Raster Mode Research Articles

Radiation induced changes in chemical and electronic properties of few-layer MoS2 and MoTe2 films

We investigate the changes in chemical and electronic properties of partially oxidized MoS2 and MoTe2 films of a few atomic layers during X-ray photoelectron spectroscopy (XPS) measurements at different power densities and exposure times. Our results show that MoTe2 films undergo severe photon-induced chemical changes from surface TeO2 to MoTe2 by Te-O dissociation, while MoS2 undergoes much less change. We find that the reduction of p-dopant TeO2 in MoTe2 results in an upward shift of the Fermi level due to electron injection. These electronic changes in the materials can lead to misleading interpretations of device performance and operating mechanisms during operando analysis. To minimize the damage, we propose two protocols, namely “unscanned mode” and “raster mode”, with high X-ray power density and short acquisition time. These protocols enable reliable operando-XPS analysis of 2D FETs using high photon flux and allow intermediate states to be observed under device operation within seconds to minutes.

Soil Erosion Estimation of Wadi Medjerda in Algeria Using the Revised Universal Soil Loss Equation (RUSLE) through GIS

Abstract Water erosion is a major problem in the semi-arid environments of Algeria. In this vein, the objective of this study is to use the Revised Universal Soil Loss Equation (RUSLE) on the watershed of Medjerda which is located at the extreme of the North-Eastern part of the Algerian territory. Based on the crossing of various factors in raster mode under ArcGIS allows the production of diverse thematic maps corresponding to multiple factors: erosivity of precipitations, erodibility of soils, topography, the vegetal cover and the anti-erosive practices. Moreover, the risks’ map of water soil erosion was obtained depending on the combination of the previous thematic maps with four class risks has been made up indicating an average erosion value of 2.68 t/ha/year. However, this value is relatively reasonable in relation to the given rate by the interpretation of the bathymetric measures carried out in the Ain Dalia dam.

Introducing an Experimental Approach to Predict Spot Scanning Time Parameters for a Superconducting Cyclotron Proton Therapy Machine

Proton pencil beam scanning (PBS) delivery sequence varies a lot among institutions due to the differences in vendors, machine types, and beamline configurations, which impacts PBS interplay effects and treatment delivery time estimation. This study aims to develop an independent experimental approach to predict the spot scanning time parameters for a clinical superconducting cyclotron proton therapy machine. This independent experimental approach employed an open-air parallel-plate detector with a temporal resolution of 0.05ms. A series of spot, energy, and dose rate patterns were designed and delivered, including (1) Spot switching time (SSWT) under different spot spacing for IEC-X, IEC-Y directions and diagonal direction (traveling in both X and Y direction) for three energy layers (110, 170 and 230 MeV); The Wilcoxon test is used to validate the prediction of SSWT along the diagonal direction. (2) Energy layer switching time (ELST) with different descending energy gaps for a fixed initial energy and different initial energies for a fixed descending energy gap. (3) Dose rate (MU/min) are measured for different minimum-MU-per-energy-layer (MMPEL), which are compared with the previous publication. A SSWT jump at 10mm (can be customized) spot spacing is observed because of triggering the machine's "raster mode" threshold. Discontinuous two variable piecewise linear functions were used to fit the SSWT in X/Y for spot spacing and energy. SSWT in X/Y is increasing as spot spacing and energy increase. SSWT in the diagonal direction is determined by the time either in the x-direction or y-direction, whichever takes longer (see Table 1 for one example of validations). ELST is linear depending on descending energy gap. The dose rate dependence on MMPEL is confirmed with previous publications of a similar type of machine. The study provided the first independent quantitative experimental modeling of the beam delivery time parameters without any information from vendors. Such machine-specific delivery sequence models could pave the foundation of precise interplay effect evaluation for clinical decision-making.

Pattern-Dependent Radio Frequency Heating of Laser-Induced Graphene Flexible Heaters.

