Surface Potential Distribution Research Articles

Surface potential distribution of resist exposed by electron beam and the non-charging exposure conditions

Surface potential distribution of resist exposed by electron beam and the non-charging exposure conditions

Preparation and Characterization of Epoxy-Based Composite Materials Reinforced with Graphene Oxide

In this study, modified graphene oxide (GO) with γ-APS silane coupling agent before being dispersed into an epoxy/4,4’-diamino diphenyl methane matrix to prepare a composite material using the bar-coating technique. The modified GO materials with the γ-APS silane (GOS) were characterized by infrared spectrum, Zeta potential, and TG/DSC thermal analysis. The amount of silane grafted on the GO is ~ 3.3 wt.%; the Zeta potential value shifted from the negative to the positive region was observed on the surface potential distribution diagram. Scanning electron microscopy, DSC thermal analysis, and dielectric constant were used to characterize the obtained composite epoxy/GO material properties. The results show that graphene oxide, after modification with γ-APS silane agent, has good dispersion ability in the epoxy resin matrix. Composite material epoxy/GOS presented a high dielectric constant value (εaverage = 6.19, at 1 kHz), increasing thermal stability, which is a suitable material promising for future applications.

Frequency-Enhanced Geometric-Constrained Reconstruction for Localizing Myocardial Infarction in 12-Lead Electrocardiograms.

Determining the location of myocardial infarction is crucial for clinical management and therapeutic stratagem. However, existing diagnostic tools either sacrifice ease of use or are limited by their spatial resolution. Addressing this, we aim to refine myocardial infarction localization via surface potential reconstruction of the ventricles in 12-lead electrocardiograms (ECG). A notable obstacle is the ill-posed nature of such reconstructions. To overcome this, we introduce the frequency-enhanced geometric-constrained iterative network (FGIN). FGIN begins by mining the latent features from ECG data across both time and frequency domains. Subsequently, it increases the data dimensionality of ECG and captures intricate features using convolutional layers. Finally, FGIN incorporates ventricular geometry as a constraint on surface potential distribution. It allocates variable weights to distinct edges. Experimental validation of FGIN confirms its efficacy over synthetic and clinical datasets. On the synthetic dataset, FGIN outperforms seven existing reconstruction methods, attaining the highest Pearson Correlation Coefficient of 0.8624, the lowest Root Mean Square Error of 0.1548, and the highest Structural Similarity Index Measure of 0.7988. On the clinical public dataset (2007 PhysioNet/Computers in Cardiology Challenge), FGIN achieves better localization results than other approaches, according to the clinical standard 17-segment model, achieving an average Segment Overlap of 87.2%. Clinical trials on 50 patients demonstrate FGIN's effectiveness, showing an average accuracy of 91.6% and an average Segment Overlap of 88.2%.

Additive and interface passivation dual synergetic strategy enables reduced voltage loss in wide-bandgap perovskite solar cells

The open-circuit voltage (VOC) loss for wide-bandgap (WBG) perovskite solar cells (PSCs) is a significant obstacle to their further development. Herein, we introduce a dual approach involving mixed potassium thiocyanate and potassium chloride (KSCN+KCl) additives combined with 2-thiophene methylamine iodine (2-ThMAI) post-passivation strategy to mitigate VOC loss in WBG PSCs. In the mixed additives, KSCN can expand the grains and reduce the grain boundary, while KCl can inhibit the migration of halogen ions, effectively preventing phase segregation in WBG perovskites under the combination of both. However, due to the substantial energy level mismatch at the perovskite/electron transport layer (ETL) interface, suppressing phase segregation alone is insufficient to reduce the VOC loss. Therefore, introducing 2-ThMAI interface passivation could uniform spatial distribution of perovskite surface potential, promote energetic alignment at perovskite/electron transport layer interface, and further reduce the VOC loss. With these optimizations, the champion WBG PSCs achieved an enhanced VOC of 1.327 V and a promising power conversion efficiency (PCE) of 19.44 %. Additionally, these modified WBG PSCs retained 94 % of their initial efficiency after 500 hours of continuous light soaking at maximum power point tracking in ambient conditions.

