Expert sample preparation techniques for SEM

By Luigi Raspolini - Aug 17, 2017

When using a scanning electron microscope (SEM) for the first time, you might have doubts about what can be imaged. You might also struggle to get the image quality you were expecting. Luckily, you can easily improve your results by following the simple yet powerful sample preparation techniques for SEM in this blog. Read on! 


Free Sample Preparation E-guide
Download this free Sample Preparation E-guide to obtain great results from the most common samples


SEM: samples & vacuum

First things first: SEM’s operate in a vacuum. Samples can be seriously affected by a vacuum. For example, loose particles can detach from any surface, all liquids will evaporate immediately, and delicate materials will outgas. This is the reason why a fly can be easily imaged.

 

Fly Eye.jpg
Fig.1: SEM image of a fly's eye 

But do the same with a fly larva, and you will most likely get a splatter scenario. Larvae can be understood as small liquid pockets: if the water inside evaporates, the skin can collapse due to the internal pressure and, in the worst cases, it might ‘explode’. Gasses and particles can then access the electron column and compromise image quality for good.

How to image high moisture content samples with SEM

  • Operate at a lower vacuum level;
  • Freeze your sample;
  • Dry your sample.

apple0001.jpg
Fig.2: SEM image of an apple at -25°C

 

In addition, you should consider the effect of electrons accumulating on your sample. This translates into an image with bright areas where all the details can no longer be observed. This is typical when imaging polymers and other non-conductive materials.

Once again, sample preparation is the key to a good image.

How to image non-conductive samples with SEM

  • Create a connection to the ground using metallic tape and image your sample in the nearby area;
  • Sputter coat your sample with gold or other conductive coating materials;
  • Operate at a lower vacuum level.

wool-coated.jpg
Fig.3: SEM image of a non-conductive wool sample


We have more
recommendations on how to prepare your sample properly!

You can find great yet easy sample preparation tips and tricks in this Sample Preparation e-Guide. Get your free copy here!

desktop-sem-sample-preparation-e-guide


About the author

Luigi Raspolini is an Application Engineer at Thermo Fisher Scientific, the world leader in serving science. Luigi is constantly looking for new approaches to materials characterization, surface roughness measurements and composition analysis. He is passionate about improving user experiences and demonstrating the best way to image every kind of sample.

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