Electron Optical Images Research Articles

Off-axis electron holography of Néel-type skyrmions in multilayers of heavy metals and ferromagnets

Magnetic skyrmions are complex swirling spin structures that are of interest for applications in energy-efficient memories and logic technologies. Multilayers of heavy metals and ferromagnets have been shown to host magnetic skyrmions at room temperature. Lorentz transmission electron microscopy is often used to study magnetic domain structures in multilayer samples using mainly Fresnel defocus imaging. Here, off-axis electron holography is used to obtain in-focus electron optical phase images of Néel-type domains and skyrmions in an Ir/Fe/Co/Pt multilayer sample. The preparation of the sample, reconstruction of the holograms and influence of sample tilt angle on the signal-to-noise ratio in the phase images are discussed. A good agreement is found between images of individual skyrmions that are stabilized using an external magnetic field and simulated images based on theoretical models of Néel-type skyrmions.

Nature-inspired PDMS cumulonimbus micro-energy-harvesting cloud

Here in this work, nanoenergy-generating films mimicked from cumulonimbus cloud were prepared using deionised water (DI) in polydimethylsiloxane (PDMS). Various characterisation methods have been adopted to verify the content of water as well as the resemblance of the morphological structure of the water-entrapped polymer films with clouds which include scanning electron microscopy and optical reflectance imaging techniques. The water content entrapment in the polymer is verified using the ATR-IR spectroscopy by finding absorbance peaks at 3266 and 1634 cm−1. Polyethylene terephthalate (PET) sheets with a copper coating (Cu-PET) were used as contact electrodes, and the device was fabricated by the simple sandwiching process. Dielectric studies of the device under an applied electric field were used to illustrate the presence of interfacial hopping as well as orientational polarisation in the device. The device fabricated shows an enhancement of 218% and 562% with an increase in water content from 4:1 to 1:1 and a decrease of 26% and 36.5% with a further increase in water for the generated voltage and current measured, respectively. The optimum concentration of polymer to water is selected as 1:1 and the decrease in current and voltage may be due to the condensation of water molecules leading to fewer contact sites between the water and polymer molecules. The devices showed an increment of voltage and current of 171.1 V and 29.16 nA, respectively, with an increase in the force of 1–5 N by using an automated input system. The device was tested under various mechanical inputs, and the generated energy used as sensors in the knock sensor, home doorbell system and seabed vibration detector and as a secondary powering source for charging mobile phones and lighting LED.

Performance Evaluation of Textured Inserts with MQL in Machining of PH Stainless Steel

This present investigation presents the method of texture fabrication and performance analysis of machinability of a textured and conventional Tungsten Carbide (WC) tool inserts. An endeavour has been taken to increase the performance of machining with different type of textured inserts. Texturing on the rake face of the inserts was fabricated using Wire Electrical Discharge Machine (WEDM). Experiments were conducted with different set of machining parameters on PH Stainless Steel (PHSS) with conventional and textured inserts and machinability analysis were evaluated. Tangential cutting force, surface roughness, and tool wear have been opted as the responses. Scanning electron microscope and optical microscopic image were used to evaluate the tool wear for different type of texture inserts. Based upon the outcomes attained, it is observed that the cutting tool with diamond shape texture exhibits the better performance in reduction of cutting force, tool wear and also improves the surface finish.

Flexure and Twist Test Reliability Assurance of Flexible Electronics

Abstract Additively printed flexible electronics in wearable application may be subjected to twisting or flexing depending on the form factor and the intended use. There is a dearth of standards for testing and reliability assurance of flexible electronics and reliability data for various use conditions. In this paper, a test protocol has been developed for twisting and flexing on aerosol-jet additively printed flexible circuits. Test patterns with commonly used traces geometries have been developed, aerosol-jet printed, and thermally sintered at various conditions. Effect of sintering temperature on fatigue robustness in cyclic-flexing and cyclic-twisting has been studied for straight, horse-shoe, and zig-zag trace geometries. Reliability data have been acquired under both twist and flex using continuous resistance monitoring until 100,000 cycles. Failure mechanisms have been studied for both cyclic-flexure and cyclic-twist using scanning electron microscopy (SEM) and optical imaging.

