Single Bandgap Research Articles

Attenuation enhancement for the inertial amplification metamaterial using multiple local resonators

The bandgap generated by inertial amplification metamaterial (IAM) features broad width and low-frequency, but weak attenuation strength within a large part of the bandgap. Introducing local resonators is the most common way to enhance low-frequency vibration attenuation characteristics. However, discrete bandgaps are usually observed for the metamaterials containing non-uniform resonators. In this paper, two resonators are attached to the baseline mass and the inertial amplifier of IAM, respectively. The merging of locally resonant bandgaps is realized by coupling them with the inertial amplification bandgap. The attenuation characteristics of the coupled bandgap are first studied, including the number and positions of attenuation peaks. Then, the methods to enhance the attenuation strength are explored. It is found that two attenuation peaks are attributed to zero effective stiffness while another one is induced by infinite effective mass. The conditions for the triple peaks occurring in a single bandgap are derived according to the rational polynomial form of the dispersion relation. Additionally, the attenuation strength within the coupled triple-peak bandgap is enhanced by increasing the mass of the resonator on the baseline mass and adjusting the coupling degree between the inertial amplification and the resonance of the local resonator on the inertial amplifier. Finally, to overcome the decrease in attenuation level when the attenuation-enhanced region widened, a supercell with high attenuation strength is designed by combining unit cells with different attenuation peaks. Compared to the IAM with double-peak bandgap in the previous study, the minimum attenuation level in the enhanced region is increased by 84%. This study gives guidance to enhance the attenuation characteristics of metamaterials in the low-frequency region.

Physical properties of La:ZnO thin films prepared at different thicknesses using spray pyrolysis technique

Herein we investigate the impact of film thickness on the physical properties of Lanthanum (La) doped ZnO thin films. The films were fabricated using the spray pyrolysis technique with a consistent La content of 5 weight (wt) % in the initial solution. X-ray diffraction analysis indicated the presence of a hexagonal ZnO phase with preferred orientation along the (002) direction and no other phases were detected. The crystallite sizes were calculated using the Halder-Wagner equation, with a maximum size of 16.1 nm observed for a film thickness of 106 nm. Field-emission scanning electron microscopy (FE-SEM) images revealed the formation of a continuous film with an average grain size that increased as the thickness of the film increased. The grain size ranged from 74.5 to 136 nm as the film thickness varied from 106 to 426 nm. Films with lower thicknesses up to 196 nm exhibited two band gaps at approximately 3.2 and 4 eV, while films with higher thicknesses displayed a single band gap around 3.2 eV. The refractive index dispersion for all films was modeled using the Cauchy model, with parameters showing high dependence on the thickness values.The refractive index at high frequency, as calculated using the Cauchy model, was observed to decrease with increasing film thickness, ranging from 1.87 at 106nm to 1.63 at 426nm. Similar values were obtained by fitting the optical refractive index data with the Wemple-DiDomenico relation. Additionally, the UV sensing performance of the films was evaluated against UV light of a single wavelength (365 nm) at applied voltages of 10, 20, and 30V. The rise and decay times were measured, with the film thickness of 426 nm exhibiting the shortest rise and decay times at a specific applied voltage.

Topology-optimized photonic topological crystalline insulators with multiband helical edge states

Abstract Photonic topological crystalline insulators (PTCIs) with helical edge states provide an alternative way to achieve robust electromagnetic wave transport and processing. However, most existing PTCIs only involve a single topological bandgap, and generally support a pair of gapped helical edge states, restricting the scope of applications in various fields such as multiband waveguides, filters, and communication systems. Here, we design dual-band PTCIs, in which multiple helical edge modes appear within two distinct bulk gaps, for transverse electric (TE) and transverse magnetic (TM) modes, respectively, by introducing the topology optimization method into the photonic crystals with glide symmetry. For PTCIs with TE modes, the mismatched frequency ranges of edge modes hosted by two orthometric boundaries offer an opportunity to realize a photonic demultiplexer. For PTCIs with TM modes, we show the enhanced second harmonic (SH) generation through the coupling of multiband edge modes by matching the frequency ranges of edge modes within the first and second bandgaps to fundamental and SH waves, respectively. This work provides a new way for designing multiband PTCIs with helical edge states, having promising potentials in developing multiband topological photonic devices for both linear and nonlinear applications.

