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TECHNICAL FEATURES

Scanning Electron Microscope (SEM)

The SEM EVO HD25 located at the CLPU has been provided by Carl Zeiss Microscopy (http://www.zeiss.es/microscopy/es_es/home.html).

The SEM methodology consists of scanning the surface of the specimen focusing electron beams. The signal provided by the scattered electrons is collected by the different detectors installed into the vacuum chamber and processed by the control software providing high resolution images (around 20 nanometres).

Specs:

  • Thermoionic electron canyon with LaB6 filament 
  • Vacuum cleaner, turbomolecular pump
  • Variable pressure (10 – 400 Pa)
  • Three sorts of detector to optimize results:
      • SED (Secondary Electrons Detector), to get the image in real time.
      • VPSE (Variable Pressure Secondary Electrons), to avoid the charge effects by using a gas that ionizes molecules; neutralizes electrons trapped in surface, so the SE emission stabilizes.
      • BSD (Backscatter Detector) detection based on the collection and analysis of backscattered electrons.
  • A wide vacuum chamber (rotating carousel of 9 bases of 12 mm diameter)
  • Eleven ports for detector accessories and possible extension to 3000 Pascal.

The SEM installed at the CLPU has also been equipped with another three additional detectors:

# STEM (Scanning Transmission Electron Microscopy), is a kind of Transmission Electron Microscope (TEM) where electrons pass through the sample. The main difference relies on that the STEM works at low voltages (30 keV maximum) compared with TEM (50 keV minimum). Consequently STEM works correctly as long as the specimen is sufficiently thin.

# EDS (Energy Dispersive Spectroscopy) provides the chemical composition of the samples based on the analysis of the dispersive X-rays. This process occurs when the primary electron beam interacts with atoms causing in the specimen shell transitions that result in the emission of an X- ray. The emitted X-ray has an energy characteristic of the parent atomic element.

# EBSD (Electron Backscatter Diffraction Detector) Electron backscatter diffraction is a SEM based microstructural-crystallographic technique to measure the crystallographic orientations which is applicable in principle to any crystalline material. You can find more detailed information about this technique in: http://www.ebsd.com/

General requirements of the samples (download)

NOTE: The quality of the images strongly depends of the sample preparation and it turns important when a high definition images are required. The CLPU is not involved in the preparation of the different specimens. The potential users are responsible of their correct preparation (coating, polishing, cutting, …) according to the general requirements.