Broad Band Gap Research Articles

A broadband 3-way power divider based on gap waveguide for Ka-band applications

The present study aims to design a broadband gap waveguide-based 3-way power divider in Ka-band. Gap waveguide technology is employed to remove serious challenges of fabrication in mmWave frequencies using printed and hollow waveguide technologies. The validation of proposed structure is performed with experimental measurements. There are better isolation and return loss between the output ports than around 20 dB over 27.4–35.1 GHz frequency range. There is less amplitude imbalance between the output ports than ± 0.42 dB. A close agreement exists between measured and simulated results. The results are beneficial for the design, fabrication, integration and expansion of mmWave components.

N-AlInN/p-Si Heterojunction Solar Cell Growth by RF Sputtering via Down-Converting Layers Co-Dopedwith Tb3+/Yb3+ Rare Earth Ions

Nowadays, III-nitrides are widely recognized as highly desirable semiconductors for electronic and opto-electronic devices, thanks to the distinctive properties of these materials. It is worth mentioning that aluminum-indium nitride (AlInN) alloys have become important contenders, showing great potential for photovoltaic applications. This is attributed to their broad direct bandgap energy, encompassing the solar spectrum from 0.7 eV (InN) to 6.2 eV (AlN). Furthermore, their exceptional resistance to high temperatures and resistance to high-energy particles further enhance their suitability for various technological applications. In this study, we will examine the optimization of the AlInN/Silicon heterojunction PV cell growth by the RF sputtering technique. Our approach is founded on prior investigations already conducted by our research group, which focused on down-conversion through the utilization of 70 SiO2–30 HfO2 glass-ceramic layers co-doped with Tb3+/Yb3+ rare earth ions to optimize the efficiency of the PV cells under investigation.

Effect of Water Adsorption on Bilayer h-BN: First-Principles Study

Recent years have seen a great deal of excitement in the study of the structural, electronic and magnetic behavior of two-dimensional (2D) materials. This has great promise for improved electronics, fascinating quantum technologies, and energy-efficient gadgets. In the current work, we have investigated the structural, electronic, and magnetic properties of bilayer h-BN and water adsorption on pristine h-BN bilayer supercell material using the density functional theory (DFT) method. We have examined the structural properties, and found that they are structurally stable materials. We have examined the band structure and density of states (DoS) calculations of h-BN, and water adsorbed h-BN materials. It is found that water adsorbed on pure h-BN is an n-type Schottky semiconducting material, and pristine h-BN is a broad bandgap p-type Schottky material. P-type insulating material becomes n-type semiconducting material when water molecules are adsorbed. Additionally, after looking the materials' magnetic properties through their DoS and partial density of states (PDoS) analysis. We found that h-BN, and water adsorbed h-BN have non-magnetic properties. Thus, they have been employed extensively in many different industries because of their bandgap energy and non-magnetic in nature.

Novel broadband near-infrared emission in Cr3+-activated Sr3ZnGe5O14 phosphor for an electroluminescent stable pc-LED

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have exhibited tremendous potential in spectroscopic technology, promoting the demand of developing novel NIR materials with excellent properties. In this paper, a series of germanate based NIR phosphors Sr3ZnGe5O14: xCr3+ (0 ≤ x ≤ 0.05) were synthesized by high temperature solid state reaction. The X-ray diffraction (XRD), scanning electron microscopy (SEM), Ultraviolet diffuse reflection, photoluminescence spectra and PL decay were measured to analyze the crystal structure, morphology properties and elements composition, PL emission properties and lifetimes of these NIR phosphors. Results demonstrated that phosphors Sr3ZnGe5O14: xCr3+ (0 ≤ x ≤ 0.05) crystallized in a trigonal with a space group of P321(150) with a broad band gap (Eg) of 4.70–4.59 eV. Sample Sr3ZnGe5O14: 0.03Cr3+ with the best PL emission properties showed a good thermal stability with the PL emission intensity remains 69 % of its initial value at 420 K. It's worth noting that the NIR device based on Sr3ZnGe5O14: 0.03Cr3+ displays an impressive electroluminescent emission stability, for example, the electroluminescent emission intensity is still about 92.3 % of its initial value when the NIR pc-LED light up for 18 h. These research results provided an important guidance for developing novel Cr3+ doped germanate based NIR phosphors with excellent thermal and electroluminescent emission stability.

