Shift In Band Gap Research Articles

Lightweight panels based on Helmholtz resonators for low-frequency acoustic insulation

In this study, we propose a novel lightweight acoustic metamaterial panel composed of coupled Helmholtz resonators, designed to insulate low-frequency broadband noises effectively. Through finite element analysis, we observe the emergence of band gaps with varying widths, depending on the unit cell dimensions, the band gaps start at 100 Hz, and as the scale decreases, the band gaps shift to higher frequencies within specific ranges. These band gaps arise from the coupling of two Helmholtz resonators with different volumes but a common neck. For our work, we use ABS materials, which facilitate easy panel manufacturing. Moreover, we also explored the potential of other materials to enhance the low-frequency broadband sound insulation performance of the system. The results obtained from this research provide promising insights into developing lightweight panels for efficient low-frequency broadband sound insulation.

Bandgap prediction for a beam containing membrane-arch-mass resonators

This work aims to propose a promising locally resonating system consisting of a tensioned elastic membrane and two-arch masses attached on the membrane surface. Traditional membrane-type resonators, which usually create one obvious attenuation zone at low frequencies, might not be efficient in multi-frequency vibration suppression. The proposed structure can produce an extra clear flexural attenuation region and shift bandgap frequencies below 300 Hz. By adjusting geometric parameters (thickness, width, and location) of the arch mass, the bandgap region can be tuned. Introducing a feasible analytical model for accurately predicting the first and second initial frequencies of the bandgaps for a beam structure containing membrane-arch-mass resonators is another focus of this study. The proposed theoretical framework can be used to tune the bandgap to different target frequency ranges without knowing the actual width of the bandgap. Finite-element analysis and experiments are conducted to verify the theoretical predictions. A good agreement is seen among the theoretical, finite-element analysis, and experimental results. In addition, adjacent cells with different arch-mass distributions can generate two pairs of flexural bandgaps, increasing the practicality in engineering applications. The proposed structure might be used in low-frequency vibration isolation and filters.

Tailoring the Structural, Optical and Electrical Properties of Zinc Oxide Nanostructures by Zirconium Doping

Owing to its low resistivity, high transmittance, and tunable optical band gap, ZnO is of great interest for optoelectronic applications. Herein, the sol–gel technique was used to synthesize un-doped and zirconium-doped zinc oxide (ZZO) nanostructures with different concentrations of Zirconium (Zr). X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, and photoluminescence (PL) measurements were used to investigate the influence of Zr doping on the structural, optical, and electrical properties of developed nanostructures. XRD and SEM confirmed the increase in crystallite size with increasing concentrations of Zr. Raman analysis indicated the presence of oxygen vacancies in synthesized nanostructures. UV-Vis spectroscopy illustrated the blue shift of band gap and red shift of the absorption edge for ZZO nanostructures with increasing concentrations of Zr. For the measurement of electrical properties, the spin-coating technique was used to deposit un-doped and Zr-doped ZnO layers of ~165 nm thickness. The four-probe-point (4PP) method illustrated that the doping of Zr caused a reduction in electrical resistance. Hall Effect measurements showed a high value, 3.78 × 1020 cm−3, of the carrier concentration and a low value, 10.2 cm2/Vs, of the carrier mobility for the Zr-doped layer. The high optical transmittance of ~80%, wide band gap of 3.51 eV, low electrical resistivity of 1.35 × 10−3 Ω·cm, and maximum carrier concentration of 3.78 × 1020 cm−3 make ZZO nanostructures one of the most promising candidates for the application of transparent conductive oxide (TCO) in optoelectronic devices.

