Search

The present study extends the stereoscopic imaging principle for estimating the surface topography to two orientations, namely, normal to the electron beam axis and inclined at 70° as suited for EBSD analyses. In spite of the large angle difference, it is shown that the topography can be accurately determined using regularized global Digital Image Correlation. The surface topography is compared to another estimate issued from a 3D FIB-SEM procedure where the sample surface is first covered by a Pt layer, and its initial topography is progressively revealed from successive FIB-milling. These two methods are successfully compared on a 6% strained steel specimen in an in situ mechanical test. This analysis is supplemented by a third approach estimating the change of topography from crystal rotations as measured from successive EBSD images. This last technique ignores plastic deformation, and thus only holds in an elastic regime. For the studied example, despite the large plastic flow, it is shown that crystal rotation already accounts for a significant part of the deformation-induced topography. [ABSTRACT FROM AUTHOR]

We present a proof-of-concept attesting the feasability to obtain orientation maps of polycrystalline materials within a conventional Scanning Electron Microscope (SEM) using a standard goniometer and Back Scattered Electron (BSE) detector. The described method is based on the analysis of the contrast variation of grains due to the channeling of incident electrons on a rotating sample. On each pixel of the map, experimental intensity profiles as a function of the rotation angle are obtained and compared with simulated ones to retrieve the orientation. From first results on aluminum polycrystals, the angular resolution is estimated to be better than one degree. [ABSTRACT FROM AUTHOR]

In situ SEM mechanical tests are key to study crystal plasticity. In particular, imaging and diffraction (EBSD) allow microstructure and surface kinematics to be monitored all along the test. However, to get a full benefit from different modalities, it is necessary to register all images and crystallographic orientation maps from EBSD into the same frame. Different correlative approaches tracking either Pt surface markings, crystal orientations or grain boundaries, allow such registrations to be performed and displacement as well as rotation fields to be measured, a primary information for crystal plasticity identification. However, the different contrasts that are captured in different modalities and unavoidable stage motions also give rise to artifacts that are to be corrected to register the different information onto the same material points. The same image correlation tools reveal very powerful to correct such artifacts. Illustrated by an in situ uniaxial tensile test performed on a bainitic-ferritic steel sample, recent advances in image correlation techniques are reviewed and shown to provide a comprehensive picture of local strain and rotation maps. [ABSTRACT FROM AUTHOR]

This work presents recent advances in transmission scanning electron microscopy (t-SEM) imaging control capabilities. A modular aperture system and a cantilever-style sample holder that enable comprehensive angular selectivity of forward-scattered electrons are described. When combined with a commercially available solid-state transmission detector having only basic bright-field and dark-field imaging capabilities, the advances described here enable numerous transmission imaging modes. Several examples are provided that demonstrate how contrast arising from diffraction to mass-thickness can be obtained. Unanticipated image contrast at some imaging conditions is also observed and addressed. [ABSTRACT FROM AUTHOR]

Orientation contrast obtained by an in-lens secondary electron detector in a scanning electron microscope from electropolished/etched metals is reported. The imaging conditions for obtaining such orientation contrast are defined. The mechanism responsible for the formation of the orientation contrast is explained, and an application example of this new imaging method is given. [ABSTRACT FROM AUTHOR]

Abstract: We introduce diffracted electron tracking (DET), which combines two electron microscopy techniques, electron backscatter diffraction and the use of an environmental cell in a scanning electron microscope to measure changes in nanocrystal-orientation. The accuracy of DET was verified by measuring the motion of a flat gold crystal caused by the rotation or tilting of the specimen stage. DET was applied to measure the motion of semi-fixed gold nanocrystals in various environments. In addition to large motions induced in water environment, DET could detect small differences in the three-dimensional (3D) motion amplitude between vacuum environment and an Ar gas environment. DET promises to be a useful method for measuring the motion of single nanocrystals in various environments. This measuring technique may be used in a wide range of scientific fields; for example, DET may be a prospective method to track the single molecule dynamics of molecules labeled with gold nanocrystals. [Copyright &y& Elsevier]