Surface Passivation with Tailoring Organic Potassium Salt for Efficient FAPbI3 Perovskite Solar Cells and Modules

AbstractPassivating surface defects on perovskite films with tailored functional materials has emerged as one of the most effective strategies for achieving high‐performance perovskite solar cells (PSCs). Among existing material selections, potassium salts stand out for their effective passivation of defects surrounding perovskite grain boundaries. However, the widely used potassium salts are inorganic and only soluble in highly polar solvents, which limits their practical application for surface passivation. Herein, a novel organic potassium salt (KCFSO), with multiple organic functional groups and good solubility in low polar isopropanol, is reported to function as a post‐treatment agent for perovskite. Combined with experimental results and theoretical calculations, the formed multiple intermolecular interactions between KCFSO and perovskite are revealed to play a vital role in determining the defect passivation effect. Thus, the KCFSO‐modified film shows a more uniform surface potential distribution, dramatically decreased defect density, and improved charge transfer, leading to a champion power conversion efficiency (PCE) of 25.11%, and good stability for the derived PSCs. As a demonstration of scalability, the centimeter‐sized PSCs and 5 cm × 5 cm mini‐modules also demonstrate impressive PCEs of 24.17% and 20.18%, respectively. These findings provide insights into passivator design principles to achieve efficient and stable perovskite photovoltaics.

Influence of gas adsorption on surface potential of porphyrin functionalized boron doped diamond thin films

Porphyrins functionalized diamond surfaces are interesting candidates for wide variety of applications due to their remarkable physical and chemical properties. In this work, the properties of 5-(4-carboxyphenyl) triphenyl porphyrins functionalized boron-doped diamond (BDD) surface followed by gas adsorption were studied at room temperature. After structural and morphological characterizations of the bare BDD surface and porphyrins functionalized BDD surface, a scanning Kelvin probe system was used to investigate the surface potential distribution due to the adsorption of volatile organic compounds (VOCs) under visible light illumination conditions. Gas adsorption studies showed poor response in bare BDD surfaces under different gas atmospheres. On the other hand, a significant response with discriminable gas interactions was achieved in porphyrins functionalized BDD surface under visible light illumination. The obtained results suggest that visible light has influenced gas interactions because of porphyrins. The increased response (∼ 2.5 times) of metal-free porphyrin functionalized BDD thin film towards triethylamine (TEA) is accounted to the donor nature of TEA. This study helps in developing a new generation of novel conductive type diamond-based photo enhanced gas sensors at room temperature that can be utilized for fish freshness monitoring.

Charge interaction behaviors at interfacial domains in DC GIL insulators

Long-term operation of high voltage direct current at elevated temperatures can result in the accumulation of surface charges in DC gas-insulated transmission line (GIL) insulators. Such a phenomenon leads to localized electric field distortion, increasing the risk of surface discharge. The analysis of interaction behaviors between surface charge and space charge at interfacial domains of GIL insulators is a complex task, which requires a comprehensive understanding of physical mechanisms of the gas–solid interface charging. In this work, a two-dimensional bipolar charge transport and interaction (2D BCTI) model is established, with the consideration of both surface and space charge dynamics. Pulsed electroacoustic tests and surface potential measurements are conducted on DC GIL insulator materials under different electrical-thermal coupling conditions. Experimental results exhibit great consistency with the predictions from the 2D BCTI model. The local accumulation of space charge near interfaces has certain effects on surface potential distribution, which in turn influences charge injection behavior from electrodes. In comparison to traditional surface charge simulation models, the consideration of space charge–surface charge interaction behaviors proves to be essential for estimating the polarity and amplitude of surface potential distribution. This model holds promise for assessing charge characteristics in electrical equipment where direct measurement is challenging.

Method for Measuring Surface Charge on Insulating Materials Based on the Vibrating Capacitor Method

The phenomenon of surface charging, known as contact electrification or tribocharging, has wide-ranging applications but also notable hazards. Precisely measuring surface charge density in insulating materials is crucial for optimizing tribocharging and mitigating adverse effects. Although the vibrating capacitor method is commonly used for this purpose, its principle, designed for conductive materials, limits direct application to insulating surfaces, leaving the relationship between measured surface potential and surface charge density unclear. To address this issue, this study simulated the process of measuring the surface potential of insulating materials using Comsol simulations. It analyzed the effects of charged area size, probe height, and probe position, and utilized the spatial distribution of potential measurement values of surface point charges to derive an integral relationship between the distribution of measured surface potential values and the distribution of surface charge density. The integral relationship of surface potential distribution under different forms of surface charge density distributions calculated from this formula largely matches the numerical simulation results. Based on this, a relationship between the distribution of surface charge density and surface potential measurement values was further derived. This relationship can be used for measuring the surface charge density of insulating materials.