Shape‐Tunable BaTiO3 Crystals Presenting Facet‐Dependent Optical and Piezoelectric Properties

BaTiO3 octahedra, edge-, and corner-truncated cubes, and cubes with four tunable sizes from 132 to 438nm are synthesized by a solvothermal growth approach. Acetic acid treatment can cleanly remove BaCO3 impurity. Rietveld refinement of X-ray diffraction patterns and Raman spectra help to confirm the particles have a tetragonal crystal structure. The crystals also exhibit size- and facet-dependent bandgap shifts. BaTiO3 octahedra show larger piezoelectric, ferroelectric, and pyroelectric effects than truncated cubes and cubes. The measured dielectric constant differences should be associated with their various facet-dependent behaviors. Piezoelectric nanogenerators fabricated from BaTiO3 octahedra consistently show the best performance than those containing truncated cubes and cubes. In particular, a nanogenerator with 30 wt.%-incorporated octahedra displays an open-circuit voltage of 23V and short-circuit current of 324 nA. The device performance is also highly stable. The maximum output power reaches 3.9 µW at 60 MΩ. The fabricated nanogenerator can provide sufficient electricity to power light-emitting diodes. This work further demonstrates that various physical properties of semiconductor crystals show surface dependence.

Energy Yield Modeling of Bifacial All‐Perovskite Two‐Terminal Tandem Photovoltaics

AbstractAll‐perovskite two‐terminal tandem photovoltaics offer high power conversion efficiencies (PCEs) that can surpass the limits of single‐junction photovoltaics. In this study, energy yield (EY) simulations are performed to assess the performance of bifacial all‐perovskite tandem solar cells. Under standard test conditions, in the absence of albedo, bifacial tandems demonstrate a 4.9% relative lower PCE compared to equivalent monofacial tandems due to transparency losses at the semitransparent rear side. However, under realistic irradiation conditions, albedo irradiation leads to an enhancement in EY for bifacial cells. This enhancement enables bifacial cells to produce more energy than monofacial cells, even over relatively low average reflectance (RA) ground such as dark sandstone (RA = 9%). The EY gain for bifacial cells rises to a maximum of 40–50% for ground modeled as a perfect reflector (RA = 100%), accompanied by a shift in optimum top subcell bandgap to 1.56 eV. This shift is of particular interest as low‐bandgap perovskite semiconductors (with lower bromide concentrations) offer enhanced stability under realistic operation conditions. Finally, this work presents a route to increase the PCE of simulated monofacial and bifacial cells, to 31.9% and 30.8%, respectively, by optimizing the optical and electrical performance of the cells.

High-temperature photoluminescence OF CsPbBr3 perovskite nanocrystals in the fluorophosphate glasses

For the first time the temperature dependence of the photoluminescence of the semiconductor CsPbBr3 perovskite nanocrystals with sizes of 6.0–9.0 nm in fluorophosphate glass were investigated in the temperature range from 300 K to 423 K. It was shown that temperature dependence of the photoluminescence intensity and the band gap shift coefficient change at 350 K corresponding to the isostructural phase transition. The photoluminescence intensity decreased radically above this temperature. The temperature energy gap coefficients of the CsPbBr3 nanocrystals depending on the size and temperature range were found.

Defects and oxygen vacancies modified properties of transition metal doped Ce0.95X0.05O2 (X = Fe, Co, Ni) nanoparticles

In this study, pure and transition metal doped (TM = Fe, Co, and Ni), cerium oxide nanoparticles have been synthesized by the co-precipitation techniques. Rietveld refined X-ray diffraction (XRD) patterns affirm the monophase nature with cubic symmetry having an Fm3m space group and crystalline size varies in the range of 9–14 nm calculated by Debye Sherer's formulation. The morphological study has been done by scanning electron microscope (SEM) technique anticipated that agglomerated grains symmetry with the typical grain size distribution varies from 45 to 52 nm. The effect of transition metal doping on bending/stretching vibrational modes has been effectively investigated by FTIR analysis. The strong absorbance edge was seen in the UV region and shifted in the red region with the doping of transition metal ions. The tauc’s plot of UV–vis absorption uncovers the bandgap decreased from 2.87 eV to 2.42 eV on transition metal doping. The photoluminescence spectroscopy (PL) technique was used to investigate the presence of oxygen vacancies and intrinsic defects in the host CeO2 lattice when doped with transition metal ions. These imperfections induce the lattice disorder and shift in the energy bandgap from the UV to the visible region of the spectrum by affecting its electronic transitions. The CIE chromaticity coordinates of pure and transition metal doped compounds observed in the blue region might be applicable in display devices. In this manner, these materials can be fascinating for tuneable electrical and optical devices.

