Vacuum Scanning Electron Microscopy Research Articles

In-situ SEM microrobotics for versatile force/deformation characterization: application to third-body MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$MoS_2$$\\end{document} wear particles

This article explores the challenges and solutions in the physical characterization of materials at the microscale using robotized systems, with a specific focus on manipulating and characterizing micrometer-sized particles with different and complex 3D shapes and internal sub-micrometer structures. In this paper, the studied particles are Molybdenum diSulfide (MoS2) based materials generated within the contact interface during friction. These particles are being studied because they offer a particularly promising solution for reducing mechanical friction and the associated high energy losses. However, they are distributed randomly within the contact area and possess intricate sub-micrometer structures. Characterization demands precise manipulation techniques in an in-situ Scanning Electron Microscope(SEM) environment. To address these challenges, existing commercial micro and nanomanipulation tools are integrated within a vacuum SEM chamber, and robotics strategies are investigated to enable the whole process from particle preparation, and manipulation setup definition, to effective MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} particle characterization all in-situ SEM. A set of several complementary experimental investigations are done and involve force measurement and deformation estimation studies, leading to the first qualitative results on MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} based particles directly from the friction track. The work contributes to advancements in both microscale manipulation and characterization. It also has implications for lubrication research.

A simple, static and stage mounted direct electron detector based electron backscatter diffraction system

To engineer the next generation of advanced materials we must understand their microstructure, and this requires microstructural characterization. This can be achieved through the collection of high contrast, data rich, and insightful microstructural maps. Electron backscatter diffraction (EBSD) has emerged as a popular tool available within the scanning electron microscope (SEM), where maps are realized through the repeat capture and analysis of Kikuchi diffraction patterns. Typical commercial EBSD systems require large and sophisticated detectors that are mounted on the side of the SEM vacuum chamber which can be limiting in terms of widespread access to the technique. In this work, we present an alternative open-hardware solution based upon a compact EBSD system with a simple, static geometry that uses an off-the-shelf direct electron detector co-mounted with a sample. This simple stage is easy to manufacture and improves our knowledge of the diffraction geometry significantly. Microscope and detector control is achieved through software application programming interface (API) integration. After pattern capture, analysis of the diffraction patterns is performed using open-source analysis within AstroEBSD. To demonstrate the potential of this set up, we present two simple EBSD experiments using a line scan and area mapping. We hope that the present system can inspire simpler EBSD system design for widespread access to the EBSD technique and promote the use of open-source software and hardware in the workflow of EBSD experiments.

Micromorphology of the Adhesive Interface of Self-Adhesive Resin Cements to Enamel and Dentin.

Interfaces between dentin, enamel and luting agents were characterized using low vacuum Scanning Electron Microscopy (SEM). After smear layer creation, one of three luting agents (RelyX Unicem 2, Clearfil SA Cement and Panavia F 2.0/ED Primer II) was applied on 60 enamel-dentin specimens and dual-cured or self-cured. Specimens were polished (Experiment 1) and subsequently demineralized and deproteinized (Experiment 2). Adhesive interfaces were analyzed (low vacuum SEM, ×3000). Presence of an interdiffusion zone, tag-like structures (dentin) and marginal gaps (enamel) were assessed. Non-parametrical tests (χ2-test, α = 0.05) were performed. The first null-hypothesis was that the adhesive interface micromorphology between enamel and dentin and self-adhesive resin cements (SARCs) is similar with conventional resin cement used with a self-etch adhesive (CRC+SE). The second null-hypothesis was that the micromorphology is not influenced by curing modes. Interdiffusion zones and tag-like structures (dentin) were observed more frequently for CRC+SE compared to SARCs. For each luting agent, there was a non-significant (p > 0.05) tendency for interdiffusion zone and tag-like structures detectable in more specimens after self-curing compared to dual-curing. Marginal gaps (enamel) were found only for SARCs. The first null-hypothesis was not rejected fully: Tag-like structures and interdiffusion zones in dentin were found for CRC+SE and SARCs. The second null-hypothesis was not rejected.

Skeleton bones in museum indoor environments offer niches for fungi and are affected by weathering and deposition of secondary minerals.

