In the electron microscope (EM) the image is created by the interaction of electrons with the object.
In the scanning electron microscope (SEM) the electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image.
Characteristic are images of surfaces with a high depth of focus.
Usual resolution: 1-30nm (depending on the instrument). The limit is currently approx. 0.4 nm.
Usual magnifications: 10 - 300.000x
Typical options
Detection of backscattered electrons or secondary electrons
Chemical element analysis using EDX (energy dispersive X-ray spectroscopy)
Reflected light microscopy
Characteristics
The object is illuminated from above (reflected light microscopy). This also allows the observation of compact samples
Usual resolution: 5µm- max. 0.5µm. For comparison: The resolution of human eye it is about 330 µm.
Usual magnifications: 6-150x
Stereomicroscopy
Two optical beam paths provide a three-dimensional impression of the object under investigation.
Due to the three-dimensional imaging, the stereomicroscope is ideally suited for preliminary examinations of samples and the selection of areas to be examined at higher magnifications (e.g. in an electron microscope).
Optical magnification of transparent objects (e.g. extremely thin cross-sections)
Maximum resolution: approx. 200 nm
Usual magnifications: 40-1000x
Options
Brightfield: the light passing through the object is observed. Contrast formation due to absorption in high density areas.
Darkfield: Observation of scattered light. Structures of transparent objects with low contrast can be displayed well.
Transmission Electron Microscopy
Features
In the electron microscope (EM) the image is created by the interaction of electrons with the object.
In the transmission electron microscope (TEM) the electrons are transmitted through a sufficiently thin object (usually 10 - 100nm thick).
The entire internal structures are pictured.
Resolution limits
The resolution limits in the life science field depend on the chosen method.
Examples: - Cryo-electron tomography: ~4 nm - Negative contrasting of macromolecules: ~ 1.5 nm - 3D cryo electron microscopy of macromolecules: ~ 2 Å - Electron crystallography of macromolecules: ~ 1 Å