Mechanical vibration absorber for flexural wave attenuation in multi-materials metastructure

Vibration isolation is a promise to suppress mechanical vibration from a host structure, similarly, a mechanical vibration absorber, a simple but effective device to attenuate flexural wave propagation, which has been implemented in civil and mechanical engineering. This paper presents a type of composite sandwich phononic crystal to attenuate the flexural wave propagation in a beam structure, which can effectively suppress mechanical vibration in a broad band gap by repetitively arranging phononic crystal. First, the elastic wave dispersion characteristic in a composite sandwich beam structure is derived, and a triangular shape phononic crystal for flexural wave attenuation by taking advantage of destructive interference is presented. Then two dimensional phononic crystals are designed by assembling four different unit-cells of metabeam. Finally, numerical experiments are conducted to verify the effectiveness of the proposed mechanical metamaterial absorbers to attenuate flexural wave propagation, the numerical results indicate that the proposed metamaterial is of good performance in mechanical vibration suppression, which can effectively mitigate structure vibration in low-frequency domain than the structure without phononic crystal and single layer metamaterial beam structure. It is the first attempt to design a mechanical metamaterial absorber with the mechanism of destructive interference with composite sandwich phononic crystal.

The electronic and optical properties of InSe/ZnO van der Waals heterojunction:First principles study

The efficient, simple and low-cost photocatalysts has become a hot topic in the field of photocatalysis, ZnO has attracted the attention of researchers due to its high photocatalytic efficiency. Although, the broad band gap of around 3.4 eV in ZnO greatly limits its optical absorption efficiency. Based on this, two types of InSe/ZnO heterojunction models with different configurations are constructed, their electronic and optical properties are studied through first principles calculations. The results indicate that the II InSe/ZnO heterojunction has a band gap of 1.84 eV, which compensates for the shortcomings of ZnO monolayer broad band gap absorption of visible light and the difficulty of InSe monolayer in participating in water splitting oxidation reactions. The construction of heterojunctions using InSe and ZnO significantly improves the light absorption efficiency, especially in the visible spectral region, compared to ZnO monolayers, accelerating the generation and migration efficiency of photo generated electrons, thereby improving the catalytic efficiency of ZnO.

Bandgap and vibration isolation properties of cylindrical metastructure with chiral ring oscillators

A cylindrical metastructure with chiral ring oscillators is proposed for broadband vibration isolation, and experimental studies are carried out. The vibration transmission characteristics of cylindrical chiral metastructure is calculated and analyzed. Vibration transmission of three prototypes of cylindrical chiral metastructure is tested, and the results by using numerical simulation method are validated by the experimental results. It can be found that the broad bandgap can be created by the coupling bandgap between the multiple locally resonant bandgaps and Bragg scattering bandgap. Therefore, the good low-frequency vibration isolation performance can be achieved by designing the suitable parameters of chiral ring oscillators.

Multi-Order Asymmetric Acoustic Metamaterials with Broad Bandgaps at Subwavelength Scales.

Noise manipulation at the subwavelength scale remains a challenging problem. To obtain better broadband sound isolation within the subwavelength range, a class of asymmetric acoustic metamaterials (AAMs) based on rotation is proposed, and this class of AAMs can further improve subwavelength sound isolation performance by introducing multi-orders. The influences of changing the alternate propagation length of the coiled channel and the square cavity in the unit cell on the band frequency distribution and the omnidirectional band structure were investigated. The effective parameters are calculated with the S-parameter retrieval method, and the generation and change mechanisms of the bandgaps were elucidated. The calculation of sound transmission characteristics showed that, in the asymmetric mode, the overall sound isolation performance of the structure was greatly improved, and the relative bandwidth expanded as the alternate propagation length of the coiled channel and square cavity increased. The omnidirectional bandgaps from the first-order to the third-order AAMs occupied 63.6%, 75.96%, and 76.84% of the subwavelength range, respectively. In particular, the first bandgap moves to the low frequency and becomes wider. Both the experimental results and numerical analyses consistently showed that disrupting structural symmetry enhances acoustic metamaterials for superior broadband sound isolation, inspiring broader applications for asymmetry in this field.

