Low Band Gap Research Articles

Enhancing Spray Charge and Abaxial Deposition on Hydrophilic Substrates Using Hypervalent Oxometallate Salt KMnO4.

The pursuit of innovative and excellent additives that augment the negative charges of sprayed droplets is crucial due to their potential applications in agricultural, industrial, and daily sterilization/disinfection processes. However, traditional additives have shown limited efficacy in enhancing the electrification of water droplets. Herein, we introduce hypervalent oxometallate salts (HOMs) as innovative additives to address this challenge. Notably, KMnO4 exhibits a remarkable effect on spray charge properties, enhancing the abaxial deposition efficiency on hydrophilic substrates by a factor of 4-fold compared to pure water spraying. This enhancement is attributed to the distinctive features of [MnO4]-, such as low energy band gap and electrostatic and zeta potentials, strong electron acceptance ability, and low binding energy with water molecules. These properties significantly promote the polarization of water molecules and amplify the spray charge capacity. Additionally, the underlying mechanisms of promoting abaxial deposition on a hydrophilic substrate are attributed to the interface reactions on the adaxial side and an increase in positive charge on the abaxial surface. This work introduces an additive for enhancing the negative charge of a spray, marking a pivotal improvement in the utilization efficiency of chemicals in the agricultural and industrial sectors.

Advancing intercalation strategies in layered hybrid perovskites by bringing together synthesis and simulations

Finding ways to modify the electronic structure of halide perovskites is desireable as they have applications in a variety of devices, from photovoltaics to LEDs. Additionally, designing functional materials can be facilitated through the use of computation. Here, we have used a combination of synthesis and computation to screen for intercalated, layered hybrid perovskites. 54 compositions were screened and five compounds containing intercalated halogens were prepared as single crystals. A further compound, which was not screened and contained IBr, was prepared. We computationally identified an intercalated layered hybrid perovskite with a low bandgap and prepared it as a thin-film. Through examination of single crystal X-ray diffraction data, we provide some design guidelines for intercalation. The conformational flexibility in the organic ammonium cation allows rotations in the carbon backbone which change upon intercalation. Optoelectronic properties were studied using photoluminescence spectroscopy and preliminary photovoltaic device testing.

Low frequency band gap prediction and broadband vibration reduction of multi-scale elastic metabeams with particle damping

Low frequency band gap prediction and broadband vibration reduction of multi-scale elastic metabeams with particle damping

Synergistic impact of a low band gap polyanionic-cluster (NaCuPO4) and super-high surface area activated carbon on rechargeable Na-ion battery performance

Synergistic impact of a low band gap polyanionic-cluster (NaCuPO4) and super-high surface area activated carbon on rechargeable Na-ion battery performance

A graph neural network assisted reverse polymers engineering to design low bandgap benzothiophene polymers for light harvesting applications

A graph neural network assisted reverse polymers engineering to design low bandgap benzothiophene polymers for light harvesting applications

SiGe-Surrounded Bitline Structure for Enhancing 3D NAND Flash Erase Speed

Three-dimensional NAND Flash has adopted the cell-over-peripheral (COP) structure to increase storage density. Unlike the conventional structure, the COP structure cannot directly increase the channel potential via substrate bias during the erase operation. Therefore, the gate-induced drain leakage (GIDL) erase method, which utilizes band-to-band tunneling (BTBT) to raise the channel potential, is employed. However, compared to bulk erase, the BTBT-based erase method requires a longer time to generate holes in the channel, leading to erase speed degradation. To address this issue, we propose a structure which enhances the erase speed by surrounding the bitline (BL) PAD with SiGe. In the case of a SiGe thickness (tSiGe) of 13 nm, the lower bandgap of SiGe increases the BTBT generation rate, boosting the channel potential rise at the end of the erase voltage ramp-up by 861% compared to the Si-only structure, while limiting the reduction in read on-current to within 4%. We modeled the voltage and electric field across the SiGe layer, as well as BTBT generation rate and GIDL current in the SiGe layer, by varying tSiGe, Ge composition ratio (SiGeX), and the voltage difference between VBL and VGIDL_TR.