Graphene is an excellent choice for heating applications due to its high thermal conductivity and is considered an interesting candidate for application in flexible heaters. The major challenge, though, is the costly and chemical-intensive pathways to produce graphene on a large scale. Laser ablation of polymeric substrates is a relatively recent technique for a facile, single-step, chemical-free fabrication of graphene, referred to as laser-induced graphene (LIG). This work demonstrates the fabrication of patterned LIG-based flexible heaters and their response to radio frequency (RF) electromagnetic waves. Polymeric substrates were scribed with laser patterns in both raster and vector modes and subjected to RF electromagnetic fields to test their heating response. We confirmed different graphene morphologies of the lased patterns through various materials characterization methods. The maximum steady-state temperature observed for the LIG heater was approximately 500 °C. Unprecedented heating rates, as high as 502 °C/s, were observed when LIG heaters were exposed to RF fields at 200 MHz frequency and 4.6 W power. Mechanical and thermal stability tests for the best heater were also performed showing a stable thermal response for 1000 bending cycles and 20 cycles of the heating test for 8.5 h, respectively. Our work suggests that LIG heaters produced in vector mode lasing outperformed those lased in raster mode which can be attributed to the improved graphene quality for RF absorbance.

Fabrication of PEG-Plasticized Epoxy Resin-Based Microfluidic Chips by Casting over PMMA Mold for PCR Applications: Influence CO2 Laser-Ablation Parameters of Mold

Despite dimethyl siloxane (PDMS) being one of the most used microfluidics chips, its micromachining techniques are infeasible for the mass production of commercial devices. This study proposed Epoxy Resin (ER) as a promising, cost-effective alternative to PDMS in lab-on-chip applications, including Polymerase Chain Reactions (PCR). Moreover, a novel, rapid and non-photolithographic approach has been developed for micromachining epoxy microfluidic chips. A new method for fabricating epoxy resin and polyethylene glycol (PEG) hybrid (ER-PEG) microchannels was developed by casting replication over PMMA molds. A PMMA piece was engraved with a CO2 laser in the raster mode to produce the mold for the ER-PEG casting first. A positive mold was fabricated from a polymethyl methacrylic acid (PMMA) sheet (6mm) by CO2 laser ablation. The microfluidic chips with the negative pattern were replicated by casting thermoset epoxy resin onto the micro-machined PMMA mold. The entire process, from device design conception to working device, can be completed in minutes. Herein, to enhance the surface roughness (Ra) of the ablated mold surface, different Distances to Focus (DF) were tried. The low Ra in the mold results in a low Ra in the replica. Also, the performance of ER-PEG in PCR was evaluated to verify the compatibility of the chip material to the PCR test.

Using logistic regression model selection towards interpretable machine learning in mineral prospectivity modeling

Regression or regression-like models are often employed in mineral prospectivity modeling, i.e., for the targeting of resources, either based on 2D map images or 3D geomodels both in raster mode or based on spatial point processes. Machine learning techniques like artificial neural networks are often applied and give decent results in the prediction of target events. However, they typically provide little insight into the problem regarding the importance, or relevance, of covariables. On the other hand, logistic regression has a well understood statistical foundation and uses an explicit model from which knowledge can be gained about the underlying phenomenon. Establishing such an explicit model is rather difficult for real world problems. In the context of mineral prospectivity modeling additional challenges arise, such as rare events, i.e. only a small fraction of data instances describes a positive target event, which is the event of interest.In this paper, we propose a model selection procedure applied to logistic regression incorporating explicit nonlinearities. The model selection procedure, based on the Wald test and the Bayes' information criterion (BIC), as proposed in this paper is new. The performance regarding the predictive power of the obtained model is comparable to logistic regression using a stepwise model selection and to neural networks on several real world datasets, one of them a dataset for the detection of gold mineralizations in Ghana. However, our new method is significantly faster than standard stepwise selection, while selecting fewer variables for the final model. In our numerical experiments, the prediction accuracy is also comparable to a neural network, which is currently in use in industry.In applications, the method can aid the model building process through an explicit model. Furthermore, it may be used as preprocessing step for other machine learning algorithms such as neural networks. In this paper, we intend to present mathematics of prospectivity modeling with the potential to contribute to bridging the gap between statistical and machine learning. Big Data and Artificial Intelligence are of increasing importance in mineral exploration. At the same time there is a growing demand for mathematically rigorous machine learning methods, which can still be interpreted by experts. This paper is a contribution to this field.

Laser Processing of Polymer Films Fabricated from PHAs Differing in Their Monomer Composition.

