SCANNING TRANSMISSION ELECTRON MICROSCOPY
Scanning Transmission Electron Microscopy (STEM) imaging differs from TEM in that, as opposed to the entire specimen being simultaneously illuminated by the electron beam, the beam is reduced to a much smaller diameter and scans in a raster pattern across the specimen. The scanning transmission technique was not fully developed until the 1970’s, where a modern STEM was created by Albert Crewe at the University of Chicago by first creating the FEG (Field Emission Gun) and adding a high-quality objective lens. Improvements have been ongoing regarding this technique and now it is particularly useful when viewing stained samples and when samples are thicker than that required by TEM.
Conventional STEM Microscopes
Although not very common, purely dedicated STEM microscopes are manufactured and are just as large and expensive as conventional TEM’s. The more common practice is to equip additional scanning coils or detectors to an already very bulky and complex TEM microscope, thereby enabling the microscope to switch between imaging modes. To proficiently image in STEM mode, stable room conditions must be invoked, meaning no vibrations, no temperature fluctuations, and no acoustic or electromagnetic waves must be present.
How LVEM does STEM
Both the LVEM5 and LVEM25 models have the ability and capacity for the STEM imaging option to be added to their base configurations. Unlike conventional TEM’s with STEM addons, the LVEM microscopes do not require any such special treatment like anti-vibration platforms or temperature controlled rooms. Detectors are added to pick up the transmitted electrons from the sample, and an image is formed via a photomultiplier. The low-voltage inherent with the LVEM microscopes ensure strong interaction with samples allowing for higher contrast imaging in STEM mode. The LVEM’s are 3-in-1, cost-effective options that offer more imaging capabilities for less space and money. For more details, please visit the product details pages for the LVEM5 an the LVEM25.
LVEM Samples and Applications for STEM
|EXAMPLES OF STEM SAMPLES|
|Biologic thin sections||Nanotubes|
|Polymer thin sections||Nanoparticles|
|Polymer nanoparticles||Quantum dots|
|EXAMPLES OF STEM APPLICATIONS|
|Structure characterization of semiconductors||Structure characterization of nanowire catalysts|
|Structure characterization of 2D bulk materials||Study of ultrastructure|
|Particle characterization||Particle morphology|
|Phase behaviour||Phase composition|
|Crystal Structure||Observation of silicon transistors|
LVEM Sample Prep for STEM
Bulk materials like polymers or biological thin sections are generally required to be thin-sectioned for TEM analysis. The LVEM25 can work with thin sectioned materials prepared in the same way as that of a conventional TEM, at around 100nm. For best results with the LVEM5, thin sections need to be in the range of 50 nm or thinner. As is the case with both LVEM units, the staining of samples is not required but can still be accommodated.
Particulate materials such as nanoparticles, nanotubes, viruses and DNA can easily be deposited at the appropriate concentration onto a TEM grid with a carbon support. For more details, please visit our page on sample preparation.
Visit our photo gallery for a better look at what scanning electron microscopy within the LVEM5 microscope can do for you.