Defect Layer Research Articles

Tailoring Second Harmonic Generation via Strong Coupling in a One‐Dimensional Photonic Crystal Heterostructure

Controlling harmonic generation is crucial for nonlinear optics and nanophotonic devices. Herein, a 1D photonic crystal heterostructure is theoretically proposed comprising a metal film, a lithium niobate layer, and a distributed Bragg reflector with a defect layer. The Tamm state and the defect state for dual‐band second‐harmonic generation (SHG) enhancement simultaneously are numerically investigated. Finite‐element method simulations indicate that SHG efficiencies based on Tamm plasmons and the defect state are 6.85 × 10−6 and 3.28 × 10−4, respectively. Intriguingly, the strong coupling between the defect state and Tamm plasmons enables spatial energy exchange, leading to the SHG switching between them. In the strong coupling region with Rabi splitting energy up to 5.5 meV, the SHG conversion efficiency reaching 5 × 10−5 is observed for both two new hybridized states. During the entire anticrossing Rabi splitting process, the SHG efficiency difference between two resonances can be modulated by up to two orders of magnitude. The coupling strength between two resonances is adjusted by varying the position of the defect layer. Simulation results are consistent with the coupled oscillator model. This work not only offers a platform for studying nonlinear frequency conversion but also establishes a new method of using strong coupling to tailor SHG.

Achieving 34 % efficiency with a dual-absorber solar cell design using CaRbCl3 and Ca3NCl3 perovskites

This study’s DFT calculations show that the direct bandgaps of perovskite CaRbCl3 and Ca3NCl3 are 1.386 eV and 1.430 eV, respectively, confirming their semiconducting nature. The study also provides density of states and dielectric constant data for these materials. In photovoltaic (PV) technology, perovskites are highly valued as solar absorber materials for their exceptional optical properties, low cost, high efficiency, and lightweight design. This study presents a structure (Al/FTO/CdS/dual absorber (CaRbCl3/Ca3NCl3)/V2O5/Au) incorporating a CdS electron transport layer (ETL) and a V2O5 hole transport layer (HTL) with a double perovskite absorber layer (DPAL) of CaRbCl3 and Ca3NCl3 using SCAPS-1D. The results show that the DPAL-based perovskite solar cell (PSC) outperforms single-layer PSCs, with significant efficiency gains when HTL is included. The study thoroughly examines the effects of layer thickness, doping levels, and defect densities on key electrical parameters such as VOC, JSC, FF, and PCE. It also explores J-V and QE characteristics and the impact of temperature. The ideal absorber thickness for achieving the highest PCE is 500 nm for CaRbCl3 and 600 nm for Ca3NCl3, combined with a doping density of 1 × 1017 cm−3, a defect density of 1 × 1011 cm−3 and interface defect density of 1 × 1010 cm−2. While single-absorber solar cells achieve maximum efficiencies of 24.40 % (CaRbCl3) and 24.02 % (Ca3NCl3), the DPAL setup reaches an optimized efficiency of 27.66 %, further increasing to 34.39 % with a VOC of 1.295 V, FF of 83.95 %, and JSC of 31.63 mA/cm2 when using V2O5 HTL. This research provides valuable insights and a practical strategy for developing cost-effective CaRbCl3/Ca3NCl3 thin-film solar cells.

A Simulation Study on the Effect of Supersonic Ultrasonic Acoustic Streaming on Solidification Dendrite Growth Behavior During Laser Cladding Based on Boundary Coupling