Adhesive joint properties of advanced carbon/ceramic composite and tungsten–copper alloy for the hybrid rocket nozzle

A hybrid rocket nozzle is made up of several different functional components using different materials. The joint properties of these different parts are critical to ensure the service reliability and robustness of the nozzle structure. In this paper, three kinds of anti-ablation materials were selected, bonded together, then tested to assess their joint bonding capability in a hybrid rocket motor. Boron containing phenol-formaldehyde with 40 wt% SiC powder was used as adhesive on fine woven punctured felt preform carbon/ceramic composite (punctured ceramic), needled carbon cloth/felt layers preform carbon/ceramic composite (needled ceramic), and tungsten-copper alloy (W–Cu alloy). Thermogravimetric (TG) and differential scanning calorimetry (DSC) tests were conducted to characterize the high temperature performance of the adhesive. Scanning electron microscopy (SEM) and optical microscope images of the hybrid joints were used to find the failure mechanisms and failure propagations. The cohesion failure mode applied to all test specimens indicated that failure occurred in the adhesives, while the mechanical test of these hybrid joints showed that the needled ceramic/W–Cu alloy has the highest shear strength of 13.79 MPa. The demo firing test was used to demonstrate the joints behavior in a real environment. The results showed that the adhesive gap was strong enough to withstand the shear stress caused by combustion flow, and was capable of bearing 200 s of burning ablations.

Improved mechanical and electromagnetic interference shielding performance of segregated UHMWPE/CNTs via microwave-assisted sintering

Constructing the segregated networks is an efficient strategy to simultaneously achieve the high electrical conductivity and electromagnetic interference (EMI) shielding performance in conductive polymer composites (CPCs). Herein, an advanced molding technique based on microwave (MW)-assisted sintering was proposed to prepare the segregated ultrahigh molecular weight polyethylene/carbon nanotube (UHMWPE/CNT) composites. Scanning electron microscopy and optical microscopy images indicated that CNTs enriched on the surfaces of UHMWPE granules through ball milling, and the clear and complete conductive networks were observed in UHMWPE/CNT composites in the following MW sintering process, revealing that a perfect segregated structure was successfully constructed. The segregated UHMWPE/CNT composites exhibited an excellent electrical conductivity and EMI shielding performance of 49.3 S/m and 50 dB, respectively, along with a low percolation threshold of 0.10 vol%. Meanwhile, benefiting from the volumetric heating, an ideal mechanical property was also obtained in prepared composite by MW sintering. Compared with the conventional molding method, MW-assisted sintering shows its unique advantages, including better structural construction, shorter processing time, and lower energy consumption, which provides an efficient and environment-friendly method to fabricate CPCs with superior conductive and EMI shielding performance.

Unraveling VEALYL Amyloid Formation Using Advanced Vibrational Spectroscopy and Microscopy

Intermediate species are hypothesized to play an important role in the toxicity of amyloid formation, a process associated with many diseases. This process can be monitored with conventional and two-dimensional infrared spectroscopy, vibrational circular dichroism, and optical and electron microscopy. Here, we present how combining these techniques provides insight into the aggregation of the hexapeptide VEALYL (Val-Glu-Ala-Leu-Tyr-Leu), the B-chain residue 12–17 segment of insulin that forms amyloid fibrils (intermolecularly hydrogen-bonded β-sheets) when the pH is lowered below 4. Under such circumstances, the aggregation commences after approximately an hour and continues to develop over a period of weeks. Singular value decompositions of one-dimensional and two-dimensional infrared spectroscopy spectra indicate that intermediate species are formed during the aggregation process. Multivariate curve resolution analyses of the one and two-dimensional infrared spectroscopy data show that the intermediates are more fibrillar and deprotonated than the monomers, whereas they are less ordered than the final fibrillar structure that is slowly formed from the intermediates. A comparison between the vibrational circular dichroism spectra and the scanning transmission electron microscopy and optical microscope images shows that the formation of mature fibrils of VEALYL correlates with the appearance of spherulites that are on the order of several micrometers, which give rise to a “giant” vibrational circular dichroism effect.