Solution‐Processed Amorphous Zero‐Dimensional Organic Metal Halide Hybrid Films for Direct X‐ray Detectors

Zero‐dimensional (0D) organic metal halide hybrids (OMHHs) are emerging materials with significant potential for optoelectronic applications, including direct X‐ray detectors. While 0D OMHH single crystals exhibit excellent X‐ray detection properties, their scalability remains a significant challenge due to the time‐intensive growth process and difficulty in producing large single crystals exceeding a few centimeters. This limitation hinders their practicality for large‐area detector applications. Here, we report for the first time the development of amorphous 0D OMHH films via solution processing for efficient direct X‐ray detection. By reacting a non‐crystalline organic halide, triphenyl(9‐phenyl‐9H‐carbazol‐3‐yl)phosphonium bromide (TPPCarzBr), with zinc bromide (ZnBr2), we have successfully produced amorphous 0D (TPPCarz)2ZnBr4 films with controlled thickness via facile solution processing. The organic cations (TPPCarz+) feature a lower bandgap than the ZnBr42‐ anions, enabling efficient molecular sensitization, where ZnBr42‐ anions serve as X‐ray absorbers and TPPCarz+ cations as charge transporters. Direct X‐ray detectors based on 0D (TPPCarz)2ZnBr4 films demonstrate outstanding performance, achieving a stable X‐ray detection sensitivity of 2,165 μC Gyair−1cm−2 at 20 V.mm−1 and a detection limit of 6.01 nGyair s−1. The amorphous nature of these films enhances their processability, allowing for fabrication in various sizes and shapes, and making them highly adaptable for scalable detector applications.

Solution-Processed Amorphous Zero-Dimensional Organic Metal Halide Hybrid Films for Direct X-ray Detectors.

Zero-dimensional (0D) organic metal halide hybrids (OMHHs) are emerging materials with significant potential for optoelectronic applications, including direct X-ray detectors. While 0D OMHH single crystals exhibit excellent X-ray detection properties, their scalability remains a significant challenge due to the time-intensive growth process and difficulty in producing large single crystals exceeding a few centimeters. This limitation hinders their practicality for large-area detector applications. Here, we report for the first time the development of amorphous 0D OMHH films via solution processing for efficient direct X-ray detection. By reacting a non-crystalline organic halide, triphenyl(9-phenyl-9H-carbazol-3-yl)phosphonium bromide (TPPCarzBr), with zinc bromide (ZnBr2), we have successfully produced amorphous 0D (TPPCarz)2ZnBr4 films with controlled thickness via facile solution processing. The organic cations (TPPCarz+) feature a lower bandgap than the ZnBr42- anions, enabling efficient molecular sensitization, where ZnBr42- anions serve as X-ray absorbers and TPPCarz+ cations as charge transporters. Direct X-ray detectors based on 0D (TPPCarz)2ZnBr4 films demonstrate outstanding performance, achieving a stable X-ray detection sensitivity of 2,165 μC Gyair-1cm-2 at 20 V.mm-1 and a detection limit of 6.01 nGyair s-1. The amorphous nature of these films enhances their processability, allowing for fabrication in various sizes and shapes, and making them highly adaptable for scalable detector applications.

Mechanical and Electrical Properties of Free-standing Polycrystal Diamond Membranes.