Tuning Surface Potential Polarization to Enhance N2 Affinity for Ammonia Electrosynthesis.

Electrocatalytic N2 reduction reaction (NRR) to synthesize ammonia is a sustainable reaction that is expected to replace Haber Bosch process. Laminated Bi2WO6 has great potential as an NRR electrocatalyst, however, the effective activity requires that the inert substrate is fully activated. Here, for the first time, success is achieved in activating the Bi2WO6 basal planes with NRR activity through Ti doping. The introduction of Ti successfully tunes the surface potential distribution and enhances the N2 adsorption. The subsequently strong hybrid coupling of d(Ti)-p(N) orbitals fills the electronic state of N2 antibonding molecular orbital, which greatly weakens the bonding strength of N≡N bonds. Further, in situ synchrotron radiation-based Fourier transform infrared(SR-FTIR) spectrum and theoretical calculations show that surface potential polarization enhances the adsorption of HNN* by Bi-Ti dual-metal sites, which is beneficial for the subsequent activation hydrogenation process. The Ti-Bi2WO6 nanosheets achieve 11.44% Faradaic efficiency (-0.2V vs. RHE), a NH3 yield rate of 23.14µgmg-1h-1 (15N calibration), and satisfactory stability in 0.1M HCl environment. The mutual assistance of theory and experiment can help understand and develop of excellent two-dimensional (2D) materials for the NRR.

Two-dimensional analytical model for a non-lightly doped drain SOI MOSFET

A two-dimensional (2D) analytical model considering the effects of the gate oxide region, channel region, and buried oxide region for a non-lightly doped drain (LDD) SOI MOSFET is proposed. The top and bottom surface potential distributions have been derived on the basis of solving 2D Poisson’s equation and using an evanescent mode analysis. The potential distribution, threshold voltage, and threshold voltage roll-off have been verified by Silvaco ATLAS simulated results for the proposed device with different device parameters. The model agrees well with the simulation results under the above-mentioned conditions. Therefore, the analytical model provides the basic designing guidance for non-LDD SOI MOSFETs.

SiC-on-insulator based lateral power device and it’ s analytical models

This paper proposes the concept of SiC-on-insulator (SiCOI) lateral power device and its analytical models. The SiCOI technology provides dielectric isolation and improves the vertical breakdown. The analytical models provide the physic insight of the surface potential and electric field distributions for both full and partial depletion cases. The optimal breakdown voltage and doping concentration are deduced to analyze the breakdown mechanism qualitatively. The specific on-resistance in the drift region was also calculated to analyze the conduction characteristics. The influences of the structure parameters on the performances of the SiCOI lateral power device are investigated by the analytical model and numerical simulation. The analytical results of the proposed model are well agreement with the numerical results, confirming the validity of the proposed unified analytical model. Both the analytical and numerical results provide the physical explanation and effective solution for optimizing the electric field and improving breakdown voltage for the SiCOI lateral power device.

Probing the surface electrical properties of clay minerals with electrostatic force microscopy and kelvin probe force microscopy

Many surface processes of clay minerals require in-depth understanding of their surface electrical properties, such as surface charge density, surface potential distribution, etc In this paper, electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM) were used to study the surface charge densities, surface potentials, electric field intensities, and electric field force gradients of three common clay minerals: kaolinite, montmorillonite, and illite. The properties were directly imaged, and the average surface permanent charge densities of kaolinite, montmorillonite, and illite were obtained to be −0.0060, −2.136, and −5.456 μC m−2, respectively. In addition, a good linear relationship was found between the surface charge densities obtained by KPFM and the layer charges calculated from the mineral chemical formulas of three clay minerals.

