3D Digital Microscope Research Articles

Application of XRD and digital optical microscopy to investigate lapidary technologies in Pre-Pottery Neolithic societies

Beads were an important form of personal ornamentation in southern Levantine Pre-Pottery Neolithic societies and hold information on symbolic practices and exchange networks engaged by these communities. Establishing the exact mineralogical composition of stone beads and the precise methods used to manufacture beads are key to documenting shifts in these systems, but so far visual inspection has served as the primary mode of analysis for most assemblages. Here, we apply XRD and 3D digital optical microscopy to investigate raw material selection and bead manufacture at the Pre-Pottery Neolithic (PPN) settlement of el-Hemmeh, Jordan. Analyses reveal that PPNA bead assemblages emphasize the color green but included a wide variety of mineral types. The LPPNB assemblage exhibits a greater diversity in shape and color, including an emphasis on the use of red minerals, but consist of a more restricted range of minerals and lack the rectangular beads found in the PPNA. Color rather than suitability of material properties for bead making appears to have motivated choices for mineral selection. Bidirectional perforation was codified into the technological system and was consistently used to produce beads during the PPNA regardless of their size, thickness, or hardness.

Effect of cementation, cement type and vent holes on fit of zirconia copings

ObjectivesTo investigate the effect of cementation, cement type and vent-holes on the marginal and internal fit of Zirconia (Zr) Copings. Materials and methodsExtracted premolars (N = 100) were mounted in resin and prepared for Zr crowns. Samples were randomly divided into 5 groups (n = 20); A: No Cementation; B: Cementation with Glass-Ionomer (GI); C: GI + Vent-Holes; D: Cementation with Resin Cement (RC); E: RC + Vent-Holes. The copings were fabricated using semi sintered Zr Blocks with a standardized cement space of 20 µm. Groups C & E were designed to have 0.5 mm of Vent-Holes on the Buccal and Lingual Cusp Tips. The copings were tried, cemented, thermocycled, re-embedded in resin and cross sectioned into two halves. The copings were examined with 3D-Digital Microscope (HIROX, KH-7700, Tokyo, Japan) at 50-200X. The gaps were recorded at 9 predetermined points. ResultsThe non-cemented groups showed statistically better fit compared to the cemented groups P < 0.05 except vs Group E (RC plus vent holes). No significance was found between the cemented groups P > 0.05. Copings with vent-holes showed statistically better fit than copings without holes P < 0.05. ConclusionMarginal and Internal gap values designed in the software programs differed than the actual values measured for the non-cemented copings. Cementation process also influenced the fit of the Zr copings, the resin cement being the more accurate. The addition of vent-holes on the occlusal surface improved the fit.

New Insights into Use-Wear Development in Bodily Ornaments Through the Study of Ethnographic Collections

The use of microwear analysis has made substantial contributions to the study of archaeological bodily ornaments. However, limitations persist with regard to the interpretation of use and the reconstruction of systems of attachment, hampering a holistic understanding of the diversity of past bodily adornment. This is because the complexities of ornament biographies and the resulting wear traces cannot be grasped exclusively from the study of experimental reference collections. In this paper, we propose to bridge this gap in interpretation by systematically researching ethnographic collections. We conducted a microscopic study of 38 composite ornaments from lowland South America housed at the Musée du quai Branly (Paris). These objects involve organic, biomineral, and inorganic components, attached through different string configurations. The combined use of optical and 3D digital microscopy at different magnification ranges provided a thorough understanding of wear trace formation, distribution, and characterization. We demonstrate how individual beads develop characteristic use-wear in relation to one another and to the strings. We further challenge common assumptions made in the analysis of archaeological ornaments. In sum, this research addresses methodological and interpretative issues in the study of bodily adornment at large, by providing insight into the biographies of objects that were actually worn in a lived context. In the future, our results can be applied as reference for a more effective understanding of the use of ornaments worldwide.