The study reports results of using a CO2-laser in continuous wave (3 W; 2 m/s) and quasi-pulsed (13.5 W; 1 m/s) modes to treat films prepared by solvent casting technique from four types of polyhydroxyalkanoates (PHAs), namely poly-3-hydroxybutyrate and three copolymers of 3-hydroxybutyrate: with 4-hydroxybutyrate, 3-hydroxyvalerate, and 3-hydroxyhexanoate (each second monomer constituting about 30 mol.%). The PHAs differed in their thermal and molecular weight properties and degree of crystallinity. Pristine films differed in porosity, hydrophilicity, and roughness parameters. The two modes of laser treatment altered these parameters and biocompatibility in diverse ways. Films of P(3HB) had water contact angle and surface energy of 92° and 30.8 mN/m, respectively, and average roughness of 144 nm. The water contact angle of copolymer films decreased to 80–56° and surface energy and roughness increased to 41–57 mN/m and 172–290 nm, respectively. Treatment in either mode resulted in different modifications of the films, depending on their composition and irradiation mode. Laser-treated P(3HB) films exhibited a decrease in water contact angle, which was more considerable after the treatment in the quasi-pulsed mode. Roughness parameters were changed by the treatment in both modes. Continuous wave line-by-line irradiation caused formation of sintered grooves on the film surface, which exhibited some change in water contact angle (76–80°) and reduced roughness parameters (to 40–45 mN/m) for most films. Treatment in the quasi-pulsed raster mode resulted in the formation of pits with no pronounced sintered regions on the film surface, a more considerably decreased water contact angle (to 67–76°), and increased roughness of most specimens. Colorimetric assay for assessing cell metabolic activity (MTT) in NIH 3T3 mouse fibroblast culture showed that the number of fibroblasts on the films treated in the continuous wave mode was somewhat lower; treatment in quasi-pulsed radiation mode caused an increase in the number of viable cells by a factor of 1.26 to 1.76, depending on PHA composition. This is an important result, offering an opportunity of targeted surface modification of PHA products aimed at preventing or facilitating cell attachment.

CO2 laser machining for microfluidics mold fabrication from PMMA with applications on viscoelastic focusing, electrospun nanofiber production, and droplet generation

In this study, a new method for the fabrication of polydimethylsiloxane (PDMS) microchannels through the replication of plexiglass molds was developed. A plexiglass slab is machined with CO2 laser in the raster mode to produce the mold for the PDMS casting. Then, the PDMS replica of the mold is plasma bonded to a substrate by applying more pressure than standard to overcome the surface roughness inherited from the laser machining process. Depending on the channel complexity, a ready to cast mold in the size of a glass slide can be achieved in 5–20min, including the design, machining, and cleaning steps. This fully automated and cost-effective mold making method proved to be the fastest among all methods, and it enables up to 2.5 aspect ratio microchannels, down to a width of 60μm, and a height of 23μm. The raster mode of the laser provides features lower, in size, then the laser beam waist radius. The produced microchannels were validated using several applications, such as droplet generation, nanofiber production, and viscoelastic microparticle focusing.

Features of Electron Probe Microanalysis of Nitrogen-Containing Compounds

This work is aimed at development of a method of investigation into the chemical composition of natural and synthetic nitrogen-containing compounds using electron probe microanalysis (EPMA) and its application for identification of the form of inclusion of light elements (C, N, O) in complex anions and cations. The analysis was performed using Kα lines appearing upon electron transfer from valence 2p states to internal 1s states. The characteristic features of Kα spectra of C, N, and O, which affect the correctness of the EPMA results, were revealed, and adjustments accounting for integral line intensity, self-absorption of the nitrogen line, and absorption of background absorption by nitrogen were determined. The procedure is multifunctional: it is intended for analysis of various nitrogen-containing samples, including diamonds produced by detonation synthesis. The surface of such samples is usually coated with a layer of oxygen- and nitrogen-containing functional groups. The experiments are aimed at detection of the optimum conditions of excitation and recording of Kα lines. The applied accelerating voltage is 10 kV; the beam current is 50–120 nA. When analyzing the recording of the signal amplitude in the differential mode, we apply a universal (for all samples) empirical equation describing the curve of background intensity in the area of the nitrogen line. The resistance of samples against the action of the electron beam is improved by the raster mode with linear size of 20–40 μm and movement of sample in the area of ~100 × 100 μm2 (if allowed by sample size). The concentrations of the detected elements were calculated by the PAP program using Henke absorption coefficients. At 80 nA, the detection limits of carbon, oxygen, and nitrogen were 0.33, 0.46, and 0.86 wt %, respectively.

