Defect Levels Research Articles

Sulphur/functionalized graphene composite as cathode for improved performance and life cycle of lithium-sulphur batteries

Over the past years, significant advantages have been introduced to upgrade the performance of lithium-sulfur battery (Li-S) batteries since their prototype in the 1960s. Due to high theoretical energy density and cost efficiency, Li-S batteries have obtained great attention and have made great progress in the last few years. In this work, we developed the sulfur-attached few-layer graphene composite (S/FLG), sulfur-attached functionalized few-layer graphene using acetic acid (S/FLG-COOH) and sulfur-attached functionalized few-layer graphene using strong acid H2SO4 and HNO3 (S/FLG-OH) as a cathode material with high sulfur loading. The material’s structure is confirmed through XRD. The surface morphology is confirmed through SEM and elemental composition has been obtained through EDAX. The functional groups are confirmed through FTIR. The defect level and number of layers are confirmed through Raman characterization with an excitation laser wavelength of 532 nm. The electrochemical performance of three cathodes is also identified through EIS, CV, and GCD characterization. Meanwhile, highly developed defects and edges found in the functionalization of few-layer graphene using the strong acid (H2SO4 and HNO3) which consists of a hydroxyl functional group (FLG-OH) serve as polysulfide reservoirs to mitigate the shuttle effect. Among these cathodes, S/FLG-OH shows a high specific capacitance of 157.4 F g−1 and when applied as a cathode host on a coin cell it obtained a voltage of about 2.6 V. Well-performed S/FLG-OH cathode was used to fabricate the Coin Cell. The fabricated Coin Cell with S/FLG-OH as the cathode shows a stable potential over 50 cycles.

Suppression of irradiation effect on electrical properties of silicon diodes by iron in p-silicon

Radiation-hardness of silicon (Si) has been the subject of interest due to the damage of the material-based detectors during and after operation. In this work, the effects of 4 MeV proton-irradiation on the electrical properties of devices fabricated on undoped and Fe-doped p-Si were investigated using current-voltage (I-V) and capacitance-voltage (C-V) techniques. A decrease in current and capacitance is less pronounced and the conduction mechanism remains unchanged on Fe-doped p-Si diode after proton-irradiation. This insignificant change of electrical parameters of the Fe-doped diode after proton-irradiation indicates the suppression of the radiation effect by Fe in Si. The electrical properties of the diode are less dependent on incident radiation, because of the possible prevention of further dislodgement of atoms by incident radiation. As a result, the material becomes resistant to radiation damage, making the electrical properties of the diode independent of incident radiation due to Fe atoms in Si. As a result of the ohmic behaviour displayed by the Fe-doped Si diode, it is possible that in Si, Fe is responsible for generation-recombination (g-r) centres, which are defect levels positioned at the middle of the energy gap of Si. The possibility of these defects being responsible for the suppression of the radiation effect is explained in this work, making Fe a promising dopant to improve the radiation-hardness of Si.

Negative slope polarization in ferroelectric hysteresis loop engineered by defect dipoles

The power dissipation in conventional microelectronic devices is facing a fundamental barrier of Boltzmann Tyranny. The negative capacitance (NC) effect in ferroelectric materials provides possible solution to overcome this impending problem and gets a lot of attention. Here we report a novel method to design negative capacitance in ferroelectrics by the introduction of defect-dipole engineering. In the molecular dynamics simulations of a first principles-based effective Hamiltonian, an abnormal polarization with negative slope and corresponding differential capacitance are observed in the polarization-electric field (P-E) hysteresis loops when the applied electric field is perpendicular to the direction of the defect dipoles in acceptor-doped BaTiO3 single crystals. This phenomenon is attributed to the fact that the polarization overshoots, oscillates and finally gradually switches to the direction of defect dipoles by their restoring forces during the polarization switching near the coercive field. The P-E loop exhibits abnormal NC response only at a certain range of defect levels, and there are double loops at high level and typical square-shaped loops at low level. Moreover, in the experiments of poled 1 mol.% Mn-doped BaTiO3 ceramics, the abnormal negative slope polarization in P-E loops is confirmed, which are in good agreement with the simulation results.