Laser cladding has unique technical advantages, such as precise heat input control, excellent coating properties, and local selective cladding for complex shape parts, which is a vital branch of surface engineering. During the laser cladding process, the parts are subjected to extreme thermal gradients, leading to the formation of micro-defects such as cracks, pores, and segregation. These defects compromise the serviceability of the components. Ultrasonic vibration can produce thermal, mechanical, cavitation, and acoustic flow effects in the melt pool, which can comprehensively affect the formation and evolution for the microstructure of the melt pool and reduce the microscopic defects of the cladding layer. In this paper, the coupling model of temperature and flow field for the laser cladding of 45 steel 316L was established. The transient evolution laws of temperature and flow field under ultrasonic vibration were revealed from a macroscopic point of view. Based on the phase field method, a numerical model of dendrite growth during laser cladding solidification under ultrasonic vibration was established. The mechanism of the effect of ultrasonic vibration on the solidification dendrite growth during laser cladding was revealed on a mesoscopic scale. Based on the microstructure evolution model of the paste region in the scanning direction of the cladding pool, the effects of a static flow field and acoustic flow on dendrite growth were investigated. The results show that the melt flow changes the heat and mass transfer behaviors at the solidification interface, concurrently changing the dendrites’ growth morphology. The acoustic streaming effect increases the flow velocity of the melt pool, which increases the tilt angle of the dendrites to the flow-on side and promotes the growth of secondary dendrite arms on the flow-on side. It improves the solute distribution in the melt pool and reduces elemental segregation.

Selective passivation of 2D MoS2 nanosheets surface defects by spontaneous growth of Au nanoparticles for full response-recovery NO2 detection at room temperature

Full recovery at room temperature (RT) is quite challengng for two dimensional transition metal dichalcogenides chemiresistive gas sensors. The main reason for the incomplete recovery is the strong bonding of gas molecules onto sensing layer defects. Here, we show that the recovery rate of MoS2 chemiresistive NO2 sensors can be improved by selective passivation of MoS2 nanosheets (NSs) defects with Au nanoparticles (NPs) via a simple spontaneous reduction method. MoS2 NSs were produced by liquid shear exfoliation. Pristine and Au NPs functionalized MoS2 were characterized using ς-potential, UV–Visible spectroscopy, TEM, SEM, AFM, EDS, XRD, XPS and Raman spectroscopy. The analyses confirm the presence of Au NPs on the edges of MoS2 NSs at defective sites with NP sizes of 1–4 nm and 5–30 nm. Both pristine MoS2 and Au-decorated MoS2 NSs were employed to fabricate NO2 chemiresistive devices. Au-decorated MoS2 sensors showed an improved performance (for 1 ppm NO2, Au-MoS2 sensor exhibited a response of 5.6 % instead of 2.2 % for MoS2 sensor), and gave faster response and better recovery time. Concurrently, the functionalization is independent of the adsorption and desorption of NO2. Most importantly, the functionalization of MoS2 NSs helps to full response-recovery within one hour, without either thermal or UV irradiation treatment.

Enhanced Performance of Fluidic Phononic Crystal Sensors Using Different Quasi-Periodic Crystals

In this paper, we introduce a comprehensive theoretical study to obtain an optimal highly sensitive fluidic sensor based on the one-dimensional phononic crystal (PnC). The mainstay of this study strongly depends on the high impedance mismatching due to the irregularity of the considered quasi-periodic structure, which in turn can provide better performance compared to the periodic PnC designs. In this regard, we performed the detection and monitoring of the different concentrations of lead nitrate (Pb(NO3)2) and identified it as being a dangerous aqueous solution. Here, a defect layer was introduced through the designed structure to be filled with the Pb(NO3)2 solution. Therefore, a resonant mode was formed within the transmittance spectrum of the considered structure, which in turn shifted due to the changes in the concentration of the detected analyte. The numerical findings demonstrate the role of the different sequences such as Fibonacci, Octonacci, Thue–Morse, and double period on the performance of the designed PhC detector. Meanwhile, the findings of this study show that the double-period quasi-periodic sequence provides the best performance with a sensitivity of 502.6 Hz/ppm, a damping rate of , a maximum quality factor of 8463.5, and a detection limit of 2.45.

An inorganic lead-free Cs2SnI6-based perovskite solar cell optimization by SCAPS-1D

Cs2SnI6 is an environmentally friendly and reliable perovskite solar cell (PSCs) material. Its optimal band gap and strong light absorption make it a promising candidate for the absorption layer. However, the current challenge is to improve its photoelectric conversion efficiency. To address this, this study investigates the performance of PSCs based on Cs2SnI6 using SCAPS-1D simulation. The influence of various factors on PSC performance is examined, including different hole transport layers(HTLs) and electron transport layers(ETLs), perovskite layer thickness, ETL doping density, HTL doping density, absorber doping density, perovskite layer defect density, different back contacts and temperature. Finally, a Cs2SnI6-based solar device with an inorganic configuration of FTO/NiO/Cs2SnI6/SnO2/Au has been developed, reaching the power conversion efficiency(PCE) of 28.69 %. The study demonstrates that Cs2SnI6 PSCs exhibit promising photovoltaic performance, offering valuable insights for the solar energy sector in the production of cost-effective, efficient, and environmentally friendly Cs-based perovskite solar cells.