In this study, we demonstrate a novel approach for synthesizing free-standing and transferable polycrystalline diamond membranes (PCDm) to overcome these constraints, thus enabling a much wider spectrum of applications. Two types of PCDm cantilevers -Top-Surface-Up (TSU) and Bottom-Surface-Up (BSU) are fabricated, each with two different sets of dimensions: 150 µm (width) × 1200 µm (length) and 300 µm (width) × 2000 µm (length). Their mechanical and electrical properties are systematically investigated. Atomic Force Microscopy (AFM) analysis revealed that TSU-PCDm has a higher elastic modulus than BSU-PCDm, attributed to differences in grain size and defect distribution. Despite these differences, all PCDms in our work exhibit consistently high modulus values with minimal mechanical degradation across various cantilever geometries. Bandgap measurements using X-ray Photoelectron Spectroscopy (XPS) and UV-vis absorption spectroscopy indicated a lower bandgap for TSU-PCDm due to boron incorporation, while BSU-PCDm exhibited a higher bandgap due to increased hydrogen content. Electrical characterization showed that the sheet resistance of TSU-PCDm decreases under strain, whereas BSU-PCDm maintains stable resistance. These findings unveil the material properties of PCDm and their potential usage for myriad diamond-based electronic applications.

Acceleration of Carrier Transport in an Individual Microplate of Mixed-Halide Perovskite after Phase Segregation.

The band gap energy of lead mixed bromide-iodide perovskite can be simply tuned by adjusting the ratio between the composing halide anions, which would be segregated again upon continuous light illumination to form the iodide-rich domains. Here, we have employed transient absorption microscopy to investigate the carrier diffusion dynamics in an individual CsPbBr1.5I1.5 microplate under the influence of such iodide-rich domains. As expected in the phase-segregated microplate, the lifetime of charge carriers is shortened owing to their migration into the iodide-rich domains with a low band gap energy. Surprisingly, the diffusion coefficient of charge carriers is significantly increased in the phase-segregated microplate, signifying their effective acceleration by the iodide-rich domains according to our Green's function simulations. The above findings have advanced the understanding of the carrier diffusion dynamics in mixed-halide perovskites, which would facilitate their potential applications in various optoelectronic devices such as solar cells and photodetectors.

Ag nanoparticles in metal oxide highly supportive for photocatalytic and cytotoxic properties: experimental and theoretical analysis

ABSTRACT In this paper, Ag NPs doped metal oxides (MO-Ag NPs), such as ZnO NPs, CuO NPs, and NiO NPs, were prepared and completely characterised by different analytical methods (XRD, SEM, EDS, TGA, Raman, TEM, and HRTEM). The crystal size determined by XRD is about 15–36 nm, consistent with those estimated by HRTEM. The bandgap energy determined for the samples is corroborated with a density of states (DOS) derived from Density Functional Theory (DFT), showing a lower bandgap energy for the samples MO NPs-Ag NPs. Metal oxide Ag doping was modelled as Ni160O160-Ag16, Cu160O160-Ag16, and Zn150O150-Ag16 to show the semiconducting nature with a wide bandgap, observing the enhancement of the conductivity properties. A decrease of electrochemical charge transfer resistance (RCT) was seen (855 Ω for ZnO-Ag 5%, 536 Ω for CuO-Ag 5%, and 611 Ω for NiO-Ag 5% as compared to 1278 Ω for ZnO NPs, 1958 Ω for CuO NPs, and 1441 Ω for NiO NPs due to the presence of Ag NPs in the samples. The above samples were used to oxidise methylene blue (MB) under UV light, exhibiting a significant effect from the Ag loading, consisting of adsorption and antibacterial properties. The cytotoxicity of the materials was evaluated using confocal cell imaging, which brightened if the Ag NPs were present.

Insight into the Mechanism of α-, β-, γ-, and δ-MnO2 in Catalyzing Ammonium Perchlorate Decomposition: Superoxide Promotion (SOP) Effect.

