Band Gap Properties Research Articles

Investigation and optimal design of band gap tunability in fractal phononic crystals

This study investigates the properties of band gaps of circular core filling fractal phononic crystals (CCFFPCs), specifically focusing on the impact of different filling positions on the frequency of band gaps. The research demonstrates that core filling at the central positions significantly influences the formation and widening of low-frequency band gaps, while filling at corner edges predominantly affects mid-frequency band gaps, and filling at edge centers effectively opens and broadens high-frequency band gaps. These results reveal the relationship between filling positions and band gap tuning, providing a theoretical foundation for precise band gap control across a full frequency range. Moreover, this study is the first to systematically clarify the impact of core filling positions on band gap frequencies, expanding the design strategies for band gaps in fractal phononic crystals. Furthermore, this study employs genetic algorithm optimization to achieve the maximum band gap width at different frequencies, enhancing the practical value of fractal phononic crystals in engineering applications. This research deepens theoretical understanding and provides valuable guidance for optimizing their use in broadband acoustic control and energy harvesting applications.

A comprehensive review of yttrium aluminum nitride: crystal structure, growth techniques, properties, and applications

YAlN has emerged as a wide band gap semiconductor with high potential to compete with ScAlN in industrial applications. Theoretical predictions about YAlN’s material properties have been the main motivation for conducting experimental investigations and verify simulated results. However, several challenges have been faced in experimental studies on YAlN that contradict theoretical data, especially when trying to reach higher alloy concentrations. This work presents a systematic review analyzing different material properties including structural characterization, elastic properties, and thermal features. It combines all available experimental data on the growth and reported material parameters, such as band gap, lattice parameters, and electrical properties with the aim of introducing a new motivation to further study YAlN’s potential in various fields of device applications. The review provides a comprehensive overview on the current state of knowledge on YAlN, highlighting the discrepancies between theoretical predictions and experimental results. By providing information from multiple studies, this work offers valuable insights into the challenges and opportunities associated with YAlN development, paving the way for future research directions and potential industrial applications of this promising wide band gap semiconductor.

Investigation of bandgap and optical properties of Ag+/Al3+ co-alloyed lead-free double perovskite Cs2NaBiCl6

Investigation of bandgap and optical properties of Ag+/Al3+ co-alloyed lead-free double perovskite Cs2NaBiCl6

Viscous Fluid Dissipation for Filtering Poor Bandgaps and Achieving Low‐Frequency Bandgaps in Metamaterials

AbstractEmbedding viscous fluids in soft elastic metamaterials offers transformative potential for engineering applications, particularly in vibration control and acoustic filtering. Despite this promise, effectively leveraging fluid viscosity to achieve low‐frequency, high‐quality bandgaps remains a significant challenge. Specifically, fluid viscosity shifts local resonance modes to lower frequencies while mitigating negative dynamic effective properties, resulting in smoother transmission spectra. By incorporating viscous liquids as resonant units, it is demonstrated how vibrational acoustic coupling and viscous dissipation can be harnessed to engineer superior bandgap properties. The bandgap characteristics of locally resonant metamaterials with viscous liquid fillings are systematically investigated through theoretical analysis, numerical simulations, and experimental validation. The bandgap shifted to lower frequencies by up to 5.6% within the concerned viscosity range, accompanied by a 4.1% bandwidth expansion. This overturns the conventional notion that viscous dissipation reduces system performance, showcasing its positive impact on bandgaps. This work redefines viscous dissipation, usually considered a limitation, as a key enabler for achieving broadband, high‐performance low‐frequency bandgaps, unlocking new possibilities for advanced acoustic and vibration isolation technologies.

Exploring bandgap tuning and vibration isolation performance of innovative negative stiffness metastructures

Negative stiffness metamaterials with tunable bandgap properties present promising applications in vibration control and mechanical property enhancement. This study proposes and compares two metastructures with unit cells exhibiting negative stiffness, achieved through the snap-through behavior of a top beam under displacement. The vibration isolation performance of these models is investigated through theoretical and finite element analyses, with experimental verification of transmission results. Both structures demonstrate significant band gaps, and mode shape analysis of the unit cells reveals the mechanisms underlying bandgap formation. A parametric study examines the effects on bandgap characteristics, including opening and closure, as well as transmission behavior in arrayed configurations. Results indicate that both metamaterial models, with their negative stiffness properties, can create multiple band gaps and achieve excellent vibration isolation, making them strong candidates for vibration isolation applications in engineering structures.

