Broad Band Gap Research Articles

Multiconnected Beam Gradient Seismic Metamaterials for Broadband Rayleigh Wave Attenuation

Local resonance metamaterials have addressed the limitations of Bragg scattering‐type periodic structures in low‐frequency applications, providing a new path for the development of new seismic systems. However, achieving broadband attenuation of low‐frequency seismic waves within a compact structural design remains challenging. This article presents a novel local resonance seismic metamaterial (SM) with an ultra‐low frequency broad bandgap. It consists of an external steel frame, peripheral steel connecting beams, bottom rubber cushions, and a central steel resonator. By combining dispersion analysis and acoustic cone methods to calculate its bandgap, the attenuation range of the SM is clarified, and the influence of structural parameter changes on the upper and lower limits of bandgap is discussed. The results demonstrate that the attenuation domain can be further broadened through parameter gradient design, and frequency domain analysis confirms that the proposed gradient local resonance SM can achieve broadband seismic wave attenuation from 1.0611 to 10.895 Hz. Finally, time‐domain analysis elucidates the dynamic response of the SM, further validating the study's effectiveness. The SM proposed herein has practical and economic applications in surface vibration isolation, effectively protecting large infrastructure and civil engineering structures.

Catalyst-assisted growth of CsPbBr3 perovskite nanowires.

Halide perovskites (HPs), particularly at the nanoscale, attract attention due to their unique optical properties compared to other semiconductors. They exhibit bright emission, defect tolerance, and a broad tunable band gap. The ability to directly transport charge carriers along the HPs nanowires (NWs) has led to the development of methods for their synthesis. Most of these methods involve some version of an oriented attachment step with various modifications. In this study, we introduce CsPbBr3 nanowires produced via the solution-solid-solid (SSS) catalyst-assisted growth mechanism for the first time. We explored the kinetics of this process and examined the connection between the catalyst phase and its reactivity. We show how HP NWs grow with different SSS catalysts (i.e., Ag2S, Ag2Se, CuS) and discuss the required conditions for successful synthesis utilizing this mechanism. This method opens up a new avenue for producing HP NWs, which can be used to design and form new types of hybrid nanostructures.

Observation of Cartesian light propagation through a three-dimensional cavity superlattice in a silicon photonic band gap crystal

We experimentally investigate peculiar light propagation inside a three-dimensional (3D) superlattice of resonant cavities that are confined within a 3D photonic band gap. To this end, we fabricated 3D diamondlike photonic crystals from silicon with a broad 3D band gap in the near-infrared and doped them with a periodic array of point defects. In position-resolved reflectivity and scattering microscopy, we observe narrow spectral features that match well with superlattice bands in band structures computed with the plane-wave expansion. The cavities are coupled in all three dimensions when they are closely spaced (aSL≤3a), and uncoupled when they are further apart. The superlattice bands correspond to light that hops in high-symmetry directions in 3D (“Cartesian light”) that opens applications in 3D photonic networks, 3D Anderson localization of light, and future 3D quantum photonic networks. Published by the American Physical Society 2024

First-principles study of the electronic, vibrational, thermodynamic properties and phase stability of orthorhombic KClO4 under pressure

The purpose of this study is to deeply understand the basic physical properties of potassium perchlorate (KClO4) as a typical ionic energetic material under pressure. KClO4 Received attention for its widespread use in explosives, fireworks, safety matches and rocket propellants. In this paper, we systematically study the basic physical properties of KClO4 under 0-20 GPa pressure, including electrons, mechanical, vibrations, and thermodynamic parameters, based on density functional theory (DFT). The accuracy of the calculations was verified by optimizing the lattice parameters of the crystal structure and comparing them with previous experimental values. Electronic structure analysis revealed that KClO4 is a broadband gap nonconductor. Electronic density of states (DOS) analysis revealed strong covalent bonding between Cl-O bonds. Based on the phonon information, this study calculates the thermodynamic properties of KClO4 and analyzes a function of the relevant thermodynamic quantities under pressure. Combined with the structural phase transition phenomena observed in high pressure experiments, we analyze the dynamic and mechanical instability. These analyses help to understand the behavior of KClO4 under high pressure conditions and are crucial for its application in energetic materials.

