Historically, examining liquid samples under a transmission electron microscope (TEM) has been challenging for researchers. TEMs are extremely practical for observing fine details in isolated, dry, conditions, but the high-vacuum conditions in the microscope rule out liquid environments.
Studying samples in their native liquid environments holds a number of benefits, so this is a problem for researchers. Imaging samples utilizing in situ liquid cells with electron microscopy can give unique insights into biological systems, for example cells containing labeled proteins.
TEMs can also provide understanding of materials science processes, like electrochemical deposition and nanoparticle synthesis. The majority of real-world processes and materials happen in environments containing some moisture, so for researchers, discovering a solution to examine these samples with TEM can be crucial.
Specialized liquid cell in situ TEM holders permit researchers to observe samples in liquid environments within the TEM. They are unable to visualize materials that exist naturally in liquid environments, such as biological structures and organic compounds, without these holders.
Three of the most important benefits of in situ TEM holders for liquid samples are outlined below:
Nucleated nanoparticles suspended in liquid using in situ liquid cell TEM. Image courtesy Aidan Taylor, University of California, Santa Barbara.
1. Introducing Liquids into TEM Safely
In order to create and control the precise beam of electrons successfully, TEMs need vacuum conditions. The small wavelength of the accelerated electrons permits the TEM to gather fine detail of the sample but when the researcher is trying to study samples in real environments it causes a problem.
It is necessary to utilize a vessel that seals the liquid layer safely, whilst staying transparent to the electron beam, as water vaporizes under high vacuum. In situ TEM holders for liquid environments can do this, which enables the visualization of nanoscale processes in liquid settings.
2. Supporting EDS Compatibility
When examining samples under TEM, EDS can be extremely useful. Characteristic x-rays emitted from the sample are unique to each element, so researchers can identify the composition of samples. In the past it has been challenging to study samples in liquid environments whilst employing energy-dispersive x-ray spectroscopy (EDS); because of the closed-cell design, silicon chips and other materials can block x-rays emitted from samples from reaching the detector.
To permit EDS analysis, in situ TEM holders for liquid environments need a design that allows direct line-of-sight from the detector to the sample. The most recent designs are made of less material and feature a profile that contains the liquid layer without shadowing the EDS detector and maximizing counts per second (CPS).
Maximizing the line of sight from the sample to detector improves CPS
3. Acting as a Specimen Holder
A key challenge with studying liquid cells under a TEM is containing the liquid sample. They are very expensive, and if liquid escapes from the sample it could possibly destroy the equipment.
Specialized liquid TEM holders act as sealants, they encapsulate liquid reliably within the microscope. The holders utilize electron-transparent membranes to secure liquids so that viewing is not interrupted. This ability is also useful for the study of live samples because the holder encases them within an observable window.
In situ TEM holders for liquid environments have revolutionized the research possibilities of the transmission electron microscope in their relatively brief history. Researchers began using them to examine biological cells, supporting profound observation possibilities, for example complete eukaryotic cells in their native environments.
Scientists will continue to utilize liquid in situ TEM holders in the near future, to expand into new areas of material science, semiconductors, cancer research, battery research, structural biology, corrosion, and more.
This information has been sourced, reviewed and adapted from materials provided by Protochips.
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