Microstructure of four-graded roller compacted concrete

This paper presents an experimental study on microstructure of four-graded RCC. Two temperatures of 20 °C and 40 °C were picked to represent interior and surface layers of four-graded RCC. The most used fly ash contents of 50% and 70% were selected, and two ages of 28 days and 56 days were tested. Three levels of paste, mortar and concrete were used to simulate different microstructural regions in four-graded RCC. 3D digital microscope experiment, micro-hardness test and back-scattered electron image analysis were carried out sequentially. It was found that four-graded RCC microstructure can be divided into three characteristic parts: bulk paste, interface transition zone around fine aggregate (ITZ-f) and interface transition zone around coarse aggregate (ITZ-c). By comparing the average wear width and depth, the strength and bonding ability of bulk paste was the highest, followed by ITZ-f and ITZ-c. Compared to the surface layer, the micro-mechanical strength of bulk paste and ITZ-f was higher in the interior layer, but that of ITZ-c was opposite. At early age, 50% fly ash content was more conducive to microstructure than 70%. The micro-hardness value of ITZ-c presented a decreasing trend with age and that of ITZ-f did not grow. In terms of product structure, Ca(OH)2 content in ITZ-c gradually decreased from aggregate surface to paste part, and Ca(OH)2 in ITZ-f had been partially converted to C-S-H gel. The proportions of hydration product and porosity were highest in ITZ-c, followed by ITZ-f, with bulk paste having the lowest. Microstructure of four-graded RCC was significantly affected by the combination of aggregate size and free water content on aggregate surface.

Knock induced erosion on Al pistons: Examination of damage morphology and its causes

Abstract In the present study, a systematic and deep examination of knocking damage on Al pistons is carried out, highlighting that only when exceeding a certain threshold knock compromises engine functionality. Controlled knocking combustions were induced during bench tests, by varying the spark advance for each cylinder. Several knock intensities and frequencies were investigated, with the aim to evaluate the possible knocking damages and to understand their influence on piston functionality. All the observed damages have been separately described and studied through failure analysis techniques, in particular optical and scanning electron microscopy and 3D digital microscopy, providing explanations of their occurrence. Among them, the erosion damage was predominantly observed and therefore fully evaluated. Preliminary attempts to relate engine parameters to knock damage were also made. This study is part of a wider project, whose aim is to increase knocking limits from the “safe calibration area” up to the limits which produce acceptable damages on pistons, in order to enhance engine efficiency.

The cake layer formation in the early stage of filtration in MBR: Mechanism and model

It is important to clarify the mechanism of the cake layer formation in the early stage of filtration (initial stage and pseudo-steady stage). In this paper, a series of short-term dead-end microfiltration of sludge suspensions domesticated at three different ratios of carbon to nitrogen (C/Ns) (63:10, 100:5, 200:5) were conducted in constant pressure mode. Flux decline behaviors were analyzed and the structure of cake layer was characterized by 3D optical digital microscope (3D-ODM) to explore the mechanism of the cake layer formation. Results showed that the sludge floc was the key substance in the initial stage of the cake layer formation while colloid matters dominated later. Based on the inhomogeneous structure of the formed cake, a dynamic traversing mechanism was proposed to show the fact that colloid matters traveled through the hole formed by sludge flocs and accumulated on the membrane surface. Meanwhile, a piecewise function about the relationship of accumulated filtrated volume (v) and filtration time (t) was established to reveal this mechanism. Moreover, the model predictions showed good agreement with experimental data and its applications were also approved by other activated sludge suspensions, kaolin suspensions and real wastewater.

Novel transparent nano-pattern window screen for effective air filtration by electrospinning

In this paper, novel transparent nano-pattern window screen was successfully prepared by electrospinning. SEM, VHX 3D digital microscope and tensile tester were employed to characterize the morphology and the mechanical properties, which indicated that the nanofibers in the PA66 nano-patterned membranes are uniform and the diameter of about 200 nm, and there is no adhesion between nanofibers. In addition, we could find that the surface of the PA66 transparent nano-patterned membrane was more flat. Simultaneously, Mechanical properties of the PA66 nano-pattern membrane are better than those of the PA66 random orientation membrane. Moreover, applications of the PA66 transparent nano-pattern window screen as a filter for air filtration, we could find that the window screen showed excellent filtration efficiency for the PM0.3-5.

