Preparation of samples for electron probe micro-analysis

Some sample preparation is required for most quantitative analytical work using an electron microprobe. Using its on-site saws, laps and polishing equipment, the Museum’s analysis centre produces a range of thin and polished sections, blocks and wafers of palaeontological, mineralogical, biological and industrial materials such as concretes.

Stages of sample preparation:

  1. Cutting with a saw and trimming to a size that can be mounted.
  2. Mounting in one of two ways:
    • Into a resin block: the sample is placed in a circular mould and impregnated with a resin. This option allows for additional imaging with an optical microscope using reflected light.
    • Onto a glass slide: the sample is affixed to a standard size glass slide with resin for further lapping and polishing. This method allows imaging to be achieved using both transmitted and reflected light microscopy.
  3. Removal of excess sample and grinding to ensure the top and base of resin blocks are parallel.
  4. Lapping to produce a smooth surface. This may be performed by hand or on an automated jig using fine (600 grade) abrasive - usually silicon carbide.
  5. Polishing - carried out in steps on a special cloth with a slurry of very fine alumina, or diamond, ranging in size from 6 to 0.3 microns.

Carbon-coating

Prior to analysis many samples - particularly those containing minerals - need to be coated with a thin film of conducting media to dissipate excess charge produced by the electron beam. Usually carbon is used and the film is typically 30 nanometres thick.