluorophenyl) acetamide) (AIFPA) was as-synthesized via a condensation reaction of (E)-N-(4-fluorophenyl)-2-(hydroxyimino) acetamide with acrylic acid to polymerize it via free radical polymerization (PAIFPA). over and above, the synthesized PAIFPA was inserted in more polymerization action with polystyrene sulfonate through the grafting process (PAIFPA-co-PSS). The chemical structures and morphology of AIFPA, PAIFPA, and PAIFPA-co-PSS were characterized by 1H NMR, FTIR, and XRD. The crystallinity index of PAIFPA, and PAIFPA-co-PSS was studied, affording that PAIFPA-co-PSS has the highest crystallinity. Moreover, The optical bandgap that obtained from absorbance analysis was encountered to be in the range of 2.6 eV to 3.5 eV. Ultimately, the dielectric properties of PAIFPA, and PAIFPA-co-PSS showed that electric conductivity values ranged from 6.12 × 10–8 to 7.11 × 10–7 S.cm−1, and 5.48 × 10–10 to 7.75 × 10–8 S.cm−1, respectively. It has a great deal of interest of PAIFPA-co-PSS which has wide band gap energy as short-wavelength light absorbers to be used in tandem polymer solar cells.

Outdoor performance of GaAs/bifacial Si heterojunction four-terminal system using optical spectrum splitting

Bifacial photovoltaics and multijunction systems represent the most promising alternatives to overcome the theoretical limit of single-junction Si photovoltaics, and these solutions can also be combined to achieve higher performances. This work investigates the outdoor performance of a bifacial four-terminal photovoltaic system based on combining a III-V semiconductor with the silicon heterojunction technology. By exploiting the wide band gap energy of GaAs, the bifaciality of the Si heterojunction and the spectrum-splitting capability of dichroic mirrors, an optimal voltage match between mini-modules of the two solar cells was achieved, with an open-circuit voltage mismatch of 4% of the average value. In this study, we demonstrate the full functionality of bifacial operation with a 17% increase of power conversion efficiency throughout the day compared to monofacial operation. Furthermore, we show that though the solar spectrum is subjected to strong variations from morning to afternoon, which lead to changes of the ratio of the GaAs to the Si mini-module short-circuit currents up to 43% throughout the day, the variation of the overall system power conversion efficiency remains quite limited, less than 16% of the maximum value thanks to the efficient coupling of the two mini-modules.

Nanohybrids that consisit of p-type, nitrogen-doped ZnO and graphene nanostructures: synthesis, photophysical properties, and biosensing application

ZnO, a promising material for optoelectronic applications, has attracted considerable attention due to its wide and direct band gap and large exciton binding energy. To understand the applications of this material, fabrication of high quality p-type ZnO is a key step. However, a reliable p-type doping of this material remains a major challenge. In this study, we report p-type nitrogen-doped ZnO nanoparticle, grown in a nitrogen doped graphene layer matrix by a plasma heating process using a natural protein and zinc nitrate as the precursors. The structural characterizations are developed by several microscopic techniques including the field emission electron microscopy, high resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and micro-Raman analysis. In addition, the ultraviolet (UV)–visible absorption characteristics and photoluminescence properties of the samples are studied. Its p-type conduction behaviour is confirmed by the Hall effect measurement, which was ascribed to the high nitrogen dopant concentration in the Zn-poor ZnO, and the related mechanism for the p-type behaviour is also discussed. Moreover, the results of the glucose detection based on the strong green luminescence of glucose indicate that the nitrogen-doped ZnO nanodots/nitrogen-doped graphene layer nanohybrid is also a competitive candidate in the biosensing field.

Role of Titanium replacement with Pd atom on band gap reduction in the anatase Titanium Dioxide: First-Principles calculation approach

Titanium dioxide (TiO2) is one of the highly promising energy materials. Nevertheless, it has a wide energy bandgap that restricts its absorption capacity within the visible light spectrum. To investigate the effects of doping the transition-metal Palladium (Pd) into anatase TiO2, we perform first-principles calculations in the framework of density functional theory (DFT). All calculations are carried out in the scheme of Hubbard potential (U) correction to account for the correlated effects in TiO2. For this purpose, the first-principles calculations are carried out with the CASTEP code in the formalism of GGA + U. The Pd-doped TiO2 was examined in detail for its electronic structure, lattice parameters, E-K representation, the density of states and optical properties. The results showed that lattice parameters of TiO2 changed after doping. The band structure, partial density of state (PDOS), total density of state (TDOS), complex dielectric function, refractive index, optical absorption, and energy loss function of Pd-doped anatase are improved drastically. It was observed that the doping process adds Pd 4d electronic states into different energy ranges and thus reduces middle states within the band gap region. Our electronic structure calculations indicate augmentation of d-states around the Fermi level, induced by doping Pd. Additionally, compared with the undoped TiO2, the absorption edges of Pd-doped TiO2 show a shift from the UV spectrum towards the visible light region. The results indicate that the GGA + U approach is unique in determining the real band structure of semiconductors which is close enough to empirical results.