Surface wave manipulation by metasurfaces in unsaturated soil: theoretical study

Metasurfaces provide a promising solution for modulating low-frequency surface waves (SW) in sub-wavelength size. However, they were coupled with single-phase soil or saturated soil in previous investigations, rather than the more common unsaturated soil whose properties cannot be simply evaluated from single-phase and saturated soils. Otherwise, they would not be operational in the intended frequency range. In addition, the screening performance of metasurfaces in unsaturated soils is unknown to us due to the complex physical fields and constitutive relationships of unsaturated soils. In this work, an analytical formulation is proposed to investigate interactions between SW and an array of resonators located atop the free surface of unsaturated soil semi-space and to evaluate the vibration damping performance of the metasurface in single-phase, saturated and unsaturated soils. The incident and scattered wave fields are clearly captured by using the Green's functions of an unsaturated semi-space subjected to a harmonic excitation source. Based on the multiple scattering theory, the displacement of the total wave field as well as some complex phenomena (surface-to-bulk wave conversion) are obtained and also validated in a 2D finite element model. It is notable that incorporating a resonator with different natural frequency create a new bandgap, implying that we can broaden the bandgap by installing more resonators with different natural frequencies. We expect this analytical formulation could solve SW scattering problems in geotechnical engineering, and the system with a broad bandgap could provide a conceptual design for weakening SWs.

Ultra-wide low-frequency bandgap characteristics of auxeticity-based composite resonator for elastic wave manipulation and machine learning-based inverse structural design

Although auxetic metamaterials are generally light in weight, strong in compression and superior in energy absorption, less research has focused on their low-frequency bandgap realization and inverse structural design. Moreover, broadening the width of bandgap of auxetic metamaterials keep challenging as well in practical low-frequency applications. To broaden their applications, this work provides a new auxeticity-based composite resonator design by filling hard engineering material into the soft auxetic structure perforated by orthogonally-arrayed peanut-shaped holes to achieve ultra-wide low-frequency bandgap. The soft material is silicone rubber and the hard material may be concrete, steel or plumbum. Firstly, the wave propagation mechanics of the present composite structure is studied and then the bandgap characteristics are thoroughly investigated by parameter analysis. On this basis, a machine learning (ML) method combining the standard back-propagation neural network and genetic algorithm is proposed for bandgap prediction and inverse structural design. Results indicate that the present composite structure performs well in generating ultra-wide low-frequency bandgap, i.e. [11.35, 24.07] Hz, and the relative bandgap width reaches 71.76 %. Moreover, the present ML method is effective in the forward prediction of bandgap and the inverse structure design fitting the specific bandgap requirement. For the created optimal designs, the ML method and the finite element simulation can give similar results, and the maximum relative error between them is just about 5 %, which verifies the accuracy of the ML design method. This work provides a new way to realize the structural design of auxeticity-based acoustic metamaterials with low-frequency and broad bandgap.

Topology Optimization Enabled High Performance and Easy‐to‐Fabricate Hybrid Photonic Crystals

AbstractPhotonic crystals (PtCs) can confine and guide electromagnetic waves within specific frequency ranges, forming the foundation for promising optical applications. To numerically design PtCs with broad bandgaps, materials with high dielectric constants are favored. However, fabricating these high dielectric constant materials into microstructures is extremely challenging and it suffers from limitation of low fabricating resolution. To address this problem, this paper proposes hybrid microstructures composed of an easy‐to‐fabricate core and a high dielectric constant coating layer, which leverages the strength of both materials. This paper establishes a topology optimization algorithm to generate these PtCs with maximized bandgaps. Numerical examples demonstrate the effectiveness of the proposed method in generating optimized unit cells for both transverse magnetic (TM) and transverse electric (TE) modes. The hybrid PtCs offer unprecedented opportunities for the fabrication of optical devices, encouraging further research on multimaterial optical systems and advanced optimization methods to explore photonic bandgap materials beyond those offered by the current photonic technology.