Structural phase transition and charge carrier dynamics in Dy containing La6MoO12 ionic conductor

The solution combustion method was adopted to prepare a single-phase La6MoO12 compound by doping 10% Dy in the La site and sintered at 800 °C, 1000 °C, and 1200 °C temperatures. The X-ray diffraction patterns confirmed a phase transition of the samples from the cubic fluorite phase (Fm3‾m) to a complex rhombohedral structure (R3‾m) with increasing sintering temperature. The microstrain and particle size show the opposite behaviour in the case of 800 °C and 1200 °C sintered samples. The FE-SEM and XRD results corroborated the increment of particle size with sintering temperature. Elemental mapping confirmed the uniform distribution of elements in the compositions. Red and blue shifts in optical bandgap were observed with sintering temperature. All samples show a negative temperature coefficient of resistance (NTCR) behaviour. The sample sintered at 1200 °C has the highest ionic conductivity of 1.03×10−4Ω−1cm−1 at 540 °C. The reciprocal temperature dependence of conductivity followed the VTF equation. The dielectric loss tangent indicated that all samples have a single relaxation process. The time-temperature superposition principle has been verified from the scaling of the dielectric loss tangent.

Influence of deposition power and annealing on the performance of RF-sputtered SnS for infrared photodetection

Tin sulfide has shown their great potential in electronic and photonic systems due to its unique optoelectronic properties, less toxic nature, cost-effective and economically earth-abundant elements. The multivalence of Sn and stereochemical activity endow it with rich phase spaces and susceptible internal structures, which in turn directly affect its properties. In this paper, optimization studies towards the influence of RF power and post-deposition annealing temperature on the micro structure and photodetection performance of SnS are achieved by RF magnetron sputtering method. The structural characterizations confirm the significance of RF power for phase formation and photoelectric conversion ability. The optical band gap shifts from 1.41 eV to 1.30 eV as RF power increasing from 30 W to 50 W, in the meantime, the optoelectronic performances such as responsivity and specific detectivity are subsequently improved to be 226.55 mA/W and 1.76 × 1010 Jones. Further, the variations in infrared photodetection performance correlated with the annealing temperature exhibite a more well-behaved photoresponse at 300 °C. The results pave the way to discern the growth − structure − property relationships and then guide potencial applications of tin sulfide family.

Effect of 4He2+ ion irradiation on the optical, electrical, morphological, and structural properties of ZnO thin films

A study of the effect of 2.5 MeV 4He2+ ion irradiation on the optical, electrical, morphological and structural properties of ZnO thin films is presented. Polycrystalline zinc oxide thin films were deposited on soda lime glass substrates using the spray pyrolysis technique. During the process, the substrates’ surfaces were kept at 400, 450 and 500 °C. The samples were analyzed by different techniques and the optical results showed a red shift in the energy band gap after irradiation. It was also confirmed that the wurtzite-type hexagonal structure of the ZnO films remained after irradiation, the crystallite size increased and the lattice parameters decreased due to He2+ irradiation. SEM micrographs revealed that ion irradiation favors the nucleation and the formation of grains in the films. Micrographs showed nanometric particles with spherical and flake-like forms, which depend on the deposition temperature. A decrement in the average particle size of the samples deposited at 400 and 450 °C was observed after irradiation; meanwhile, an increase in the particle size was detected in the film deposited at 500 °C. The resistivity values increased with He2+ ion irradiation.

