Scanning Electron Microscopy
The Scanning Electron Microscopy (SEM) is a method for the high-resolution imaging of surfaces. It uses electrons for imaging, much as a light microscope uses visible light. In contrast to the light microscopy the SEM generates a much higher magnification varying between 100 and 1.000.000.
|Thomas Heinig, Scanning Electron Microscope|
The Helmholtz Institute Freiberg for Resource Technology has two scanning electron microscopes (FEI Quanta 650F MLA-FEG) mainly used for the Mineral Liberation Analysis (MLA).
- High-resolution imaging of surfaces
- Detecting rupture types and behaviours
- Displaying particle morphology
- Measuring particle sizes and structures
- Measuring in secondary (SE) and backscattered electron contrast (BSE)
- Electron beam resolution 1.0 nm at 30 kV (SE), 2.5 nm at 30 kV (BSE)
- Sample stage size: 150 mm
- Solid, vacuum-resistant, vaporized with carbon
- Sample types:
- Round micropscope slides 25, 30 or 40 mm
- Thin and thick sections 28 x 48 mm
- Single samples 15 x 15 cm
|Scanning Electron Microscopy Scheme|
|Foto: Thomas Heinig|
How does it work?
To create a SEM image a focused primary electron beam is scanned in a raster pattern across the sample's surface. The electron bombarding causes secondary electrons (SE) as well as backscattered electrons (BSE) to be emitted from the sample.
While secondary elecontrons have an energy lower than 50 eV, backscattered electrons show much higher energies.The distinctive electrons are therefore detected by two different, energy selective detectors.
The detected electrons are then converted into signals, amplified and visualized on a monitor. The result is a tremendously vivid surface image. Since secondary electrons can only be emitted from the surface the resolution of the corresponding image is very good. It ranges between 5 and 10 nm. Backscattered electrons are generated at greater depths. Therefore, the resolution of the corresponding image is significantly lower. SEM have a field depth that is much higher than the one from optical microscopes.