SEM Sample Preparation
Both techniques involve the following steps:
Cleaning - The samples must be free of oil and loose particles. Some soils will need salts, organics and carbonate removed.Drying - It is often necessary to dry samples to remove water from the sample this can be achieved by placing the samples in a low temperature oven or freeze drying the sample.
Mounting - Samples must be mounted in a fashion which allows them to be placed in the instrument. A variety of methods can be used. Some of the most common mounts are petrologic thin sections, one inch round thin sections or mounts, epoxy filled molds, and double sided carbon tape attached to a SEM stub.
Polishing - For quantitative analysis a flat horizontal surface provides the best analysis. Also the quality of the BSE image will improve on a flat surface. However polishing is not necessary and sometimes counter productive for SEM analysis.
Mapping - Samples should be well mapped before coating so that the area or areas of interest can be found when the sample is in the instrument. Suitable methods include sketching, photographing or scanning the sample.
Coating - Non-conductive samples must have a conductive material such as gold or carbon applied to the surface of the sample. This conductive coating prevents charging under electron bombardment.Gold has a higher SE yield, whereas carbon has a minimal effect on the X-ray spectrum.