Modifying the buried interface by a sulfamate enable efficient perovskite solar cells with high stability

The buried interface between the pivotal perovskite layer and the electron transfer layer (ETL) greatly affects the photoelectric property of perovskite layer and the final performance of a perovskite solar cell (PSC). Effectively modifying the buried interface is feasible to improve the photoelectric conversion efficiency (PCE) and stability of PSCs. Herein, we employ a sulfamate sodium 4-aminoazobenzene-4′-sulfonate (SABS) with zwitterion to modify the SnO2 film surface to improve the performance of PSCs. The post-treatment makes the surface of SnO2 film smoother and also passivate the anion and cation vacancies of SnO2, which are benefit to the growth of perovskite crystals and strengthen the interface contact between SnO2 layer and perovskite layer. Furthermore, SABS molecules can passivate defects of perovskite layer at the buried interface. By using this post-treating method, the PCE of the final PSC is increased from 21.76 % to 23.86 %, and the storage and operational stability are also significantly improved. This promotion the buried interface via post-treating the SnO2 film with a zwitterion passivator provides a convenient strategy to effectively improve the performance and stability of PSCs.

Hydrogenation of graphene on Ni(111) by H2 under near ambient pressure conditions

Graphene hydrogenation on Ni(111) in the mbar region has been investigated by combining Near Ambient Pressure X-ray Photoemission Spectroscopy and Density Functional Theory calculations. A complete and nearly perfect graphene single layer and an incomplete defective monolayer were exposed to a methanation mixture (H2 + CO and H2 + CO2, respectively) with a large excess of H2. The observed behavior is quite different for the two systems. In the former case, the C 1s spectrum of the initially strongly interacting graphene shows the appearance of new components corresponding to hydrogenated C atoms and their first nearest neighbors. The defective carbon layer, grown in the presence of sulfur contamination and consisting of a mixture of strongly and weakly interacting graphene with a significant amount of dissolved C, initially shows the same C species and then evolves with the formation of sp3 carbon and patches of Ni oxide/hydroxide. NiO forms by CO2 dissociation, while sp3 carbon is indicative of a rumpling of the graphene adlayer induced by hydrogenation. Both species disappear when annealing in H2. Dissociation of H2 and graphene hydrogenation is possible thanks to the presence of the Ni substrate which makes the reaction weakly exothermic and significantly reduces the barrier for H2 dissociation.

Microstructure and corrosion property evolution of a surface-nanostructured 15–15Ti austenitic steel during immersion in liquid LBE at 550 °C

This study investigated the compatibility of surface-nanostructured 15–15Ti austenitic steel in 550 °C LBE with an oxygen concentration of 5 × 10−7 wt.% for various exposure durations (759, 1638, 2404, and 3012 h). The results demonstrate that the grain size was reduced from 33.50 μm to the nano-scale after shot-peening (SP), achieving 17.62, 15.44, and 14.25 nm under SP pressures of 0.06, 0.15 and 0.25 MPa, respectively. The untreated steel experienced severe oxidation and dissolution corrosion, whereas the surface-nanostructured steel exhibited only mild oxidation and was resistant to dissolution corrosion. The enhanced corrosion resistance of surface-nanostructured steel is attributed to the higher protectiveness of the Cr-rich spinel layer and the less defective Ni-rich layer beneath it. Recrystallization occurred exclusively in the Ni-rich region, while the deformed steel underwent recovery during exposure. The thickness of the recrystallization layer was 2.9 μm at 759 h, increased to 8 μm at 1638 h, and remained stable thereafter. The size of recrystallized grains in SP-samples processed under pressure of 0.06 MPa and 0.15 MPa was approximately 2.92 μm, whereas it was about 1.32 μm for 0.25 MPa processed sample.

