Low-voltage Scanning Electron Microscopy Research Articles

Revealing Spider Silk's 3D Nanostructure Through Low Temperature Plasma Etching and Advanced Low-Voltage SEM

The excellent mechanical properties of spider dragline silk are closely linked to its multiscale hierarchical structuring which develops as it is spun. If this is to be understood and mimicked, multiscale models must emerge which effectively bridge the length scales. This study aims to contribute to this goal by exposing structures within Nephila dragline silk using low-temperature plasma etching and advanced Low Voltage Scanning Electron Microscopy (LV-SEM). It is shown that Secondary Electron Hyperspectral Imaging (SEHI) is sensitive to compositional differences on both the micro and nano scale. On larger scales it can distinguish the lipids outermost layer from the protein core, while at smaller scales SEHI is effective in better resolving nanostructures present in the matrix. Key results suggest that the silks spun at lower reeling speeds tend to have a greater proportion of smaller nanostructures in closer proximity to one-another in the fiber, which we associate with the fiber's higher toughness but lower stiffness. The bimodal size distribution of ordered domains, their radial distribution, nanoscale spacings, and crucially their interactions may be key in bridging the length scale gaps which remain in current spider silk structure-property models. Ultimately this will allow successful biomimetic implementation of new models.

Pervaporation membranes of a simplex type with polyelectrolyte layers of chitosan and sodium hyaluronate

Self-supporting multilayer films containing a polyelectrolyte complex (PEC) were prepared by the sequential layering of sodium hyaluronate (HA, MW 5.4 × 104) and chitosan (CS, MW 1.6 × 105, the degree of deacetylation 0.80) in different orders. Imaging with low-voltage scanning electron microscopy (LVSEM) showed that the CS/HA films had a multilayer structure, while X-ray diffraction (XRD) indicated significant structuring of the CS layer near the PEC-CS region. Analysis of the thermal properties of the CS/HA films revealed differences in the structural organization and morphological features of the polymer layers and high thermal stability of the PEC layer. Testing of the transport properties of the CS/HA film in pervaporation (PV) separation using different compositions of ethanol-water mixtures indicated that the multilayer membrane was selective across a wide range of concentrations in the feed. Separation of an azeotropic ethanol-water mixture containing 5 wt% water yielded a permeate consisting of about 100 wt% water. LVSEM revealed that the membrane microstructure changed during the PV process due to membrane swelling and changes in the arrangement of the macromolecules during transport of the penetrant. The results support the use of CS/HA composite films as highly effective PV membranes. In addition to pervaporation separation, CS/HA multilayer films can also be used for drug delivery, tissue engineering, and wound healing applications.

Low-Voltage Scanning Electron Microscopy and Energy-Dispersive X-Ray Microanalysis of the Interface of Multilayer Polymer Composite

The morphology of the layer of polyelectrolyte complex, which is formed in the composite based on chitosan and sulfoethyl cellulose during the contact of a solution of one of them with a gel film of the other one, has been investigated by the low-voltage (≤3 kV) scanning electron microscopy. A technique for eliminating the effects related to charge accumulation on the dielectric film surface is proposed.

Potential Images of Ferroelectric Domain Structures Formed by Electron Beam in Lithium Niobate Crystals

Ferroelectric domain structures formed by an electron beam in lithium niobate crystals are studied using low-voltage SEM microscopy. The structures are formed in crystals with different conductivity, including samples with high-resistance congruent composition (CLN) and samples with conductivity increased by reductive annealing (RLN). The potential nature of the contrast of the domain structures observed in the secondary electron mode depending on the conductivity of the samples and the direction of spontaneous polarization of the domains is analyzed. It is assumed that the domain contrast in CLN crystals is associated with long-lived charges localized near domain walls and in the irradiated areas. The recorded domain structures in the CLN crystals are visualized on polar and nonpolar cuts. In the RLN crystals with improved conductivity compared to CLN, the potential contrast of the periodic domain structures is found only on the polar cuts, where vector Ps of the domains is perpendicular to the irradiated surface. This contrast is likely because the field of the spontaneous electric polarization charges influences the secondary electrons.

