Bandgap Control Research Articles

Electric Control of Quasiparticle Band Gap and Electron–Hole Excitation in the Bilayer of Janus Structure MoSeS

Electric Control of Quasiparticle Band Gap and Electron–Hole Excitation in the Bilayer of Janus Structure MoSeS

Catalytic effects of iron adatoms in poly(para-phenylene) synthesis on rutile TiO2(110).

n-Armchair graphene nanoribbons (nAGNRs) are promising components for next-generation nanoelectronics due to their controllable band gap, which depends on their width and edge structure. Using non-metal surfaces for fabricating nAGNRs gives access to reliable information on their electronic properties. We investigated the influence of light and iron adatoms on the debromination of 4,4''-dibromo-p-terphenyl precursors affording poly(para-phenylene) (PPP as the narrowest GNR) wires through the Ullmann coupling reaction on a rutile TiO2(110) surface, which we studied by scanning tunneling microscopy and X-ray photoemission spectroscopy. The temperature threshold for bromine bond cleavage and desorption is reduced upon exposure to UV light (240-395 nm wavelength), but the reaction yield could not be improved. However, in the presence of codeposited iron adatoms, precursor debromination occurred even at 77 K, allowing for Ullmann coupling and PPP wire formation at 300-400 K, i.e., markedly lower temperatures compared to the conditions without iron adatoms. Furthermore, scanning tunneling spectroscopy data reveal that adsorbed PPP wires feature a band gap of ≈3.1 eV.

Optical bandgap tuning in SnO2–MoS2 nanocomposites: manipulating the mass of SnO2 and MoS2 using sonochemical solution mixing

This study investigates controlled optical bandgap tuning through precise adjustment of the SnO2 and MoS2 mass in nanocomposites. A sonochemical solution mixing method, coupled with bath sonication, is employed for the preparation of SnO2–MoS2 nanocomposite. This approach allows for comprehensive characterization using UV–Vis FTIR, XRD, EDX, Raman spectroscopies, and FESEM, providing insights into morphology, chemical, and optical properties. Increasing the SnO2 mass leads to a linear decrease in the optical bandgap energy, from 3.0 to 1.7 eV. Similarly, increasing the MoS2 mass also results in a decrease in the optical bandgap energy, with a limitation of around 2.01 eV. This work demonstrates superior control over optical bandgap by manipulating the SnO2 mass compared to MoS2, highlighting the complexities introduced by MoS2 2D nanosheets during sonication. These findings hold significant value for optoelectronic applications, emphasizing enhanced control of optical bandgap through systematic mass manipulation.

Composition-Tunable Bandgap Engineering of Horizontally Guided CdSxSe1-x Nanowalls for High-Performance Photodetectors.

Composition-adjustable semiconductor nanomaterials have garnered significant attention due to their controllable bandgaps and electronic structures, providing alternative opportunities to regulate photoelectric properties and develop the corresponding multifunction optoelectronic devices. Nevertheless, the large-scale integration of semiconductor nanomaterials into practical devices remains challenging. Here, we report a synthesis strategy for the well-aligned horizontal CdSxSe1-x (x = 0-1) nanowall arrays, which are guided grown on an annealed M-plane sapphire using chemical vapor deposition (CVD) approaches. Microstructural characterizations demonstrate these structures as horizontally guided nanowalls with high-quality crystallinity. Microphotoluminescence (μ-PL) reveals the CdSxSe1-x nanowalls exhibiting continuously tunable spontaneous emissions from 509 nm (pure CdS) to 713 nm (pure CdSe), further confirming that CdSxSe1-x alloys have a continuously tunable bandgap. Notably, a photodetector based on CdSxSe1-x nanowalls displays excellent photoelectric performance, such as high responsivity (3 × 102 ∼ 1 × 103 A/W), high external quantum efficiency (1.01 × 103 ∼ 2.93 × 103), and fast response speed in the millisecond magnitude. Furthermore, the CdS nanowall-based photodetectors exhibit a remarkable image-sensing capability, indicating potential applications in high-performance image sensing in the future. Bandgap continuously tunable nanowall arrays with high-quality crystallinity inject great vitality into the manufacturing of high-performance integrated optoelectronic devices.