Large skeleton specimens are often featured as iconic open displays in Natural History Museums, for example, the blue whale 'Hope' at the Natural History Museum, London. A study on Hope's bone surface was performed to assess the biodeterioration potential of fungi. Fungi were isolated, and a fungal internal transcribed spacer (ITS) clone library survey was performed on dust and bone material. Mineral particles derived from bone and dust were analysed using energy dispersive X-ray spectroscopy, variable pressure scanning electron microscopy (SEM) and high vacuum SEM. Results showed that bone material, although mainly mineral in nature, and therefore less susceptible than organic materials to biodeterioration phenomena in the indoor environments, offers niches for specialized fungi and is affected by unusual and yet not so well-documented mechanisms of alteration. Areas of bone surface were covered with a dense biofilm mostly composed of fungal hyphae, which produced tunnelling and extensive deposition of calcium and iron-containing secondary minerals. Airborne halophilic and xerophilic fungi including taxa grouping into Ascomycota and Basidiomycota, capable of displacing salts and overcome little water availability, were found to dominate the microbiome of the bone surface.

In-Situ Characterization of Lithium Native Passivation Layer in A High Vacuum Scanning Electron Microscope.

A technique to characterize the native passivation layer (NPL) on pure lithium metal foils in a scanning electron microscope (SEM) is described in this paper. Lithium is a very reactive metal, and consequently, observing and quantifying its properties in a SEM is often compromised by rapid oxidation. In this work, a pure lithium energy-dispersive x-ray spectrum is obtained for the first time in a high vacuum SEM using a cold stage/cold trap with liquid nitrogen reservoir outside the SEM chamber. A nanomanipulator (OmniProbe 400) inside the microscope combined with x-ray microanalysis and windowless energy dispersive spectrometer is used to fully characterize the NPL of lithium metal and some of its alloys by a mechanical removal procedure. The results show that the native films of pure lithium and its alloys are composed of a thin (25 nm) outer layer that is carbon-rich and an inner layer containing a significant amount of oxygen. Differences in thickness between laminated and extruded samples are observed and vary depending on the alloy composition.

Investigation of Three-Dimensional Microstructure of Tricalcium Silicate (C₃S) by Electron Microscopy.

A serial block-face scanning electron microscopy (SBFSEM) system, composed of a scanning electron microscope (SEM) and an ultra-microtome installed within the SEM vacuum chamber, has been used to characterize the three-dimensional (3D) microstructure of tricalcium silicate (C3S) grains embedded in epoxy resin. A selection of C3S grains were segmented and rendered with 3D-image processing software, which allowed the C3S grains to be clearly visualized and enabled statistically quantitative analysis. The results show that about 5% of the C3S grains have volumes larger than 1 μm3 and the average volume of the grains is 25 μm3. Pores can also be clearly seen in the biggest C3S grain, the volume of which is 3.6 × 104 μm3, and the mean volume and total volume of all the pores within this grain are 4.8 μm3 and 3.0 × 103 μm3, respectively. The reported work provides a new approach for the characterization of the 3D spatial structure of raw C3S materials, and the resulting 3D structure of the raw C3S is important for further systematic research on the relationships between the spatial microstructure and the hydration kinetics of C3S and other cement minerals.

Smallest microhouse in the world, assembled on the facet of an optical fiber by origami and welded in the μRobotex nanofactory

In this study, the authors have demonstrated that it is possible to realize several three-dimensional (3D) micro- and nanostructures, by the fabrication of the smallest microhouse using a dual beam scanning electron microscope (SEM)/focused ion beam (FIB) Auriga 60 from Zeiss together with a six degree of freedom robot built with SmarAct components. In this new type of nanolab, cutting, etching, folding, assembling, and then welding thin membranes of silica on top of a cleaved optical fiber SMF28, or production of micro- and nanostructures, like the microhouse, are possible. The authors have experimentally shown that FIB can be used, in this new generation of micro/nanofactory, in combination with SEM, and gas injection system, in order to fabricate three-dimensional microstructures: a microhouse in this study, with ultrahigh accuracy assembly down to 10 nm. By using the theory of sputtering, the authors are able to propose a model of folding thin membranes of numerous materials such as metals, polymers, or crystals, i.e., silica, silicon, potassium tantalite, or lithium niobate. This method is usually described as origami in the literature [W. J. Aroa, H. I. Smith, and G. Barbastathis, Microelectron. Eng. 84, 1454 (2007); W. J. Aroa et al., J. Vac. Sci. Technol., B 25, 2184 (2007); and K. Chalapat et al., Adv. Mater. 25, 91 (2013)]. The experimental results indicate that the introduction of a microrobot inside the SEM vacuum chamber will provide the means to enlarge the scope of clean room facilities to build complex and smart 3D microsystems with heterogeneous materials, especially on the facet of an optical fiber in the lab on fiber new field. The authors propose a new way to easily manufacture many kinds of optical functions for light trapping based on nanoantennas, nanophotonic crystal, axicon or lattice, 3D biosensor with origami, and nanopatterning surfaces or carbon nanotubes, etc.