An (AlN/GaN)N D (AlN/GaN)N Photonic Crystal-based Gas Sensor

Over the past few years, more studies have been conducted on the use of photonic crystals (PCs) in the detection field. Particularly fascinating for use as gas sensors are these materials’ outstanding spectrum sensitivity and small design. Using one-dimensional PCs as the theoretical foundation, this work aims to develop and analyze a nanoscale system that can identify the concentration of gases in ambient air and differentiate it from contaminated air. The intended structure is composed of layers of gallium nitride (GaN) and aluminum nitride (AlN) that alternate. In between these layers is a defective layer cavity that is filled with polluted air, which has a refractive index that is quite similar to pure air. The transfer matrix method (TMM) was used to perform numerical results for the proposed sensor. This sensor achieves average sensitivity of 1791 nm/RIU, average quality factor and figure of merit (FoM) of 1833 and 2287, respectively. We therefore think that the suggested detector’s design offers a strong candidate for accurate and efficient detection.

Field test of internal visualization of deep-water pile foundation using ultrasonic waves

Early-age internal visualization is critical for timely assessing the quality of pile foundations, especially as super cross-sea bridges increase the diameter and length of pile foundations beyond the capabilities of traditional cross-hole sonic logging (CSL). This article introduces two innovations. First, ultrasonic instruments are specially developed to transmit waves through a concrete pile with a diameter of 4 m, a length of 92 m, and a water depth of 63 m, before the full hardening of concrete. Second, an imaging method is proposed to upgrade traditional CSL from 1D detection to 3D visualization. Both large-scale experiments and field tests are tested in the first 7 days after the concrete casting. The experiments successfully visualize typical construction defects, achieving a detection resolution of 18 cm for layered defects and 15 cm for void defects. During the field test, a low-pixel region is observed at the pile head, extending approximately 2.1 m deep, attributed to mud floating up during concrete casting into the steel casing. These developments in instrument technology and visualization methods provide essential tools for the quality evaluation of super pile foundations. Furthermore, the visualization data can support digital twin modeling in subsequent stages of construction and maintenance planning.

Waste to Wealth: One-Step Exfoliating of Spent Graphite to Build a Low-Cost Cathode for Lithium-Sulfur Batteries.

With the booming development of Li-ion batteries (LIBs), the recycling and reusing of spent graphite (SG) from LIBs is becoming increasingly crucial. Meanwhile, developing low-cost and efficient carbon hosts for lithium-sulfur (Li-S) batteries has gained widespread attention in the past decade. Nevertheless, the processing of carbon materials as sulfur hosts is often energy-consuming and complex. Herein, a simple and environmental-friendly strategy is proposed to reuse the SG to prepare graphene/sulfur composite cathode for Li-S batteries. Due to expanded layer spacing and defects of SG, sulfur molecules can strip it into a graphene-type host via ball milling. By optimizing the S/SG ratio and ball milling time, the as-prepared graphene/sulfur composite cathode with 70 wt.% sulfur content exhibits a high capacity of 1000 mAh g-1. With a high sulfur loading of 4.68 mg cm-2, the graphene/sulfur cathode can maintain 526 mAh g-1 after 400 cycles. This work provides a novel waste-to-wealth perspective for recycling spent graphite from LIBs to reuse in Li-S batteries.

Long-term stability in perovskite solar cells through atomic layer deposition of tin oxide.

Robust contact schemes that boost stability and simplify the production process are needed for perovskite solar cells (PSCs). We codeposited perovskite and hole-selective contact while protecting the perovskite to enable deposition of SnOx/Ag without the use of a fullerene. The SnOx, prepared through atomic layer deposition, serves as a durable inorganic electron transport layer. Tailoring the oxygen vacancy defects in the SnOx layer led to power conversion efficiencies (PCEs) of >25%. Our devices exhibit superior stability over conventional p-i-n PSCs, successfully meeting several benchmark stability tests. They retained >95% PCE after 2000 hours of continuous operation at their maximum power point under simulated AM1.5 illumination at 65°C. Additionally, they boast a certified T97 lifetime exceeding 1000 hours.