Theoretical calculations of vibration reduction band gaps characteristics of novel phononic-like crystal Euler beam structure

The elastic wave band gap (BG) property of locally resonant phononic crystal (LRPC) enables it to control and attenuate the propagation of elastic waves in its internal structure in the BG frequency range. In particular, it has unique advantages in obtaining low-frequency BG and can be used for the control and attenuation of low-frequency vibration. Therefore, the LRPC is of great significance in the field of low-frequency vibration reduction and has broad application value and prospect. However, the LRPC has the defects of narrow BG width and only one BG, which makes it limited in engineering application. In response to the problems of narrow BG width and only one BG in traditional LRPC Euler beams, this paper establishes a novel phononic-like crystal (PLC) Euler beam model that can open up multi-frequency and low-frequency vibration reduction BGs. The PLC Euler beam model considers the non rigidity of the contact interface between the wrapping layer and the scatterer and matrix, the foundation constraint effect, and the damping characteristics of the wrapping layer material. The vibration reduction BG characteristics of the PLC Euler beam are studied through theoretical calculations and analysis. Firstly, the improved transfer matrix method (ITMM) is derived for calculating the band structure of the PLC Euler beam, and the results are compared and verified with those obtained from the finite element method (FEM). Secondly, the spectral element method (SEM) is derived for calculating the frequency response function (FRF) of the PLC Euler beam, and to evaluate its attenuation effect on vibration elastic waves. The theoretical calculation results show that the PLC Euler beam opens up 6 low-frequency vibration reduction BGs, exhibiting good attenuation effects on vibrational elastic waves within the BG frequency range, with the maximum attenuation value at the BG starting frequency. The novel PLC Euler beam has a broad prospect in controlling and attenuating low-frequency and multi-frequency vibrations, and its design idea has a unique novelty, which provides theoretical support and design idea for broadening the BG width and number of LRPC Euler beam structures, and provides theoretical methods and ideas for designing and studying LRPC with low-frequency and multi-frequency BGs.

Microwave Dielectric Properties and Defect Behavior of xTiO2-(1-x)SiO2 Glass.

xTiO2-(1-x)SiO2 (x = 2.9~8.2 mol%) glass specimens were synthesized using the flame hydrolysis technique. This study aimed to elucidate the influence of TiO2 incorporation on the optical characteristics, defect behavior, and microwave dielectric performance of these materials. UV-vis and near-infrared spectroscopic analyses were employed to investigate the hydroxyl and optical bandgap properties. Electron paramagnetic resonance (EPR) and AC impedance spectroscopy were utilized to examine oxygen vacancies, Ti3+ defects, and their respective behaviors. The findings revealed that, with increasing TiO2 content, the generation and migration of defects became more favorable, consequently leading to higher dielectric losses. The imaginary component of the electric modulus experimental data was fitted using the modified Kohlrausch-Williams-Watts (KWW) function, while the frequency-dependent AC conductivity was analyzed using the Jonscher power law. The calculated activation energy exhibited a decreasing trend with increasing TiO2 content, consistent with the characteristics of doubly ionized oxygen vacancies, suggesting the involvement of identical charge carriers in the relaxation and conduction mechanisms. Notably, the 8.2TiO2-91.8SiO2 glass specimen demonstrated exceptional microwave dielectric performance, exhibiting εr = 4.13, Q × f = 57,116 GHz, and τf = -4.32 ppm/°C, rendering it a promising candidate for microwave substrate applications.

Study on the modulation mechanism of the optoelectronic properties based on common electrode metal atom adsorption on graphene/MoTe2.