Effects of stray AC on corrosion of 3-layer polyethylene coated X70 pipeline steel and cathodic delamination of coating with defects in 3.5 wt-% NaCl solution

ABSTRACTIn this work, the effects of stray alternating current (AC) on the corrosion of coated X70 pipeline steel and the delamination of 3-layer polyethylene (3PE) coatings with defects were investigated using COMSOL Multiphysics simulation, electrochemical impedance spectroscopy and three-dimensional (3D) digital microscope techniques. The results showed that under the same level of AC interference, pits with deeper maximum pit depth were observed at the smaller defect areas than those at larger defect areas. It was consistent with the simulation results that a greater corrosion current density was accompanied on samples with smaller defects. According to 3D digital images, the larger delamination of 3PE coatings was found on samples with smaller defects. With the increase of current density, the impedance of samples with small defects decreased, while that of samples with large defects increased. Additionally, with the same defect size, the maximum pit depth became deeper and the corrosion was more severe.

Statistical Comparison between Low-Cost Methods for 3D Characterization of Cut-Marks on Bones

In recent years, new techniques for the morphological study of cut marks have become essential for the interpretation of prehistoric butchering practices. Different criteria have been suggested for the description and classification of cut marks. The methods commonly used for the study of cut marks rely on high-cost microscopy techniques with low portability (i.e., inability to work in situ), such as the 3D digital microscope (3D DM) or laser scanning confocal microscopy (LSCM). Recently, new algorithmic developments in the field of computer vision and photogrammetry, have achieved very high precision and resolution, offering a portable and low-cost alternative to microscopic techniques. However, the photogrammetric techniques present some disadvantages, such as longer data collection and processing time, and the requirement of some photogrammetric expertise for the calibration of the cameras and the acquisition of precise image orientation. In this paper, we compare two low-cost techniques and their application to cut mark studies: the micro-photogrammetry (M-PG) technique presented, developed, and validated previously, and a methodology based on the use of a structured light scanner (SLS). A total of 47 experimental cut marks, produced using a stainless steel knife, were analyzed. The data registered through virtual reconstruction was analyzed by means of three-dimensional geometric morphometrics (GMM).

Texture and design of green chip seal using recycled crumb rubber aggregate

The depletion of natural resources forces the construction industry to explore using cleaner recycled material as replacements of virgin construction materials. A new eco-friendly chip seal pavement, in which the mineral aggregate was replaced by crumb rubber obtained from scrap tires, was investigated in this study. A total of 142 chip seal specimens were prepared and tested to investigate the impact of using recycled rubber aggregate on the chip seal's micro and macro texture and their impacts on the skid resistance. The microtexture of the new proposed recycled aggregate was examined using a high-resolution 3D digital microscope. The macrotexture of the new chip seal pavement was examined using image processing and sand patch methods. The skid resistance of the new chip seal under both ambient and elevated temperatures was then explored. Two types of emulsions, two types of asphalt cement binders, two types of mineral aggregate as well as two types of recycled crumb rubber were involved in the examined test matrix. This study concluded that the crumb rubber can be used in the chip seal as partial or full replacement of mineral aggregates. Using crumb rubber has a significant impact on improving both macrotexture and microtexture of chip seal. In addition, the low thermal conductivity of crumb rubber helped the chip seal resist elevated temperature without significant loss in skid resistance. A 3D geometrical model was then proposed to simulate the aggregate embedment so it can be used to design the required binder application rate that provides adequate embedment depth and skid resistance.

Assessment of statistical agreement of three techniques for the study of cut marks: 3D digital microscope, laser scanning confocal microscopy and micro-photogrammetry.

In the last few years, the study of cut marks on bone surfaces has become fundamental for the interpretation of prehistoric butchery practices. Due to the difficulties in the correct identification of cut marks, many criteria for their description and classification have been suggested. Different techniques, such as three-dimensional digital microscope (3D DM), laser scanning confocal microscopy (LSCM) and micro-photogrammetry (M-PG) have been recently applied to the study of cut marks. Although the 3D DM and LSCM microscopic techniques are the most commonly used for the 3D identification of cut marks, M-PG has also proved to be very efficient and a low-cost method. M-PG is a noninvasive technique that allows the study of the cortical surface without any previous preparation of the samples, and that generates high-resolution models. Despite the current application of microscopic and micro-photogrammetric techniques to taphonomy, their reliability has never been tested. In this paper, we compare 3D DM, LSCM and M-PG in order to assess their resolution and results. In this study, we analyse 26 experimental cut marks generated with a metal knife. The quantitative and qualitative information registered is analysed by means of standard multivariate statistics and geometric morphometrics to assess the similarities and differences obtained with the different methodologies.