Comparative Analysis of Simultaneous Electrochemical and Electrodischarge Machining Process

Abstract Recent advances have established electrochemical discharge machining (ECDM) as an effective alternative to electrical discharge machining (EDM) for producing microholes in conductive materials. However, ECDM leaves nonuniform layers, including recast layers and heat-affected zones, rendering it unsuitable for materials vital to aerospace, defence, and biomedical applications. To address this issue, the present work investigates a novel electrochemical machining (ECM)-based frugal engineering process known as simultaneous electrochemical and electrodischarge machining (SECEDM) for microhole fabrication. To evaluate the process effectiveness, the machining results of the SECEDM process were compared with ECDM, EDM, and ECM. The obtained results present the fundamental distinction between the process mechanism of SECEDM and ECDM. SECEDM has been reported to produce microholes with improved machined surfaces characterized by their freedom from recast layer and ECDM-induced defects. Moreover, SECEDM facilitated meticulously controlled high-speed anodic dissolution of work material, surpassing the material removal rate (MRR) achieved through ultrasonic-assisted ECDM (U-ECDM), ECM, and EDM processes by 2.67, 4.2, and 6.2 times, respectively. Furthermore, the substantial 67.72% and 68.82% reduction in the average machined hole diameter than ECM and U-ECDM, respectively, with a noteworthy 13.69% enhancement in average roundness error achieved while maintaining the repeatability accuracy with an accuracy range within ±0.009 mm through SECEDM process underscore SECEDM's accuracy and repeatability. In addition, lower surface roughness by 31.6% and 68% compared to ECM and EDM, along with reduced carbon and oxygen content as examined through energy dispersive X-ray (EDX) analysis, signifies the SECEDM process efficiency in microfabrication.

Дослідження кольматувальної добавки та преспективи її застосування в дорожніх цементобетонах

ntroduction. Cement concrete, like most other porous materials, easily absorbs and retains moisture. Moisture can be absorbed by the reinforced concrete foundation if there are defects in the external waterproofing layer, leading to the development of mold, mildew, efflorescence, reinforcement corrosion, and damage to the finishing materials in the basement. The greatest danger is that frozen water expands and, through its pressure, destroys the structure from within. Waterproofing additives in cement concrete are used to improve the strength, corrosion resistance, impermeability, and frost resistance of concrete. Problem Statement. Ensuring the reliability of road pavement in the post-war period. Objective. To investigate the feasibility of using a waterproofing additive in a cement concrete mix using the example of the colmatant additive Penetron Admix.

Fabrication and optical characterization of porous silicon heterostructure as matrix for sensing organic solvent via resonance peak and Q factor shift

Porous silicon heterostructures with an extensive photonic band gap, featuring a microcavity defect layer, have been successfully fabricated and applied as sensor devices for detecting organic solvent species. These sensors utilize both the resonance peak shift and the inverse Q-factor as sensing parameters. Similar to conventional porous silicon microcavities immersed in various organic solvents, the resonance peak exhibits a linear dependence on the solvent refractive index. However, in the proposed structure, the inverse Q-factor also displays a comparable linear trend with the refractive index, but with greater sensitivity to solvent mixtures. This increased sensitivity arises because the inverse Q-factor deviates from linearity when the prior solvent is not adequately removed from the porous structure before reflectance measurements — a condition not commonly detected by the resonance peak shift. To improve the performance of these sensors, the porous structures were passivated by thermal oxidation. For sensor applications, it is crucial that the contrast in the effective refractive index between the high and low porosity layers of the passivated structures be sufficiently large. Otherwise, when the porous matrix is immersed in solvents, it loses its resonance peak, rendering the structure ineffective for sensor applications.

Fracture behavior of SiCf/SiC cladding with prefabricated cracks on the inner/outer wall

This study investigated the fracture behavior of SiCf/SiC cladding with axial cracks in the CMC layer/monolithic SiC layer on the inner and outer wall via an expanding plug test. The specimen with a prefabricated crack on the outer wall fractured in no specific direction. After the first load drop, fracture sources can be detected not only near the notch but also in other directions within the CMC layer. The simulation shows a homogeneous stress distribution resulting in a similar hoop strength to the specimen without prefabricated cracks. In contrast, the specimen with a prefabricated crack on the inner wall fractured along the notch. After the first load drop, fracture sources can be detected only near the notch. The simulation demonstrates stress concentration, resulting in a lower hoop strength. Therefore, considering the nuclear application of SiCf/SiC cladding, we are supposed to pay more attention to the defects in CMC layer in the fabrication process of SiCf/SiC cladding.