Quantitative analysis of backscattered electron (BSE) contrast using low voltage scanning electron microscopy (LVSEM) and its application to Al0.22Ga0.78N/GaN layers

A novel method to quantify and predict the material contrast using Backscattered Electron (BSE) imaging in Scanning Electron Microscopy (SEM) is presented while using low primary electron beam energies (Ep). In this study, the parameters for BSE imaging in Low Voltage Scanning Electron Microscopy (LVSEM) are optimized for the layer system Al0.22Ga0.78N/GaN, which is typically used in High Electron Mobility Transistors (HEMTs). The layers are imaged at high resolution and the compounds are identified based on the quantitative BSE material contrast between Al0.22Ga0.78N and GaN. The quantification process described in this study is based on an analytical description that predicts the material contrast using a function that correlates the effective backscattering coefficient (η) with the atomic number Z.

Direct imaging of uncoated biological samples enables correlation of super-resolution and electron microscopy data

A simple method for imaging biological tissue samples by electron microscopy and its correlation with super-resolution light microscopy is presented. This room temperature protocol, based on protecting thin biological specimens with methylcellulose and imaging with low voltage scanning electron microscopy, circumvents complex classical electron microscopy sample preparation steps requiring dehydration, resin embedding and use of contrast agents. This technique facilitates visualization of subcellular structures e.g. synaptic clefts and synaptic vesicles in mouse brain tissue and the organization of mitochondrial cristae in the zebrafish retina. Application of immunogold protocols to these samples can determine the precise localization of synaptic proteins and, in combination with super-resolution light microscopy methods clearly pinpoints the subcellular distribution of several proteins in the tissue. The simplicity of the method, including section collection on a silicon wafer, reduces artefacts and correlates protein location with sample morphology.

Low-voltage SEM contrasts of steel surface studied by observations and electron trajectory simulations for GEMINI lens system.

Scanning electron microscopy (SEM) is a powerful tool for observing the surface of materials. Modern SEM systems have multiple detectors with different geometries. Consequently, the SEM image contrast depends on the instrument and experimental conditions even for the same sample. Understanding the SEM imaging mechanism is necessary to clarify SEM contrast. In this paper, low-voltage (LV)-SEM image contrast is investigated by comparing LV-SEM images and electron trajectory simulation results. Surface observations of oxides on a steel surface, positive charging contrast and topographic contrast in the image systematically changed with the working distance (WD). The electron trajectory simulation revealed the sharing of emitted electrons by the in-lens and Everhart-Thornley detectors, and systematic changes in the electron sharing caused by changes in WD. The image contrast was reasonably explained by the kinetic energy and take-off angle (acceptance plots) of the detected electrons derived by the electron trajectory simulations. This approach is essential to understanding the SEM image contrast obtained by SEM systems with multiple detectors. Thorough image simulations based on acceptance plots are required in future work.

Origin and suppression of critical deep pit in high-electron-mobility transistor structure using GaN on Si technology with strained-layer superlattice

For the utilization of high-electron-mobility transistor (HEMT) devices fabricated on GaN on Si structure as high-power devices, deep pits, which are known as inverted pyramid-shaped defects formed in the surface of a HEMT structure, are critical because they act as leakage pathways and degrade the breakdown property. We investigated in detail the origin of pits in the HEMT structure with a strained-layer superlattice (SLS). The pits were found to emerge from rotation domains, in which the crystal structure rotates around the c-axis, in the AlN buffer layer. The analysis by ultra low voltage scanning electron microscopy (ULV-SEM) revealed that the domains were formed on dense Al regions in Al preseeding layer. By optimizing Al pre flow conditions, we eliminated dense Al regions in Al preseeding layer, consequently, no rotation domains in the AlN buffer layer. An extremely low pit density of the HEMT structure with fine breakdown property was successfully achieved.

Influence of hydrogen intercalation on graphene/Ge(0 0 1)/Si(0 0 1) interface

Hydrogen intercalation is widely used to weaken graphene-substrate interactions and as a result enhancing graphene’s electronic properties. This paper presents the study of microstructure of hydrogen intercalated graphene grown on Ge(0 0 1)/Si(0 0 1) substrate using Low-Voltage Scanning Electron Microscopy. The findings reveal a significant change in the surface morphology of germanium substrate: faceting structure disappears almost completely, the germanium surface flattens, and steps/terraces are formed. This leads to degradation of graphene’s electronic properties, which shows the negative impact of hydrogen intercalation when graphene is grown on the germanium substrate.

