Over the last decade, electron microscopy has evolved into one of the most powerful tools for evaluating nanomaterials at the atomic scale. Ultimately, the goal is to obtain the three-dimensional structure, which is quite difficult since microscopic particles are typically susceptible to electron irradiation. Nonetheless, quantifying individual atomic positions is critical for understanding the relationship between the composition and physicochemical properties of these (nano)materials.
In this article, we’re going to highlight the recent breakthroughs in electron microscopy and describe the challenges we can expect to meet later on as the opportunity to push the limits of electron microscopy even further becomes even more apparent.
Before we discuss the advancements, let’s first review the advantages and disadvantages of electron microscopy that are already established.
Advantages of Electron Microscopy
Electron microscopy has several significant advantages. Among these are:
● Diverse Applications
Electron microscopy has a broad array of applications in various fields of research, including biomedical science, technology, industry, and chemistry. Some of the applications include semiconductor inspection, computer chip manufacturing, quality control and assurance, atomic structure analysis, and medication development.
● Magnification and Higher Resolution
It’s important to note the edge of electron microscopes over light microscopes, like how are magnification and resolution different in the former. Electron microscopy utilizes electrons instead of light waves, thus can be used to examine structures that aren’t visible otherwise. The resolution of electron microscopy images is up to 0.2 nm, which is 1000 times more detailed than light microscopy.
● High-quality Imaging
With sufficient training, an electron microscope end-user may utilize the system to generate high-quality images of structures that are rich in detail, showing intricate formations that other techniques may fail to reproduce.
Disadvantages of Electron Microscopy
Various limitations may suggest that alternative techniques, particularly light microscopy and super-resolution microscopy, are more beneficial to end-users than electron microscopy. They include the following:
Despite technological advancements, electron microscopes are still massive, bulky pieces of equipment that take up a lot of space in a laboratory. Also, since they’re sensitive, magnetic fields and vibrations from other lab equipment may interfere with their performance. If you’re looking to install an electron microscope in your laboratory, this must be taken into consideration.
Electron microscopes are highly-specialized equipment that comes with a hefty price tag. Since most projects are capped in terms of resources, procuring an electron microscope in the research may prove counterproductive. However, operating expenses can be comparable to alternatives such as confocal light microscopes. Therefore, investing in a basic electron microscope is still worthwhile even if financial concerns are significant in decisions against using the technology.
Electron microscopes require professional operators, who must go through years of training to efficiently use the equipment and technology.
These elements might be present in the generated image. Artifacts are remnants of sample preparation that require a professional understanding of sample preparation techniques to avoid.
● Black and White Images
An electron microscope can only produce black and white images. Therefore, resulting images must be artificially colorized.
● Inability to Analyze Live Specimens
Samples must be examined in a vacuum since other molecules easily disperse electrons in the air. This means that researchers cannot use this method to study live specimens. As a result, biological interactions cannot be viewed properly, limiting the applicability of electron microscopy in biological research.
The following are breakthroughs in electron microscopy that demonstrate how state-of-the-art electron microscopy coupled with advanced computing techniques will investigate the 3D atomic structure of nanoparticles and microclusters.
Qualitative to Quantitative Electron Microscopy
Aberration-corrected high-angle annular dark-field imaging (HAADF) generates atomically resolved incoherent images that researchers can utilize for visual 2D structural and chemical characterization. These images can serve as input for quantitative interpretation methodologies. Over the past decade, innovative image processing techniques that can improve the signal-to-noise ratio (SNR) of experimental images or be used to precisely calculate atomic column positions and image intensities have become possible.
Improved Signal-to-Noise Ratio through Template Matching
Nanostructures are typically sensitive to electron irradiation, and the electron microscopy observation period is usually limited to a few seconds, making their characterization quite complicated. It is critical to keep the electron dose to a minimum to minimize the effect of the beam and reduce any structural modifications. Unfortunately, this results in images with a low signal-to-noise ratio (SNR).
A template matching method can be applied to the gathered data to address this issue. This procedure makes it easy to locate certain regions in an image that corresponds to a pre-defined template.
Electron Tomography of Nanoparticles at Atomic Resolution
Quantitative methods, as previously discussed, allow for the investigation of nanostructures at the atomic scale. High-angle annular dark-field (HAADF) images, on the other hand, are 2D projections of 3D objects. This limitation can be circumvented using electron tomography. Images of the object are captured at varied tilt angles in this case.
After precisely aligning the captured images in relation to each other and along a common axis, a 3D reconstruction of the item can be generated by inputting them as part of a mathematical algorithm.
3D Atomic Resolution of Heterogeneous Nanostructures
The inclusion of several elements in the same nano-object has previously been identified as a path toward synthesizing nanostructures with improved features such as stability, catalytic activity, and electrical response. However, atom-counting applications on hetero-nanostructures are more complex since the HAADF image intensities depend on thickness and composition.
In compositional studies, a linear dependency on concentration is frequently assumed, although slight changes in the atom ordering in the column might alter the scattering cross-section. As a result, a quantitative approach capable of recognizing all possible 3D column configurations is required.
From Small to Smaller and Smallest
Recent breakthroughs in nanotechnology enable the creation of smaller and more complex nanostructures, forcing us to push the limits of electron microscopy even further.
Such complex nanomaterials include ultra-small sub-nanometer nanoparticles or clusters. Although there’s a clear requirement for a thorough 3D characterization of such materials since they can no longer be regarded as periodic objects, this is far from being simplistic.
Despite electron microscopy’s historical successes, the scientific motivation for boosting spatial resolution alone as a future approach is still inadequate. There’s a significant scientific interest to achieve atomic or molecular resolution assessments of functionality at short time frames and in actual environments.
As a result, future opportunities will include 3D imaging of defects, dopants, impurities, and vacancies, as well as chemically determining these impurities in the energy domain to associate their behavior with distinct electron, orbital, and spin states. We can now image atoms and acquire single atom spectra in steady states and vacuum using ultramodern electron microscopy.
Future breakthroughs will necessitate atomic-level imaging and spectroscopy. For instance, in liquid, gas, during electrochemical deposition, in-situ and in-operando oxidation and corrosion, and under different applied stimuli.
Developing a new generation of electron microscopes with innovative fs to ps temporal-resolution and functionality for measuring materials functionality and equating structure across a broad range of length scales from atomic- to nano- and meso-scale will have a significant impact on the research areas at the heart of many cross-cutting disciplines.