Digital description model of a three-dimensional arrangement structure of conductive fiber of electromagnetic shielding fabric

PurposeThe three-dimensional arrangement structure of the conductive fiber is an important factor of the shielding effectiveness of the electromagnetic shielding fabric (EMSF). However, until now, the three-dimensional arrangement structure has not been described because of the complex structure, which leads to many difficulties for the subsequent analysis of the electromagnetic characteristics. Therefore, the purpose of this paper is to propose a feature extraction method to describe the arrangement structure of the conductive fiber based on the three-dimensional calibration and image processing technology, providing a new idea for the above problem.Design/methodology/approachFirst, the three-dimensional positions of the conductive fibers in the EMSF are calibrated using the VHX-600 3D digital microscope and the MATLAB7.5 software. The arrangement characteristics of the conductive fibers are analyzed, and equivalent twist, cross-sectional content, and average angle of a single fiber are proposed to describe the arrangement characteristic of the conductive fiber. Then, a digital description model of the conductive fiber is constructed according to the feature parameters and its three-dimensional structures are reproduced using CATIA. Finally, the reliability of the model is verified by an FDTD example, and the significance and application of the model are given.FindingsThe proposed method can provide the feature extraction and description for the complex spatial three-dimensional arrangement structure of conductive fibers. The feature parameters can reflect different micro arrangement features of the conductive fiber. The proposed idea and method can provide a solid foundation for subsequent studies of the electromagnetic properties of the EMSF.Originality/valueThe study in this paper is of great significance and academic value. This paper provides a new three-dimensional calibration method and constructs multiple feature parameters to describe the complex three-dimensional arrangement structure, providing a new effective method to overcome the problem of the conductive fiber description. The proposed method provides an important basis for the shielding mechanism, transmission characteristics, electromagnetic calculation and product design, and woven technology of the EMSF.

3D 디지털 현미경으로 측정한 당백가시 인쇄본의 형상 특징

ë¥˜ì½”ì¿ ëŒ€í•™ 소장 「당백가시」를 중심으로 3D 디지털 현미경으로 인쇄된 ì¢ ì´ 표면에 남아있는 금속활자의 미세표면을 관찰하여 굴곡구조와 표면 ê±°ì¹ ê¸°ë¥¼ ì •ëŸ‰í™”í•˜ëŠ” ì¸¡ì • 방법을 ì†Œê°œí•˜ê³ ìž 한다. 인쇄된 ì¢ ì´ 표면을 기준으 로 활자 표면의 굴곡 현상을 ì„ ìœ¼ë¡œ ì¸¡ì •í•˜ê³ í™œìžì˜ 미세표면은 면으로 ì¸¡ì •í•˜ì—¬ 수치화하여 인쇄된 ì¢ ì´ 표면의 특성 을 ì œì‹œí•˜ì˜€ë‹¤. 3D 디지털 현미경 ì¸¡ì • 방법은 ë¹„ì ‘ì´‰, 비파괴 방법으로 많은 자료 분석과 반사광에 의한 ì§ì ‘ 관찰이 가능하다. ê·¸ë¦¬ê³ í´ë¦¬ë‹ì´ë‚˜ ë°°ì ‘ ê·¸ë¦¬ê³ ì£¼ë¦„ì„ 펴기 위하여 강한 힘으로 ì••ë ¥ì„ 주는 ê³¼ì •ì—ì„œ ê³ ë¬¸ì„œì— í•¨ìœ ëœ ì •ë³´ê°€ ì†ì‹¤ë ìˆ˜ 있으므로 ì‚¬ì „ 조사 방법으로 ì¢ ì´ 표면에 남아있는 인쇄 ì •ë³´ë¥¼ 수집하는데 ìœ ìš©í•œ ë°©ë²•ì´ë¼ê³ í• ìˆ˜ 있다. 중심어: 금속활자, ë¹„ì ‘ì´‰, 비파괴, í‘œë©´ê±°ì¹ ê¸°, 3D 디지털 현미경

Stress Corrosion Cracking on a Stainless Steel Container Triggered by the Ageing of a Polyurethane Insulation

Abstract A failure in the form of leakages caused by crack formation occurred after approximately 25 years of operationn on a type 1.4301 stainless steel container thermally insulated with polyurethane. From the appearance of the damages it was clear that the failure was caused by stress corrosion cracking. It was shown that chloride release by the ageing of the PU foam was responsible for the corrosion. The damages were documented via 3D digital microscopy and metallography. To avoid these kinds of damages, insulation materials free of halogen compounds should be used. Regular checks of old stainless steel reactors insulated with PU foam and operated at elevated temperatures are recommended.