Polymerization-induced highly brilliant and color-recordable mechanochromic photonic gels for ink-free patterning

Mechanochromic photonic crystals (MPCs) are extremely attractive since they can adjust their structural color by forces. However, the poor color saturation and color-recordability of conventional MPCs significantly limit their practical applications. Herein, a highly brilliant and color-recordable MPC gel (MPCG) has been fabricated by photopolymerizing the liquid photonic crystals with silica particles non-closely packed in acrylate, dichlorobenzene, and oleylamine. Photopolymerization induces elastic gradient non-close-packing structures and thus broad photonic bandgaps (>100 nm), resulting in 1) high color saturation despite possessing a small refractive index contrast (0.06), 2) remarkable mechanochromic properties, including a large wavelength tuning range (228 nm), fast responsiveness (8.8–10.3 nm/ms), and high sensitivity (4.4 nm/kPa), and 3) unconventional color-recordable properties. MPCGs were experimentally proved to be ideal rewritable papers for constructing multicolor and high-resolution patterns in an ink-free way, difficult for traditional MPC-based units. The unique working mechanism of polymerization-induced phase separation and thus continuous swelling and gelation, and precise design of materials and structures are the keys to MPCGs’ characteristics. This study paves a new way for constructing advanced stimulus-responsive photonic structures and will promote their applications in printing, display, anti-counterfeiting, etc.

Floating periodic pontoons for broad bandgaps of water waves

Floating periodic pontoons for broad bandgaps of water waves

Gradient Hole Injection Inducing Efficient Exciton Recombination in Blue (475 nm) Perovskite QLEDs.

Perovskite quantum dots (QDs) are emerging as excellent light sources for light-emitting diodes (LEDs). However, the performance of blue perovskite QD-based LEDs (QLEDs) still lags behind that of red and green counterparts, which is hindered by blue perovskite QDs with broad bandgaps that tend to increase nonradiative recombination. Here, we designed a gradient energy for hole injection utilizing multiple hole injection layers (HTLs) combined with carbazole-based small-molecule modification to reduce the hole injection barrier between HTLs and QD layers and improve the hole injection efficiency, realizing efficient exciton recombination in blue perovskite QLEDs. Moreover, the QD film on the designed HTLs demonstrates a lower surface roughness and improved photoluminescence properties. The optimized blue CsPbCl3-xBrx QLEDs exhibit an impressive external quantum efficiency of 20.7% with an electroluminescence peak at 475 nm and a turn-on voltage of 2.6 V, representing the state-of-the-art for blue perovskite LEDs emitting in the range of 460-480 nm.

Precisely Tuning Band Gaps of Hexabenzocoronene-Based MOFs Toward Enhanced Photocatalysis.

Precise adjusting the band gaps in metal-organic frameworks (MOFs) is crucial for improving their visible-light absorption capacity during photocatalysis, presenting both a formidable challenge and a charming opportunity. This present study employed a symmetry-reduction strategy to pre-design six novel 4-connected ligands with systematic substituents (-NO2, -H, -tBu, -OCH3, -OH and -NH2) and synthesized the corresponding pillared-layer Zr-MOFs (NKM-668) retaining the hexaphenylbenzene fragment. Subsequently, the NKM-668 MOFs were transformed into large-π-conjugated hexabenzocoronene-based MOFs (pNKM-668) via the Scholl reaction. These twelve MOFs exhibited broad and tunable band gaps over 1.41 eV (ranging from 3.25 eV to 1.84 eV), and the photocatalytic CO2 conversion rate raised by 33.2-fold. This study not only enriches the type of hexaphenylbenzene-based MOFs, but also paves the way for nanographene-containing MOFs in the further application of photocatalysis.

