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Multimodal materials analysis with transmission electron microscopes
The structure, behavior, and properties of materials are determined by their elemental composition and the positioning of their atoms. High-resolution transmission electron microscopy (TEM) is capable of visualizing the atomic-scale organization of atoms in a broad range of samples, helping to guide material development and optimization.
This page explores some of the most prominent techniques utilized within a transmission electron microscope to obtain multimodal atomic-scale information, including scanning transmission electron microscopy (STEM), which combines the benefits of TEM and scanning electron microscopy (SEM). Specialized TEM techniques can also be used to image challenging samples, such as Lorentz electron microscopy for the non-destructive imaging of magnetic materials (which are typically incompatible with TEM) or differential phase contrast imaging (DPC), which can show the electric and magnetic fields of a sample at nanoscale.
Frequently, the structural information provided by high-resolution imaging must be paired with chemical characterization to obtain truly complete information about a sample. In TEMs, this can be accomplished through a combination of energy dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS).
With high-resolution imaging, atomic-resolution data, and information on chemical composition, TEM and STEM provide invaluable insights into the structure and properties of materials at the nanoscale and beyond.
TEM sample preparation
The preparation of a high-quality TEM sample is a critical foundation for successful TEM analysis. This can, however, be a challenging undertaking, requiring substantial experience and skill. Additionally, many “classical” methods used for sample thinning are quite slow, requiring many hours or even days of effort by highly trained personnel. This is further complicated by the variety of different materials that could potentially be investigated with transmission electron microscopy.
Thermo Scientific focused ion beam scanning electron microscopes (FIB-SEMs) are designed to simplify and speed up TEM sample preparation. These instruments enable rapid and reliable in-situ sample preparation with minimal training thanks to specialized software and automation algorithms.
Aluminum sample, where a 5x6 array of TEM lamellae has been prepared with Thermo Scientific AutoTEM Software. The lamellae were undercut and ready for lift-out in 6 hours.
High-resolution TEM and STEM
High-resolution transmission electron microscopy provides exceptional details on the atomic organization of materials. However, to obtain this information reliably, it is necessary to use exceedingly thin (i.e., <10 nm thick) samples and specialized software to interpret the images. To alleviate this often time-consuming and demanding process, alternative methods have been developed, such as high-resolution imaging with scanning transmission electron microscopy.
STEM raster-scans the sample surface pixel by pixel with a finely focused electron beam; the electrons are deflected by the composition of the sample and a detector assigns an intensity based on this sample interaction at each pixel. Several images can be obtained in on shot, thereby providing information about various aspects of the sample. The most common property of interest is atomic positions within the sample; this is much more straightforward in STEM mode, as the sample does not need to be extremely thin, and software solutions can help to record focused images. Additionally, the images are directly interpretable with STEM, meaning no software treatment is necessary afterwards.
Energy-dispersive X-ray spectroscopy
Energy-dispersive X-ray spectroscopy (EDS) is a microanalysis method that provides in-depth elemental and phase analysis at the atomic scale. When electrons hit a material, characteristic X-rays are generated. With the help of an EDS detector, it is possible to record these X-rays, producing a spectrum that shows the sample’s elemental composition at the position where the electron interaction occurred. This information is complimentary to TEM imaging and is often critical for a full understanding of materials and their properties.
Modern advances in EDS analysis have made this technique capable of providing both qualitative and quantitative insights into chemical components. Thermo Scientific instruments combine multiple EDS detectors and utilize unique windowless detectors for reliable, quantitative EDS analysis regardless of atomic number, even for light elements.
Electron energy-loss spectroscopy
Electron energy-loss spectroscopy (EELS) is an elemental and structural characterization technique that can fingerprint a material based on its chemical composition. EELS fine structure provides access to a broad range of detailed material information including chemical bonding, oxidation states, and even electronic properties.
Advanced TEM instrumentation, such as the Thermo Scientific Talos (S)TEM, is designed to support this critical technique through components like the X- CFEG electron source, which is well-suited for EELS characterization, as it provides high brightness and stability for high-energy-resolution imaging and analysis. These systems allow you to perform ultra-high-resolution EELS characterization, generating valuable structural, elemental, and chemical information at the atomic scale.
