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Multimodal TEM analysis enabled by complementary transmission electron microscope techniques
Atomic structure and composition ultimately dictate macroscopic properties and behavior, whether in biological samples or novel materials. Leading research and development is increasingly looking for information at these scales to finely tune next-generation materials, therapeutics, and other advancements that are making our world healthier, cleaner, and safer.
Transmission electron microscopy (TEM) is one of the highest resolution imaging techniques available, capable of regularly attaining sub-nanometer, or even atomic, resolution information for an exhaustive variety of samples. Modern TEM instruments incorporate a range of components and detectors to enable a variety of spectroscopic techniques within the microscope, including energy-dispersive X-ray spectroscopy (abbreviated as either EDX and EDS), electron energy-loss spectroscopy (EELS), and more.
Additionally, the quality of TEM data is often highly dependent on the quality of the samples being analyzed, which must be thin enough for electrons to pass through. TEM sample preparation is therefore a critical technique that dictates the success of all subsequent TEM characterization and analysis.
Here we present just a few of the most critical and widely known techniques related to transmission electron microscopy. For a closer look at specialized TEM techniques relevant to various disciplines, visit the corresponding materials science and life sciences pages below.
TEM sample preparation
The preparation of high-quality samples is the foundation of any successful TEM investigation. It can also be highly challenging, requiring time, experience, and a range of skills.
Many “classical” methods used to prepare thin TEM samples are slow, often requiring many hours or even days of effort by highly trained personnel. This is further complicated by the variety of different materials that can be investigated. Thermo Scientific focused ion beam scanning electron microscopes (FIB-SEMs) are designed to simplify and accelerate this process, providing advanced in-situ sample preparation. These advanced instruments incorporate automation and software algorithms, reducing the training needed so that even non-specialists can produce high-quality TEM samples in a robust and reliable manner.
Aluminum sample showing an array of TEM lamella prepared with FIB-SEM.
Scanning transmission electron microscopy
Scanning transmission electron microscopy (STEM) combines the principles of TEM with scanning electron microscopy (SEM).
Like TEM, STEM requires very thin samples and looks primarily at beam electrons transmitted by the sample. Just as in SEM, STEM also scans a very finely focused beam of electrons across the sample in a raster pattern. Interactions between the beam electrons and sample atoms allows for simultaneous acquisition of multi-modal data, which is correlated with beam position to build a virtual image in which the signal level at any location in the sample is represented by the contrast of the image.
The primary benefit of STEM over conventional SEM imaging is an improvement in spatial resolution. One of the principal advantages of STEM over TEM is that it enables the use of other signals that cannot be spatially correlated in TEM, such as characteristic X-rays (for EDS analysis) as well as EELS spectra.
With STEM, extremely localized analytical data can be collected for your sample. This includes large-area, high-resolution EDS maps, probing of oxidation states using EELS, and atomic-resolution imaging of material interfaces.
Energy-dispersive X-ray spectroscopy
EDS enables in-depth elemental analysis of materials within an electron microscope, providing oftentimes crucial complementary information to the high-resolution imaging generated by transmission electron microscopy.
When electrons hit a material, characteristic X-rays are generated by the individual atoms in the material. With the help of an EDS detector, it is possible to record these element-specific X-rays, producing a spectrum that shows the sample’s elemental makeup. Enabled by advancements in EDS detectors, both qualitative as well as quantitative compositional insights can now be obtained reliably with EDS, even for light elements.
EDS is widely used in materials science, chemistry, and geology research, and is even finding applications in pharmaceutical research, making it a useful addition to any shared, inter-disciplinary facility.
Cell and tissue imaging with TEM
Transmission electron microscopy offers high-resolution visualization of internal cellular structures, including membranes, organelles, and protein complexes. The addition of Thermo Scientific software solutions specifically designed for TEM, provide easy-to-use workflows for large-area imaging of cells and tissues, 3D imaging of internal cellular structures at nanometer resolution, and correlative light and electron microscopy (CLEM) studies.
Cryo-electron microscopy
Cryo-electron microscopy (cryo-EM) describes a collection of techniques used to analyze cryogenically frozen samples in specially designed transmission electron microscopes (cryo-TEMs). Recent advancements, including improved sample preparation tools, detectors, and analytical computer algorithms, have enabled the determination of 3D cryo-EM structures down to atomic resolution.
While cryo-EM is sometimes used synonymously with the most popular technique, single particle analysis, there are a suite of analytical methods that can be performed in a cryo-TEM, including cryo-electron tomography and microcrystal electron diffraction.
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