Processing and evaluation of thermal-sprayed high-performance polymer fiber reinforced Zn metal matrix composites

This novel research work reports the possibility of using a high-performance polymer fiber as a potential reinforcement in a suitable metal matrix for the development of composites. The manufacturing route is an additive process using High-Velocity Oxy-Fuel Thermal-Spray technique. Continuous strands of Poly-benzobisoxazole and para-aramid were used as high-performance polymer reinforcement in a uni-directional configuration, and Zinc metal was used as matrix material. The developed Thermal-Spray composites were subjected to mechanical tensile test and characterized by Scanning Electron Microscopy and Optical Microscopy. The results of the tensile tests revealed a substantial increase in the tensile properties and the investigation of Scanning Electron Microscopy and optical images showed a good deposition of matrix material on the reinforcing polymer fibers. The testing and characterization results were conclusive of the fact that Poly-benzobisoxazole and para-aramid can be used as an effective reinforcement even at low volume content for high strength structural applications.

Revealing the Improved Catalytic Properties of Modified Graphene-like Structures

The surface morphology and electronic structure of hexagonal graphene onion rings (HGORs), a modified graphene structure, were investigated to confirm the possibility as an efficient catalyst when compared to graphene. After confirming the formation of HGORs with a smaller width (~4.2 μm) from scanning electron microscopy (SEM) and optical microscopy images, we compared the catalytic activities of HGORs and graphene by measuring the rate of oxidation of thiophenol using high-resolution photoemission spectroscopy (HRPES). In addition, we also assessed in 4-chlorophenol degradation and the OH radical formation with a benzoic acid to confirm the possibility for photocatalytic activities of HGORs. As a result, we confirmed that HGORs, which has an increased active site due to its three-dimensional structure formed by the reaction of graphene with hydrogen, can act as an effective catalyst. In addition, we could also realize the possibility of optical applicability by observing the 0.13 eV of band gap opening of HGORs.

Tunable light emission from chemical vapor deposited two-dimensional MoSe2 by layer variation and S incorporation

Mono- and few-layer thick MoSe2 and MoSxSe2 − x domains were grown on insulating SiO2/Si substrates by chemical vapor deposition. Scanning electron microscopy and optical contrast images were used to determine the domain size and morphology. The structure, crystallinity, and the thickness (number of layers) of the as-synthesized domains were determined from Raman spectroscopy. The light emission was determined from photoluminescence (PL) spectroscopy. The PL emission started appearing only in domains having four layers or less, with the intensity increasing as the number of layers decreased. The PL peak position varied between 1.48 eV (∼838 nm) for four layers to 1.55 eV (∼800 nm) in the monolayer limit. Sulfur incorporation was done to enable a further tunability of the bandgap. The monolayer bandgap changed from 1.55 eV for MoSe2 to 1.64 eV (∼756 nm) for MoS0.32Se0.68. The other effect of S incorporation was the formation of larger area domains in the alloy as compared to binary MoSe2 with an improvement in the structural properties, thus providing a pathway to improve the properties of two-dimensional semiconductors by mixing of two materials with similar atomic arrangements.

Influence of geomagnetic field on the imaging performance of a streak tube

Abstract Streak cameras are widely used as ultrafast diagnostic tools in several research fields as the spatiotemporal measurement is of great significance in physics, chemistry, and biomedical research. However, as action objects, electron beams inside streak tubes are easily affected by the surrounding environment, which may lead to deterioration in the performance. In this study, the influence of a geomagnetic field on a streak tube is verified through a simulation. Based on the simulation results, the variation in the image shape due to the geomagnetic field and the overall camera imaging characteristics are analysed theoretically for the first time. The experimental result demonstrates that the imaging characteristics are better after a theoretical analysis is conducted and the final image is adjusted according. We discuss how this analysis can further develop other types of electron optical imaging systems and experiments.