Guest Editorial Special Section on Ultrawide/Wide Bandgap Device, Packaging, Control, EMI, and Applications for Power Electronics

Guest Editorial Special Section on Ultrawide/Wide Bandgap Device, Packaging, Control, EMI, and Applications for Power Electronics

Oxygen vacancies enriched Z-scheme BiOI/Bi2O3 heterojunction with controllable band-gap for dye degradation and Cr (VI) reduction

Oxygen vacancies enriched Z-scheme BiOI/Bi2O3 heterojunction with controllable band-gap for dye degradation and Cr (VI) reduction

Luminescence Mechanisms of Quaternary Zn-Ag-In-S Nanocrystals: ZnS:Ag, In or AgInS2:Zn?

Highly emissive Zn-Ag-In-S nanocrystals have attracted attention as derivatives of I-III-VI2-type nanocrystals without the use of toxic elements. The wide tunability of their luminescence wavelengths is attributed to the controllable bandgap of the solid solution between ZnS and AgInS2. However, enhancement of the photoluminescence quantum yield (PL-QY) depending on the chemical composition has not been elucidated. Here, the luminescence mechanisms of Zn-Ag-In-S nanocrystals were studied from the perspective of ZnS doped with Ag and In, although previous research has proposed a hypothesis that Zn is a radiative recombination centre in the AgInS2 host. The Zn-Ag-In-S nanocrystals were synthesized by systematically varying the Zn, Ag, and In contents. The nanocrystals exhibit a structure in which a part of the Zn in the cubic ZnS is substituted with Ag and In. Luminescence was ascribed to a donor-acceptor pair (DAP) recombination between electrons trapped in In donors and holes trapped in Ag acceptors. The composition-dependent enhancement of PL-QYs was attributed to an increase in donor and acceptor concentrations. The DAP characteristics were maintained over a wide range of Ag and In contents because of the localized character of the band edge states dominated by Ag and In orbitals, as suggested formerly by simulation.

Electrochemical Synthesis of Tellurium Nanostructure on Non-Conductive Substrateby Redox Reaction of Tellurium Ions

In recent years, the utilization of low-dimensional nanodevices has emerged as a promising avenue for advancing Moore’s Law. With remarkable electrical characteristics, controllable bandgap, and favorable environmental stability, tellurium nanostructures have attracted considerable interest for their potential applications in next-generation electronics and optoelectronic devices. Consequently, investigations into manipulating the dimensions, morphology, and configuration have been conducted to improve the electrical characteristics of tellurium nanostructures. Electrochemical deposition is suitable for synthesizing tellurium nanostructure, enabling control over the nanostructure through manipulation of deposition parameters such as applied potential, temperature, agitation speed, and the incorporation of additives. Despite this advantage, electrodeposition encounters a challenge in detaching the electrodeposits from the conductive substrate for accurate characterization and advanced device fabrication. To address this issue, redox reaction of tellurium ions can be utilized for deposition on insulators, even those unable to conduct electrons required for ion reduction. By controlling the generation of tellurium ionic states (Te4+, Te0, and Te2-) and triggering the redox reaction involving these ions, tellurium nanostructures can be synthesized on insulators using the following reaction: 2H2Te(aq) + HTeO2+ (aq) → 3Te(s) + 2H2O + H+ In this research, we synthesize tellurium nanostructure on the insulators, overcoming the limitation of electrodeposition, which only can deposit on conducting materials. Linear sweep voltammetry is conducted to study the electrochemical behavior of tellurium ions. Based on this analysis, the redox reaction of tellurium is induced on an insulator between Au microelectrodes, which are used for further analyses and application. The nanostructures of tellurium are controlled by manipulating the parameters of electrodeposition. The investigation into the structure and crystallinity of tellurium nanostructures is carried out, alongside the characterization of their electrical properties for electronics applications. This discovery addresses the primary challenge associated with electrodeposition by effectively depositing of metal chalcogenides and other chalcogen elements onto an insulator, thereby broadening its potential applications in advanced electronics fields.