Assessment of radicular dentin permeability after irradiation with CO2 laser and endodontic irrigation treatments with thermal imaging.

Previous studies have demonstrated that the permeability changes due to the surface modification of dentin can be quantified via thermal imaging during dehydration. The CO2 laser has been shown to remove the smear layer and disinfect root canals. Moreover, thermal modification via CO2 laser irradiation can be used to convert dentin into a highly mineralized enamel-like mineral. The purpose of this study is to evaluate the radicular dentin surface modification after CO2 laser irradiation by measuring the permeability with thermal imaging. Human molar specimens (n=12) were sectioned into 4 axial walls of the pulp chamber and treated with either 10% NaClO for 1 minute, 5% EDTA for 1 minute, CO2 laser or none. The CO2 laser was operated at 9.4 μm with a pulse duration of 26 μs, pulse repetition rate of 300 Hz and a fluence of 13 J/cm2. The samples were dehydrated using an air spray for 60 seconds and imaged using a thermal camera. The resulting surface morphological changes were assessed using 3D digital microscopy. The images from digital microscopy confirmed melting of the mineral phase of dentin. The area enclosed by the time-temperature curve during dehydration, ΔQ, measured with thermal imaging increased significantly with treatments with EDTA and the CO2 laser (P<0.05). These results indicate that the surface modification due to CO2 laser treatment increases permeability of radicular dentin.

Use of THz Reflectometry for Roughness Estimations of Archeological Metal Surfaces

In this work, using a time domain spectrometer, we have investigated the reflection of terahertz (THz) pulses from surfaces that exhibit a variable degree of roughness. The study was mainly aimed at assessing the influence of the surface texture on the amplitude and the shape of the pulses reflected by stratified materials and at exploring the potential of this technique for achieving quantitative information on the roughness of the material interfaces hit by the THz beam. The behavior of the reflected THz pulses was investigated by considering angular measurements on a set of suitable mock-ups. Measurements were carried out on an authentic archeological Roman coin that exhibited different corrosion situations. An electromagnetic model was used for estimating the roughness of outer and inner surfaces. The comparison of the results with those provided by other techniques made it possible to parameterize the surface texture such as the traditional contact micro-profilometry and the more recently used 3D digital microscopy.

Сравнительный анализ работы фемтолазерных установок Фемто Визум (Россия) и Femto LDV Z6 (Швейцария). 3D-цифровая оценка морфометрических параметров роговичного клапана в эксперименте

Purpose . To perform a comparative 3D digital morphometric assessment of corneal flap formed using a femtosecond laser Femto Visum and Femto LDV Z6. Material and methods . Experiment was performed on 20 cadaver eyes, on which corneal flaps were formed using the femtosecond laser systems Femto Visum (Optosystems, Russia) (Group 1 – «Femto Visum» – 10 eyes) and Femto LDV Z6 (Ziemer, Switzerland) (Group 2 – «Femto LDV Z6» – 10 eyes). In both groups, the corneal flap was formed on the set parameters: side cut angle – 70°, the flap thickness – 100 µm, diameter of stromal bed – 9.0 mm. By using 3D digital microscope Hirox KH-8700 (Japan) the side cut angle of the flap, the flap thickness and diameter of the stromal bed were measured. Results . With 3D digital estimation we obtained following results in group 1 («Femto Visum»): side cut angle – 74.61±3.09°, the flap thickness – 87.91±6.93 µm, diameter of the stromal bed – 8.88±0.09 mm; in group 2 ( «Femto LDV Z6») – side cut angle – 74.06±3.08°, the flap thickness – 87.92±7.79 µm, diameter of the stromal bed – 8.83±0.06 mm. Those parameters are not statistically different between the two groups (p>0.05, Mann-Whitney U-test). Conclusions . 1. 3D digital microscope Hirox KH-8700 allows precise measurements of morphometric parameters of corneal flap in the coordinates X, Y, Z. 2. Femtosecond laser systems, Femto Visum and Femto LDV Z6, allow us to create the corneal flap such that the side cut angle and the diameter of the corneal stromal bed meet the set parameters, with no statistically significant difference between systems (p>0.05). The flap thickness was thinner than desired, («Femto Visum» and «Femto LDV Z6»), but there was no statistical difference between two groups (p>0.05).