Design for an aberration corrected scanning electron microscope using miniature electron mirrors

Resolution of scanning electron microscopes (SEMs) is determined by aberrations of the objective lens. It is well known that both spherical and chromatic aberrations can be compensated by placing a 90-degree bending magnet and an electron mirror in the beam path before the objective lens. Nevertheless, this approach has not led to wide use of these aberration correctors, partly because aberrations of the bending magnet can be a serious problem. A mirror corrector with two mirrors placed perpendicularly to the optic axis of an SEM and facing each other is proposed. As a result, only small-angle magnetic deflection is necessary to guide the electron beam around the top mirror to the bottom mirror and around the bottom mirror to the objective lens. The deflection angle, in the order of 50 mrad, is sufficiently small to avoid deflection aberrations. In addition, lateral dispersion at the sample plane can be avoided by making the deflection fields symmetric. Such a corrector system is only possible if the incoming beam can pass the top mirror at a distance in the order of millimeters, without being disturbed by the electric fields of electrodes of the mirror. It is proposed that condition can be satisfied with micro-scale electron optical elements fabricated by using MEMS technology. In the proposed corrector system, the micro-mirrors have to provide the exact negative spherical and chromatic aberrations for correcting the aberration of the objective lens. This exact tuning is accomplished by variable magnification between the micro-mirrors and the objective lens using an additional transfer lens.Extensive optical calculations are reported. Aberrations of the micro-mirrors were analyzed by numerical calculation. Dispersion and aberrations of the deflectors were calculated by using an analytical field model. Combination aberrations caused by the off-axis position of dispersive rays in the mirrors and objective lens were also analyzed. It is concluded that the proposed corrector system will be a promising candidate for simple and low-cost aberration correction in low-voltage SEMs.

Потенциальные изображения сегнетоэлектрических доменных структур в кристаллах ниобата лития после формирования электронным лучом

AbstractFerroelectric domain structures formed by an electron beam in lithium niobate crystals are studied using low-voltage SEM microscopy. The structures are formed in crystals with different conductivity, including samples with high-resistance congruent composition (CLN) and samples with conductivity increased by reductive annealing (RLN). The potential nature of the contrast of the domain structures observed in the secondary electron mode depending on the conductivity of the samples and the direction of spontaneous polarization of the domains is analyzed. It is assumed that the domain contrast in CLN crystals is associated with long-lived charges localized near domain walls and in the irradiated areas. The recorded domain structures in the CLN crystals are visualized on polar and nonpolar cuts. In the RLN crystals with improved conductivity compared to CLN, the potential contrast of the periodic domain structures is found only on the polar cuts, where vector P _ s of the domains is perpendicular to the irradiated surface. This contrast is likely because the field of the spontaneous electric polarization charges influences the secondary electrons.

Variation of the Linewidth Values during Measurements in a Low-Voltage SEM

Variation of the Linewidth Values during Measurements in a Low-Voltage SEM

Comparative study of image contrast in scanning electron microscope and helium ion microscope.

Images of Ga+ -implanted amorphous silicon layers in a 110 n-type silicon substrate have been collected by a range of detectors in a scanning electron microscope and a helium ion microscope. The effects of the implantation dose and imaging parameters (beam energy, dwell time, etc.) on the image contrast were investigated. We demonstrate a similar relationship for both the helium ion microscope Everhart-Thornley and scanning electron microscope Inlens detectors between the contrast of the images and the Ga+ density and imaging parameters. These results also show that dynamic charging effects have a significant impact on the quantification of the helium ion microscope and scanning electron microscope contrast.

Formation of basal plane stacking faults on the ([formula omitted]) facet of heavily nitrogen-doped 4H-SiC single crystals during physical vapor transport growth

The formation of stacking faults in heavily nitrogen-doped (mid-1019cm−3) 4H-SiC boules grown by the physical vapor transport (PVT) growth method was investigated by studying surface morphologies on the (0001¯) facet of the boules. Low-voltage scanning electron microscopy (LVSEM) observations detected stacking faults on the (0001¯) facet of heavily nitrogen-doped 4H-SiC crystals. LVSEM and atomic force microscopy (AFM) studies revealed that the stacking faults showed characteristic morphologies, which stemmed from the interaction between stacking faults and surface steps. These observations also revealed that heavy nitrogen doping resulted in the nucleation of a number of surface hillocks on the (0001¯) facet; the hillocks were never observed on the facet of conventionally doped (nitrogen concentration: mid-1018cm−3) 4H-SiC boules. Furthermore, the hillocks were nucleated only on the facet and never observed on the outer regions of the facet. Based on these results, the stacking fault formation mechanism in heavily nitrogen-doped 4H-SiC crystals is discussed.