Analysis and Design of Low Noise Voltage Regulator With Integrated Single BJT Bandgap Reference Upto 10 mA Loads

Analysis and Design of Low Noise Voltage Regulator With Integrated Single BJT Bandgap Reference Upto 10 mA Loads

Synergetic Triple Absorber Based High‐Efficiency Solar Cell Design

AbstractComputational analysis of triple absorber‐based solar cell structure is undertaken. This solar cell device configuration allows better utilization of the incident solar spectrum. Three different absorbers with a band gap in the range 1–1.5 eV are sandwiched between high‐doped p+ and n+ regions in descending order of electron affinity to form an energy‐matched multiple absorber device. A comprehensive analysis of key device parameters influencing performance, including band gap, conduction band alignment, interfacial defects, and thickness, is presented. The optimized triple absorber device shows beyond Shockley–Queisser limit (SQ limit) performance under the constraint of passivated interfaces with defect density below 1013 cm−2. Wide spectrum coverage leads to high short circuit current and an efficiency of 40.3%, which is higher than the SQ limit for single band gap solar cell.

Surface wave propagation control with locally resonant metasurfaces using topology-optimized resonatorsa).

Locally resonant elastodynamic metasurfaces for suppressing surface waves have gained popularity in recent years, especially because of their potential in low-frequency applications such as seismic barriers. Their design strategy typically involves tailoring geometrical features of local resonators to attain a desired frequency bandgap through extensive dispersion analyses. In this paper, a systematic design methodology is presented to conceive these local resonators using topology optimization, where frequency bandgaps develop by matching multiple antiresonances with predefined target frequencies. The design approach modifies an individual resonator's response to unidirectional harmonic excitations in the in-plane and out-of-plane directions, mimicking the elliptical motion of surface waves. Once an arrangement of optimized resonators composes a locally resonant metasurface, frequency bandgaps appear around the designed antiresonance frequencies. Numerical investigations analyze three case studies, showing that longitudinal-like and flexural-like antiresonances lead to nonoverlapping bandgaps unless both antiresonance modes are combined to generate a single and wider bandgap. Experimental data demonstrate good agreement with the numerical results, validating the proposed design methodology as an effective tool to realize locally resonant metasurfaces by matching multiple antiresonances such that bandgaps generated as a result of in-plane and out-of-plane surface wave motion combine into wider bandgaps.

Multifrequency topological interface modes in a nonlocal acoustic system with large winding numbers

Topological interface states have wide applications for their robustness and energy localization. Multiple topological interface states in 1D acoustic systems are preferred for signal enhancement at specific frequencies. However, previous 1D topological systems with local interactions can realize only one topological interface state in a bandgap. Here, we find that connected acoustic Su–Schrieffer–Heeger (SSH) chains with nonlocal interactions can achieve two or more topological interface states at different frequencies in a single bandgap, even in the subwavelength region. The difference in frequency can be modulated by merely adjusting the structural design at the interface. A mechanical metamaterial with a large winding number is designed to realize multiple nondegenerate topological interface states. This metamaterial can enhance weak acoustic signals at multiple specific frequencies simultaneously and has applications in the fields of acoustic detecting and color imaging.

Robust multi-band acoustic router by hybridizing distinct topological phases

The acoustic router, capable of guiding sound waves along specific paths, holds a significant value in both science and engineering. Compared to traditional methods of implementing acoustic routing, the recently developed concept of topological acoustics, with its nontrivial topological phases, offers the potential to achieve a robust acoustic routing device. However, current investigations primarily focus on individual topological phases within a single bandgap, thereby limiting the exploration of diverse topological phases in multiple bandgaps and their hybridizations. In this study, we utilize topological acoustics to construct a robust dual-band acoustic router, which is challenging to achieve with traditional acoustics. By calculating Chern and valley topological phases in different bands, we reveal the competitive relations between different topological phases in a specific bandgap. Furthermore, by modifying the boundary meta-atoms, we have increased the operational frequency bands and proposed a triple-band acoustic router.

Single walled carbon nanotubes band gap width measurement and the influence of nitrogen doping research.

The adjustment and measurement of the band gap width of single-walled carbon nanotubes are crucial for optimizing the design and enhancing the performance of carbon-based devices. This study utilizes the relationship between the band gap and temperature of semiconductor-based carbon nanotubes. The electrical conductivity of carbon nanotubes was obtained at various temperatures, and the corresponding band gap width (0.57 eV) was determined. The introduction of nitrogen results in a reduction of the band gap width and an increase in current flow between the device source and drain electrodes. Theoretical calculation demonstrated that nitrogen doping not only increases the conductivity of carbon nanotubes but also effectively inhibits the Schottky barrier between carbon nanotubes and metal electrodes. The Schottky barrier and the internal electric field can be effectively modulated via nitrogen doping in carbon nanotubes, which enhances the performance of carbon-based devices.