Determination of the formability limits for Grade 1 titanium sheet by means of ALSAD method

Stamping is one of the most widely used sheet metal forming processes. Esthetics and durability of the deformed products are limited by defects in the form of strain localization, grooves or cracks. Forming limits, e. g. in form of forming limit curve (FLC), help to avoid above-mentioned defects in the sheet metal during forming. Besides the common steel sheets for deep drawing processes, e.g. DC04, components can also be made of metal with specified strength and chemical resistance properties. One of such materials is titanium sheet. In this paper, FLC for GR1 titanium sheet will be presented. It was obtained by means of a new author’s method named as ALSAD (Analysis of Laser Speckle Activity Differences). So far, applied methods of FLC determination have been mainly based on the measurement of the strain distribution in the area of the created groove, deformation gradient and deformation speed. For this reason, detection of strain localization has been dependent on the strain measurement method. The ALSAD, based on laser speckle phenomenon allows detection of defects initiation on the sample surface independently of the strain distribution measurement and it allows, for example, to relate a moment of defect initiation directly to the sample height or forces occurring in the process. In this paper strain values for strain localization, grooves and cracks for GR1 titanium sheet will be shown. Obtained results show good formability of this material, which was verified by means of 3D digital microscope. Such results allow tracing precisely the formation of the defects starting from strain localization up to the crack appearance, which would be helpful for advanced numerical simulations.

Microscopic analysis of “iron spot” on blue-and-white porcelain from Jingdezhen imperial kiln in early Ming dynasty (14th-15th century)

"Sumali," as an imported cobalt ore from overseas, was a sort of precious and valuable pigment used for imperial kilns only, which produces characteristic "iron spot" to blue-and-white porcelain in early Ming Dynasty (A.D. 14th-15th century). Although there were some old studies on it, the morphology and formation of iron spot has not been fully investigated and understood. Therefore, five selected samples with typical spot from Jingdezhen imperial kiln in Ming Yongle periods (A.D. 1403-1424) were analyzed by various microscopic analysis including 3D digital microscope, SEM-EDS and EPMA. According to SEM images, samples can be divided into three groups: un-reflected "iron spot" without crystals, un-reflected "iron spot" with crystals and reflected "iron spot" with crystals. Furthermore, 3D micro-images revealed that "iron spots" separate out dendritic or snow-shaped crystals of iron only on and parallel to the surface of glaze for which "iron spot" show strong metallic luster. Combining with microscopic observation and microanalysis on crystallization and non-crystallization areas, it indicates that firing oxygen concentration is the ultimate causation of forming reflective iron spot which has a shallower distribution below the surface and limits crystals growing down. More details about characters of "iron spot" used "Sumali" were found and provided new clues to coloration, formation mechanism and porcelain producing technology of imperial kiln from 14th to 15th centuries of China.

Film-forming mechanism and properties of Ti/Zr/Mo colored conversion coating prepared on aluminum alloy

A multi-metal Ti/Zr/Mo combined inorganic salt coating was prepared on 6063 aluminum alloy using chemical conversion technology. 3D super depth digital microscope clearly showed the coating have a color appearance after the TiZrMoC (Ti/Zr/Mo chemical conversion) process. The comparison tests of adhesion force with polyester coating and electrochemical properties demonstrated this TiZrMoC process have good potential as a kind of alternatives for traditional Cr6+ toxic process. In order to discuss the film-formation mechanism of the coating, The scanning electron microscopy (SEM/EDS) and X-ray photoelectron spectroscopy (XPS) technologies were used to analysis the surface characteristic of different treating time samples. The XPS and EDS results showed that Al, Ti, Mo, Mg, O, F are the main component elements of the Ti/Zr/Mo coating. The whole conversion process can be divided into two stages generally: Firstly F- eroded the aluminum matrix and bonded with the alloy element Mg formed MgF2. At the same time Al2O3 phase also came into being as the ground layer, subsequently a mass of TiO2, Mo2O5, and bits of MoO3 were formed at the micro-cathode area as the top-layer.