Low-voltage scanning electron microscopy of multilayer polymer systems

The possibilities of low-voltage scanning electron microscopy for visualization of specific features of the microstructure in internal layers of multilayer polymer films are demonstrated by the example of “chitosan–polyelectrolyte complex–alginic acid” composite. The process of electron beam interaction with a sample at low electron energies is considered. The key parameters of low-voltage electron microscopy, which make it possible to increase the resolution of SEM images of polymer systems, are discussed.

Scanning Electron Microscope Observations of Powder Sticking on Punches during a Limited Number (N

To obtain quantitative information and mechanistic insight into the problem of sticking of acetylsalicylic acid tablets on a metallic punch. Low voltage scanning electron microscopy was used to observe punch area coverage and morphology of adhered powder on a flat punch used for a limited number of compactions. Material accumulation in terms of area coverage of the punch per compaction cycle was determined at two pressures over five compactions. The distribution of the adhered material on the punch was non-uniform with more material left on the center of the punch. The sizes of the adhered particles range from 1 to 100μm, with 50% of the punch surface coverage from particles of an equivalent diameter>30μm. Three types of adhered particles were identified after the first compaction: (a) fragments of initial particles with very high aspect ratio, (b) nearly equiaxed fragments with multiple cracks, (c) heavily deformed islands of low profile. Some preliminary ideas that explain these observations are presented and discussed. The ability of SEM to provide quantitative information on sticking from few compactions presents an interesting possibility for a material sparing technique that provides insight on the propensity of sticking.

Damage-less Chemical State Analysis by Using Soft X-ray Emission Spectroscopy in Low Voltage SEM

Damage-less Chemical State Analysis by Using Soft X-ray Emission Spectroscopy in Low Voltage SEM

Nanoscale Mapping of Bromide Segregation on the Cross Sections of Complex Hybrid Perovskite Photovoltaic Films Using Secondary Electron Hyperspectral Imaging in a Scanning Electron Microscope.

Mixed halide (I/Br) complex organic/inorganic hybrid perovskite materials have attracted much attention recently because of their excellent photovoltaic properties. Although it has been proposed that their stability is linked to the chemical inhomogeneity of I/Br, no direct proof has been offered to date. Here, we report a new method, secondary electron hyperspectral imaging (SEHI), which allows direct imaging of the local variation in Br concentration in mixed halide (I/Br) organic/inorganic hybrid perovskites on a nanometric scale. We confirm the presence of a nonuniform Br distribution with variation in concentration within the grain interiors and boundaries and demonstrate how SEHI in conjunction with low-voltage scanning electron microscopy can enhance the understanding of the fundamental physics and materials science of organic/inorganic hybrid photovoltaics, illustrating its potential for research and development in “real-world” applications.

Investigation of the Surface Morphology and Stacking Fault Nucleation on the (000-1)C Facet of Heavily Nitrogen-Doped 4H-SiC Boules

The stacking fault formation during physical vapor transport growth of heavily nitrogen-doped (mid-1019 cm−3) 4H-SiC crystals was investigated. Low-voltage scanning electron microscopy (LVSEM) observations detected the stacking fault formation on the (000-1) facet of heavily nitrogen-doped 4H-SiC crystals. Stacking faults showed characteristic morphologies, and atomic force microscopy (AFM) studies revealed that these morphologies of stacking faults stemmed from the interaction between surface steps and stacking faults. Based on these results, the stacking fault formation mechanism in heavily nitrogen-doped 4H-SiC crystals is discussed.

A study of extracellular vesicles isolated from blood plasma conducted by low-voltage scanning electron microscopy

Extracellular vesicles secreted by cells represent an almost spherical membrane structures enriched with biological molecules of different types. The number and molecular composition of these structures depend on both the physiological state of an organism and underlying diseases. Despite extracellular vesicles playing an important role in intercellular communication and being potential biomarkers of pathological processes, the mechanisms of their formation, their functions, and their morphological characteristics are poorly studied. Low-voltage scanning electron microscopy is a promising method for studying extracellular vesicles, since it does not need a layer of conductive covering and, consequently, permits morphological details of studied objects to be vizualized at a high resolution in a nanometer range. The results of investigation of the morphology and sizes of objects in blood-plasma fractions by low-voltage scanning electron microscopy are presented in this study.