Structural, Electric transport and Photocatalytic properties of Gd3+ / ZnO nanostructures

Metal oxide nanoparticles have gained a lot of popularity in recent years because of their broad band gap and several practical uses in solar, catalysis, sensors, actuators, and other domains. This work investigates the effects of Gd ion substitution on structural and electrical transportation properties in co-precipitated ZnO nanostructures. The prepared samples were characterized using XRD, field emission scanning electron microscopy, FT-IR (infrared spectroscopy), PL (photoluminescence), and complex impedance spectroscopy. The XRD data with crystallite size of 29 nm revealed the wurtzite hexagonal structure in space group P63mc. The morphology micrograph shows where the samples have accumulated. For two hours, a photocatalytic reactor was used to measure the photocatalytic degradation of Gd-doped ZnO nanoparticles. Degradation efficiencies (ϳ%) for the ZnO sample doped with Gd are 81 percent.

Vibration attenuation band tuning by active stiffness control of local resonators of metamaterials

This paper presents a design of metamaterials with a broader bandgap by active stiffness control of local resonators. A series of cantilever beams are connected to the host structure, serving as local resonators to open the bandgap for vibration attenuation. The piezoelectric transducers bonded on the cantilever beams are shunted to a negative capacitance-negative inductance series circuit (NCNL). The variation of the effective modulus of the piezoelectric sample when connected to NCNL is discussed. In addition, the effect of the NC circuit and negative capacitance in series with positive inductance (NC-L) circuit on the effective modulus of shunted piezoelectric transducers is also analyzed for comparison. By tuning the NCNL circuit, the elastic modulus of the beam-type resonator exhibits frequency-dependent, which will achieve active stiffness tuning. Subsequently, the transmittance analysis of a metamaterial beam with active stiffness resonators is conducted using finite element method. The finite element results show that a broader attenuation band can be achieved by properly selecting the parameters of NC-NL circuits. This work provides a promising method for effective vibration attenuation using metamaterials.

Research On Mg Doping in Nitride Semiconductor Materials

Summarized the achievements of various model research directions in nitride Mg doped semiconductors in this thesis. Due to the Internal properties of Mg acceptors which resulting the low ionization rate of acceptor, and the low hole mobility in heavily Mg doped nitrides, the conductivity of Mg doped nitrides is limited. At present, research is divided into three categories of models, one is a new type of polarization model. This model adopts a built-in electron polarization ionization acceptor dopant in the bulk uniaxial semiconductor crystal, and provides an attractive solution for the problem of P-type and n-type doping in broadband gap semiconductors. The other two are the traditional thermal activation model. There are mainly ultra-high-pressure-annealing (UHPA) and multicycle rapid thermal annealing (MRTA) respectively. Both of these schemes can activate more Mg impurities, resulting in higher conductivity in nitrides. The principles, advantages and disadvantages, and future development prospects will be explained of these three models in this thesis.

Tunable low-frequency broadband metamaterial beams composed of hierarchical annular cantilevers

Tuning the resonance frequency of the local resonators in an active way and obtaining a broad bandgap at low frequency is a long-lasting challenge for traditional elastic metamaterials. This work proposes a kind of tunable metamaterial beam to isolate flexural waves, which are composed of hierarchical annular cantilevers with a steel mass block embedded in the center of each unit cell. To obtain a broad low-frequency bandgap, a genetic algorithm-based size optimization is utilized to determine the optimal geometry parameters of the unit cell. The tunability of the metamaterial beam is realized by attaching different numbers of permanent magnets to the embedded mass block. Such a tuning approach makes the change of the resonator’s mass available. Moreover, based on the rainbow effect, ultra-broadband flexural wave attenuation is realized by forming a gradient metamaterial beam. Both numerical and experimental results verify the good flexural wave attenuation ability of our proposed tunable metamaterial beam.

A thorough investigation of the utilization of metal-organic framework (MOF) coated titanium dioxide in photocatalytic applications: A review

Overall, this review provides accessible information about Metal-organic frameworks (MOFs) coated on TiO2 surfaces that can advance the photocatalytic activity of designing and creating more efficient materials as well as promoting application. TiO2 photocatalyst has been extensively studied for the unraveling of various environmental issues. Despite its potential, the high rate of recombination of photogenerated charge carriers and its broad band-gap energy pose obstacles to its application in photocatalysis. In order to overcome these hurdles, our research has concentrated on the incorporation of MOF coatings. The production of photoactive MOF coatings is a key issue because they have excellent photocatalytic performance and offer many industrial opportunities for photocatalysis. Different methods have been applied to produce MOF shell or layer on TiO2 NRs, NTs, NWs, and hollow particles. The object of this review is to supply an overview of the research on applying the MOF coating to the titania surface.