Quasi-Flat Narrow Bandgap Copper Indium Gallium Selenium Bottom Cell Application in Perovskite/Copper Indium Gallium Selenium Tandem Solar Cells

Cu(In 1− x Ga x ) Se 2 (CIGS) is a promising and ideal material for bottom cell in tandem solar cells, which can break the double junction solar cell’s Shockley–Queisser theoretical efficiency to above 40%. However, the high-efficiency CIGS solar cells deposited by the 3-stage process is normally double grading, leading to an incomplete absorption in the bottom cells. In this study, single bandgap grading and quasi-flat bandgap CIGS solar cells are proposed and fabricated for perovskite/CIGS 4-terminal tandem solar cells, which are more favorable for long-wavelength absorption and higher short-circuit current density J sc . Various characterizations have been performed to investigate the crystallization, crystal defects, composition depth profile, and carrier dynamics of the CIGS thin films. Our study reveals that the performance of CIGS solar cells with high Ga content is worse than expected. Using bandgap engineering, we can obtain CIGS solar cell with an efficiency above 16.5% regardless of the GGI [Ga/(Ga + In)] varying from 0.27 to 0.40. However, CIGS solar cells with less Ga content and low bandgap exhibit superior long-wavelength spectral response, making them more suitable for bottom cell applications in tandem solar cells. In combination with an 18.9% semitransparent inorganic perovskite solar cell, a 25.6% perovskite/CIGS tandem device in 4-T configuration is demonstrated.

Higher-order topological states in dual-band valley sonic crystals

As a quantum state of frequency extrema in the momentum space of acoustic systems, sonic valley pseudospin provides a new degree of freedom for controlling acoustic waves. Higher-order topological insulators (HOTIs) have extended the traditional bulk-edge correspondence principle and are a crucial concept for classic wave regulation. However, HOTIs in valley sonic crystals (VSCs) only appear in a single bandgap, which limits the multi-frequency selectivity of the corner state and is not conducive to the design of multi-frequency acoustic communication devices. Here, we demonstrate “Y-shaped” acoustic crystals with C3 symmetry that form a double-band VSC, and the topological phase transitions in both low- and high-frequency band gaps coincide. We realize theoretically and experimentally higher-order states in dual-band valley sonic crystals. Our work enriches the application of HOTIs in acoustic multi-frequency regulatory systems and provides different avenues for designing of multi-band acoustic devices.

Synthesis of Black Phosphorene/P-Rich Transition Metal Phosphide NiP3 Heterostructure and Its Effect on the Stabilization of Black Phosphorene

Black phosphorus (BP), as a direct band gap semiconductor material with a two-dimensional layered structure, has a good application potential in many aspects, but the surface state of it is extremely unstable, especially that of single-layer black phosphorus. In this study, BP crystals and two-dimensional black phosphorus (2D BP) are prepared by a mechanical ball-milling–liquid-phase exfoliation method. The X-ray diffraction (XRD) spectrum and high-resolution transmission electron microscopy (HRTEM) results showed that red phosphorus (RP) successfully turned to BP by the mechanical ball-milling method. The spectrophotometric analysis has detected absorption peaks at 780 nm, 915 nm, and 1016 nm, corresponding to single, double, and three-layer BP bandgap emission. A simple solvothermal strategy is designed to synthesize in-plane BP/P-rich transition metal phosphide (TMP) heterostructures (BP/NiP3) by defect/edge-selective growth of NiP3 on the BP nanosheets. HRTEM analysis indicates that the metal ions are preferentially deposited on the defects of 2D BP such as edges and unsaturated sites, forming a 2D BP/NiP3 in-plane heterojunction.

Customizable multiband second-order sonic topological insulators via inverse design

The second-order sonic topological insulators (SSTIs) with topologically protected corner states offer promising opportunities for developing novel acoustic devices. However, most of the current SSTIs are designed via trial-and-error and are only able to host the second-order topological phases within a single bandgap, leaving the topic of second-order topological phases within multiple bandgaps rarely studied. Here, we exploit a topology optimization method to customize and optimize multiband SSTIs. To begin with, we create multiple dual-band SSTIs with customizable dual bandgaps for hosting dual-band corner states. On that basis, a three-band SSTI with three bandgaps is constructed for hosting three-band corner states. Experimental validation is performed to prove the existence of the three-band corner states. This study ushers in a route for customizing high-performance multiband SSTIs, and the designed multiband SSTIs have potential for designing robust multiband acoustic devices.