Fatigue and creep-fatigue crack growth in alloy 709 at elevated temperatures

ABSTRACTFatigue crack growth (FCG) and creep-fatigue crack growth (CFCG) in austenitic stainless-steel Fe-25Ni-20Cr (Alloy 709) were measured experimentally and simulated using the finite element method. Temperature conditions investigated were 550°C, 600°C and 700°C, with load hold times of 0 s, 60 s and 600 s. Fracture surface was investigated using scanning electron microscopy and optical imaging. Experiments indicated that crack growth exhibits minimal sensitivity to the various loading conditions evaluated. At 600°C, crack growth rates were independent of hold time or loading frequency. At 700°C, there was a small increase in crack growth rate as a function of hold time, with a 600s hold time causing a factor of 2 increase in crack growth rate over FCG. Finite element simulations were performed to compute plasticity-induced crack closure in the presence of creep deformations at the crack tip. The simulations produced FCG and CFCG rates similar to the experimental results.

Characterization and Accelerated Erosion Testing of WC-Co-Cr- and CoNiCrAlY-Coated CA6NM Turbine Steel

In the present study, in-depth characterization of the high-velocity oxy-fuel (HVOF)-spray WC-Co-Cr and CoNiCrAlY coatings deposited on CA6NM turbine steel was done using scanning electron microscope (SEM), x-ray diffraction (XRD), roughness tester, microhardness tester, and optical image analyzer. Further, these coatings were tested under accelerated slurry erosion conditions using a high-speed erosion test rig. The effects of three different parameters related to actual operating conditions, namely erodent velocity relative to target surface, average erodent particle size, and slurry concentration on erosion behavior of these coatings, were investigated. SEM images on the specimen surface taken before and after erosion tests were carefully examined to understand the possible erosion mechanism. The study revealed that HVOF-sprayed WC-Co-Cr coating was found to impart higher erosion resistance in comparison with CoNiCrAlY coating under all the slurry erosion conditions. The reason for this behavior may be attributed to the higher hardness of HVOF-sprayed WC-10Co-4Cr coating in comparison with CoNiCrAlY coating.

Measurement of charge density in nanoscale materials using off-axis electron holography

Three approaches for the measurement of charge density distributions in nanoscale materials from electron optical phase images recorded using off-axis electron holography are illustrated through the study of an electrically biased needle-shaped sample. We highlight the advantages of using a model-based iterative algorithm, which allows a priori information, such as the shape of the object and the influence of charges that are located outside the field of view, to be taken into account. The recovered charge density can be used to infer the electric field and electrostatic potential.

Effect of Austenite Reformation on Localized Corrosion Resistance of Hyper-Duplex Stainless Steel in Hot Chloride Solution

The materiality of duplex stainless steels for deep-sea applications, where high corrosive conditions prevail, was studied in the present work. The effect of annealing temperature on the phase balance of the new hyper-duplex grade and subsequent variation in their corrosion resistance at hot chloride environments were estimated. ASTM A890 grade 7A samples were soaked at 1130 °C, 1160 °C, and 1190 °C and furnace-cooled till 1060 °C followed by water quenching. Electron microscope and optical micrograph images confirmed the decrease in austenite with the rise in solutionizing temperature; but on slow cooling, major austenite reformation takes place. Energy-dispersive spectroscopy (EDS) and line-scan methods were used to find out the distribution of constituent alloying elements. The migration of Cr and Mo to the austenite phase occurred as a result of the heat-treatment processes. Potentiodynamic polarization technique was conducted at different temperatures of 30 °C, 40 °C, 50 °C, and 60 °C on all heat-treated samples. At higher temperatures, corrosion resistance improved with an increase in austenite percentage. Optical images of the corroded samples showed the metastable pit growth with an increase in chloride medium temperature.