The Use of Low Vacuum Scanning Electron Microscopy (LVSEM) to Analyze Peripheral Nerve Samples.

The use of electron microscopy allows analysis of the microarchitecture of peripheral nerves both during development and in the processes of nerve regeneration and repair.We describe a novel method for the rapid analysis and quantification of myelin in peripheral nerve using a low vacuum scanning electron microscopy protocol. For this methodology, excised nerves are prepared for traditional transmission electron microscopy (TEM) imaging, but at the stage where semi-thin sections would be taken, the resin block is instead imaged at low vacuum in the scanning electron microscope (SEM) using the backscattered electron signal. Any features in the tissue which have incorporated high concentrations of osmium from the fixation process (e.g., myelin) appear as bright regions in the image.Myelin therefore is easily identifiable in the images, and since there is a high contrast difference between it and the surrounding tissue, automated measurements for myelin thickness (e.g., G ratio) using standard and freely available image analysis software (e.g., ImageJ) are easily achievable, consistent, and repeatable. This method therefore greatly speeds up the analysis of nerve samples and, in many cases, will obviate the need for ultrathin sections and TEM for analyzing nerve morphology.Low vacuum (LV) SEM imaging has benefits compared with light microscopy; magnification is continuous, resolution is higher, and contrast and brightness are controllable. Since the resin block does not need a metal coating for imaging in LV mode, once the images have been collected, the block is still ready to section for both light microscopy (LM) and TEM.

Image-Guided Nanopositioning Scheme for SEM

Positioning of micro-nanoobjects inside a scanning electron microscope (SEM) for manipulation is a key and challenging task to perform. Often it is performed by skilled operators via teleoperation, which is tedious and lacks repeatability. In this paper, rendering this task as an image-guided problem, we present a frequency domain scheme for automatic control of positioning platform movements. The designed controller uses the relative global image motion computed using the frequency spectral information of the images as visual signal and can provide control up to five degrees of freedom. The proposed approach is validated in simulations as well as experimentally using a high-resolution piezo-positioning platform mounted inside a SEM vacuum chamber. The obtained results quantify the performance of the proposed nanopositioning scheme.

Crystal orientation measurements using SEM–EBSD under unconventional conditions

Electron backscatter diffraction (EBSD) is a micro-analytical technique typically attached to a scanning electron microscope (SEM). The vast majority of EBSD measurements is applied to planar and polished surfaces of polycrystalline bulk specimen. In this paper, we present examples of using EBSD and energy-dispersive X-ray spectroscopy (EDX) to analyze specimens that are not flat, not planar, or not bulk – but pillars, needles, and rods. The benefits of low vacuum SEM operation to reduced drift problems are displayed. It is further demonstrated that small and thin specimens enhance the attainable spatial resolution for orientation mapping (by EBSD or transmission Kikuchi diffraction) as well as for element mapping (by EDX).

Investigation of the effects of cadmium by micro analytical methods on Lycopersicon esculentum Mill. roots.

The interactions between cadmium stress and plant nutritional elements have been investigated on complete plant or at the level of organs. This study was undertaken to contribute to the exploration of the physiological basis of cadmium phytotoxicity. We examined the changes in the nutritional element compositions of the root epidermal cells of the seedlings of Lycopersicon esculentum Mill. at the initial growth stages that is known as the most sensitive stage to the stress. Effects of cadmium stress on the seedlings of Lycopersicon esculentum Mill. were examined by EDX (Energy Dispersive X-Ray Microanalysis) assay performed with using low vacuum (∼ 24 Pascal) Scanning Electron Microscopy. In the analysis performed at the level of root epidermal cells, some of the macro- and micronutrient contents of the cells (carbon, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, copper, and zinc levels) were found to change when the applying toxic concentrations of cadmium. There was no change in the manganese and sodium content of the epidermal cells. It was concluded that the changes in nutritional element composition of the cells can be considered as an effective parameter in explaining the physiological mechanisms of cadmium-induced growth inhibition.