High responsivity and multi-wavelength response photodetector based on single bandgap AlInN film by magnetron sputtering

The AlInN film with a band gap of 2.96 eV is prepared on glass by radio frequency magnetron sputtering. Photoluminescence spectra reveals that the emission band is originated from both the band-edge and some defect-related radiation. The interdigital AlInN photodetector based on metal−semiconductor−metal (MSM) structure exhibits photoresponse characteristics from ultraviolet to visible light. The defect energy level is responsible for the multi-wavelength response of the low-energy incident irradiation light. The photodetector exhibits the best performance under 660 nm illumination, with a responsivity of 102 A/W, an external quantum efficiency of 190% and a specific detectivity of 2.8 × 109 Jones. These three factors improve by 4–6 orders of magnitude compared to point electrodes. The AlInN MSM interdigital electrode structure provides a relatively promising candidate structure for achieving high-performance multi-wavelength photodetectors.

Finite-amplitude nonlinear waves in inertial amplification metamaterials: Theoretical and numerical analyses

The motivation of this study is to understand the unique characteristics of finite-amplitude elastic wave propagation in an inertial amplification (IA) system coupled with a Duffing resonator and leverage the unique opportunities offered by the IA mechanism and nonlinearities to achieve the modulation of elastic waves. Based on the assumption of the perturbation method, the effective range of the wave amplitude was investigated, which is usually ignored. Meanwhile, the obvious phenomenon of bandgap transition (between the single resonance bandgap and hybrid bandgap) is observed with varying IA levels. In particular, we demonstrated a new phenomenon of negative wave propagation and an obvious standing-wave mode in this system. Here, an analytical investigation of the amplitude-dependent and IA-dependent nonlinear dispersion is conducted based on the perturbation approach. Numerical simulations using the time-domain finite element method and Gaussian pulse excitation were performed to validate the nonlinear dispersion and negative motion of the wave packet. The research results can be used to tune wave propagation in metamaterials and provide ideas for the design of metamaterials, which can be used in practical circumstances for different energy transfer needs.

Performance Optimization of CsPb(I1–xBrx)3 Inorganic Perovskite Solar Cells with Gradient Bandgap

In recent years, inorganic perovskite solar cells (PSCs) based on CsPbI3 have made significant progress in stability compared to hybrid organic–inorganic PSCs by substituting the volatile organic component with Cs cations. However, the cubic perovskite structure of α-CsPbI3 changes to the orthorhombic non-perovskite phase at room temperature resulting in efficiency degradation. The partial substitution of an I ion with Br ion benefits for perovskite phase stability. Unfortunately, the substitution of Br ion would enlarge bandgap reducing the absorption spectrum range. To optimize the balance between band gap and stability, introducing and optimizing the spatial bandgap gradation configuration is an effective method to broaden the light absorption and benefit the perovskite phase stability. As the bandgap of the CsPb(I1–xBrx)3 perovskite layer can be adjusted by I-Br composition engineering, the performance of CsPb(I1–xBrx)3 based PSCs with three different spatial variation Br doping composition profiles were investigated. The effects of uniform doping and gradient doping on the performance of PSCs were investigated. The results show that bandgap (Eg) and electron affinity(χ) attributed to an appropriate energy band offset, have the most important effects on PSCs performance. With a positive conduction band offset (CBO) of 0.2 eV at the electron translate layer (ETL)/perovskite interface, and a positive valence band offset (VBO) of 0.24 eV at the hole translate layer (HTL)/perovskite interface, the highest power conversion efficiency (PCE) of 22.90% with open–circuit voltage (VOC) of 1.39 V, short–circuit current (JSC) of 20.22 mA/cm2 and filling factor (FF) of 81.61% was obtained in uniform doping CsPb(I1–xBrx)3 based PSCs with x = 0.09. By carrying out a further optimization of the uniform doping configuration, the evaluation of a single band gap gradation configuration was investigated. By introducing a back gradation of band gap directed towards the back contact, an optimized band offset (front interface CBO = 0.18 eV, back interface VBO = 0.15 eV) was obtained, increasing the efficiency to 23.03%. Finally, the double gradient doping structure was further evaluated. The highest PCE is 23.18% with VOC close to 1.44 V, JSC changes to 19.37 mA/cm2 and an FF of 83.31% was obtained.