Design of aluminum plate phononic crystals with wide bandgaps via free-form shape optimization using deep neural networks

Phononic crystals (PnCs) with a broad bandgap have been the subject of extensive research, particularly for their capacity to manipulate elastic waves efficiently. However, the explored design space remains relatively limited, and the shapes under consideration are often relatively simple. This study optimizes a free-form hole shape for square and hexagonal lattice aluminum plate PnCs with high relative bandgaps (i.e., ratio of bandgap to its center frequency). Optimization is implemented by leveraging the predictive capabilities of deep neural networks (DNNs). For both types of lattices, an initial training dataset is made up of 20,000 randomly generated PnCs unit cells, each containing a symmetric smooth hole. The relative bandgap is subsequently evaluated using the Finite Element Method (FEM). For each lattice, one Deep Neural Network (DNN) is trained to predict the relative bandgap, while another DNN is used to classify whether the bandgap exists. The predictive power of DNNs is exploited to search for design candidates with high relative bandgaps using the genetic optimization algorithm (GOA). The relative bandgaps of new candidates are determined and validated using FEM. The results of these analyses are then utilized to update the DNNs through active learning (AL) techniques. As a result, the relative bandgaps of the progressively refined hole shapes for square and hexagonal lattices are 2.382 and 10.383 times larger, respectively, than those of circular holes.

Suppression of low-frequency ultrasound broadband vibration using star-shaped single-phase metamaterials

In order to suppress the low-frequency ultrasound vibration in the broadband range of 20 kHz–100 kHz, this paper proposes and discusses an acoustic metamaterial with low-frequency ultrasound vibration attenuation properties, which is configured by hybrid arc and sharp-angle convergent star-shaped lattices. The effect of the dispersion relation and the bandgap characteristic for the scatterers in star-shaped are simulated and analyzed. The target bandgap width is extended by optimizing the geometry parameters of arc and sharp-angle convergent lattices. The proposed metamaterial configured by optimized hybrid lattices exhibits remarkable broad bandgap characteristics by bandgap complementarity, and the simulation results verify a 99% vibration attenuation amplitude can be obtained in the frequency of 20 kHz–100 kHz. After the fabrication of the proposed hybrid configurational star-shaped metamaterial by 3D printing technique, the transmission loss experiments are performed, and the experimental results indicate that the fabricated metamaterial has the characteristics of broadband vibration attenuation and an amplitude greater than 85% attenuation for the target frequency. These results demonstrate that the hybrid configurational star-shaped metamaterials can effectively widen the bandgap and realize high efficiency attenuation, which has capability for the vibration attenuation in the application of high-precise equipment.

The Comprehensive Features, Current Aspects, Synthesis, Characterization and Role of Nanomaterials in Modern Industries through Nanotechnology

Nanotechnology has attained the valuable significant attention throughout time because to its compelling and pioneering uses in the forthcoming industrial age, particularly in relation to nanomaterials. Nanomaterials find applications in several areas, including agriculture, biomedicine, electronics, energy, transportation, communications, cosmetics, coatings, materials, and mechanical engineering. Numerous techniques have been used to fabricate nanoparticles (NPs) with precise control over their form, size, dimensions, and structure. There may be exist two primary methodologies for the synthesis of nanoparticles, namely the top-down and bottom-up techniques. These nanoparticles include core/shell (CS) nanoparticles, gold nanoparticles (Au-NPs), nickel nanoparticles (Ni-NPs), platinum nanoparticles (Pt-NPs), copper oxide nanoparticles (CuO-NPs), zinc oxide nanoparticles (ZnO-NPs), palladium nanoparticles (Pd-NPs), and silicon nanoparticles (Si). The physicochemical qualities may vary depending on the size and form of the object. There are many categories of nanocomposites, including ceramic matrix nanocomposites, metal matrix nanocomposites, and polymer matrix nanocomposites. Semiconductor materials have characteristics that lie between those of metals and nonmetals, making them very versatile and widely used in numerous applications, as documented in the literature. Semiconductor nanoparticles have broad bandgaps, resulting in notable modifications to their characteristics via bandgap tuning. Carbon nanotubes (CNTs) and graphene are widely recognized as prominent constituents within the carbon-based nanomaterials category. There are many aspects of the functional nanomaterial needed to explore their chemical and physical potentials for the use in the sub valuable industries areas.