Zinc telluride material properties for solar cell application: Absorber layer

Over recent years, Zinc Telluride (ZnTe) has garnered significant interest from researches. This p-type semiconductors boasts a broad band gap, rendering it valuable in various optoelectronic uses like solar cells, LEDs, and laser displays. Given the growing interest in environmentally friendly energy alternatives, exploring the potential of nano-scale semiconducting materials for solar cells is particularly intriguing. ZnTe stands out due to its direct, wide, and adjustable optical band gap, along with its simple doping process, positioning it as a promising candidate for applications in photochemistry. This study aims to consolidate the research conducted by multiple investigators concerning the optical characteristics and electrical attributes of ZnTe thin films. The primary focus is on understanding how deposition methods and doping impacts these properties. The investigation reveals that the diverse doping techniques employed by different researchers have been extensively examined, demonstrating a positive influence of doping on these properties as well. Following the creation of solar cells based on ZnTe, they have emerged as viable and competitive substitutes for silicon solar cells, thanks to their economical nature and stable performance. As a result, there has been notable focus on advancing ZnTe thin film solar cell technology due to their promising capacity to serve as sustainable energy generators.

Analysis and simulation of opto-electronics characterization of two-dimensional Janus monolayers for energy applications

First-principles simulations are conducted to investigate the absorption and optoelectronic efficacy of molybdenum–sulfur–selenium, referred to here as MoSSe, and molybdenum–sulfur–oxygen, referred to here as MoSO, Janus monolayers. The materials MoSSe and MoSO demonstrate characteristics of semiconductors, as they possess bandgaps of 2.00 eV (direct) and 1.61 eV (indirect), respectively. This property renders them highly suitable for efficient light absorption. The efficiency of absorption of the device was calculated for the MoSSe and MoSO families, leading to the observation that these material families demonstrate a broad absorption range spanning from the infrared to the ultraviolet regions of the electromagnetic spectrum. This finding represents a novel discovery. Furthermore, the design as a topmost cell is particularly attractive due to its exceptional device absorption efficiency and broader bandgap. This particular family ensures that its band edges remain in alignment with the water-redox potentials. Molybdenum sulfide and molybdenum selenide exhibit promising potential as photocatalysts and in optoelectronic device applications. This is attributed to their appealing photocatalytic properties and notable efficiency in absorbing light for the purpose of water splitting.

Synthesis of Starfish-Shaped ZnS Nanostructures by Hydrothermal Method and Their Electrochemical Sensing of Dopamine.

Introduction Dopamine serves an essential function as a neurotransmitter, influencing the regulation of movement, cognitive processes, and emotional states. The identification of abnormal dopamine levels is critical for clinical diagnoses and scientific research, given its links to various disorders, including depression, schizophrenia, and Parkinson's disease. The distinctive electrochemical characteristics, stability, and broad bandgap of zinc sulfide (ZnS) nanostructures render them particularly fascinating. The hydrothermal method is recognized as an effective and economical approach for the fabrication of ZnS nanostructures, exhibiting a range of morphologies. Utilizing this method to create ZnS nanostructures leads to the formation of structures characterized by extensive surface areas, hierarchical designs, and improved electrochemical properties. Aim The objective is to examine the electrochemical characteristics of ZnS starfish-shaped nanostructures produced through the hydrothermal technique and to assess their viability as a sensing platform for dopamine detection. Materials and methods To synthesize ZnS nanoflowers, stoichiometric amounts of transition metal salts were prepared: 10 mM of Zn(NO3)2•3H2O and 30 mM of sodium thiosulfate (Na2S2O3•5H2O) were dissolved in 30 mL of deionized water and stirred for 20 minutes. The solutions were then combined and transferred into a 100 mL Teflon autoclave reactor, which was heated at 200 °C for 12 hours in a furnace. This process utilized the hydrothermal technique to produce the desired ZnS nanoflowers. Result The crystalline arrangement of ZnS was validated by X-ray diffraction (XRD) analysis, aligning with the Joint Committee on Powder Diffraction Standards (JCPDS). Moreover, field emission scanning electron microscopy (FE-SEM) illustrated the particle morphology of ZnS, showing a range between 200 and 500 nm size. Additionally, the cyclic voltammetry results indicated that the modified electrode produced a greater current response than the bare electrode, highlighting its improved sensitivity to dopamine molecules. Conclusion ZnSnanoparticles were synthesized via a hydrothermal method and characterized using XRDand FE-SEM. These nanoparticles were used for electrochemical dopamine detection, showing potential for advanced sensing platforms. Integrating ZnS into microfluidic devices enables real-time dopamine monitoring, opening new possibilities for healthcare and neurochemical research. Exploring surface engineering techniques could further enhance the electrochemical performance of ZnS-based sensors.