The two-dimensional graphene/MoTe2 heterostructure holds extensive potential applications in optoelectronic devices, sensors, and catalysts. To expand its optical applications, this study systematically investigates the adsorption stability of metal atoms (Au, Pt, Pd, and Fe) on the graphene/MoTe2 and their influence on its optoelectronic properties employing first-principles methods. The findings indicate that after the adsorption of Au and Pd, the structure retains its direct bandgap properties, while the adsorption of Pt and Fe exhibits indirect bandgap characteristics. The work functions for all adsorbed structures are lower compared to the pristine graphene/MoTe2. The total density of states is primarily derived from the C-2p, Mo-4d, Te-5p orbitals, as well as the d and s orbitals of the adsorbed atoms. The pristine graphene/MoTe2 exhibits significant absorption in the ultraviolet range. Once graphene/MoTe2 is adsorbed by metal atoms, it can significantly enhance the optical absorption across the spectrum from infrared to ultraviolet light. These findings provide important theoretical guidance for regulating the application of graphene/MoTe2 in optoelectronics and related fields. All analyses are grounded in density functional theory first principles and computed using CASTEP. Graphene/MoTe2 consists of 4 × 4 × 1 single-layer, graphene single layer, and 3 × 3 × 1 single-layer MoTe2. To prevent interactions between neighboring unit cells, a 20Å vacuum space in the z-direction is employed. The electronic exchange-correlation interactions are treated using the Perdew-Burke-Ernzerhof functional within the framework of the generalized gradient approximation. Van der Waals (vdW) interactions are incorporated using the vdW correction function proposed by Grimme, which effectively describes vdW interactions. During the simulation, the cutoff energy for plane wave expansion is set to 420eV, and the k-point grid is set to 4 × 4 × 1. The atomic displacement convergence standard is 0.002Å, the internal stress convergence standard is 0.1GPa, and the interaction force convergence standard between atoms is 0.05eV/Å. The convergence threshold for the iteration precision is set to ensure that the total energy for each atom is not less than 2 × 10-5eV/atom.

Modulation of the electronic and magnetic properties of an MnCrNO2 ferromagnetic semiconductor MXene.

MXenes are members of the rapidly expanding family of two-dimensional materials known for their electronic and magnetic properties and hold significant promise for advancements in electronics and spintronics technologies. In this study, we identified a stable MnCrNO2 MXene characterized by a band gap of 2.68 eV, a magnetic moment of 6μB, and a magnetic anisotropy energy of 78.6 μeV per transition metal atom. These properties were computed using density functional theory with an on-site Coulomb potential and HSE06 hybrid functional calculations. Manipulating the band gap and magnetic properties offers considerable advantages for tailoring MXenes for specific applications. Our investigation extended to exploring the property behaviors under biaxial strain, as well as the adsorption of Group-I and Group-II ions onto the newly discovered MXene. Our findings underscore a highly linear relationship between strain and band gap, supported by an impressive R2 score of 0.997 for the best-fit straight line. Moreover, we demonstrated the linear tunability of the material's magnetic anisotropy energy under biaxial strain, achieving an R2 score of 0.982. Adsorption of 2.2% Group-I and Group-II ions onto the MnCrNO2 MXene reveals the potential for a semiconductor-to-half-metal phase transition with K, Rb, Be, Mg, and Ca ions. These results provide pathways for leveraging MXenes for the development of next-generation electronic and spintronic devices.

Strain-engineered bright excitons and a nearly flat band in monolayer SnNBr for high-speed LED applications.

With the ever-increasing volume of data, the need for systems that can handle massive datasets is becoming gradually critical. High performance visible light communication (VLC) systems offer an expedient solution, yet its widespread adoption is hindered by the limited modulation bandwidth of light emitting diodes (LEDs). Through ab initio many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation (BSE) approach, this work introduces a novel approach to achieving exceptionally high modulation bandwidth by utilizing the nearly flat bands in two-dimensional semiconductors, using SnNBr monolayer as a prototype material for overcoming this bottleneck. Utilizing its unique properties of a direct bandgap and a nearly flat highest valence band, we demonstrate the achievement of exceptionally high modulation bandwidths on the order of terahertz, surpassing the capabilities of established materials such as InGaN and GaN. Interestingly, the excellent absorption and recombination features of the SnNBr monolayer can be modulated further by the application of in-plane tensile strain. The strain-induced proliferation of bright excitons in the visible region, coupled with enhanced absorption and accelerated recombination rates, provides a deeper understanding of the fundamental mechanisms at play in two-dimensional materials, laying the groundwork for future explorations in light-matter interactions at terahertz frequencies.