Microfluidic ratio metering devices fabricated in PMMA by CO2 laser

We describe microfluidic fabrication results achieved using a 10.6 μm CO2 engraving laser on cast PMMA, in both raster and vector mode, with a 1.5″ lens and a High Power Density Focussing Optics lens. Raster written channels show a flatter base and are more U-shaped, while vector written channels are V shaped. Cross-sectional images, and, where possible, stylus profilometry results are presented. The sides of V-grooves become increasing steep with laser power, but broader shallower channels may be produced in vector mode by laser defocus, as illustrated. Smoothing of raster engraved channels by heated IPA etch, and transparency enhancement by CHCl3 vapour treatment are briefly discussed. An asymmetric Y meter is discussed as one method of diluting acid into seawater for dissolved CO2 analysis. Alternatively, microfluidic snake channel restrictors of different lengths in 2 channels may achieve the same result. Samples are fabricated with bases bonded by CHCl3 vapour treatment, and the devices are flow tested with either dilute food dye or DI water. Microfluidics fabricated in this manner have applications in ocean sensing of dissolved CO2 and other analytes, as well as broader sensing measurements, including biomedical sensors.

Features of the X-ray microanalysis (electron probe microanalysis) of nitrogen-containing compounds

The goal of this study is development of the method for studying the chemical composition of natural and synthetic nitrogen-containing compounds using electron probe microanalysis (EPMA) and the use of EPMA for identification of the form of occurrence of light elements (C, N, O) in complex anions and cations. The analysis was performed using K α lines attributed to electronic transitions from valence 2p states to internal 1s states. The characteristic features of the K α spectra of C, N, O, which affect the correctness of the EPMA results were revealed to introduce the corrections that take into account the integrated line intensity, the effect of self-absorption of the nitrogen line and absorption of the background by nitrogen. The method is intended for studying different nitrogen-contained samples including diamonds obtained by detonation synthesis. The surface of these samples is usually covered with a layer oxygen- and nitrogen-containing functional groups. The main problem associated with the experiment is determination of optimal conditions for excitation and registration of K α lines. The accelerating voltage used is 10 kV, the beam current is 50 – 120 nA. In the analysis in the differential mode of recording the signal amplitude we use the same (for all samples) empirical formula to describe the shape of the background intensity curve in the vicinity of the nitrogen line. The resistance of the samples to the impact of the electron beam is increased when using a raster mode with a linear size of 20 – 40 μ m and sample movement within the area ~100 × 100 μ m 2 (if possible with allowance for the sample size). The concentrations of the determined elements were calculated using the PAP program with B. L. Henke absorption coefficients. The detection limits of carbon, oxygen and nitrogen at a current of 80 nA were 0.33, 0.46 and 0.86 wt.%, respectively.

Logistic regression for potential modeling

AbstractRegression or regression‐like models are often employed in potential modeling, i.e., for the targeting of resources, either based on 2D map images or 3D geomodels both in raster mode or based on spatial point processes. Recently, machine learning techniques such as artificial neural networks have gained popularity also in potential modeling. Using artificial neural networks, decent results in the prediction of the target event are obtained. However, insight into the problem, e.g., about importance of specific covariables, is difficult to obtain. On the other hand, logistic regression has a well understood statistical foundation and works with an explicit model from which knowledge can be gained about the underlying problem. However, establishing such an explicit model is rather difficult for real world problems. We propose a model selection strategy for logistic regression, which includes nonlinearities for improved classification results. At the same time, interpretability of the results is preserved.

Popular Raster-Based Methods of Prospectivity Modeling and Their Relationships

The majority of popular methods of prospectivity modeling refer to the raster mode of digital two-dimensional map images or three-dimensional geomodels, thus requiring a user decision concerning the spatial resolution right from the beginning, imposing a constraint on all subsequent computations . In contrast to geostatistics and its variogram or covariance function, the methods considered here, with the exception of convolutional neural networks, do not account for spatially induced dependence. However, spatial dependence usually exists in practice, even while it is neglected in most methods of prospectivity modeling. Thus the common mathematical models remain the same, independent of the dimension of the spatial domain of application. Their numerical realizations may require a more sophisticated data management approach for three-dimensional applications than ordinary two-dimensional GIS software usually provides. The mathematical modeling assumptions of all presented methods are made explicit here. The mathematical models may be thought of as featuring a regression or a classification approach. However, this distinction is not exclusive; for example, logistic regression can be easily turned into classification. When not linear but including interaction terms, it reveals interesting similarities with other classification methods such as support vector machines, for instance. Proceeding from statistical to machine learning, the mathematical modeling assumptions become weaker and the numerics more demanding. Thus, the modeling assumptions suggest a hierarchy of methods, from apparently simple methods such as weights of evidence which depends on the intricate assumption of conditional independence, to more sophisticated and numerically demanding methods such as multi-layer artificial neural networks. The results of the former are deemed to be straightforward to interpret but might be false if the involved assumption did not apply, while the latter are difficult to interpret in terms of newly acquired insight in the problem. Eventually this communication aims at an intuitively appealing clarification of methods and their mutual relationships.