Raman-in-SEM, a multimodal and multiscale analytical tool: Performance for materials and expertise

The availability of Raman spectroscopy in a powerful analytical scanning electron microscope (SEM) allows morphological, elemental, chemical, physical and electronic analysis without moving the sample between instruments. This paper documents the metrological performance of the SEMSCA commercial Raman interface operated in a low vacuum SEM. It provides multiscale and multimodal analyses as Raman/EDS, Raman/cathodoluminescence or Raman/STEM (STEM: scanning transmission electron microscopy) as well as Raman spectroscopy on nanomaterials. Since Raman spectroscopy in a SEM can be influenced by several SEM-related phenomena, this paper firstly presents a comparison of this new tool with a conventional micro-Raman spectrometer. Then, some possible artefacts are documented, which are due to the impact of electron beam-induced contamination or cathodoluminescence contribution to the Raman spectra, especially with geological samples. These effects are easily overcome by changing or adapting the Raman spectrometer and the SEM settings and methodology. The deletion of the adverse effect of cathodoluminescence is solved by using a SEM beam shutter during Raman acquisition. In contrast, this interface provides the ability to record the cathodoluminescence (CL) spectrum of a phase. In a second part, this study highlights the interest and efficiency of the coupling in characterizing micrometric phases at the same point. This multimodal approach is illustrated with various issues encountered in geosciences.

Cathodoluminescence-Activated Imaging by Resonance Energy Transfer: A New Approach to Imaging Nanoscale Aqueous Biodynamics

The organization, complexing, and aggregation of biomolecules in solution and in lipid membranes lie at the foundation of many critical processes in metabolism, signaling, and disease. Yet, our understanding of these phenomena remains limited by our ability to probe small aqueous volumes under physiological conditions. Here we present progress toward a high-brightness, rapidly scannable, nanoscale light source aimed at interrogating biomolecular dynamics in highly concentrated aqueous environments below the diffraction limit. This light source consists of a thin film of cathodoluminescent (CL) material excited by a low energy, tightly focused electron beam from a scanning electron microscope (SEM). By integrating the CL film into a liquid sample cell, a biological sample can be isolated from the SEM's vacuum environment.Our CL optical source consists of a highly crystalline film of cerium-doped yttrium aluminum perovskite (YAlO3:Ce3+), an efficient CL material. With our custom CL detection apparatus, we have shown that the CL excitation volume in the film is at least as small as 20 nm in diameter. Because the CL film is only 10 nm thick, optical excitations from the Ce3+ dopants in the CL film can be non-radiatively transferred to adjacent fluorescently labeled molecules in an encapsulated sample volume via Forster resonance energy transfer (FRET). We characterize this non-invasive interaction by coupling the donor CL film to various acceptor materials. When imaging biological systems, we anticipate achieving a spectrally-specific scanning optical microscopy with at least 20 nm lateral resolution and 10 nm axial resolution, with video frame rates, and no moving parts.

The surface topography of the choroid plexus. Environmental, low and high vacuum scanning electron microscopy

Environmental scanning electron microscopy (ESEM) allows the examination of hydrated and dried specimens without a conductive metal coating which could be advantageous in the imaging of biological and medical objects. The aim of this study was to assess the performance and benefits of wet-mode and low vacuum ESEM in comparison to high vacuum scanning electron microscopy (SEM) using the choroid plexus of chicken embryos as a model, an organ of the brain involved in the formation of cerebrospinal fluid in vertebrates. Specimens were fixed with or without heavy metals and examined directly or after critical point drying with or without metal coating. For wet mode ESEM freshly excised specimens without any pre-treatment were also examined. Conventional high vacuum SEM revealed the characteristic morphology of the choroid plexus cells at a high resolution and served as reference. With low vacuum ESEM of dried but uncoated samples the structure appeared well preserved but charging was a problem. It could be reduced by a short beam dwell time and averaging of images or by using the backscattered electron detector instead of the gaseous secondary electron detector. However, resolution was lower than with conventional SEM. Wet mode imaging was only possible with tissue that had been stabilized by fixation. Not all surface details (e.g. microvilli) could be visualized and other structures, like the cilia, were deformed. In summary, ESEM is an additional option for the imaging of bio-medical samples but it is problematic with regard to resolution and sample stability during imaging.