Analysis of Cylinder Comp Product Quality Control with Proposed Improvements at PT. Jakarta Automotive

In the era of globalization, the manufacturing industry faces its biggest challenge, namely the demands of consumer needs with high quality standards. Various kinds of waste often occur in the production process, one of which is caused by a poor layout of facilities, for example the arrangement of machines on the production line that is not suitable. This is a problem in the production process of machining cylinder comp at PT. Jakarta Automotive. With the aim of finding out the factors that cause product defects in machining cylinder comp and finding design of improvement proposals to reduce the defects that occur, this study uses a quantitative method to find DPMO and sigma values as an analysis of the cause of the problem. The result of this study was the discovery of less than optimal engine layout settings that caused TAP NG defects in the product. So that a design of a proposed improvement was made in the form of a change in the engine layout. In conclusion, in this study, it was identified that the non-optimal engine layout was the cause of the high defects. Therefore, improvements are proposed in the form of changing the engine layout on the production line with the aim of reducing the level of defects caused by a less than optimal layout.

Fourth-stable stochastic resonance and its application to weak fault signal detection of rotating machinery

Weak characteristic extraction is vital for weak fault signal detection of machinery. Stochastic resonance (SR) is able to transfer noise energy into weak fault characteristic frequency excited by a defect of machines. However, the potential function in SR is vital to enhance weak fault characteristic frequency and determines the capability of SR to improve the signal-to-noise ratio (SNR) of a noisy signal. Now, common potential functions include monostable, bistable and even tri-stable potentials but fourth-stable SR has not been studied and applied to detect early fault characteristic frequency. In this paper, thus, we would investigate the behaviors of SR with a fourth-stable potential subject to additive noise, in which the approximate theoretical expression of the power done by SR is derived to demonstrate the fourth-stable Sr Then, a SR method with the fourth-stable potential is proposed to enhance weak fault characteristic frequency, in which these system parameters are adjusted by using SNR as the objective function and using genetic algorithms adaptively. In this paper, thus, Finally, the proposed method is verified by using a simulated signal with noise and two early fault experiment of rolling element bearings with different levels of defects on the outer and inner races. Moreover, the proposed method is compared with wavelet denoising and fast kurtogram methods. The comparisons indicate that the proposed method has the better performance for enhancing weak fault characteristic frequency or weak useful signals than other two methods and is available to weak fault signal detection of machinery.

Quality Control to Reduce Appearance Defects at PT. Musical Instrument

This research was conducted at PT. Musical Instruments that aim to analyze quality control to reduce appearance defects in piano products on the assembling production line. The problem faced by the company is the high level of product defects which has an impact on decreasing quality and customer satisfaction. The research method used is Six sigma with a DMAIC (Define, Measure, Analyze, Improve, Control) approach. This type of research is quantitative, with data collected in the form of the number of production defects in pianos. To analyze the causes of defects, a fishbone diagram with 4M + 1E factors is used, namely Man, Machine, Method, Material, and Environment. The results of the analysis show that the main factors causing appearance defects in piano products include incompatibility with work methods, lack of worker training, use of non-standard materials, suboptimal jig conditions, and unsupportive working environment. Based on these findings, improvement proposals are given in the form of improving standard operating procedures, regular training for workers, the use of high-quality materials, regular maintenance and calibration of jigs, and improvement of work environment conditions. The implementation of this improvement proposal is expected to reduce the number of appearance defects in piano products, improve product quality, and meet the quality standards expected by PT. Musical instrument.

Analysis of Carton Packaging Quality Control Using Statistical Quality Control Methods at PT XYZ

This research focuses on analyzing the quality control of cardboard box packaging at PT XYZ using the Seven Tools method. The main problem faced by the company is the high level of defects in the cardboard box products produced, which has a negative impact on production efficiency and customer satisfaction. The aim of this research is to analyze the main causes of defects in cardboard box products and provide suggestions for improvements that can be implemented by companies. The method used in this research is Statistical Quality Control (SQC) which involves the use of Seven Tools, namely check sheets, Pareto charts, fishbone diagrams and control charts. Using these tools, data regarding defects is collected, analyzed, and interpreted to identify the main causal factors of quality problems. The analysis results show that certain factors, such as the quality of raw materials, production processes, and operator skills, have a significant contribution to the occurrence of defects. Based on these findings, this research proposes several improvements that can be implemented by PT XYZ to improve the quality of their cardboard box products. Proposed improvements include increasing control over the quality of raw materials, skills training for operators, and implementing stricter standard operational procedures in the production process. By implementing this proposed improvement, it is hoped that PT XYZ can reduce the level of defects in their products, increase production efficiency, and increase customer satisfaction.