Ag@g-C3N4/MoS2 heterostructure for efficient photocatalytic oxygen evolution under visible light irradiation.

Herein, an Ag@g-C3N4/MoS2 heterostructure is successfully synthesized for efficient solar-to-water oxidation. UV-vis DRS and steady-state PL analyses reveal the narrow band gap (2.10 eV) and efficient charge separation properties of the Ag nanoparticles and MoS2, respectively. The benefits include an excellent ∼3.2-fold increase in O2 production rate (2727 μmol g-1 h-1) compared to Ag@g-C3N4. A plausible Z-scheme mechanism is also proposed.

A photodetector based on the non-centrosymmetric 2D pseudo-binary chalcogenide MnIn2Se4.

Due to their attractive band gap properties and van der Waals structure, 2D binary chalcogenide materials have been widely investigated in the last decade, finding applications in several fields such as catalysis, spintronics, and optoelectronics. Ternary 2D chalcogenide materials are a subject of growing interest in materials science due to their superior chemical tunability which endows tailored properties to the devices prepared thereof. In the family of AIIBIII 2XVI 4, ordered ZnIn2S4-like based photocatalytic systems have been studied meticulously. In contrast, reports on disordered phases appear to a minor extent. Herein, a photoelectrochemical (PEC) detector based on the pseudo-binary MnIn2Se4 system is presented. A combination of optical measurements and DFT calculations confirmed that the nature of the bandgap in MnIn2Se4 is indirect. Its performance outclasses that of parent compounds, reaching responsivity values of 8.41 mA W-1. The role of the non-centrosymmetric crystal structure is briefly discussed as a possible cause of improved charge separation of the photogenerated charge carriers.

Band evolution and 2D nonreciprocal wave propagation in strongly nonlinear meta-plates

AbstractNonlinear meta-materials/structures can enable exotic wave phenomena, leading to extraordinary functionalities, but the bandgap properties and nonreciprocal wave manipulation in high-dimensional nonlinear metamaterials, such as plates, are not fully understood. In this study, we examine the band evolution and nonreciprocal wave propagation in a two-dimensional (2D) strongly nonlinear meta-plate based on analytical methods and numerical integration on the infinite model. The 2D dispersion curves are obtained through combining harmonic balance and Shooting-Newton iteration methods. Numerical studies show that the 2D nonlinear meta-plate exhibits band degeneration and self-adaptive propagation, analogous to 1D cases. However, as confirmed analytically, both band degeneration and self-adaptivity are regulated by the spatial wave divergence in the 2D meta-plate. Furthermore, combining nonlinear and linear portions of a meta-plate entails nonreciprocal wave propagation in 2D space with elucidated physical properties and mechanisms specific to 2D wave propagation. In light of the above, this work presents new computational methods as well as the elucidation of new wave phenomena and properties which are conducive to wave manipulation in 2D strongly nonlinear meta-materials/structures.

Nitrogen-carbon nanotubes as a basis for a new type of semiconductor materials for electronics devices

The use of semiconductor nanomaterials is currently considered to be one of the most promising device optimization methods since those materials allow controlling the electronic properties and possess high mechanical and thermal strength, providing for long device service life without the necessity of replacement or seeking new solutions. The parameters of the electronic and energy structure of new semiconductor nanomaterials based on carbon nanotubes containing substitution atoms have been studied. The test carbon nanotubes contained specific substitution atom concentrations (15, 25 and 50%). A relationship has been drawn between the band gap, conductivity and optical properties of the materials. Data on the band gap and conductivity as functions of substituting nitrogen atom concentration and tube diameter have been reported. The experimental band gap data suggest that the nanotubes in question are narrow-gap semiconductors. One can also conclude that a new semiconductor material has been synthesized on the basis of carbon nanotubes with substitution nitrogen atoms since the test tubes exhibit a redistribution of electron density towards the nitrogen atoms and positive charge localization in the vicinity of the carbon atoms. The results are of utmost importance for the design and fabrication of components and units for nanoelectronics and microsystems: our theoretical study has confirmed the possibility to control the refraction index and conductivity of media by implementing a carbon-for-nitrogen substitution reaction to various concentrations. Thus, a new electronics material has been studied, i.e., carbon nanotubes modified by substitution of nitrogen atoms.