Photodegradation of Methyl violet using Ag modified TiO2 nanotubes by UV and UV/ H2O2

Titanium dioxide (TiO2) is a semiconductor material that is frequently utilized in photodegradation applications. Its application in photodegradation is constrained by its broad band gap of 3.2 eV and increased rate of photoelectron recombination. However, by doping TiO2 with metallic nanoparticles, the band gap can be modified and photodegradation can be improved. The present study explores the fabrication of Ag-modified TiO2 nanotube photocatalysts by electrochemical anodization followed by hydrothermal method. The structural, morphological, compositional, optical, and thermal properties of prepared photocatalysts were characterized by X-ray analysis, Field emission scanning electron microscopy, N2 adsorption desorption analysis, X-ray photoelectron spectroscopy, Energy dispersive X-ray spectroscopy, UV–Vis diffuse reflectance analysis and Thermogravimetric-differential thermal analysis. The prepared photocatalyst was utilized to investigate the degradation of methyl violet in the presence of UVA and UVC radiation. The effects of UVA and UVC illumination on the degradation process, the effect of Ag loading in the TiO2 nanotube arrays and the role of H2O2 in the degradation of pollutant were studied. The degradation efficiency of methyl violet in the presence of UVC light was three times that of UVA light. For pristine TiO2 photocatalyst, the maximum degradation of 70% was obtained under UVC illumination in 8 h. When H2O2 was added, complete degradation was observed within 3 h. Reusability studies have shown that photocatalysts are stable and can be used for the degradation of methyl violet.

Broadening Low-Frequency Band Gap of Double-Panel Structure Using Locally Resonant Sonic Crystal Comprised of Slot-Type Helmholtz Resonators

An approach is presented to form and broaden the low-frequency band gap of the double panel structure (DPS) by using a locally resonant sonic crystal (LRSC) in this work. The LRSC is made of cylindrical Helmholtz resonators arranged on square lattice. Their designs are similar to a slot-type resonator, but have different depths of slot. Elongating the slit neck inward and distributing the depths of slots produce a broad local resonant band gap at low frequencies: an average insertion loss (IL) of 10.9 dB covering 520 Hz to 1160 Hz with a LRSC of 12 cm width. Next, the effect of porous material filled into the resonators on the local resonant band gap is evaluated. It is shown that filling of porous material into the resonators decreases the height and width of the local resonant band gap. Finally, the transmission losses (TLs) through the DPS with LRSC are calculated as a function of the incident angle of the sound wave for LRSC embedded in porous material and not. The results show that the porous material can be significantly reduce the incident angle dependency of TL through the DPS with LRSC.

Multiple broadband gaps and vibration suppression mechanisms for innovative star shaped metamaterial structures with triangular characteristics

Metamaterials have received extensive attention due to their special properties in the fields of wave attenuation and acoustic engineering. Many researchers have designed metamaterials with different band gap frequency ranges. In this paper, a star shaped metamaterial structure with triangular characteristics is proposed to attenuate mid and low frequency elastic waves in practical applications. The band gap and dispersion characteristics of the structure are numerically studied. The results show that the structure generates ultra-wide band gaps in the frequency range of 6000 Hz, accounting for up to 69.14%. Interestingly, by adding a support structure to the original structural unit, the bandwidth of the improved structure reached 73.89%, and multiple band gaps were opened within 2000 Hz. Finally, the vibration transmission loss of the structure is analyzed by finite element method, and the control performance of vibration transmission in periodic structures is simulated, demonstrating its potential in practical applications.

Propagation mechanism of low-frequency elastic waves and vibrations in a new tetragonal hybrid metamaterial

In order to achieve low-frequency vibration and noise reduction, artificial metamaterial with great potential in this field have been widely found. Based on previous studies, a new tetragonal hybrid metamaterial structure is proposed in this paper. It is exciting that the combination of inclusions with different material properties and sizes can affect the generation of band gaps. Then, based on the selected frequency, the propagation characteristics of waves in the structure were qualitatively analyzed using group velocity and phase velocity, and the potential for vibration reduction and noise reduction of the proposed structure was verified through finite element simulation of vibration in finite period structures. The results show that the proposed structure can open multiple broadband gaps, and the frequency range of the band gap can be flexibly adjusted according to needs. This study provides a new way for the design of low-frequency phononic metamaterial systems.