The transformation of type-I La2O3/α-Bi2O3 into multi-heterojunctions during photocatalysis with enhanced photoreactivity

A small quantity of broad bandgap rare earth lanthanum oxide (La2O3) was incorporated into monoclinic bismuth oxide (α-Bi2O3) through a one-step facile calcining route to construct an efficient type-I La2O3/α-Bi2O3 heterojunction photocatalyst for pollutant degradation under UV-light irradiation. The effect of adding La2O3 on the morphology, textural, optical, photoelectrochemical, and photocatalytic properties of α-Bi2O3 was investigated. Interestingly, feeding as low as five molar percent (5 %) La2O3 could significantly increase the BET surface area and generate more h+ and •O2− for photocatalytic reaction. Moreover, the calcining-induced carbon in La2O3/α-Bi2O3 revealed a vital role in suppressing the charge carrier recombination by quickly transferring charges to the photocatalyst's surface. In particular, during the recycling process, the in-situ formed Bi2O2CO3 changes the charge carrier transferring pathway and reveals a transformation of type-I La2O3/α-Bi2O3 into multi-heterojunction of type-I and type-II. Furthermore, the formation of Bi2O2CO3 results in more active sites for the photocatalytic reaction with improved reaction kinetics. This work provides a new direction for understanding a photocatalytic system's recycling phenomena and intrinsic kinetics.

Cyclic Atomic Layer Etching of PdSe2

AbstractThe unique characteristic of 2D transition‐metal dichalcogenide (TMD) semiconductor materials such as PdSe2 is the ability of the bandgap to vary on the basis of the number of layers present. This variation results in a broad bandgap range spanning from semi‐metallic to semiconducting materials, underscoring the significance of precisely controlling the material thickness. In this study, the thicknesses of chemical vapor deposited PdSe2 films are precisely controlled layer‐by‐layer via cyclic atomic layer etching (ALE), which comprised a radical adsorption step generated by oxygen and chlorine plasmas, followed by a desorption step with an organic solvent vapor such as formic acid. Cyclic etching with one monolayer of PdSe2/cycle is achieved using both types of adsorption gases while maintaining the ratio of Se/Pd underlying PdSe2 at ≈2. This cyclic ALE method is also applicable for smoothing TMD material surfaces by isotropically removing individual rough surface layers. Because this etching method only utilizes chemical reactions with radicals generated by plasmas and organic vapors, it is not only unaffected by the physical damage caused by the irradiation of energetic particles such as ions in plasmas, but also is applicable to 3D structure processing.

Phase Transition of a Chiral Lead‐Free Hybrid Antimony(III) Halide Crystal

AbstractChiral organic–inorganic hybrid lead halides have recently attracted great attention due to their unique chirality and diverse functional properties. However, they suffer from highly toxic lead, while lead‐free chiral hybrid metal halides especially those with phase transitions remain sparse. Here, we report a new lead‐free chiral metal halide crystal [R‐3‐fluoropiperidinium]2SbCl5 ([R‐3‐FPP]2SbCl5), which crystalizes in chiral P212121 space group at 293 K and consists of chiral [3‐FPP]+ cations and one‐dimensional [SbCl5]n2− zigzag chains of corner‐sharing SbCl6 octahedrons. Notably, [R‐3‐FPP]2SbCl5 undergoes an above room temperature phase transition at 313 K, which can be attributed to the order‐disorder transition of both the organic [R‐3‐FPP]+ cation and inorganic [SbCl5]2− anions. In addition, [R‐3‐FPP]2SbCl5 also shows a broad band gap of 3.21 eV. This work promotes the exploration of chiral lead‐free hybrid lead halides with phase transitions.