From Wide-Bandgap to Narrow-Bandgap Perovskite: Applications from Single-Junction to Tandem Optoelectronics.

As perovskite solar device is burgeoning photoelectronic device, numerous studies to optimize perovskite solar device have been demonstrated. Amongst various advantages from perovskite light absorbing layer, attractive property of tunable bandgap allowed perovskite to be adopted in many different fields. Easily tunable bandgap property of perovskite opened the wide application and to get the most out of its potential, many researchers contributed as well. By precursor composition engineering, narrow bandgap with bandgap of less than 1.4 eV and wide bandgap with bandgap of more than 1.7 eV were achieved. Optimization of both narrow and wide bandgap perovskite solar cell could pave the way to all-perovskite tandem solar cell which is combination of top cell with wide bandgap and bottom cell with narrow bandgap. This review highlights numerous efforts to advance device performance of both narrow and wide bandgap perovskite solar cell and how they challenged the issues. And finally, efforts to operate and utilize all-tandem perovskite device in real world will be discussed.

High-pressure band-gap engineering and structural properties of van der Waals BiOCl nanosheets.

van der Waals BiOCl semiconductors have gained significant attention due to their excellent photochemical catalysis, low-cost and non-toxicity. However, their intrinsic wide band gap limits visible light utilization. This study explores high-pressure band-gap engineering, a "chemical clean" method, to optimize BiOCl's electronic structure. Utilizing in situ high-pressure ultraviolet-visible (UV-vis) absorption spectra, Raman spectroscopy and XRD, we systematically investigate the effects of compression on band gap and crystal structure evolution of BiOCl. Our results demonstrate that pressure efficiently narrows the band gap from 3.44 eV to 2.81 eV within the pressure range of 0.4-44 GPa. The further Raman and XRD analyses reveal an isostructural phase transition, leading to a significant change in the compressibility of the lattice parameters and bonds from anisotropic to isotropic. These findings provide a potential pathway to tune the bandgap for enhancing the photocatalytic efficiency of BiOCl.

Modulation of Energy Band Positions in Sb2S3 Thin Films for Enhanced Photovoltaic Performance of FTO/TiO2/Sb2S3/P3HT/Au Solar Cell

Antimony sulfide (Sb2S3) has the potential as an absorber material in photovoltaics due to its suitable bandgap and favorable optoelectronic properties. However, its energy band positions are not extensively explored which are essential for effective charge separation and transfer. This study examines the energy band positions of Sb2S3 thin films as a function of annealing temperature. Sb2S3 thin films are grown by a combination of successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) method to enhance the crystallinity, tune the bandgap, and overall quality of Sb2S3 films to enhance the photovoltaic performance. Optical bandgap decreases from 2.41 to 1.67 eV from the as‐deposited films to annealed at 300 °C due to changes in interatomic distances. Energy band positions of Sb2S3 films are measured both by cost‐effective electrochemical cyclic voltammetry and Mott–Schottky analysis and validated the findings using ultraviolet photoelectron spectroscopy (UPS). The conductivity of Sb2S3 is found to be n‐type. Thin‐film solar cells are then fabricated by employing Sb2S3 as an absorber layer in an FTO/TiO2/Sb2S3/P3HT/Au structure, achieving an enhanced power conversion efficiency, increasing from 0.4 to 2.8% after annealing. These findings demonstrate the potential of Sb2S3 as a low‐cost absorber material for thin‐film photovoltaics.

