By making visible what used to be invisible, electron microscopes have expanded our understanding of the world exponentially. The first electron microscope was capable of 400x magnification and was created in 1931. Ernst Ruska and Max Knoll, it’s inventors, forever changed the way scientists image materials, and won the Nobel Prize for their work.
Their breakthrough was to utilize electrons rather than photons to capture images of materials. The wavelength of energized electrons is 50,000 times smaller than visible light photons, so electron microscopes can resolve even fine detail at magnifications over 10,000x. The Transmission Electron Microscope (TEM) instrument is optimized to permit exceptionally high magnification and resolution, which allows researchers to observe samples at the atomic level.
A TEM uses an electromagnetic lens to focus electrons into a thin beam, similar to an optical microscope. This beam travels through the sample at nearly the speed of light and – depending on the sample’s state, thickness, structure, and composition – induces a abundance of photon, electron, and phonon scattering events.
The unscattered electrons in the beam hit a fluorescent screen at the bottom of the microscope after passing through the sample, generating a shadow image of the sample. A photograph is then collected of the shadow image and examined further from there.
Since 1931 the electron microscope has evolved massively; magnification levels have grown, capabilities have expanded, and the experiments undertaken have become more complex. Through the capabilities of in situ TEM, new technology has been created that means the microscope can be turned into a nanoscale experiment chamber.
TEMs have a wide range of capabilities, they can be used for applications in semiconductor, biology, materials, and composition characterization research. They also have a number of limitations. Some of the constraints of TEM are shown below, as well as how in situ TEM addresses these challenges:
The Current Limitations of TEM
The modern transmission electron microscope can be utilized for 3D mapping of nanoscale samples through tomography, high-resolution imaging, analysis of the thermal and electronic state of a sample through Electron Energy Loss Spectroscopy (EELS), and elemental analysis with Energy Dispersive X-ray Spectroscopy (EDXS). TEM is advanced and capable of many types of experiments, but it does have some limitations.
One of the biggest limitations of TEM is that samples are totally static, and also restricted to the ultra-high vacuum conditions inside the TEM. Materials do not exist like this in the natural world – energized and dynamic reactions underpin the lives of all materials, regardless of their properties or use. These natural interactions cannot be copied with a traditional TEM, so the findings researchers can obtain about real nanoscale processes are limited.
TEMs are precise, expensive, and sensitive equipment, meaning they are difficult to use and limiting their use to industrial R&D and academic research. In addition, the samples observed under TEMs must be polished carefully to extremely thin dimensions which are 1,000 times thinner than a human hair – for proper observation. Usually, researchers create such thin samples by using successively finer polishing media, which can take hours or days to complete successfully.
The Advantages of In Situ TEM
In situ transmission electron microscopy is a method that permits researchers to study samples under real-world conditions, in real-time. As in situ tools can negate the vacuum-condition limitation of TEMs, researchers can extract much more data from their samples than they can with traditional microscopy.
A challenge for this technique is sample preparation for in situ TEM. The same challenges in sample preparation can be compounded by the requirement to place samples within the operating area of the in situ holder. However, a single sample can be used to conduct dozens of different in situ experiments – improving lab productivity by generating more results, while multiple samples are often needed for imaging in traditional TEM. Furthermore, in situ TEM can be utilized for energy-dispersive X-ray spectroscopy (EDS) analysis. This relies on X-ray excitation and permits detailed chemical characterization of samples.
In situ TEM became far more accessible recently, through the utilization of Micro-Electrical-Mechanical-Systems (MEMS) devices to control sample conditions on a silicon chip of only few millimeters. These chips are placed within the TEM holder and depending on what the researcher is aiming to study, are specialized to produce various natural-world conditions inside of the TEM. As an example, in situ TEM holders can apply atmospheric pressure, create heat conditions, and allow for the study of liquid microscopy.
The Applications and Uses of In Situ TEM
In situ TEM techniques complement the aims of research fields across the scientific discipline, ranging from life science to material science. In situ TEM has been employed in the life sciences, for studying cellular depredation, protein transport, structural biology, cancer therapies, drug delivery, and particle reconstruction. In material science, in situ TEM research is often utilized to study corrosion, catalysts, mixtures and colloids, batteries, solar cells, metals and ceramics, electronic devices, nanomaterials, polymers and semiconductors, and more.
Researchers can control the environments they observe their samples under with MEMS devices and in situ TEM holders, making it possible to perform real experiments within the TEM. In situ TEM will continue to enable new types of research in the future, and will produce further scientific discoveries.
Where TEM has limitations, in situ TEM expands upon them; a TEM is an observational tool that is designed primarily to capture a “snapshot” of a static sample, but in situ methods add experimental capabilities to the TEM, which makes it a powerful tool for many scientists.
This information has been sourced, reviewed and adapted from materials provided by Protochips.
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