Improving SEM images through sample coating

A conductive coating is often required in scanning electron microscopy (SEM) to improve the imaging of samples. Creating a conductive layer of metal on the sample inhibits charging, reduces thermal damage and improves the secondary electron signal required for topographic examination. Imaging polymeric membranes with SEM often requires a coating. The following pictures show the same sample with and without the metal coating.

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SEM image of sample with coating
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SEM image of sample without coating

Microscopists are often purists and want to analyze samples without a coating. This is understandable, as sometimes the coating can change the morphology of a sample (mainly at high resolution, like above 70,000 X magnification), and if one wants to perform elemental analysis using energy dispersive X-ray spectroscopy (EDX) the coating can hinder the efforts. But more often than not, we gain sharper, more useful images when we coat. Typically a gold, platinum, or palladium sputter coating application for two or three minutes does the trick for microfiltration, ultrafiltration, nanofiltration, or reverse osmosis membranes. This is pretty standard for whatever polymeric material, be it polyamide, polysulfone, polyvinylidene fluoride (PVDF), etc.

Here are a bunch of membrane images, all with platinum coatings. Note that most of these also have activated carbon layers (which we also call “coatings”) on the membranes.

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