Propagation characteristics of lamb waves in a functionally graded material plate with periodic gratings

The propagation characteristics of Lamb waves in a functionally graded material (FGM) plate with periodic gratings have been studied. The power series technique is employed to solve the governing differential equations with variable coefficients. In the propagation direction, the displacements of Lamb waves are expanded in the Fourier series due to the periodicity of the structure. The convergences of the power series and Fourier series are proved and the method presented in the article is verified by the finite element method (FEM). The band gaps are obtained by the couplings between the different modes of Lamb waves induced by FGM. The effects of the structural parameters (such as the periodicity, mass, and length of the gratings) and gradient coefficient on band gaps are investigated. Numerical results show that the band gaps shift up as the gradient coefficient increases and the second band gap (SBG) is closed when the gradient coefficient is large enough. The conclusions are of practical significance for designing elastic wave filters with high-performance.

Equimolar ZnO-CdS nanocomposite for enhanced photocatalytic performance

Nanocomposite of ZnO-CdS having an equal molar ratio (1:1) of the two components has been synthesized using chemical co-precipitation method, with optimized parameters for efficient photocatalytic properties. A variety of suitable techniques including synchrotron based extended X-ray absorption fine structure (EXAFS) have been used to investigate structural, morphological and optical properties of the nanocomposite. The synthesized nanostructured ZnO-CdS nanocomposite is found to have homogenously distributed crystalline grains of both ZnO and CdS. The uniform distribution of grains and the equal molar ratio of the two components have resulted in excellent optical and photocatalytic performance. The UV-Vis absorption spectrum of nanocomposite shows absorption behavior, extended almost uniformly in the entire UV-visible region, with a red shift in the optical band gap of ZnO, suggestive of efficient photocatalytic ability. The photoluminescence spectrum shows the absorbance in both UV and visible regions, corresponding to the near-band-edge emissions of the ZnO and CdS, respectively. Finally, the photocatalytic performance has been studied in photodegradation of methylene blue dye, showing an enhanced efficiency of almost 99% in 110 min, much higher than that of pristine ZnO, as well as CdS and one of the best reported in the literature.

Asymmetric encryption by optical Kerr nonlinearities exhibited by electrochromic NiO thin films.

Herein is analyzed how an electric field can induce a band gap shift in NiO films to generate an enhancement in their third-order optical nonlinearities. An electrochromic effect seems to be responsible for changes in absorbance and modification in off-resonance nonlinear refractive index. The optical Kerr effect was determined as the dominant physical mechanism emerging from the third-order optical susceptibility processes present in a nanosecond two-wave mixing configuration at 532 nm wavelength. Absence of any important multi-photonic absorption was validated by the constant trace of high-irradiance optical transmittance in single-beam mode. The inspection of nonlinear optical signals allowed us to propose an exclusive disjunctive logic gate assisted by an electrochromic effect in an optical Kerr gate. Asymmetric encryption by our XOR system with the influence of a switchable probe beam transmittance and electrical signals in the sample was studied. Immediate applications for developing multifunctional quantum systems driven by dynamic parameters in electrochromic and nonlinear optical materials were highlighted.

Electron–hole interaction in cylindrical quantum dots

The Coulomb interaction of electron and hole in a cylindrical quantum dot in the frame of the first perturbation theory and the effective mass approximation is studied. The analogue of Brus’s equation for Coulomb interaction of electron–hole pair in a spherical quantum dot is obtained for a cylindrical nanocrystal and an expression for the energy band gap shift is derived, which can be used for explaining of some experimental results obtained for MoS2 and 3C-SiC nanocrystals.