プラズマ溶射によって成膜された遮熱コーティング材の非弾性変形(<小特集>ガスタービン用遮熱/耐環境コーティング技術)

A fundamental study for an inelastic deformation of freestanding plasma-sprayed thermal barrier coatings (TBCs) has been conducted. Cantilever-type bending tests are carried out to obtain a stress-strain curve of the freestanding ceramic coating peeled from the TBC coated sample by an electrochemical treatment. In order to investigate about an inelastic deformation and its mechanism appeared in the sample, in-situ scanning electron microscope (SEM) observation is performed by means of a small tensile testing device that can be inserted into the SEM vacuum chamber. The bending test result indicated that the coating deforms with a nonlinear behavior under a monotonic loading and with a hysteresis loop under cyclic loading, in spite of that it is ceramic material. In-flight particle velocity in the spraying parameter affected the stress-strain curve significantly. In-situ SEM observation during the bending test revealed that sliding at boundary between splats plays an important role in an inelastic deformation.

Inelastic Deformation of Freestanding Plasma-sprayed Thermal Barrier Coatings

A fundamental study for an inelastic deformation of freestanding plasma-sprayed thermal barrier coatings (TBCs) has been conducted. Cantilever-type bending tests are carried out to obtain a stress-strain curve of the freestanding ceramic coating peeled from the TBC coated sample by an electrochemical treatment. In order to investigate about an inelastic deformation and its mechanism appeared in the sample, in-situ scanning electron microscope (SEM) observation is performed by means of a small tensile testing device that can be inserted into the SEM vacuum chamber. The bending test result indicated that the coating deforms with a nonlinear behavior under a monotonic loading and with a hysteresis loop under cyclic loading, in spite of that it is ceramic material. In-flight particle velocity in the spraying parameter affected the stress-strain curve significantly. In-situ SEM observation during the bending test revealed that sliding at boundary between splats plays an important role in an inelastic deformation.

Low Vacuum SEMs: Latest Generation Technologies and Applications

Abstract Since becoming popular more than a decade ago, low vacuum scanning electron microscopes (SEM) have continued to evolve. The latest systems offer uncompromised performance over an unprecedented range of sample chamber vacuum conditions. Instruments are now available that provide near-nanometer resolution in all vacuum modes and the ability to operate at pressures as high as 4000 Pascals (~30 Torr). Low vacuum operation eliminates much of the sample preparation required for conventional (high vacuum) SEM. Insulating samples can be imaged without conductive coatings. Wet, dirty, outgassing samples can be examined without drying and fixing. Systems can also be configured with a wide range of ancillary capabilities for imaging, analysis, and sample manipulation, including advanced secondary, backscattered, and transmitted electron detection, X-ray spectrometry, electron backscatter diffraction, and focused ion beam (FIB) manipulation. The current generation of systems combine speed, flexibility, repeatability, and ease of use, making them the ideal solution for any laboratory that must satisfy a wide range of imaging and analytical demands.

Imaging and Microanalysis in Environmental Scanning Electron Microscopy

A variety of gas cascade amplification and signal detection strategies have evolved for use in low vacuum and environmental scanning electron microscopy on poorly conducting specimens. These detectors have been optimized to perform well under various limitations on the range of gas pressure and working distance which may be imposed by experimental requirements. All of the detectors must produce high gains, low backgrounds, and generate a sufficient positive ion flux to the specimen to enable charge neutralization. The underlying principles of operation of each detector type are discussed, along with the range of experimental conditions appropriate to each.

Secondary electron imaging of nonconductors with nanometer resolution

The resolution of secondary electron (SE) images in scanning electron microscopy (SEM) is limited by the SE diffusion length. However, most materials are poor electrical conductors and in practice, resolution and image information content are often limited by charging. We demonstrate how charging can be eliminated as the resolution-limiting factor using a gaseous SE detector for magnetic immersion electron lenses. Charging is stabilized by ions produced in a magnetic field-assisted gas ionization cascade. The charge control self-regulation process does not quench the SE imaging signal, thereby enabling high resolution image contrast mechanisms that are suppressed in high vacuum SEM.

Charge and charging compensation on oxides and hydroxides in oxygen environmental SEM

Oxygen environment was applied to the scanning electron microscopy (SEM) analysis of insulating samples. In the high vacuum SEM, a local oxygen pressure was provided, and in the environmental SEM, oxygen atmosphere was used instead of water, the commercial mode. The charging effects in the SEM observation and component characterization of samples such as Al 2O 3, Al(OH) 3, Mg(OH) 2 and others can be eliminated or significantly reduced. The oxygen environment does not only provide a new approach to releasing the charging difficulty in the analyses using electron beam as a probe, but also provide an insightful hint to the understanding of the charging processes in general.