A novel structure design of barium strontium titanate piezoelectric coating on titanium surface enhanced its response to low-intensity pulsed ultrasound

The piezoelectric effect was an electromechanical conversion effect that can accelerate the bone repair process, relying on mechanical forces for excitation. The design of a piezoelectric coating on titanium alloy surface that can respond to small loads was an urgent problem to be solved for its application in bone repair. In this work, a strontium barium titanate rod array coating was prepared on titanium surface by designing the microstructure and composition. The formation mechanism of barium strontium titanate array structure was analyzed. The barium strontium titanate rod array coating represented excellent piezoelectric properties. The surface potential distribution of barium strontium titanate rod with different conditions was simulated. Interestingly, the surface potential distribution results of the barium strontium titanate rod array showed that the positive and negative potential were distributed simultaneously, which was further confirmed by mineralization results. The strontium barium titanate rod array coating showed no toxicity to osteoblasts. The coating surface was covered by osteoblasts after 5 days of co-culture, which showed good osteoblast proliferation and adhesion. The research results will provide data support and research ideas for the clinical application of biological piezoelectric coatings on titanium and titanium alloys surface.

Evaluation of dynamics of charge accumulation and dissipation processes in Ge15Se85 thin film under electron beam irradiation by mapping surface potential distribution

The interaction of Ge15Se85 amorphous chalcogenide films with an electron beam has been studied. Three ranges of electron irradiation doses, in which a surface relief of various shapes is formed, are found. The presence and persistence of the surface potential for a long time after film irradiation have been established using the Kelvin probe force microscopy (KPFM). It is shown that the formation of surface relief is result of the charge accumulation in the interaction region. Based on the mapping of surface potential distribution in irradiated regions using KPFM we propose models of electric field distribution in the irradiated spots and suggest mechanism of electron-induced mass transfer. It has been suggested that the formation of a high surface relief structures is due to the electron-induced plastic effect. It is shown that the appearance of asymptotically sharp Taylor cones in chalcogenide films is due to charge collapse in the interaction region when the volume charge density and internal electric field strength exceed their critical values.

Tailoring Low‐Dimensional Perovskites Passivation for Efficient Two‐Step‐Processed FAPbI3 Solar Cells and Modules

AbstractConverting PbI2 residues into low‐dimensional perovskites through post‐treatment with ammonium‐based large cations can passivate 3D perovskites, thus has emerged as an effective strategy to improve the performance of perovskite solar cells (PSCs). Herein, a dramatically improved efficiency is demonstrated for PSCs based on a two‐step‐processed FAPbI3 perovskite via post‐treatment with formamidinium (FA)‐based benzamidine hydrochloride (PFACl), outperforming the commonly used methylamine (MA)‐based benzylamine hydrochloride (PMACl). With an in‐depth exploration of the crystal structures and morphology changes of the FAPbI3 perovskite upon the PFACl post‐treatment, the preferential formation of 1D rather than 2D structures on the 3D perovskite film is identified. In contrast to the 2D counterpart, the more energetically favorable 1D structure enables a more effective elimination of PbI2 residues. As a consequence, the PFACl‐induced 1D/3D perovskite film is endowed with smoother morphology, more uniform surface potential distribution, lower trap density, faster charge transfer, and better film stability than the PMACl‐induced 2D/3D perovskite and control films, demonstrating champion efficiencies of 24.9% for a small‐size PSC, 23.6% for a 1 cm2 large‐size PSC, and 21.2% for a 5 × 5 cm2 mini‐module, which is the highest among the perovskite solar mini‐modules using the two‐step deposition method.

Quantitative characterization of built-in potential profile across GaAs p–n junctions using Kelvin probe force microscopy with qPlus sensor AFM

The electrostatic potential distribution in materials and devices plays an important role in controlling the behaviors of charge carriers. Kelvin probe force microscopy (KPFM) is a powerful technique for measuring the surface potential at a high spatial resolution. However, the measured surface potential often deviates from the potential deep in the bulk owing to certain factors. Here, we performed KPFM measurements across the p–n junction, in which such factors were eliminated as much as possible by selecting the sample, force sensor, and measurement mode. The measured surface potential distribution agrees well with the line shape of the simulated bulk potential. Our results demonstrate that KPFM is capable of quantitatively characterizing potential distributions whose changes occur on the order of 10 nm.

Vacuum Deposited Perovskites with a Controllable Crystal Orientation.