Abstract: Nanomanipulation systems require accurate knowledge of the end-effector position in all three spatial coordinates, XYZ, for reliable manipulation of nanostructures. Although the images acquired by a scanning electron microscope (SEM) provide high resolution XY information, the lack of depth information in the Z-direction makes 3D nanomanipulation time-consuming. Existing approaches for contact detection of end-effectors inside SEM typically utilize fragile touch sensors that are difficult to integrate into a nanomanipulation system. This paper presents a method for determining the contact between an end-effector and a target surface during nanomanipulation inside SEM, purely based on the processing of SEM images. A depth-from-focus method is used in the fast approach of the end-effector to the substrate, followed by fine contact detection. Experimental results demonstrate that the contact detection approach is capable of achieving an accuracy of 21.5nm at 50,000× magnification while inducing little end-effector damage. [Copyright &y& Elsevier]

Abstract: Although conventional electron microscopy (EM) requires samples to be in vacuum, most chemical and physical reactions occur in liquid or gas. The Atmospheric Scanning Electron Microscope (ASEM) can observe dynamic phenomena in liquid or gas under atmospheric pressure in real time. An electron-permeable window made of pressure-resistant 100nm-thick silicon nitride (SiN) film, set into the bottom of the open ASEM sample dish, allows an electron beam to be projected from underneath the sample. A detector positioned below captures backscattered electrons. Using the ASEM, we observed the radiation-induced self-organization process of particles, as well as phenomena accompanying volume change, including evaporation-induced crystallization. Using the electrochemical ASEM dish, we observed tree-like electrochemical depositions on the cathode. In silver nitrate solution, we observed silver depositions near the cathode forming incidental internal voids. The heated ASEM dish allowed observation of patterns of contrast in melting and solidifying solder. Finally, to demonstrate its applicability for monitoring and control of industrial processes, silver paste and solder paste were examined at high throughput. High resolution, imaging speed, flexibility, adaptability, and ease of use facilitate the observation of previously difficult-to-image phenomena, and make the ASEM applicable to various fields. [Copyright &y& Elsevier]

Abstract: The low-voltage foil corrector is a novel type of foil aberration corrector that can correct for both the spherical and chromatic aberration simultaneously. In order to give a realistic example of the capabilities of this corrector, a design for a low-voltage scanning electron microscope with the low-voltage foil corrector is presented. A fully electrostatic column has been designed and characterised by using aberration integrals and ray tracing calculations. The amount of aberration correction can be adjusted relatively easy. The third order spherical and the first order chromatic aberration can be completely cancelled. In the zero current limit, a FW50 probe size of 1.0nm at 1kV can be obtained. This probe size is mainly limited by diffraction and by the fifth order spherical aberration. [ABSTRACT FROM AUTHOR]

Signal optimization for transmission Kikuchi diffraction (TKD) measurements in the scanning electron microscope is investigated by a comparison of different sample holder designs. An optimized design is presented, which uses a metal shield to efficiently trap the electron beam after transmission through the sample. For comparison, a second holder configuration allows a significant number of the transmitted electrons to scatter back from the surface of the sample holder onto the diffraction camera screen. It is shown that the secondary interaction with the sample holder leads to a significant increase in the background level, as well as to additional noise in the final Kikuchi diffraction signal. The clean TKD signal of the optimized holder design with reduced background scattering makes it possible to use small signal changes in the range of 2% of the camera full dynamic range. As is shown by an analysis of the power spectrum, the signal-to-noise ratio in the processed Kikuchi diffraction patterns is improved by an order of magnitude. As a result, the optimized design allows an increase in pattern signal to noise ratio which may lead to increase in measurement speed and indexing reliability. • Improved transmission Kikuchi diffraction holder design is shown. • Signal to noise ratio improvement via removal of in-chamber scattered electrons. • Radial power spectra are used for signal to noise ratio quantification. • Signal to noise ratio vs sample thickness is shown. [ABSTRACT FROM AUTHOR]

Abstract: A compact and easy-to-use wavelength dispersive X-ray spectrometer using a multi-capillary X-ray lens attached to a scanning (transmission) electron microscope has been tested for thin-film analysis. B–K spectra from thin-film boron compounds (B4C, h-BN, and B2O3) samples showed prominent peak shifts and detailed structural differences. Mapping images of a thin W/Si double-layer sample resolved each element clearly. Additionally, a thin SiO2 film grown on a Si substrate was imaged with O–K X-rays. Energy and spatial resolution of the system is also discussed. [Copyright &y& Elsevier]