Synthesis of isotope‐substituted conjugated ladder polymers

AbstractConjugated ladder polymers (cLPs) represent an intriguing class of macromolecules, characterized by their multi‐stranded structure, with continuous fused π‐conjugated rings forming the backbone. Isotope substitution, such as deuteration and carbon‐13 labeling, offers unique approaches to address the significant challenges associated with elucidating the structure and solution phase dynamics of these polymers. For instance, selective deuteration can highlight parts of the polymer by controlling the scattering length density of specific molecular sections, thereby enhancing the contrast for neutron scattering experiments. In this context, deuteration of side‐chains in cLPs represents a promising approach to uncover the elusive polymer physics properties of their backbone. The synthesis of two distinct types of cLPs with perdeuterated side‐chains are reported here. During the synthesis, 13C isotope labeling was also employed to verify the low levels of defects in the synthesized polymers. Demonstrating these synthetic successes lays the foundation for rigorous characterization of the defects, conformation, and dynamics of cLPs.

First-principles investigation of positively charged and neutral oxygen vacancies in amorphous silica.

The structural parameters, electron localization functions, electron paramagnetic resonance (EPR) parameters, formation energies, and thermodynamic transition levels of various oxygen vacancy defects in amorphous silica are comprehensively and integrally investigated by using density functional theory. The trends of changes in the oxygen vacancy defect structure and electron localization induced by the increase in distance between defective silicon atoms are clearly identified. It is shown that the dimer configuration may be the potential structure of the Eδ' center. For the back-projected unpuckered configuration and the puckered configuration, whose EPR parameters are more consistent with the experimental values of the Eγ' center, the unpaired electron localized on the sp3 hybridized silicon atom is a common feature. Due to the three-coordinated oxygen atom in the forward-oriented configuration, the EPR parameters are closest to those of the Eα' center. Transformations of oxygen vacancy defects under different charge states are studied by sequentially adding and removing electrons. The thermodynamic transition level analysis reveals that the dimer and forward configurations may behave as deep traps for electron accumulation. The back-projected puckered fourfold-coordinated and fivefold-coordinated configurations are comparatively stable and may be able to function as shallow traps for electron transport. The neutral double unpuckered, neutral back-projected puckered fourfold-coordinated, and neutral back-projected unpuckered configurations are more likely to lose electrons during hole trapping. As the bias voltage is repeatedly changed, the defect density of the puckered configuration may reduce, while that of the dimer and unpuckered configuration may take an opposite trend.

Cover Picture

4‐(2‐Hydroxyethyl)piperazin‐1‐ium iodide (PZOI) is a functional ammonium salt that can simultaneously reduce shallow/deep‐level defect densities by passivation effect and form 2D component, respectively. These advances reduce the energy loss of single‐junction devices and significantly enhance the efficiency and stability of perovskite/organic tandems. More details are discussed in the article by Li et al. on page 1819—1827.image

Understanding epitaxial growth of two-dimensional materials and their homostructures.

The exceptional physical properties of two-dimensional (2D) van der Waals (vdW) materials have been extensively researched, driving advances in material synthesis. Epitaxial growth, a prominent synthesis strategy, enables the production of large-area, high-quality 2D films compatible with advanced integrated circuits. Typical 2D single crystals, such as graphene, transition metal dichalcogenides and hexagonal boron nitride, have been epitaxially grown at a wafer scale. A systematic summary is required to offer strategic guidance for the epitaxy of emerging 2D materials. Here we focus on the epitaxy methodologies for 2D vdW materials in two directions: the growth of in-plane single-crystal monolayers and the fabrication of out-of-plane homostructures. We first discuss nucleation control of a single domain and orientation control over multiple domains to achieve large-scale single-crystal monolayers. We analyse the defect levels and measures of crystalline quality of typical 2D vdW materials with various epitaxial growth techniques. We then outline technical routes for the growth of homogeneous multilayers and twisted homostructures. We further summarize the current strategies to guide future efforts in optimizing on-demand fabrication of 2D vdW materials, as well as subsequent device manufacturing for their industrial applications.