The Influence of MS Imaging Parameters on UV-MALDI Desorption and Ion Yield.

Ultraviolet matrix-assisted laser desorption/ionization mass spectrometry imaging (UV-MALDI MSI) is a widely used technique for imaging molecular distributions within biological systems. While much work exists concerning desorption in UV-MALDI MS, the effects of commonly varied parameters for imaging applications (repetition rate, use of continuous raster mode and raster speed), which determine spatial resolution and limits of detection for the technique, remain largely unknown. We use multiple surface characterization modalities to obtain quantitative measurements of material desorption and analyte ion yield in thin film model systems of two matrix compounds, arising from different UV-MALDI MSI sampling conditions. Observed changes in resulting ablation feature point to matrix-dependent spatial resolution and laser-induced matrix modification effects. Analyte ion yields of 10-9 to 10-6 are observed. Complex changes in ion yield, between spot and raster sampling and arising from varied laser repetition rate and raster speed, are observed. Graphical Abstract.

Determination of light elements C, N, O in various minerals and synthetic compounds using X-ray microanalysis

The goal of the study is developing of the methodology of X-ray microanalysis of light elements C, N and O which are jointly present in various minerals and synthetic compounds, including ultrafine diamonds, carbon filamentous fibers, etc. An accelerating voltage of 10 kV high enough to reduce the contribution of the sample surface to the intensity of the lines, and at the same time prevent from the overestimation of the corrections for the line absorption was used. The beam current ranged within 90 - 120 nA. The lines of nitrogen and oxygen are particularly strongly absorbed by carbon. The background intensity is measured near the line. In the region of Kα lines of C and O, the background changes linearly, while for oxygen exhibits a large slope. The shape of continuous X-ray spectrum from the sample at 10 kV in the region of the nitrogen line can be approximated by a polynomial dependence. We used a differential mode of the amplitude discrimination of the signal. It is shown that the position and shape of the carbon line depends on the type of the chemical bond: from covalent (diamond, graphite) to a more ionic bond with oxygen (carbonates). Wide in diamond and graphite Kα lines are shifted in carbonates to the shortwave region and substantially narrowed. An additional maximum appears due to admixing of the wave functions of 2p electrons of carbon to the wave functions of 2s electrons of oxygen. The errors related to the influence of the type of chemical bond on the shape of the spectra can be avoided by the analysis of the integrated intensities. In some cases, the resistance of the samples to the impact of the electron beam is increased by the raster mode of size 5-8 micron or by moving the sample within the area ~100 x 100 pm 2 . Calculation of the concentrations was carried out in the PAP program using B. L. Henke absorption coefficients. Some errors in the correction factors for the line absorption are usually corrected by selecting the absorption coefficients. The detection limit of carbon is 0.10 % wt. and for oxygen in carbonates it ranges within 0.39 - 0.90 % wt., whereas in the samples grown from nano-diamond colloids attains 0.75 wt. %.

Quantification of potentially toxic elements in food material by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) via pressed pellets

Here, we validated a protocol for the elemental analysis of plant and food materials using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and pressed pellets in compliance with the Green Chemistry principles, i.e. avoiding the use of hazardous reagents. The protocol included sample pre-treatment, preparation of pellets, and LA-ICP-MS optimisation for the food sample matrix using leaf certified reference materials. Sample homogenisation and particle size reduction (∼10 µm) for samples with larger initial particle sizes proved crucial in improving signal stability and analytical results, whereas the raster mode was preferred over spot mode for greater accuracy. The validation of the technique was successful for determination of Mn, Ni, Cu, Zn, As, Se, Cd and Pb (z-score values ≤2). We propose LA-ICP-MS using pressed pellets as an alternative to ICP-MS in food analysis.