The preferential orientation of the perovskite (PVK) is typically accomplished by manipulation of the mixed cation/halide composition of the solution used for wet processing. However, for PVKs grown by thermal evaporation, this has been rarely addressed. It is unclear how variation in crystal orientation affects the optoelectronic properties of thermally evaporated films, including the charge carrier mobility, lifetime, and trap densities. In this study, we use different intermediate annealing temperatures Tinter between two sequential evaporation cycles to control the Cs0.15FA0.85PbI2.85Br0.15 orientation of the final PVK layer. XRD and 2D-XRD measurements reveal that when using no intermediate annealing primarily the (110) orientation is obtained, while when using Tinter = 100 °C a nearly isotropic orientation is found. Most interestingly for Tinter > 130 °C a highly oriented PVK (100) is formed. We found that although bulk electronic properties like photoconductivity are independent of the preferential orientation, surface related properties differ substantially. The highly oriented PVK (100) exhibits improved photoluminescence in terms of yield and lifetime. In addition, high spatial resolution mappings of the contact potential difference (CPD) as measured by KPFM for the highly oriented PVK show a more homogeneous surface potential distribution than those of the nonoriented PVK. These observations suggest that a highly oriented growth of thermally evaporated PVK is preferred to improve the charge extraction at the device level.

Induced Polarization of Metal Grains: Simulations of Three‐Dimensional Electric Fields

AbstractInduced polarization (IP) method is one of the geophysical methods that utilizes polarization of subsurface materials. This method is very sensitive to the presence of (semi) conducting materials. Previous studies revealed the underlying mechanisms of metal polarization in simple geometry. However, there is a gap between such studies and the conditions in geological materials. To fill the gap, I have established the simulation method for studying the polarization of metal grains in a three‐dimensional field using the open‐source computational‐fluid‐dynamic software OpenFOAM. The three‐dimensional view of the surface potential distribution on a metal grain clarified how polarization is induced while varying geometrical constrictions. I varied the channel size, the orientation of the anisotropic grain, the elongation of the grain, and the distance of two grains. The results include: (a) a less decay of imaginary potential over distance for shorter or narrower channel, enhanced polarization in narrower channel and reduced polarization in shorter channel, (b) shift of the position of maximum imaginary potential over frequency on the surface of the oriented anisotropic grains, (c) higher peak frequency and larger polarization locally at the edge of the grains for elongated grains, and (d) enhancement of polarization by interaction of nearby grains. The underlying mechanisms were examined for each case. In addition, relationships between each scenario in my simulation and the subsurface environment were discussed. My successful implementation of the simulation for metal grains may be applied to improve the modeling, interpretation, and laboratory experimental setup.

Effect of minor Gd addition on microstructure, mechanical performance, and corrosion behavior of Mg–Y–Gd alloys

Effects of minor Gd addition on the micro-structure, mechanical performance, and corrosion behavior of Mg-1Y alloys were systematically studied. With the addition of increased Gd content, the hydrogen evolution rate of Mg-Y-Gd alloys decreased from 2.0 to 0.5 mm/y. Moreover, the alloying Gd in Mg-Y-Gd alloys leaded to the transformation of the active Mg24Y5 phase into the Mg5(GdY) phase. The high corrosion resistance of Mg-1Y-0.6Gd alloy can be attributed to the fine grain size, uniform distribution of surface potential, and the formation of protective corrosion passivation film rich in Gd2O3 and Y2O3.

Influence of the initial charge on the triboelectrification of millimeter size set of particles in an inclined tube

In this paper, the triboelectric charge buildup on a set of initially charged particles is investigated. During the study, 30 g of charged polypropylene particles of 2–3 mm size were repeatedly passed through a 1 m inclined copper or polyvinylchloride (PVC) tube. At the tube output, the charge is measured after each passage, allowing the cumulative charge evolution over time to be measured. The obtained curves are fitted to an exponential model to extract the time constant of the process. For each experience, particles are first charged at different levels and polarities relatively to the presumed saturation charge using both corona discharge and triboelectricity. The obtained results show that the initial charge value and polarity strongly affect the subsequent triboelectricity variations as well as the process speed. The triboelectric charge evolution is mainly related to the ratio between initial charge (Q0) and saturation charge value (Qs). Therefore, the particle's charge will increase if Q0 < Qs, decrease if Q0 > Qs, or be maintained at the same level when Q0 ≈ Qs. The particles can change polarity and be recharged with the opposite sign according to the tube and the initial charge level. This triboelectric charge behavior is explained based on the surface energy state in the electron transfer model. Furthermore, increasing the particles quantity from 5 g to 60 g reduces the saturation charge from 11 nC/g to 2.5 nC/g, which is approximately 77% less. Surface potential distribution measurements show an uneven distribution with less charge in large amounts compared to lower amounts.