Controllably ultrawide bandgap of a metamaterial beam based on inertial amplification and magnetorheological elastomer

This paper presents the design of a metamaterial beam for controllably ultrawide bandgap (36.3Hz–218.6Hz) and low-frequency vibration attenuation, achieved by a lever-based inertial amplification and a variable stiffness of a magnetorheological elastomer (MRE) modulated by an external magnetic field. The metamaterial is formed by periodical mass-lever inertial amplifier and spring-MRE resonators connected to a base beam. The Galerkin method is employed to theoretically investigate the controllably ultrawide tunability of a low-frequency bandgap in terms of the MRE properties, the mass-lever inertial amplification and the geometric nonlinearity conditions. The results obtained are validated through numerical simulations. The study further extends to lightweight design of metamaterials, where the target frequency that depends on controllably ultrawide bandgap is introduced. With the same target frequency of bandgap, the proposed system exhibits a lighter resonator mass than the traditional metamaterials. Finally, a target frequency-based bandgap control strategy is developed, enabling real-time tunability of the bandgap within a low-frequency wideband range without changing the mass of the resonator or reconstructing the structure. Compared to typical "mass-spring" metamaterials, the proposed system shows superiority in achieving ultrawide bandgaps. This metamaterial offers a promising solution for creating controllably ultrawide vibration-attenuating structures, making it highly suitable for practical applications.

A DFT study on the role of excitons and electric field-induced symmetry breaking and topological properties of ZrBr

The control of band gap and topological properties is a crucial objective in the field of materials science, particularly for the application of 2D materials such as topological insulators. Zirconium monobromide (ZrBr), a topological insulator with band inversion, holds significant potential for various applications. In this study, we used Density Functional Theory (DFT) with different approximations namely, Generalized Gradient Approximation (GGA) with and without spin orbit coupling (SOC) as well as hybrid functional to investigate the electronic structure and the band gap of this compound. In addition, we introduced the excitonic effect by considering GW plus Bethe–Salpeter equation (GW-BSE) to compute the optical band gap and quasi-particle energy. We found that ZrBr present a low static dielectric function and weak exciton binding energy, generally lower than those of conventional semiconductors. This behavior is due to the reduced Coulomb interaction in the material. To further explore the material’s behavior, we apply an electric field in three directions to observe symmetry breaking and its impact on band gap tuning. This comprehensive analysis aims to explore the understanding and the potential applications of ZrBr as a topological insulator.

Guest Editorial Special Section on Ultrawide/Wide Bandgap Device, Packaging, Control, EMI, and Applications for Power Electronics

Guest Editorial Special Section on Ultrawide/Wide Bandgap Device, Packaging, Control, EMI, and Applications for Power Electronics

Modulation of bandgap and transport properties by stacking symmetry in bilayer binary materials

The interlayer interactions in layered two-dimensional materials, which are formed by Van der Waals forces, significantly influence the control of electronic and transport properties. The manipulation of the stacking order can modulate these interlayer interactions by altering the atomic arrangement in different layers. In this study, we conducted a systematic examination of the bandgap modulation of bilayer two-dimensional binary materials at high symmetry stackings. A general trend of bandgap modulation has been proposed through a tight-binding model and corroborated by density functional calculations. The mechanisms of bandgap modulation can be leveraged to control the transport properties of devices built with bilayer two-dimensional binary materials. Our research findings offer valuable insights for the control of bandgap in layered two-dimensional materials and their application in transport devices.

Magnetorheological metamaterials for active broadband tuning of vibration attenuation

We propose a class of magnetorheological metamaterial plates with tunable band gaps achieved by means of a frequency-feedback control law. This approach allows for the intelligent tracking of excitation frequencies that enables an active control of band gap bounds. The active control mechanism is implemented through intelligent local resonators integrated into a main structure which comprise a mass and a magnetorheological elastomer (MRE) sensitive to an external magnetic field. The influence of the external magnetic field on vibration attenuation is examined using the Galerkin method. Next, a closed-loop frequency feedback control strategy is employed to dynamically adjust the band gap in response to excitation frequencies. This strategy significantly broadens the effective band gap range of the metamaterial plate. Besides, we studied the effect of MRE damping on broadband vibration reduction, underscoring its pivotal role in the band gap control for our magnetorheological metamaterials.