Relationships between Compositional Heterogeneity and Electronic Spectra of (Ga1–xZnx)(N1–xOx) Nanocrystals Revealed by Valence Electron Energy Loss Spectroscopy

Many ternary and quaternary semiconductors have been made in nanocrystalline forms for a variety of applications, but we have little understanding of how well their ensemble properties reflect the properties of individual nanocrystals. We examine electronic structure heterogeneities in nanocrystals of (Ga1–xZnx)(N1–xOx), a semiconductor that splits water under visible illumination. We use valence electron energy loss spectroscopy (VEELS) in a scanning transmission electron microscope to map out electronic spectra of (Ga1–xZnx)(N1–xOx) nanocrystals with a spatial resolution of 8 nm. We examine three samples with varying degrees of intraparticle and interparticle compositional heterogeneity and ensemble optical spectra that range from a single band gap in the visible to two band gaps, one in the visible and one in the UV. The VEELS spectra resemble the ensemble absorption spectra for a sample with a homogeneous elemental distribution and a single band gap and, more interestingly, one with intraparticle compositional heterogeneity and two band gaps. We observe spatial variation in VEELS spectra only with significant interparticle compositional heterogeneity. Hence, we reveal the conditions under which the ensemble spectra reveal the optical properties of individual (Ga1–xZnx)(N1–xOx) particles. More broadly, we illustrate how VEELS can be used to probe electronic heterogeneities in compositionally complex nanoscale semiconductors.

Bandgap properties and multi-objective optimization of double-cone pentamode metamaterials with curved side

Pentamode metamaterials (PM) have a promising application in noise reduction fields. In this paper, in order to improve the acoustic modulation capability of PMs, several novel curve PMs are proposed by replacing the straight sides of conventional PMs with curves. At first, the elliptic PMs (EPMs) with various unit cell arrangements (i.e., triangular, square, and hexagonal) are designed, respectively, and their bandgap properties are studied numerically in detail. The EPM with hexagonal unit cell arrangement (EPMH) presents better comprehensive bandgap properties in the EPMs. Subsequently, sinusoidal and power curves are introduced into the EPMH respectively to explore the influences of curve types on bandgap properties. The results show that the bandgap properties improvement of EPMH is higher in comparison with introducing other curves, and the reasons behind these improvements are carefully disclosed in combination with the spring-mass system. Finally, to further improve the bandgap properties of EPMH, a high accuracy Kriging model is constructed according to both the Latin hypercube design and double-point infilling. The Pareto optimal solution sets are determined using a non-dominated sorting genetic algorithm (NSGA-II), and the final compromise solution is gained by employing a fitness function. The bandwidths of phononic bandgap and single mode bandgap, and the total bandwidth of optimized EPMH are increased respectively by about 114.5, 4.3, and 7.7 times than those of the conventional straight side PMs. This investigation provides a fresh strategy for designing PMs with excellent bandgap properties.

Parametric Analysis and Multi-Objective Optimization of Pentamode Metamaterial

Pentamode metamaterial (PM) has enormous application potential in the design of lightweight bodies with superior vibration and noise-reduction performance. To offer systematic insights into the investigation of PMs, this paper studies the various effects (i.e., unit cell arrangement, material, and geometry) on bandgap properties through the finite element method (FEM). With regards to the influences of unit cell arrangements on bandgap properties, the results show that the PM with triangular cell arrangement (PMT) possesses better bandgap properties than the others. The effects of material and geometry on bandgap properties are then explored thoroughly. In light of the spring-mass system theory, the regulation mechanism of bandgap properties is discussed. Multi-objective optimization is conducted to further enhance the bandgap properties of PMT. Based on the Latin hypercube design and double-points infilling, a high-accuracy Kriging model, which represents the relationship between the phononic bandgap (PBG), single mode phononic bandgap (SPBG), double-cone width, and node radius, is established to seek the Pareto optimal solution sets, using the non-dominated sorting genetic algorithm (NSGA-II). A fitness function is then employed to obtain the final compromise solution. The PBG and total bandgap of PMT are widened approximately 2.2 and 0.27 times, respectively, while the SPBG is narrowed by about 0.51 times. The research offers important understanding for the investigation of PM with superior acoustic regulation capacity.

Correction: Recent advances in single crystal narrow band-gap semiconductor nanomembranes and their flexible optoelectronic device applications: Ge, GeSn, InGaAs, and 2D materials

Correction for ‘Recent advances in single crystal narrow band-gap semiconductor nanomembranes and their flexible optoelectronic device applications: Ge, GeSn, InGaAs, and 2D materials’ by Shu An et al., J. Mater. Chem. C, 2023, 11, 2430–2448, https://doi.org/10.1039/d2tc05041b.