Green synthesis of magnesium oxide nanoparticles using Hyphaene thebaica extract and their photocatalytic activities

Magnesium oxide nanoparticles (MgO NPs) represent an interesting inorganic material widely utilized across various fields including sensing, antimicrobial applications, optical coatings, water purification, fuel additives, absorbents, and catalysis, owing to their exceptional broad energy band gap, surface affinity, and strong chemical and thermal durability. In this investigation, MgO NPs were successfully synthesized through a green approach employing fruit extract from the gingerbread tree (Hyphaene thebaica). Analysis via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed their agglomerated quasi-spherical shape with a size range of 20–60 nm. The X-ray diffraction (XRD) pattern exhibited prominent peaks at planes (200) and (220), indicating the high crystallinity of MgO NPs with a crystallite size of 32.6 ± 5 nm while Energy-dispersive X-ray spectroscopy (EDS) analysis highlighted the composition comprises 40.47% Magnesium and 48.64% Oxygen by weight. Fourier transform infrared spectroscopy (FT-IR) revealed characteristic Mg-O bonds through peaks at 560 cm−1 and 866 cm−1, while Raman spectroscopy affirmed the cubic structure of MgO. Subsequently, the photocatalytic performance of MgO NPs under visible light irradiation was evaluated. Remarkably, the addition of 1 g/L of MgO nano-catalyst resulted in a degradation efficiency of 98% after 110 min on methylene blue dye, showcasing the high catalytic activity of MgO NPs. This remarkable photocatalytic efficiency emphasizes the potential of MgO NPs in environmental remediation.

Improvement of SAW Resonator Performance by Petal-like Topological Insulator.

This article introduces a novel petal-like SAW topology insulator, which can transmit sound waves with low loss and high flexibility in an ultra-wide frequency band by simultaneously adjusting multiple structural parameters of phononic crystals. Using finite element analysis, it was found that adjusting these parameters can generate a broadband gap of 55.8-65.7 MHz. This structure can also achieve defect immunity and sharp bending in waveguide transmission. When this topology insulator is applied to resonators, compared to traditional designs, the insertion loss is reduced by 22 dB, the on-load quality factor is increased by 227%, the off-load quality factor is increased by 1024.5%, and the quality sensitivity is improved by 3.7 times compared to bare devices.

The Influence of Defects on the Structural, Optical, and Antibacterial Properties of Cr/Cu Co-Doped ZnO Nanoparticles

In this research, Cu/Cr codoped ZnO nanoparticles (Zn₀.₉₉₋ₓCu₀.₀₁CrxO) were prepared using the sol-gel technique. The dopant ratio was systematically varied, ranging from x = 0.01 to 0.05 in increments of 0.01. This variation allowed for an exploration of the impact of defects on the structural, microstructural, optical, and antibacterial properties of Cu/Cr-codoped ZnO nanoparticles. Structural analysis of the Zn₀.₉₉₋ₓCu₀.₀₁CrxO nanoparticles was conducted using X-ray diffraction. The findings confirmed the presence of a hexagonal wurtzite structure in the ZnCuCrO nanoparticles, as determined by the c/a ratios in the range of 1.6013 and 1.6039. The surface morphology, crystallite size, and nanoparticle shapes were determined through scanning electron microscopy. The nanoparticle elemental compositions were analyzed through electron dispersive spectroscopy. The optical characteristics of the samples were assessed using a UV spectrophotometer. The energy band gaps for the nanoparticles were computed, and we discussed how dopant elements and defects affected their optical properties. We determined the refractive index using five distinct models. Notably, the highest band gap was observed for Zn₀.₉4Cu₀.₀₁Cr₀.₀5O (Eg=3.27 eV).Positron annihilation lifetime spectroscopy was employed to investigate the defect type, defect density, and crystal quality of Cu/Cr-codoped ZnO nanoparticles. The shortest lifetime τ1 obtained the highest value (0.181 ns) for Zn0.97 Cu0.01Cr0.02O nanoparticles. Zn₀.₉₉₋ₓCu₀.₀₁CrxO NPs were assessed for their antibacterial effects on E. coli (gram-negative) and S. aureus (gram-positive). Cu/Cr codoped ZnO nanoparticles show potential as materials for optoelectronic and sensor applications due to their broad band gap (Eg > 3) and high refractive index (n > 2).