Guest Editorial Special Section on Ultrawide/Wide Bandgap Device, Packaging, Control, EMI, and Applications for Power Electronics

Guest Editorial Special Section on Ultrawide/Wide Bandgap Device, Packaging, Control, EMI, and Applications for Power Electronics

Bandgap Control of Local Resonance Sandwich Meta-Plate with Cantilevered Archimedean Spiral Beam-Mass Resonators

In order to attenuate the various low-frequency vibrations that may cause structural fatigue and damage, impact human health and affect work efficiency, this paper presents a novel local resonance metamaterial sandwich meta-plate structure containing a cantilever spiral beam-mass resonator, and investigates vibration reduction effects of it within the obtained low-frequency bandgap range. For this purpose, a theoretical model of the low-frequency resonator being composed by a cantilever Archimedean spiral beam and cylindrical mass is established. The natural frequency of it is calculated by solving the Euler-Lagrange equation of the resonator. The accuracy and reliability of the theoretical model are verified through COMSOL simulation. The stress distribution of five types of cantilever spiral beam mass resonators (i.e. Archimedes spiral, triangle spiral, square spiral, pentagon spiral and hexagon spiral) and different cross-sectional shapes (rectangular, square, circular, diamond and triangular) are analyzed. Then, a unit cell model of a sandwich meta-plate with a cantilever Archimedean spiral beam resonator is selected. Hamilton’s principle is used to deduce the bandgap range under infinite periods, and the theoretical solutions are also verified. The parameter optimization of the substrate plate and resonator are also studied. Moreover, the effects of the various structural variables on the bandgap range are systematically explored. Finally, the dynamic responses of the sandwich meta-plate composed of [Formula: see text]-unit cells under different excitation frequencies, boundary conditions and structural damping are analyzed.

Highly sensitive full solar-blind ultraviolet spectrum detection and imaging based on PdSe2/Ga2O3 vdW heterojunction.

Solar-blind ultraviolet (UV) photodetectors are in great demand for both military and civilian applications. Here, we have successfully demonstrated the synthesis of the Sn-doped Ga2O3 films with controllable bandgaps to construct PdSe2/Ga2O3 van der Waals (vdW) heterojunctions achieving highly sensitive full solar-blind UV spectrum detection. The assembled device demonstrates a full solar-blind UV spectral self-powered response, with a large responsivity of 123.5 mA/W, a high specific detectivity of 1.63 × 1013 Jones, and a rapid response time of 0.15/2.3 ms. Importantly, an outstanding solar-blind UV imaging application based on an integrated PdSe2/Ga2O3 device array has been demonstrated. Our work paves a feasible path toward achieving highly sensitive solar-blind UV detecting and imaging based on wide-bandgap Ga2O3 films.

Enhancement of Cd‐Free All‐Dry‐Processed Cu(In1‐x,Gax)Se2 Thin‐Film Solar Cells by Simultaneous Adoption of an Enlarged Bandgap Absorber and Tunable Bandgap Zn1‐xMgxO Buffer

Attempts to remove environmentally harmful materials in mass production industries are always a major issue and draw attention if the substitution guarantees a chance to lower fabrication cost and to improve device performance, as in a wide bandgap Zn1‐xMgxO (ZMO) to replace the CdS buffer in Cu(In1‐x,Gax)Se2 (CIGSe) thin‐film solar cell structure. ZMO is one of the candidates for the buffer material in CIGSe thin‐film solar cells with a wide and controllable bandgap depending on the Mg content, which can be helpful in attaining a suitable conduction band offset. Hence, compared to the fixed and limited bandgap of a CdS buffer, a ZMO buffer may provide advantages in Voc and Jsc based on its controllable and wide bandgap, even with a relatively wider bandgap CIGSe thin‐film solar cell. In addition, to solve problems with the defect sites at the ZMO/CIGSe junction interface, a few‐nanometer ZnS layer is employed for heterojunction interface passivation, forming a ZMO/ZnS buffer structure by atomic layer deposition (ALD). Finally, a Cd‐free all‐dry‐processed CIGSe solar cell with a wider bandgap (1.25 eV) and ALD‐grown buffer structure exhibited the best power conversion efficiency of 19.1%, which exhibited a higher performance than the CdS counterpart.