Abstract: Observations of carbon nanotubes under exposure to electron beam irradiation in standard transmission electron microscope (TEM) and scanning electron microscope (SEM) systems show that such treatment in some cases can cause severe damage of the nanotube structure, even at electron energies far below the approximate 100keV threshold for knock-on damage displacing carbon atoms in the graphene structure. We find that the damage we observe in one TEM can be avoided by use of a cold finger. This and the morphology of the damage imply that water vapour, which is present as a background gas in many vacuum chambers, can damage the nanotube structure through electron beam-induced chemical reactions. Though, the dependence on the background gas makes these observations specific for the presently used systems, the results demonstrate the importance of careful assessment of the level of subtle structural damage that the individual electron microscope system can do to nanostructures during standard use. [Copyright &y& Elsevier]

Abstract: A new contrast mechanism is reported that visualizes doped areas in semiconductors in very low-energy electron micrographs. The method is based on the use of the cathode lens principle in a scanning electron microscope, in order to form a primary beam of energy in units of electron volts. Below about 3eV the doped areas exhibited a strong contrast, the explanation of which is based on the injection and recombination of electrons and on the ability of the small negative surface charge thereby created to decrease the very low landing energy of incident electrons near enough to conditions of total reflection. This imaging method enables one to study the charge injection effects in semiconductors, and in view of its high contrast the mode may offer fast image acquisition, while the extremely low-electron energy ensures operation free of any radiation damage to the specimen. [Copyright &y& Elsevier]

The use of electron mirrors in aberration correction and surface-sensitive microscopy techniques such as low-energy electron microscopy has been established. However, in this work, by implementing an easy to construct, fully electrostatic electron mirror system under a sample in a conventional scanning electron microscope (SEM), we present a new imaging scheme which allows us to form scanned images of the top and bottom surfaces of the sample simultaneously. We believe that this imaging scheme could be of great value to the field of in-situ SEM which has been limited to observation of dynamic changes such as crack propagation and other surface phenomena on one side of samples at a time. We analyze the image properties when using a flat versus a concave electron mirror system and discuss two different regimes of operation. In addition to in-situ SEM, we foresee that our imaging scheme could open up avenues towards spherical aberration correction by the use of electron mirrors in SEMs without the need for complex beam separators. • An electrostatic electron mirror in an SEM reflects the beam towards the sample. • This imaging scheme could be beneficial to the in-situ SEM community. • We compare the micrographs when using a flat mirror and a curved aperture mirror. • This imaging scheme could lead to simpler mirror aberration correction in SEMs. [ABSTRACT FROM AUTHOR]

Here we demonstrate the use of nanofabricated grating holograms to diffract and shape electrons in a scanning electron microscope. The diffraction grating is placed in an aperture in the column. The entire diffraction pattern can be passed through the objective lens and projected onto the specimen, or an intermediate aperture can be used to select particular diffracted beams. We discuss several techniques for characterizing the diffraction pattern. The grating designs can incorporate features that can influence the phase and intensity of the diffracted SEM probe. We demonstrate this by producing electron vortex beams. • We demonstrate electron beam shaping in a conventional scanning electron microscope. • We developed a method to characterize the shape of the structured electron beam. • As an example, we produce and characterize electron vortex beams. • This opens the door to develop new techniques in a scanning electron microscope. [ABSTRACT FROM AUTHOR]

A monolithic active pixel sensor based direct detector that is optimized for the primary beam energies in scanning electron microscopes is implemented for electron back-scattered diffraction (EBSD) applications. The high detection efficiency of the detector and its large array of pixels allow sensitive and accurate detection of Kikuchi bands arising from primary electron beam excitation energies of 4 keV to 28 keV, with the optimal contrast occurring in the range of 8–16 keV. The diffraction pattern acquisition speed is substantially improved via a sparse sampling mode, resulting from the acquisition of a reduced number of pixels on the detector. Standard inpainting algorithms are implemented to effectively estimate the information in the skipped regions in the acquired diffraction pattern. For EBSD mapping, an acquisition speed as high as 5988 scan points per second is demonstrated, with a tolerable fraction of indexed points and accuracy. The collective capabilities spanning from high angular resolution EBSD patterns to high speed pattern acquisition are achieved on the same detector, facilitating simultaneous detection modalities that enable a multitude of advanced EBSD applications, including lattice strain mapping, structural refinement, low-dose characterization, 3D-EBSD and dynamic in situ EBSD. • A monolithic active pixel sensor based direct detector is implemented for EBSD. • High resolution pattern and high mapping speed can be achieved simultaneously. • The detector allows sensitive and accurate band detection from 4 keV to 28 keV. • Sparse sampling on the detector enables high speed pattern acquisition. • Reliable indexing is demonstrated using pattern inpainting and spherical indexing. [ABSTRACT FROM AUTHOR]