Defect-controlled fabrication of reduced graphene oxide/ZnO/PMMA-based solid-state optical limiting filters with SA/RSA switching property

A solid-state optical limiting filter was fabricated by noncovalently functionalizing a graphene-based nanocomposite with a polymer. Graphene oxide was reduced by varying reducing agent concentration and functionalized with metal oxide nanoparticles to enhance electronic transitions and third-order nonlinear optical characteristics. The nanocomposite was dispersed over the PMMA polymer framework, and thin films with μm-scale thickness were fabricated using the dip coating method. XRD analysis confirmed the wurtzite crystal structure of ZnO nanoparticles and the amorphous nature of PMMA. The carbon structural integrity was analyzed using Raman spectra. Linear optical studies revealed a redshift in the π-π* transition peak in rGO, suggesting enhanced conjugation. Third-order nonlinear refraction and absorption properties were assessed using the Z-scan technique, revealing a switching behavior in nonlinear absorption at different input intensities. An increase in the relative concentration of sp2 domains enhanced the nonlinear absorption. Optical limiting potential, determined using open aperture Z-scan data, yielded a threshold value of 0.066 GW/cm2. This study aims to develop a solid-state optical filter with a high laser damage threshold by adjusting the reduction rate, tuning defect levels, and analyzing its effect on the optical limiting potential.

Optical and electrochemical studies on single-phase ZnSnO3 nanostructures—A photosensitive approach

A sol-gel-combustion reaction approach is used to synthesize nanocrystalline, single-phase ZnSnO3 phosphor. XRD with the Rietveld refinement investigation reveals a previously unreported orthorhombic structure of ZnSnO3. FTIR analysis confirms the formation of the ZnSnO3 phase. Microstructural SEM and TEM examinations affirm the petal-like morphology of the ZnSnO3 nanostructure. UV-DRS analysis signifies ZnSnO3 as a semiconducting material with a lowest energy band gap of 2.94 eV, which has never been recorded before. Photoluminescence (PL) studies reveal defect-related emission in ZnSnO3. Cyclic voltammetry measurements confirm the redox process and photo-generated carrier recombination via defect levels. ZnSnO3 is identified as a p-type semiconductor by Mott-Schottky analysis. When irradiated with 397 nm UV light, the semiconducting nanostructures emit near-white light. Finally, the investigation of ZnSnO3 nanopowder for latent fingerprint impressions reveals an unusual diffuse reflection and high-resolution images under a sodium vapour lamp and LASER-LED illumination.

Gas-phase and liquid-phase purification of plastic waste derived carbon nanotubes: Effect of purification agent and operational parameters

The preparation of carbon nanotubes (CNTs) by catalytic pyrolysis of waste plastics is one of the most promising technologies to realize the harmless and high-value recycling of waste plastics. However, there are limited studies on the purification of waste-derived carbons, which is of significance for downstream applications. In this paper, the effects of different gas-phase purification conditions (temperature, gas type), liquid-phase purification (hydrochloric and nitric acid reflux), and combined gas-liquid purification on the properties of CNTs prepared from waste plastics were investigated. The as-obtained and purified CNTs were characterized using SEM, TEM, TPO, XRD, XPS, Raman spectroscopy, and FTIR spectroscopy. Results showed that operational temperatures have distinct impacts on the properties of CNTs during gas-phase purification. An appropriate temperature range for gas-phase purification was determined, with temperatures around 450 °C for air, 650 °C for CO2, and 700 °C for steam respectively, so that the amorphous carbon could be removed and the graphitization of CNTs was retained. Approximately 93 wt% of the metal catalyst particles could be removed with acid treatment for 4 h. In addition, carboxyl and hydroxyl functional groups were introduced to CNTs after acidic treatment. Furthermore, it was found that the approach combining CO2 treatment and nitric acid washing yielded CNTs with relatively higher quantities and lower defect levels. Results showed the properties of CNTs varied from the purification methods, which could meet different needs based on the downstream specific application requirements.