Automated Analysis of Spatially Resolved X-ray Scattering and Micro Computed Tomography of Artificial and Natural Enamel Carious Lesions

Radiography has long been the standard approach to characterize carious lesions. Spatially resolved X-ray diffraction, specifically small-angle X-ray scattering (SAXS), has recently been applied to caries research. The aims of this combined SAXS and micro computed tomography (µCT) study were to locally characterize and compare the micro- and nanostructures of one natural carious lesion and of one artificially induced enamel lesion; and demonstrate the feasibility of an automated approach to combined SAXS and µCT data in segmenting affected and unaffected enamel. Enamel, demineralized by natural or artificial caries, exhibits a significantly reduced X-ray attenuation compared to sound enamel and gives rise to a drastically increased small-angle scattering signal associated with the presence of nanometer-size pores. In addition, X-ray scattering allows the assessment of the overall orientation and the degree of anisotropy of the nanostructures present. Subsequent to the characterization with µCT, specimens were analyzed using synchrotron radiation-based SAXS in transmission raster mode. The bivariate histogram plot of the projected data combined the local scattering signal intensity with the related X-ray attenuation from µCT measurements. These histograms permitted the segmentation of anatomical features, including the lesions, with micrometer precision. The natural and artificial lesions showed comparable features, but they also exhibited size and shape differences. The clear identification of the affected regions and the characterization of their nanostructure allow the artificially induced lesions to be verified against selected natural carious lesions, offering the potential to optimize artificial demineralization protocols. Analysis of joint SAXS and µCT histograms objectively segmented sound and affected enamel.

An image-processing method to detect sub-optical features based on understanding noise in intensity measurements

Accurate quantitative analysis of image data requires that we distinguish between fluorescence intensity (true signal) and the noise inherent to its measurements to the extent possible. We image multilamellar membrane tubes and beads that grow from defects in the fluid lamellar phase of the lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine dissolved in water and water-glycerol mixtures by using fluorescence confocal polarizing microscope. We quantify image noise and determine the noise statistics. Understanding the nature of image noise also helps in optimizing image processing to detect sub-optical features, which would otherwise remain hidden. We use an image-processing technique “optimum smoothening” to improve the signal-to-noise ratio of features of interest without smearing their structural details. A high SNR renders desired positional accuracy with which it is possible to resolve features of interest with width below optical resolution. Using optimum smoothening, the smallest and the largest core diameter detected is of width 88 pm 23 and 6860 pm 50 nm, respectively, discussed in this paper. The image-processing and analysis techniques and the noise modeling discussed in this paper can be used for detailed morphological analysis of features down to sub-optical length scales that are obtained by any kind of fluorescence intensity imaging in the raster mode.

Raster-Mode Continuous-Flow Liquid Microjunction Mass Spectrometry Imaging of Proteins in Thin Tissue Sections.

Mass spectrometry imaging by use of continuous-flow liquid microjunction sampling at discrete locations (array mode) has previously been demonstrated. In this Letter, we demonstrate continuous-flow liquid microjunction mass spectrometry imaging of proteins from thin tissue sections in raster mode and discuss advantages (a 10-fold reduction in analysis time) and challenges (suitable solvent systems, data interpretation) of the approach. Visualization of data is nontrivial, requiring correlation of solvent-flow, mass spectral data acquisition rate, data quality, and liquid microjunction sampling area. The latter is particularly important for determining optimum pixel size. The minimum achievable pixel size is related to the scan time of the instrument used. Here we show a minimum achievable pixel size of 50 μm (x-dimension) when using an Orbitrap Elite; however a pixel size of 600 μm is recommended in order to minimize the effects of oversampling on image accuracy.

Interpretation of the surface charge decay kinetics on insulators with different neutralization mechanisms

Surface charge decay kinetics on corona-charged polymeric insulators were studied. In the experiment, the sample surface exposed to corona was kept open to ambient air whereas the opposite surface was in contact with a grounded plate. The resulting surface potential distribution was scanned in a raster mode using a Kelvin electrostatic probe, from which the relief map of charge density was obtained by an inverse calculation method. The developed procedure allowed for implementation of two study cases: (i) gas neutralization took place under natural conditions, with enhanced concentration of free ions, and with limited gas volume; (ii) surface charge decay occurred only due to bulk neutralization. Three mechanisms were considered responsible for surface charge decay, i.e., bulk neutralization, gas neutralization, and surface conduction. They were discussed separately with the help of numerical models, which quantified the relative importance of each mechanism on the total process of charge decay. The results of the latter case were further utilized to determine the energy distribution of electron and hole traps of the materials based on the isothermal relaxation current theory.