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SEM Principle and Instruments
SEM Principle and Instruments
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Labelled SEM / EDX InstrumentPrinciple of SEM/EDX

An SEM is essentially a high magnification microscope, which uses a focussed scanned electron beam to produce images of the sample, both top-down and, with the necessary sample preparation, cross-sections. The primary electron beam interacts with the sample in a number of key ways:-

  • Primary electrons generate low energy secondary electrons, which tend to emphasise the topographic nature of the specimen.
  • Primary electrons can be backscattered which produces images with a high degree of atomic number (Z) contrast.
  • Ionized atoms can relax by electron shell-to-shell transitions, which lead to either X-ray emission or Auger electron ejection. The X-rays emitted are characteristic of the elements in the top few μm of the sample and are measured by the EDX detector.

Our SEM/EDX Instruments

The scanning electron microscope is an instrument used for the imaging and analysis of a wide range of materials in a wide range of applications. The laboratory has 2 such instruments in house, one with a LaB6 tip and one with a tungsten filament, and 5 very experienced SEM analytical scientists.  Additionally the company has access to higher resolution FEG (Field Emission Gun) instruments and environmental SEMs at trusted partner laboratories when required.

SEM Instruments - Philips XL30 Scanning Electron Microscopes and EDAX


Large SEM vacuum chamber taking oversize samplesThe main features and benefits of the SEM are:-

  • Image magnification and resolution
  • Magnification range X 15 - X 200,000
  • Resolution 2 nm
  • Accelerating voltage 1 - 30 keV
  • Secondary and backscatter electron imaging
  • Stereo imaging and stereo height measurement
  • EDX analysis of known or unknown materials (www.edax.com)
  • Qualitative and quantitative analysis for all elements from carbon upwards
  • Quantitative analysis of bulk materials and features ≥ 2 μm
  • Qualitative analysis of features ≥ 0.2 μm
  • Detection limits typically 0.1 - 100 Wt% for most elements
  • Multi-element X-ray mapping and line scans
  • Multi-layer, multi-element thin film analysis - Thickness and composition
  • Particle / Phase analysis - Detection, analysis, morphology and size
  • Image Analysis
  • Automatic particle counting and characterisation
  • Large samples can be analysed up to half a house brick size.


UK Institute of Physics Electron Microscopy & Analysis Group (MAG): http://groups.iop.org/EM/
Museum of Science- How an SEM Works www.mos.org/sln/sem/intro.html

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