Oriented growth of 5-inch optical polycrystalline diamond films by suppressing dark features

Optical diamond materials are essential for infrared optical windows, microwave windows, and laser windows due to their exceptional properties. However, dark features inside the diamond are significant factors limiting optical properties, particularly at high deposition rates. This work focuses on adjusting crystallographic parameters to prepare (110) oriented optical-grade polycrystalline diamond films, aiming to mitigate dark features. Diamond films deposited via microwave plasma chemical vapor deposition (MPCVD) exhibit discernible quality stratification. Characterization analysis of diamond film samples with varying levels of black defects reveals a correlation: films with higher dark feature content tend to exhibit a preference for the (111) orientation, accompanied by a significant presence of penetration twins and interstitial voids. Conversely, transparent diamond films demonstrate a prominent (110) orientation, featuring numerous contact twins that alleviate competition from penetration twins and original grains during growth. Electron backscatter diffraction (EBSD) and scanning electron microscope (SEM) results reveal that transparent diamond films cultivated with a pronounced preference for the (110) orientation manifest consistent and seamless contact twins, leading to fewer dark features and improved optical transmittance. In contrast, (111) oriented diamond film exhibits numerous penetration twins, and holes form between them. Based on the analysis, 5-inch optical polycrystalline diamond films with (110) orientation were achieved successfully by suppressing dark features.

The Effect of Oxygen Vacancy Defects on the Structure and Electrochemical Behaviors of LiMn0.65Fe0.35PO4 Cathode

The presence of oxygen vacancy defects significantly impacts the crystal structure and electrochemical attributes of phosphate cathodes. In this investigation, LiMn0.65Fe0.35PO4 materials with varying levels of oxygen vacancy defects were synthesized via hydrogen plasma-induced reduction. It was observed that the content of oxygen vacancy defects on the crystal surface increased proportionately with the rise in hydrogen (H2) flow rate. Notably, the LMFP-3 sample, prepared with an H2 flow rate of 10 ml min−1, demonstrated superior electrochemical performance, characterized by a 159.7 mAh g−1 discharge capacity at 0.1 C and a remarkable 99.8% capacity retention at 5 C after 200 cycles. This enhancement in electrochemical performance is attributed to the improved intrinsic conductivity of the LiMn0.65Fe0.35PO4 material due to the presence of oxygen vacancy defects. However, it is important to note that an excessively high H2 flow rate can lead to the formation of Fe2P impurities, which hinder lithium ion (Li+) diffusion. Furthermore, theoretical calculations conducted using density functional theory provide a rational explanation for the observed improvement in electronic conductivity. The introduction of oxygen vacancy defects results in a significant reduction in the Band gap, which is highly beneficial for enhancing the intrinsic conductivity of the LiMn0.65Fe0.35PO4 materials.

Energy transfer and a novel SBR thermometry of SrY2O4:Sm3+/Eu3+ phosphor based on redshift of charge transfer band edge

In this study, a solid-state reaction was employed to synthesize SrY2O4: Sm3+, SrY2O4: Eu3+ and SrY2O4: Sm3+/Eu3+ phosphors. An intriguing redshift phenomenon from charge transfer band (CTB) edge was investigated for single-band ratiometric (SBR) thermometry applications. The phosphors synthesized exhibited an orthogonal CaFe2O4 structure with Pnam (62) space group. The Y3+ sites from host lattice were most likely to be replaced by Sm3+/Eu3+ ions. The sample of SrY2O4: 0.03 Sm3+/0.3Eu3+ showed a large degree of agglomeration with elongated particles, having an average size of approximately 4 μm. The energy bandgap decreased due to increased surface imperfections, resulting in enhanced defect level concentration. The dipole-dipole interaction could be used to explain energy transfer (ET) of Sm3+-Sm3+ and Sm3+-Eu3+. Furthermore, the energy transfer (ET) efficiency of Sm3+→Eu3+ in Sr2YO4 reached 77.7 %. The sample exhibited a good thermal stability (90.956 %@423 K) with Ea of 0.31 eV, which was an important parameter for broadening thermometry range. A thermometry strategy utilized this redshift phenomenon from CTB edge with anti-thermal quenching behavior and other peaks or bands with thermal quenching was therefore proposed. The high Sr value of 1.533 % K−1@298 K provides a great potential for optical thermometry application, contributing significantly to the advancement of single band ratiometric thermometry technologies.