To date, the catalytic mechanism of metal oxides in the thermal decomposition of ammonium perchlorate (AP) remains unclear and hinders the design and manufacture of efficient AP catalysts. Herein, a catalytic mechanism of the superoxide promotion (SOP) effect is reported, and the more oxygen vacancies and the lower band gaps of the catalysts allow deep decomposition of AP by •O2-. With the addition of 2 wt % δ-MnO2, the HTD temperature of AP decreases from 419.4 to 298.8 °C, and the ΔH increases from 585.5 to 1446.0 J g-1. The SOP effect accelerates the thermal decomposition of AP at low temperatures. Moreover, density functional theory (DFT) calculations confirm that the elongation of the O-O bond (1.34 Å) facilitates the activation of the O2 adsorbed on these vacancies. δ-MnO2 shows the most powerful SOP effect; thus, it is one of the best catalysts for AP thermal decomposition. In addition, ΔT and the ratio of NO2/N2O are highly correlated with •O2-; these results indicate that the diverse catalytic activity exhibited by the different crystal phases of MnO2 on AP is caused by the differences in the SOP effect.

Computational Investigation of Structural, Optoelectronic, and Charge Transport Properties of Heteroatoms Doped Graphene Quantum Dot with Lithium and Potassium Polysulfides.

In this study, we investigate the effect of heteroatom doping in graphene quantum dots (GQDs) in boosting the performance of metal-sulfur batteries using density functional theory (DFT) calculations. The properties, such as highest occupied and lowest unoccupied molecular orbits levels, absorption spectra, fundamental bandgap, adsorption energies, density of states, and charge transport properties of GQDs, heteroatom-doped GQDs, S8, Li2Sx (x=2, 4, 6, and 8), and K2Sx (x=2, 4, 6, and 8), are compared to evaluate the best dopant in the carbon matrix. Our results show that the heteroatom-doped systems have a lower bandgap and, therefore, better conductivity. Further, based on adsorption energy calculations, we find that Li2S8 and K2S8 exhibit strong interaction with P- and S-doped GQDs, and thus, heteroatom doping can help to lower the shuttle effect. In addition, electron mobilities in N-, P-, and S-doped GQDs are larger than in the GQDs. The detailed analysis suggests that P and S are better dopants owing to their catalytic behavior toward soluble polysulfide apart from increasing the conductivity. This study can be helpful for the design and development of an efficient cathode matrix for lithium and potassium sulfur batteries.

Thiazole-Flanked Para-Azaquinodimethane-Based Organic Polymer Semiconductors: Synthesis and Optoelectronic Properties.

Modifying the polymer backbone through N⋯S non-covalent interactions is an effective approach to enhance the properties of organic semiconducting polymers. Following this strategy, we designed and synthesized two new quinoidal polymers based on asymmetric and symmetric thiazole-flanked para-azaquinodimethane (p-AQM), named PAQM-TTTz and PAQM-TzTTz. To assess the impact of the thiazole unit, we also synthesized a reference polymer, PAQM-TTT, and compared its optoelectronic, thermal, and polymer backbone planarity properties with those of PAQM-TTTz and PAQM-TzTTz. Both PAQM-TTTz and PAQM-TzTTz exhibited dual-band absorption in solution, indicating pre-aggregation due to enhanced intermolecular interactions. Both polymers exhibited a low band gap. Density functional theory (DFT) studies revealed that while the thiazole unit does not alter the bond lengths of adjacent thiophenes, but it reduces torsional disorder by forming N⋯S non-covalent interactions with adjacent thiophenes in PAQM-TTTz and PAQM-TzTTz. However, due to the reduced electron richness of the conjugated backbone, a lower charge carrier mobility was observed in field-effect transistors for PAQM-TTTz and PAQM-TzTTz in comparison to PAQM-TTT. Our results highlighted the interest of non-covalent interactions in quinoidal polymers and present an alternative design strategy to control the properties of p-AQM-based quinoidal semiconducting polymers.

