cryoTEM Electron Diffraction

The JEOL JEM 3200FS is a 300 kV transmission electron microscope (TEM) equipped with a thermal field emission gun (FEG) and an anti-contaminator that allows it to record images when the specimen is held at liquid nitrogen temperatures. Our 3200FS is also equipped with an in-column energy filter and the hardware necessary for bright field and high angle annular dark field scanning transmission electron microscopy (BF- and HAADF-STEM). Details of the instrument itself can be found here.

The folllowing paragraphs briefly describe the types of imaging that this hardware allows and provide links to further information about each of them.

Transmission Electron Microscopy (TEM) - Transmission electron microscopes form images using an electron beam in a manner analogous to the way optical microscopes form images using visible light: lenses focus and magnify the beam of light (or electrons) after it has been transmitted through a thin specimen and eventually project a final image onto some sort of imaging device. Most modern electron microscopes operate over a magnification range from as low as 50x up to several 1,000,000x, often with the best images recorded in the range of 5000 to 100,000x due to limitations of the electron microscope and/or its operating environment. This type of operation is sometimes referred to as conventional TEM (cTEM) to distinguish it from imaging modes that put more stringent requirements on the instrument itself or its environment, or that require additional hardware. In this most simple mode of operation (pioneered in the 1930's by the likes of (further info...)

Scanning TEM (STEM) - STEM imaging is fundamentally different from cTEM and its related imaging modes, and requires additional hardware that is not normally available on standard transmission electron microscopes. When forming a STEM image, the electron beam is focused on the specimen to a small point (frequently as small a point as possible) and moved across the specimen in a raster pattern. An image is formed by counting the scattered electrons at every point in this raster pattern, and assembing the raw electron counts into an image. The movement of the focused electron beam is controlled by additional scan coils (affecting beam shift) which operate between the C2 condensor lens and the specimen area. STEM imaging requires detectors that are very different from photographic film or CCD cameras, and that count the electrons scattered over (further info...)

High Resolution TEM (HRTEM) - HRTEM is identical to TEM imaging except that the magnifications used are high enough to see easily the lattice spacing of inorganic materials (typically on the order of several Å). Although such lattice spacings can easily be recorded onto film at moderate magnifications (the 3.4 Å spacing between graphite layers can be recorded onto film at magnifications as low as 10,000-15,000x), CCD cameras and much higher magnifications (usually above 200,000 or 300,000x at the plane of the imaging device) allow the user to control the defocus much more easily and produce the best HRTEM images. Visualization of these atomic spacings requires a more stable goniometer, a brighter electron source and more stable electronics than are found in most electron microscopes not designed for HRTEM. Virtually all recently built intermediate voltage instruments (i.e., electron microscopes operating at 200, 300 and 400 kV) meet the necessary requirements for HRTEM, and it is more often (further info...)

Energy Filtered TEM (EFTEM) - Image formation using EFTEM is the same process that is found in cTEM and HRTEM imaging: electron lenses are used to magnify and focus the electron beam after it has passed through the specimen. The difference between EFTEM and these other TEM imaging techniques is that for EFTEM imaging, an "energy filter" is placed between the specimen and the plane where the final image is recorded. Since some of the electrons in the electron beam will lose energy when they interact with the specimen, the energy filter is used to select for image formation only the electrons that have a defined energy spread. Energy filters can be used to form images using only those electrons that (further info...)

cryoTEM - cryoTEM (or simply cryo-electron microscopy - cryoEM) is a buzzword that encompases the field of structural biology where the principle experimental technique is TEM followed by extensive image processing. The "cryo" designation in cryoTEM arises from the observation made in the 1980's that the extensive radiation damage to unstained biological materials due to the electron beam can be lowered to managable levels by holding the specimen near liquid N2 temperatures and using "minimal dose imaging techniques" during the image recording process. These innovations have allowed structural biology using the electron microscope to begin to fullfill the promise of near atomic resolution structures of biological macromolecules (further info...)

Electron Diffraction - Electron diffraction is clearly not an imaging mode for an electron microscope. It also differs significantly from the techniques listed under nanoscale analysis in that every TEM is capable of electron diffraction (i.e., no additional equipment such as scanning coils, annular detectors or an energy filter is needed). Thus electron diffraction falls into the grey area outside of imaging or (further info...)