Non-linear dynamics and bandgap control in magneto-rheological elastomers metamaterials with inertial amplification

Sandwich plate structures are extensively utilized in engineering due to their favorable stiffness-to-weight ratio. Nonetheless, these lightweight thin-walled structures frequently encounter challenges related to inadequate low-frequency vibration performance, which significantly restricts their applications, particularly in the realm of precision instruments which is sensitive to vibration. This study introduces an innovative design of an active nonlinear metamaterial, to achieve tunable broadband low-frequency bandgaps for sandwich plates. The nonlinear oscillator incorporates an inertia amplification mechanism (IAM), Euler-buckled beams, mass elements, and magneto-rheological elastomers (MREs), which are modulated via external magnetic fields to adjust the material's stiffness dynamically. Employing Hamilton's principles and the plate wave expansion method (PWE), the dispersion relations for the metamaterial plate are derived, elucidating the dispersion surfaces and the band structures within its sandwich-like plates.The dynamical equations of the metamaterial plate are formulated and validated through numerical simulations using the Galerkin method, confirming the theoretical predictions. The results demonstrate effective control over low-frequency and broadband bandgaps under low mass ratio conditions through strategic manipulation of the inertia amplification factor and magnetic flux. The study extensively explores the nonlinear dynamic responses of the metamaterial, highlighting the significant impact of excitation amplitudes on the amplitude-dependent bandgaps.

Intelligent mechanical metamaterials towards learning static and dynamic behaviors

The exploration of intelligent machines has recently spurred the development of physical neural networks, a class of intelligent metamaterials capable of learning, whether in silico or in situ, from observed data. In this study, we introduce a back-propagation framework for lattice-based mechanical neural networks (MNNs) to achieve prescribed static and dynamic performance. This approach leverages the steady states of nodes for back-propagation, efficiently updating the learning degrees of freedom without prior knowledge of input loading. One-dimensional MNNs, trained with back-propagation in silico, can exhibit the desired behaviors on demand function as intelligent mechanical machines. The framework is then employed for the precise morphing control of the two-dimensional MNNs subjected to different static loads. Moreover, the intelligent MNNs are trained to execute classical machine learning tasks such as regression to tackle various deformation control tasks. Finally, the disordered MNNs are constructed and trained to demonstrate pre-programmed wave bandgap control ability, illustrating the versatility of the proposed approach as a platform for physical learning. Our approach presents an efficient pathway for the design of intelligent mechanical metamaterials for a wide range of static and dynamic target functionalities, positioning them as powerful engines for physical learning.

Solution processable Zn-salphen containing π-conjugated polymers with unique aggregation behavior as organic optoelectronic materials

Series of π-conjugated polymers containing electron-withdrawing Zn-Schiff base complex (Zn-salphen) were reported. These polymers can be easily obtained with controllable optical bandgap (Egopt) varying from 1.50 to 2.13 eV by changing the π-conjugated comonomers, and together with excellent thermal stabilities. It was found that the introduction of alkyl chains could provide good solution process-ability for these polymers in chlorobenzene solutions. All the polymers exhibit high hydrophilic characteristics compared to traditional semi-conducting polymers. This is caused by the large polarity of Zn-salphen, which results in strong inter-molecular interactions for the polymers analyzed based on their optical properties. Interestingly, these aggregation behaviors are highly dependent on the type of solvents and coordinating additives such as pyridine, which can be observed from their UV–vis absorption and photoluminescence (PL) spectra. In addition, the film morphologies of these polymers can be modified by using pre- and post-treatments such as thermal annealing, solvent annealing and additives. This work introduces a new strategy for constructing semi-conducting polymers by solving the problem of poor solubility of Zn-salphen complex, and preliminarily studies the feasibility of these Zn-salphen containing polymers regarding their solution process-ability, optical adjustment and morphology optimization. These polymers are considered potential candidates for applications in photoelectric devices.