Hands on experience with an SEM.

Due to the constant barrage of assignments at uni I have had little time for Reprap related projects recently. So instead I would like to share my excitement after having my first undergrad laboratory session with an electron microscope.

In case your unaware, an electron microscope can be thought of as an optical microscope but rather than light, uses electrons. Why use electrons? Because their tunable wave length is much smaller than that of light, which is the limiting factor for optical microscope resolution no matter how perfect the lenses. In addition, the electro-negativity of electrons means they interact strongly with matter and so allow for much more useful information to be gathered.

The electron microscope used during the laboratory session is located at the Monash centre for electron microscopy (MCEM) located on the Monash Clayton Campus in Victoria, Australia.

The MCEM Building. Image from the Monash MCEM website.

This new building was especially designed to house a range of different sensitive electron microscopes and I can only assume its architecture was intentional made to look similar to a diffraction grating. As well as shielding its 3 SEM and 4 TEM from the elements the building also protects the equipment from vibrations and radiation. I’m told that some of the equipment is so sensitive that with out shielding they can detect the stray magnetic fields created by moving electric trains kilometres away. The buildings most powerful piece of equipment is the new A$9Million dollar Titan, which has no less than 22 separate magnetic lenses and is one of only 4 in the world

The particular piece of equipment used during my own lab session was the Japanese made JEOL 6300F Field Emission Gun SEM.

JEOL 6300F Field Emission Gun SEM.

This 20 year old microscope was donated to the university by BHP lab’s. Although its passed its prime in terms of resolution, it is still a very powerful piece of equipment and more than adequate for the task at hand. The column on left in the image above is the microscope its self. This column is under a high vacuum (2×10^-8Pa) produced by two ion pumps. However is still requires the cooling produced by liquid nitrogen (Image of it being pored in by the demonstrator) to condense any remaining atoms in the column onto a surface so that they do not interfere with beam.

At the top of the column is a very expensive  ‘cold field emitter’  (SEM Image of it here) which has a point so fine that electrons can be stripped off it be applying a field just below it. These electrons are accelerated and focused through the columns magnetic lenses and are made to scan across  a sample the size of a finger nail line by line. The sample is housed in the lower part of the column in the image above. The electrons interact with the sample and a number of detectors collect information from the resulting scatter of electrons or from xrays produced by interactions with the sample.

This allows images such as the one below of beach sand (ZRSiO3) at 22,000x magnification to be produced.

An image of beach sand produced at 22,000x.

To get a rough idea of scale, compare the scale bar on the image above to the scale bar on this this fantastic image from the wikipedia page on SEM’s.

Images can also be produced at magnifications obtainable by optical microscopes such as the same grains of sand below. However, a SEM has the added advantage of a greater depth of field so that more parts of the object are in focus at the same time.

Also, by using different detectors different types of image can be formed that tell you different things about the sample being looked at.

The same area of a sample viewed in different detection modes.

Perhaps most useful though is the ability to select a particular section on an image and produce an xray spectrum such as the one shown below for a sample of Rhodonite (MnSi03) shown below.

An xray spectrum for a sample of Rhodonite

As each element has a specific xray ‘finger print’ which is identified by the computer and labelled on the image. This allows a whole host of chemical information can be obtained.

So do you fancy getting some hands on experience with your own scanning probe microscope? If so then take a look at the SXM project and you will be amazed at the resolution you can achieve with in your own home.

A open-source scanning tunneling microscope you can build at home.

Adrian blog’ed about this project here, which is how I first came across it.

Moving off topic for a second, its now only a few months until the end of semester and starting my own Mendel build. However until then I wont have time for this blog while I focus on my studies.Ha


About Richard

I am a Materials Engineering working in the field of Magnetic Materials in Melbourne, Australia. This blog covers my personal interest in all things CNC.
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