How to prevent oxidative damage to a scanning electron microscope sample

By Luigi Raspolini - Dec 7, 2017

O2 is an extremely reactive gas, and some materials don’t get along well with it. Oxidation processes are activated as soon as certain samples are exposed to the atmosphere and this affects the structure and characteristics of the samples — in most cases permanently. This blog explains how such effects can be prevented and how SEM analysis can be performed on oxygen-sensitive samples without compromising the structure of the sample itself.

Samples and oxidation

The rate of oxidation reactions can be very different: iron rusting takes years, methane burns in a few milliseconds.

Lithium-based compounds tend to be extremely reactive when in contact with oxygen, which makes the development of new materials for battery electrodes more complex.

The same applies to Phosphor, Fluorine and several other elements of the periodic table. Some compounds are so sensitive to oxygen that they can even trigger explosive reactions when ignition is provided.

Oxygen deprivation also has a strong impact on the growth of microorganisms, and is the parameter that differentiates the normal cellular breathing from the fermentation processes or, sometimes, the inhibition of microbial growth. The latter effect is largely employed in food production and preservation, where N2, a gas with high chemical inertia, is used to replace oxygen in food packages, or to create a safe environment at the production site in order to prevent the growth of pathogens.

As a side effect, this technique also prevents oxidation reactions on the food, which stays fresh and has a longer shelf life.

How to prevent the oxidation of samples in a lab

The same technique is largely adopted in laboratories, where the samples are manufactured or prepared in an oxygen-free environment. These so-called ‘glove boxes’ are big, sealed containers in which the atmosphere is conditioned and the air is replaced by a gas with high chemical inertia: typically Argon or N2.

The choice between which of the two gasses to apply, typically depends on the nature of the sample and on the environment in which it is being manipulated.

example-glovebox-environment.jpeg

Image 1: an example of a typical glovebox environment


When exposed to high tensions, N
2 can generate nitrogen radicals that can interact with the sample and change its structure. Argon is a noble gas, therefore its chemical inertia is even higher than the N2 gas, making it the ultimate solution for glove box conditioning and operation.

The considerable cost of a glove box, and of the large amount of gas that is used to fill it, - makes the space inside the glove box extremely valuable. That’s why — when SEM analysis is necessary — desktop instruments are the only reasonable choice. On the other hand, Argon is very sensitive to high tension and tends to create sparks when high tension connections are exposed. This makes imaging the samples and performing EDS analysis a quite more complex task, as a high voltage electron beam is involved.

Nevertheless, desktop SEMs that are protected against this effect exist, and can provide outstanding images and accurate EDS analysis of sensitive samples. Find out how by downloading the free Phenom ProX specification sheet: 

ProX specification sheet


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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