One-dimentional periodic structure infiltrated by (PVA/CV + CF)-polymer for high-performance sensitivity

In the current work, we demonstrate a design to act as a Gamma-ray radiation dosimeter based on the one-dimensional photonic crystal (1D-PhC). The basic concept of the present dosimeter is based on a Porous Silicon (PSi) infiltrated by poly-vinyl alcohol (PVA)-polymer doped with crystal violet (CV) and carbol-fuchsine (CF) dyes. The mechanism of suggested dosimeter is based on the shift of the photonic bandgap (PBG) to higher wavelengths as exposed to gamma-ray radiation doses from 0 to 70 Gray (Gy). The basic axes of the current theoretical treatment are the transfers matrix method (TMM), Bruggeman's effective medium equation, and the fitted experimental data to the refractive index of the doped PVA-Polymer. The obtained results showed the proposed sensor is characterized by high stable sensitivity varied from (178–186 nm/ RIU) along an applied γ-dose from (10–70 Gy) in the visible range. In addition, we compared these results with previous researches. In addition, based on the our knowledge may be it is the first time that a 1D-PhC has been used for gamma-ray detection by using (PVA/CV + CF) based on Porous Silicon.

Ge/Al and Ge/Si3N4/Al Core/Shell Quantum Dot Lattices in Alumina: Boosting the Spectral Response by Tensile Strain.

We investigated the production conditions and optoelectrical properties of thin film material consisting of regularly ordered core/shell Ge/Al and Ge/Si3N4/Al quantum dots (QDs) in an alumina matrix. The materials were produced by self–assembled growth achieved by means of multilayer magnetron sputtering deposition. We demonstrated the successful fabrication of well-ordered 3D lattices of Ge/Al and Ge/Si3N4/Al core/shell quantum dots with a body-centred tetragonal arrangement within the Al2O3 matrix. The addition of shells to the Ge core enables a strong tuning of the optical and electrical properties of the material. An Al shell induces a bandgap shift toward smaller energies, and, in addition, it prevents Ge oxidation. The addition of a thin Si3N4 shell induces huge changes in the material spectral response, i.e., in the number of extracted excitons produced by a single photon. It increases both the absolute value and the width of the spectral response. For the best sample, we achieved an enhancement of over 250% of the produced number of excitons in the measured energy range. The observed changes are, as it seems, the consequence of the large tensile strain in Ge QDs which is induced by the Si3N4 shell addition and which is measured to be about 3% for the most strained QDs. The tensile strain causes activation of the direct bandgap of germanium, which has a very strong effect on the spectral response of the material.

Room-Temperature Ferromagnetism in Cu/Co Co-Doped ZnO Nanoparticles Prepared by the Co-Precipitation Method: For Spintronics Applications

In current work, pure ZnO and Zn0.96–xCu0.04CoxO (0 ≤ x ≤ 0.05) nanoparticles were synthesized by the co-precipitation method. Structural analysis and phase determination of the formed nanoparticles was carried out using X-ray diffraction (XRD) and Williamson–Hall plots. The hexagonal wurtzite structure was manifested by all the samples with divergent microstructures. The change in lattice parameters, bond length, dislocation density, and lattice strain indicates that Cu and Co were successfully incorporated. Average crystallite size was found to be in the range of 32.16–45.42 nm for various doping concentrations. Field emission scanning electron microscopy results exhibited that the surface morphology is an amalgam of spherical-like and hexagon-like structures. Spherical-shaped grains were homogeneous and evenly distributed all over the structure. Fourier transform infrared spectra indicated that the absorption bands were blue-shifted with increasing Co concentration. The UV–visible absorption spectra showed high absorption in the UV region and weak absorption in the visible region. An increase in the energy band gap for the maximum absorption peak was observed from 3.49 eV for ZnO to 3.88 eV for Zn0.91Cu0.04Co0.05O. The Burstein–Moss effect explained the noticed blue shift in absorption spectra and energy band gaps. The vibrating sample magnetometer study revealed the change in the diamagnetic behavior of pure ZnO to the ferromagnetic behavior of the prepared nanoparticles at room temperature for different doping concentrations. In the current study, we have developed the room-temperature ferromagnetism (RTFM) for Cu and Co co-doped ZnO nanoparticles. Since RTFM is the key objective for dilute magnetic semiconductors, therefore it can be served as the desirable expectant for spintronics applications with improved functionalities and device concepts.

