Scanning Electron Microscopy (SEM)

The Scanning Electron Microscopy 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.

Scanning Electron Microscope runs with the MLA-Suite software by FEI

Foto: HZDR

Technical Specifications

• Two scanning electron microscopes (FEI Quanta 650F MLA-FEG) mainly used for the Mineral Liberation Analysis (MLA)
• 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)
• Non-destructive
• Sample stage size: 150 mm

Application

• High-resolution imaging of surfaces
• Detecting rupture types and behaviours
• Displaying particle morphology
• Measuring particle sizes and structures

Sample Requirements

• 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

How does it work? ►

Scanning Electron Microscopy Scheme

Foto: HZDR/ Thomas Heinig

To create a SEM image a focused primary electron beam scans across a sample surface. Due to the electron bombarding secondary electrons (SE) as well as backscattered electrons (BSE) emit from the sample.

While secondary elecontrons have an energy lower than 50 eV, backscattered electrons show much higher energies.The different electrons are therefore detected by two different, energy selective detectors which convert them into signals, amplifys and visualizes them 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.