Lead-free Cs2TiBr6 perovskite solar cells achieving high power conversion efficiency through device simulation

Recently, lead-based perovskite solar cells (PSCs) have gained significant attention in the photovoltaic industry due to their remarkable properties such as high bandgap and high absorption coefficient. However, challenges such as toxicity, instability, and short shelf life limit the use of inorganic-organic lead-based PSCs. To address these issues, researchers introduced eco-friendly, lead-free, and stable cesium titanium (Cs2TiBr6) single-halide absorber material. The aim of this work is to perform the numerical modelling and simulation of FTO/SnO2/Cs2TiBr6/CBTS/Au structure incorporating interfacial defect layers (IDL) using SCAPS-1D to examine and study its characteristics properties about various photovoltaic (PV) parameters such as light-absorbing layer thickness, charge transport layer thickness, doping, defect density, operating temperature, and quantum efficiency (QE). After evaluating these parameters, the proposed single-halide Cs2TiBr6-based structure shows superior performance as compared to previously reported experimental and simulation-based Cs2TiBr6 perovskite structures. The results show a maximum power conversion efficiency (PCE) of 24.24 %, with a fill factor (FF) of 88.9 %, an open-circuit voltage (VOC) of 1.31 V, and a short-circuit current density (JSC) of 20.76 mA/cm2. This work encourages researchers to develop low-toxic, and stable PSCs for the future solar cell industry.

Performance optimization of FASnI3 based perovskite solar cell through SCAPS-1D simulation

The article provides a detailed look at the fabrication of a high-performance structure for FASnI3-based perovskite solar cells (PSCs). The FTO/CeO2/FASnI3/CuI/Au structure is designed using the Solar Cell Capacitance Simulator in One Dimension (SCAPS-1D) to investigate the fabricated PSC's performance. This investigation's main objective is to improve PSCs performance by using non-traditional Hole transport layer (HTL) and Electron transport layer (ETL) materials, such as CeO2 and CuI, which have both been the subject of limited research. Moreover, the investigation seeks to determine the impact of several perovskite layer characteristics, including bandgap (Eg), electron affinity (χ), acceptor density (NA), thickness (t), and defect density (Nt). Additionally, this study also investigates the effect of various back contact work functions. Significant improvements in solar cell parameters, such as power conversion efficiency (PCE) from 22.06% to 24.87% and current density (Jsc) from 26.0274 to 30.675 mA/cm2, were observed by optimizing the device's parameters. In contrast, the fill factor (FF) and open circuit voltage (Voc) decreased their values from 86.13% to 87.10% and 0.9843 to 0.9308 V, respectively. These findings show that our designed solar cell structure performs better than those with conventionally used HTLs and ETLs. Consequently, this study highlights the potential benefits of lead-free PSCs and presents fresh opportunities for their development and use in various solar applications.

Fluorimetric Detection of Vapor Pollutants with Diketopyrrolopyrrole Polymer Microcavities.

The increasing prevalence and detrimental effects of volatile organic compounds are driving the need for selective on-site sensors that do not require complex sampling or instrumentation. Broadband selective sensors exhibiting selectivity based on their distinct response mechanism is becoming of increasing technological relevance in both industrial and urban settings. In this context, we propose a label-free sensor based on a polymeric planar microcavity embedded with a fluorescent organic dye, designed to detect various pollutants in the vapor phase. The sensor consists of alternating layers of cellulose acetate and poly(N-vinylcarbazole) and contains a polystyrene defect layer doped with a quadrupolar diketopyrrolopyrrole. Both the structural properties of the polymer microcavity and the dye in the defect layer contribute to the sensor's response to analytes, creating a dual-probe system where a single photonic element translates chemical signals into optical signals, namely, transmission and fluorescence spectral variations. The discrimination capability of the photonic structure arises from the physicochemical interactions between the analytes and the polymer components. To validate our approach, we evaluate the sensor's response to four distinct volatile molecules and investigate the mechanisms influencing the optical response.