Modulation of Optical Band Gap of 2-Amino Terephthalic Acid Cu-MOFs Doped with Ag<sub>2</sub>O and rGO

The synthesized MOF with copper metal dopant has shown band gap around 1.5 eV which falls in the UV region of electromagnetic spectrum. This MOF with copper turns into nano/MOF composite with addition of Ag2O and rGO to it. The results of band gap of MOF/ Ag2O and MOF/rGO showed 1.904 eV and 1.639 eV respectively. This shift in band gap supports to use them as a UV and near visible light harvest catalyst and also assist in enhancing mechanical, thermal and structural behaviour of compounds. The enhancement of band gap of MOF/nanoMO is attributed to the quantum size effect.

Pre-compressed polymer cholesteric liquid crystal based optical fiber VOC sensor with high stability and a wide detection range.

As the concentration of VOC gases is very high in organic chemical reactions, in order to ensure the safety and accuracy of the experiment, it is very important to develop a gas sensor with a wide detection range. Exploring the mechanism and law of photonic bandgap (PBG) shift after absorption of volatile organic compounds (VOCs) vapors are two basic premises of resolving the PCLC for gas detection with a wide measurement range and stability. Herein, the PCLC films doped with different concentrations of polymer are used for acetone vapor detection, and the shift law of the PBG position is analyzed. As the increase of the detected gas concentration, the intractable problem is that the PBG position of PCLC exhibits red- and blue-shifts successively. Particularly, the pre-compressed technique is highly important for development of a high-performance PCLC based fiber probe, which is crucial for effectively solving the bottleneck problem mentioned. It enables detection of a wide range of acetone vapor concentration from 0 ppm to 50×104 ppm, and the corresponding mean sensitivity of 0.23 pm/ppm. In addition, the thermal crosstalk is generally negligible at temperature below 40°C. Therefore, it is a breakthrough that the described technique not only effectively enhances the stability and robustness of the PCLC fiber probe for VOC vapor detection, but also improves its sensitivity and detection range. The pre-compressed technique provides a novel avenue for fabrication of other PCLC-based devices.

Structural, chemical, optical and photocatalytic properties of Zr co-doped anatase-rutile mixed phase TiO2: Ag nanoparticles

Zr co-doped TiO2:Ag nanoparticles were synthesized by the co-precipitation method and the influence of Zr co-dopant with varying content on the structural, optical and photocatalytic properties of TiO2:Ag photocatalysts was investigated. X-ray diffraction and Raman spectroscopy confirmed the anatase-rutile mixed phase of TiO2 and Zr content eased the anatase-rutile phase transformation. X-ray diffraction peak shift with Zr content indicated the substitutional doping of Zr4+ ions into TiO2 lattice. The optical properties of the nanoparticles were investigated with diffuse reflectance spectroscopy, photoluminescence and Fourier transform infrared spectroscopy. Zr dopants induced the Burstein-Moss effect, resulting in the broader bandgap and photoluminescence shift. X-ray photoelectron spectroscopy was utilized to reveal the surface chemical environment of the Zr co-doped TiO2:Ag nanoparticles and found the presence of Zr4+ ions on the photocatalyst surface, which act as electron traps. The dependence of operational parameters such as photocatalytic load, dye concentration and pH on Zr co-doped TiO2:Ag nanocatalyst was also monitored. The photocatalysts demonstrate improved photocatalytic activity toward methylene blue degradation with maximum efficiency achieved by the photocatalyst having the highest Zr content. 20 mg and 10.35 μM were found to be the optimum values for photocatalytic load and initial methylene blue concentration, respectively. Further, at alkaline pH, complete decolorization of the reaction mixture was observed in only 60 min with 92.6% efficiency by highest co-doped photocatalyst. The effect of Zr content on degradation rate with different parameters was also explored with a possible mechanism to understand the effect of dopants on photocatalytic activity of the photocatalysts.