Electronic and dielectric properties of rare‐earth oxides in visible and near‐infrared range: A first‐principles study

Abstract The widespread application of laser technology has increased the demand for laser‐protective materials, and rare‐earth oxides are potential materials in laser protection research due to their unique physical and optical properties. This study investigates the electronic structure, dielectric, and optical properties of a series of cubic rare‐earth sesquioxides (RE2O3, RE = Gd, Dy, Er, Yb, Lu, Sc, and Y) using first‐principles calculations. The dielectric and optical properties of RE2O3 materials in the visible‐to‐near‐infrared (VIS‒NIR) wavelength range are clarified to be governed by electronic transitions. Despite similar spectral characteristics, the peaks in the spectra of dielectric function, complex refractive index, reflectance, and absorption coefficient systematically exhibit blue shifts with increasing RE3+ cationic radius in the same group, or decreasing RE3+ cationic radius in the same period, which is inherited from the variation in band gap size. And, a guideline to search for RE2O3 materials with high reflectance in the NIR wavelength range is proposed to be correlated with high refractive index and low band gap. These findings elucidate the fundamental mechanisms governing the dielectric and optical properties of rare‐earth oxides within the VIS‒NIR range, and provide useful guidelines for the screening and optimizing RE2O3‐based materials for laser‐protective applications.

Cadmium-Free Buffer Layer Materials for Kesterite Thin-Film Solar Cells: An Overview

Kesterite (CZTS/CZTSSe) thin-film solar cells are considered an eco-friendly, earth-abundant, and low-cost photovoltaic technology that can fulfill our future energy needs. Due to its outstanding properties including tunable bandgap and high absorption coefficient, the power conversion efficiency (PCE) has reached over 14%. However, toxic cadmium sulfide (CdS) is commonly used as an n-type buffer layer in kesterite thin-film solar cells (KTFSCs) to form a better p–n junction with the p-type CZTS/CZTSSe absorber. In addition to its toxicity, the CdS buffer layer shows parasitic absorption at low wavelengths (400–500 nm) owing to its low bandgap (2.4 eV). For the last few years, several efforts have been made to substitute CdS with an eco-friendly, Cd-free, cost-effective buffer layer with alternative large-bandgap materials such as ZnSnO, Zn (O, S), In2Se3, ZnS, ZnMgO, and TiO2, which showed significant advances. Herein, we summarize the key findings of the research community using a Cd-free buffer layer in KTFSCs to provide a current scenario for future work motivating researchers to design new materials and strategies to achieve higher performance.

Enhanced Stability and Efficiency in Ge–Pb‐Based Perovskite Solar Cells through PCCMAI‐Induced Ge Defect Passivation

The advantages of the Ge–Pb‐based perovskite solar cells (PSCs), such as low bandgap, have made this kind of PSC popular nowadays. Nevertheless, they have adverse properties that need to be fixed, such as short lifetime and fast crystallization process, which causes Ge defects. In this research, the passivation of Ge defects by using pyridinium chlorochromate methylamine iodine (PCCMAI) in the perovskite film (PF) structure is investigated. By using PCCMAI, the PSC's performance enhancement and surface morphology optimization were observed. It is determined that by the reaction of PCCMAI in the perovskite solvent, a coordination polydentate is formed in Ge–Pb mixed perovskite, and it results in the improvement of crystallization quality and electron transfer. After PCCMAI treatment of the Ge–Pb‐based perovskite film, the measured power conversion efficiency (PCE) indicates that the performance of the fabricated PSC increased from 16.85% to 20.14%. Moreover, fabricated PSCs show an increment in stability after PCCMAI treatment.

MoS2 Channel-Enhanced High-Density Charge Trap Flash Memory and Machine Learning-Assisted Sensing Methodologies for Memory-Centric Computing Systems.

Driven by the shift of artificial intelligence (AI)workloads to edge devices, there is a growing demand for nonvolatile memory solutions that offer high-density, low-power consumption, and reliability. However, well-established 3D NAND Flash using polycrystalline Si (Poly-Si) channel encounters bottlenecks in increasing bit density due to short-channel effects and cell-current limitations. This study investigates molybdenum disulfide (MoS2) as an alternative channel material for 3D NAND Flash cells. MoS2's low bandgap facilitates hole-injection-based erase, achieving a broader memory window at moderate voltages. Furthermore, adopting a low-k (≈2.2) tunneling layer improves the gate-coupling ratio, reducing program/erase voltages and enhancing reliability, with endurance up to 104 cycles and retention of 105 s. Comprehensive analyses, including thickness-dependent MoS2 electrical measurements, temperature-dependent conduction studies, and Technology Computer-Aided Design (TCAD) simulations, elucidate the relationship between channel thickness and reliability metrics such as endurance and retention. Furthermore, deep reinforcement learning-driven Berkeley Short-channel IGFET Model (BSIM) parameter calibration enables seamless integration of the MoS2 model with a fabricated page-buffer chip, allowing circuit-level verification of sensing margins. This methodology can be applicable to new channel materials for next-generation memory devices. These results demonstrate that MoS2-based nonvolatile memory effectively meets high-density, low-power, and reliable storage needs, presenting a promising solution for AI-centric edge computing.