A facile approach to fabricate and embed multifunctional nano ZnO into soap matrix and liquid cleansing products for enhanced antibacterial and photostability for health and hygiene applications

• Fabrication of nano ZnO into Surfactant Polyol Assembly (SPA) for enhanced activity. • Embedding of ZnO-SPA into soap and liquid cleansing products for advanced application. • ZnO-SPA with 99.99% germ kill and photostability for health and hygiene applications. This research demonstrates, a facile approach to fabricate the nano ZnO system in an unique combination of surfactant-polyol-assembly (SPA) acting as a caging agent restricting the ZnO crystallite size in nano-regime. This SPA is suitable for health and hygiene products and such optimized technique is among the very few researches exploring the impact of embedding low concentrations of nano ZnO system into the matrix of sodium salt of long chain fatty acids (soap bar) and liquid cleansing personal care products. The fabricated nano ZnO in SPA and infused products were systematically characterized using various advanced and appropriate techniques. The hexagonal wurtzite structure of nano ZnO-SPA is evaluated based on XRD pattern which also exhibit an average crystallite size as 20.18 nm and high specific surface area as 52.99 m 2 /g. The SEM-supported morphological assessment confirms the formation of agglomerates of ultrafine ZnO rods and spherical particles. Novel nano ZnO having wideband gap energy (3.66 eV) embedded in soap bar act as a UV-blocker preventing the oxidation of unsaturated long chain fatty acids. Soap bar without ZnO experienced degradation and reduction in whiteness to 17.85% whereas 2.5 mg/g nano ZnO infused soap shows the reduction to 7.9% which clearly reflects the increased photostability of soap bar. The antibacterial efficacy of nano ZnO-SPA and infused products are investigated against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) by Zone of Inhibition (ZOI) and European standard EN:1276. Infused products exhibited high antibacterial efficacy up to 4.43 log reduction equivalent to >99.99% germ kill.

Computational Discovery and Experimental Demonstration of Boron Phosphide Ultraviolet Nanoresonators

AbstractControlling ultraviolet light at the nanoscale using optical Mie resonances holds great promise for a diverse set of applications, such as lithography, sterilization, and biospectroscopy. Access to the ultraviolet requires materials with a high refractive index and wide band gap energy. Here, the authors systematically search for such materials by computing the frequency‐dependent optical permittivity of 338 binary semiconductors and insulators from first principles, and evaluate their scattering properties using Mie theory. This analysis reveals several interesting candidate materials among which boron phosphide (BP) appears most promising. Then BP nanoparticles are prepared and it is demonstrated that they support Mie resonances at visible and ultraviolet wavelengths using both far‐field optical measurements and near‐field electron energy‐loss spectroscopy. A laser reshaping method is also presented to realize spherical Mie‐resonant BP nanoparticles. With a refractive index over three and low absorption losses in a broad spectral range spanning from the infrared to the near ultraviolet, BP is an appealing material for a broad range of applications in dielectric nanophotonics.

ZnSxSe1−x thin films: A study into its tunable energy band gap property using an experimental and theoretical approach

In recent times, ZnS and ZnSe thin films are drawing tremendous attention towards opto-electrical devices due to their optimal wide band gap energy. By alloying ZnS and ZnSe films to obtain ZnSxSe1−x thin films, the band gap of the ZnSxSe1−x film can be tuned to a value according to the device requirements. Herein, ZnSxSe1−x thin films were deposited on pre-cleaned glass substrates using a thermal evaporation system and the various properties of the obtained thin films were analyzed by altering the percentage of sulfur concentration in the films. The XRD analysis illustrated that the prepared films are polycrystalline in nature and oriented along cubic (111) plane. The deviation of (111) preferential peak position with composition ‘x’ along the absence of any secondary peaks confirms the formation of ternary ZnSxSe1−x thin films. DFT analysis verifies the formation of pristine ZnSxSe1−x alloy system. FESEM micrographs displayed that the ZnSxSe1−x thin films do not have any cracks or pinholes. EDAX analysis of the films revealed the existence of Zn, Se and S in an appropriate quantity. Optical analysis revealed the effective band gap tailoring of ZnSxSe1−x thin films. The band gap of the ZnSxSe1−x thin films increases from 2.59 eV to 3.38 eV as the composition ‘x’ varied from 0 to 1 and band composition was determined using the DOS plot obtained using VASP.

Design of a differential power oscillator for 433 MHz WPT using e-GaN HEMTs

This paper presents a new differential power oscillator design based on a differential class-E power amplifier. The designs use high power enhancement-GaN HEMT (e-GaN) for its fast switching time, low ON resistance and wide energy band gap properties. The target application is far field wireless power transfer for wireless charging applications. The initial guess for design parameters follows the well known Sokal approach then LTSpice simulator is used to finalize the design. The simulated output power of the power oscillator is 60 W at the 433 MHz ISM band with high DC-to-RF conversion efficiency. Effect of process and design parameter variability is considered to assess the design sensitivity to manufacturing tolerances in both active and passive components.

GaN Non-Volatile Memory Based on Junction Barrier-Controlled Bipolar Charge Trapping

A tunnel-oxide-free GaN-based non-volatile memory (NVM) device is proposed to untangle the trilemma among speed, retention, and endurance in the implementation of conventional NVM. The program and erase (P/E) are based on bipolar charge injection controlled by individual junction barriers, whereas the data retention relies on bipolar charge trapping in an interfacial charge storage layer. The wide bandgap energy of GaN allows the formation of deep-level traps at a dielectric/GaN interface and high junction barriers in GaN, both of which benefit long-term retention. As such, the GaN-based NVM device could get rid of the tunnel oxide, thereby enabling faster P/E processes and facilitating to decouple the enhancement of endurance from that of speed and retention. The proposed device demonstrates a P/E time of 100 ns, endurance over 10⁶ cycles, and long retention time.