Preparation of SnOx/N-GQDs composites with oxygen-rich vacancies for enhanced photoelectric properties

SnOx with oxygen-rich vacancies and SnOx/N-GQDs (Nitrogen-doped graphene quantum dots) composites were prepared by high temperature annealing and hydrothermal method, respectively. The annealing process introduced a large number of oxygen vacancies and produced defect energy levels in the band gap. The existence of the defect level effectively reduced the band gap of SnOx, enlarged the optical absorption range, and improved the light utilization. The introduction of N-GQDs also improved the carrier density and electron transport rate, and extended the carrier lifetime (τ = 7.44 ms). I-T (Transient photocurrent response) analysis results showed that when the mass ratio of Sn/SnO2 was 1:4 and N-GQDs doping content was 1 wt%, the transient photocurrent response of SnOx/N-GQDs could reach 5.51 × 10−4 A/cm2, which was 25 times higher than that of pure SnO2, and the photocurrent response value maintained 80.1 % within 500 s. EIS (Electrochemical impedance) and M-S (Mott-Schottky) analyses indicated that the appropriate amount of oxygen vacancies and N-GQDs were beneficial to reducing the charge transport resistance, inhibiting the electron-hole pair recombination, and increasing the carrier density of SnOx. The results show that SnOx/N-GQDs composites present the improved photoelectric properties with the addition of oxygen vacancies and N-GQDs, which provides a new idea for promoting the properties of semiconductors.

Quality control of garment product using DMAIC Six Sigma

Quality control is intended to ensure that the products are in accordance with the predefined standards. PT. XYZ is a garment company that manufactures products with global target market. Hence, product quality assurance becomes an important issue for PT. XYZ. This research focuses on the Just Brand-MCJA216142 jacket product at the sewing work station on line-4 of PT. XYZ. Preliminary observations show that the number of reworked-products was experiencing an increasing trend. This study aims to determine whether the company has carried out quality control properly. Specifically, the research objectives are to identify the type and level of product defects, identify the factors causing product defects, and provide proper improvement suggestions to reduce the occurrence of product defects. This study applied DMAIC (Define–Measure–Analyze–Improve–Control) Six Sigma concept. The results showed that the quality of the Just Brand-MCJA216142 jacket product has exceeded the Indonesian industry average and is classified as the USA industry average. However, quality improvement is still needed since the products are targeted for the export market. Based on Pareto diagram at the Analyze stage, it was found that the most dominant defects occurred in the Just Brand-MCJA216142 jacket production process were broken threads and puckering. The frequency of occurrence for these two types of defect reaches 23% of the total 16 types of defects. The defects were caused by human, machine, material, method, and environmental factors. Recommendations for improvement at the Improve stage are based on root cause analysis of each causative factor that is identified using a fishbone diagram. This research results strengthen the previous related researches regarding the effectivity of DMAIC Six Sigma for analyzing quality control of products.

Inference of oxidative stress in patients with hypothyroidism

Introduction and aim. Oxidative stress is one of the complications that accompany defects in thyroid hormone levels. This study was designed to evaluate oxidative stress markers in patients with hypothyroidism. Material and methods. This case control study was comprised of forty-two hypothyroid patients aged 36–46 years and forty age matched (35–43 years) healthy control participants randomly selected from the Endocrine Clinic of Al-Yarmook Hospital in Iraq. Blood levels of thyroid hormones malondialdehyde, glutathione, and paraoxonase-1 were assessed. Body mass index was calculated for each patient and control participant. Results. Regarding the data of oxidative stress markers in hypothyroid patients compared to controls, a significant elevation was reported in blood levels of malondialdehyde and a significant reduction was found in blood levels of glutathione (p=0.031). On the other hand, the blood levels of paraoxonase-1 were significantly different in hypothyroid patients compared with the control. Conclusion. Elevated blood levels of malondialdehyde and declined blood levels of glutathione in hypothyroid patients are a signal of oxidative stress and consequently increase the risk of cardiovascular complications.