Geometric distortion correction for streak camera imaging

As streak tube imaging is a concentric spherical electrostatic focusing system, geometric distortion is caused by the relative change in radial magnification. This reduces the spatial resolution of imaging. The physical principle of changing the radial magnification of an electronic optical imaging system is analyzed to correct the geometric distortion of the imaging system and to improve spatial resolution. Distortion is corrected using the calibration model of a spherical optical system. The contrast of a reticle intensity image is compared before and after correction, and the ultimate resolution is calculated. Contrast is increased by ∼4 % , and the ultimate resolution is increased by ∼2 lp / mm after correction.

Immediate development of processing windows for selective electron beam melting using layerwise monitoring via backscattered electron detection

The availability of a reliable processing window is the basic requirement for processing new materials via selective electron beam melting (SEBM). Typically, these processing windows are derived by a time-consuming procedure comprising fabrication, metallographic preparation and analysis of standardized specimens for every parameter set. This study demonstrates the immediate development of a processing window during one single SEBM process. An electron optical image acquisition system provides the necessary information for evaluation and subsequent adaption of process parameters. It is shown that this immediate approach delivers processing windows with sufficient accuracy, while the required time is substantially reduced from weeks or even months to several hours.

Surface Smoothness Evaluation of Etched and Unaltered Sand Specimens with Mechanical Behavior Assessment

Abstract Particle smoothness refers to the surface texture of a sand particle on a small scale. This parameter may be used in conjunction with roundness (angularity) and sphericity in describing particle shape for engineering purposes. Smoothness is challenging to measure and quantify. This note describes preliminary evaluation approaches used to compare two identically graded sand specimens; one with an unaltered, smooth surface texture, and the other chemically etched to create a rougher surface texture. Visual observation indicated that the unaltered specimens were essentially the same as the etched specimens in terms of macroscale particle shape features (i.e., roundness and sphericity). On the other hand, the particles were significantly different in terms of the surface texture and roughness, as shown by visual techniques using scanning electron microscope and optical microscopy images. A tentative, easy-to-implement, visual particle smoothness scale is offered, designed to complement the roundness and sphericity estimates and measures commonly used to describe particle shape. Next, several simple laboratory index tests are completed on the unaltered and the etched specimens to observe differences in mechanical behavior. Limit density, flow rate, and angle of repose tests are undertaken. The results of the testing indicate measurable differences in the mechanical behavior of the unaltered versus the etched specimens. This further supports the importance of particle surface texture on the mechanical behavior of poorly graded sands. Additional research is underway to more completely quantify the contribution of particle smoothness of sands with respect to the other macroscale particle shape features.

High-Quality Surface Finishing of Industrial Three-Dimensional Metal Additive Manufacturing Using Electrochemical Polishing

Three-dimensional (3D) additive manufacturing technologies are useful for building various and complicated shapes. Representative technologies include laser metal deposition and selective laser sintering that make metal powders melt in order to form diverse 3D structures. Although numerous well-known advantages of 3D additive manufacturing, they still have some difficulties in surface quality improvement for further applications such as food or biomedical industries because they cause rough surfaces, discoloration, unmelted particles by repeated instant dissolution and solidification of metal particles. This paper introduces an electrochemical polishing (or electropolishing, ECP) process as a possible finishing process for 3D printed parts. Conventional finishing processes including mechanical finishing can hardly polish 3D curved surface readily. In ECP, the tool electrode and the work sample are not in contact with each other. All electrically connected surface exposed to electrolyte are subject to be polished. The printed product performs in a current density region higher than the conventional current density, thereby activating the electrochemical reaction and promoting the dissolution of the metal surface, thereby smoothly polishing a very rough surface. Surface quality including roughness, splashed particle spots, smoothness, brightness, light reflection and corrosion resistance were improved by ECP. Experimental results were analyzed by scanning electron microscopy, optical and detailed atomic force microscopy images according to various ECP electrical conditions.

复合电磁同心球系统的成像电子光学. D章：近轴方程渐近解

复合电磁同心球系统的成像电子光学. D章：近轴方程渐近解