Construction of Highly Active Coral-Like Co/Ni-BTC Catalyst and Its Application in CO2-to-CO Conversion.

The photocatalytic reduction of CO2 using solar energy presents an effective strategy for CO2 mitigation and utilization. Metal-organic frameworks (MOFs), known for their exceptional CO2 adsorption capacities and unique structural features, are emerging as novel photoactive materials for CO2 reduction. In this study, rod-like, reticular, and ball-like Ni-BTC were synthesized using Ni2⁺ ions and 1,3,5-benzenetricarboxylic acid (H₃BTC). Among these, the rod-like Ni-BTC exhibited the narrowest optical band gaps and achieved an outstanding CO generation rate of 4.707mmol/g/h. To further enhance the photocatalytic performance, Co2⁺ was partially substituted for Ni2⁺ in the rod-like Ni-BTC, resulting in the construction of bimetallic coral-like Co/Ni-BTC-x (x=1, 2, 3). The incorporation of Co2⁺ facilitated the transformation of the larger rod-like Ni-BTC particles into a coral-like morphology with micro- and nanoscale dimensions. Compared to monometallic rod-like Ni-BTC, the bimetallic catalysts exhibited lower bandgap values, faster charge transfer rates, and superior photocatalytic CO₂ reduction activity. Notably, Co/Ni-BTC-2 achieved the highest CO generation rate of 7.392mmol/g/h. This study demonstrates that the combination of morphological control and bimetallic approach is an effective strategy for enhancing the performance of MOF catalysts in the photochemical reduction of CO2.

WO3/Nb2CT x MXene 2D-2D heterojunction as a high performance photoanode for photoelectrochemical water splitting.

Photoelectrochemical (PEC) water splitting plays a key role in the production of green hydrogen, which is a sustainable energy source and non-exploitative to the environment. Therefore, the development of efficient photocatalysts is essential for enabling green hydrogen generation. In this work, the synergistic effect between tungsten oxide (WO3) and Nb2CT x (MXene) was explored for PEC water oxidation, and a composite catalyst was prepared using a hydrothermal and sonication approach to obtain a 2D/2D WO3/Nb2CT x heterojunction. WO3 is a promising photocatalyst owing to its optimal band gap, stability, and cost-effectiveness, but its efficiency is hindered by poor charge transfer, rapid recombination, and weak visible light absorption. Integrating Nb2CT x , a highly conductive MXene, enhances charge separation, reduces electron-hole recombination, and strengthens photocatalytic activity. This synergy increases the number of catalytic sites, improves visible light absorption, and stabilizes WO3, leading to a more efficient and durable material for solar energy conversion and water splitting. The Tauc plot of the composite shows a slightly lower bandgap (2.56 eV) than that of pristine WO3 (2.74 eV), while the charge separation efficiency of the composite is confirmed by its lower photoluminescence intensity than that of pristine WO3. Among the synthesized catalysts, WO3@Nb2C3 showed improved PEC-OER activity by attaining a photocurrent density of 4.71 mA cm-2 at 1.23 V vs. RHE compared to the pristine WO3 that attained a photocurrent density of 2.15 mA cm-2 at the same potential. This strategy appears promising for designing catalysts for PEC water oxidation in a solar-driven hydrogen-powered future.