Multi functional ionic Ru(bpy)3(PF6)2 assisted preparation of perovskite solar cell with over 19% and superior stability

Abstract The global community is striving to advance the development of emerging perovskite solar cells (PSCs). It has been demonstrated that the utilization of passivators is an effective approach to enhance the photoelectric conversion efficiency and long-term stability of PSCs, thus attracting increasing attention to organic passivators. All-inorganic CsPbI3 PSCs play a crucial role in the next-generation photovoltaic technology due to their unique optical bandgap and excellent light absorption properties. However, due to its poor stability, CsPbI3−x Br x halide hybrid perovskite has been proposed. The spin-coating film formation method leads to the presence of a large number of vacancy defects in the film, which poses a significant challenge to the commercialization of CsPbI3−x Br x perovskite films. Therefore, in this study, a novel passivator, Ru(bpy)3(PF6)2 (TRH), was introduced. By introducing the passivator, the photoelectric conversion efficiency of PSCs in air was improved, there by optimizing the device performance. After the addition of the passivator, [Ru(bpy)3]2+ filled the defects on the surface of the film, while the free PF6 - ions passivated the negatively charged halide vacancies. The fluorine atoms effectively prevented the entry of water molecules in the air. As a result, the optimized CsPbI3−x Br x film exhibited a more compact morphology, a lower defect state density, and better carrier transport performance. Eventually, the champion device achieved a photoelectric conversion efficiency of 19.47%, and even after being placed at an ambient temperature of 25 °C–30°C and a humidity of 30%–40% for 150 d, its efficiency remained above 85% of the initial efficiency of the device.

Study on band-gap characteristics and formation mechanism of four-ligament chiral elastic metamaterials

Abstract Chiral elastic metamaterials, owing to their exceptional properties distinct from conventional materials and their superior mechanical performance, exhibit significant potential for applications in vibration reduction, noise suppression, energy absorption, and cushioning. To address the challenge of low-frequency vibration control, this paper proposes a dual-component chiral elastic metamaterial structure with four ligament elements. The study explores the bandgap characteristics and elastic wave propagation behavior of this structure within the 1000 Hz frequency range. By analyzing the vibration modes of the unit cell and calculating the group and phase velocities of elastic waves, the physical mechanism underlying bandgap formation is elucidated. The results demonstrate that the proposed four-ligament chiral elastic metamaterial exhibits excellent bandgap properties, with the bandgap covering more than 80.4% of the frequency range below 1000 Hz. This highlights its capability for low-frequency elastic wave control and offers a theoretical reference for the design of novel vibration reduction and noise suppression structures, as well as for low-frequency elastic wave regulation.

The effects of strain and interface engineering on the PbS/PbSe/CsPbI3 heterojunction

Abstract This paper investigates the PbS/PbSe/CsPbI3 heterojunction based on first-principles calculations within the framework of density functional theory and demonstrates the effects of different strains on the structural, electronic, optical properties. PbS/PbSe, PbSe/CsPbI3 and PbS/CsPbI3 all possess relatively low lattice mismatch rates (2.3%, 2.4% and 4.6%) and similar octahedral structures. The PbS/CsPbI3 heterojunction reduces carrier transfer losses between different materials. By serving as the functional layer, PbSe can alter the electron–hole recombination losses at the heterostructure interface, broaden the spectral response range, and change the electronic density around the atoms at the heterostructure interface. All three heterojunctions are direct band gap semiconductors (ΔEg: PbS/PbSe-PbSe/CsPbI3-PbS/CsPbI3, 0.632–0.856–0.523 eV). The spectral comparison shows that PbS/PbSe/CsPbI3 > PbSe/CsPbI3 > CsPbI3, indicating that PbS/PbSe/CsPbI3 exhibits superior stability, charge density transfer, and optical performance with a redshift in absorption spectra. Additionally, the band gap and optical properties of PbS/PbSe/CsPbI3 can be adjusted by applying strain, thereby affecting its optical absorption intensity. This work provides a theoretical foundation for improving the performance of PbS/PbSe/CsPbI3 heterojunction as visible-near infrared optoelectronic materials.