An atomic-resolution elemental map of a BaTiO₃/SrTiO₃ interface, produced with core-loss EELS analysis. Barium = blue, strontium = red, and titanium = green. Imaged at 80 kV (60 pA) with a 1 eV full-width at half maximum (FWHM) electron probe (49 x 49 pixels, <90 seconds).
Mapping of surface phonon modes in a magnesium oxide crystal at 60 kV using a monochromated electron probe with a FWHM electron probe of <30 meV. Specimen and analysis courtesy of Isobel Bicket and Prof. Gianluigi Botton, The Canadian Centre for Electron Microscopy, McMaster University.
In-situ TEM
Direct, real-time observation of microstructural changes with electron microscopy can reveal the underlying principles of dynamic processes such as recrystallization, grain growth, and phase transformation during heating, cooling, and wetting. In-situ TEM experiments that require thermal testing need accurate data collection, not only at one specific point in time but consistently across the entire experiment. Thermo Fisher Scientific offers a MEMS-device-based, single-tilt TEM sample holder that enables in-situ atomic-resolution imaging at elevated temperatures.
Multi-scale analysis with FIB-SEM
Focused ion beam scanning electron microscopy (FIB-SEM) is a highly complementary technique to TEM that enables the multi-scale characterization of materials, providing the broader context for the high-resolution, targeted data obtained with TEM. SEM offers nanoscale surface analysis, while the FIB is used for sample milling, including serial sectioning, sample lamella preparation, etc.
Focused ion beams can consist of either a liquid metal or plasma ion source (PFIB), both of which can be better suited for certain materials and applications. Recent PFIB-SEM instruments from Thermo Fisher Scientific even incorporate a femtosecond laser for rapid sample preparation, cross-sectioning, and serial sectioning. Following this sample preparation in the FIB-SEM tool, the specimens are transferred to a TEM for atomic-scale characterization of the sample’s elemental and structural composition.
Automated Particle Workflow
Nanoparticles are a critical class of materials with substantially different properties compared to their macroscopic counterparts. They are vital across a number of industries, from food additives, to high-performance metals, to catalysts used for process optimization. Enhancing and characterizing nanoparticles necessitates the exploration and manipulation of structures at the nanoscale. This includes the quantification of composition, size, and shape, which furthers our understanding of the particles and their relationship to performance, quality, and safety at the macro-scale.
The Thermo Scientific Automated Particle Workflow (APW) offers large-area, high-resolution imaging and data acquisition at the nanoscale with on-the-fly processing.
Imaging magnetic materials
Lorentz electron microscopy enables the imaging of magnetic materials without compromising the magnetic structure of the sample. It can be performed either in TEM or STEM mode with extremely high resolution and true field-free conditions across the entire sample.
High-angle annular dark-field (HAADF) STEM and differential phase contrast images of a cobalt film acquired in zero field.
Differential phase contrast imaging
Modern electronics research relies on nanoscale analysis of electric and magnetic properties. Differential phase contrast STEM (DPC-STEM) can image the strength and distribution of magnetic fields in a sample and display the magnetic domain structure.
The technique simultaneously acquires four signals from a dark-field detector to measure shifts in the observed diffraction pattern. The relative strength and orientation of the magnetic field in each domain indicates what type of domain walls (Bloch walls) is present, the wall thickness, and observed defects and variation in the wall structure, making it possible to understand how these factors would affect the overall performance of the material. Various other visualizations can highlight different aspects of the magnetic structure.
Because this technique works with in-focus STEM images and provides quantitative information about the field strength as well as the field orientation, it is a powerful technique for the visualization of magnetic structure. Live DPC acquisition is fully integrated into Thermo Scientific Velox Software.
DPC-STEM is not just limited to magnetic samples. Polarized materials and films exert a similar influence on the electron beam as materials containing an intrinsic electric field. DPC- STEM can reveal critical information on the charge distribution of bonds across interfaces and at surfaces, potentially revealing new aspects of a material.
DPC-STEM can provide quantitative information about the field orientation in a magnetic structure. Here, the field orientation for a hexaferrite sample is shown using a color-wheel representation. Sample courtesy of H. Nakajima and S. Mori, Osaka Prefecture University.
Arrow map representations of the strength and orientation of the magnetic field in a hexaferrite sample. Sample courtesy of H. Nakajima and S. Mori, Osaka Prefecture University.
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