Artefacts in the SEM — Science Learning Hub

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Published 29 February 2012 Referencing Hub media

Liz Girvan (Microscopy Otago) talks about the problem of artefacts in the scanning electron microscope¹ (SEM). Artefacts look like part of the microscope² sample but are actually a side-effect of sample preparation or the conditions³ in the microscope. It’s easy to be fooled into thinking that artefacts are part of your sample. Liz’s advice: know your sample well so you can spot an artefact⁴ when you see one!

Transcript

LIZ GIRVAN
It’s quite important to be very open minded about what you’re going to see. You need to make sure what you’re looking at is actually real. So you can get quite a few artefacts, anything from dust that’s fallen on your sample which can look like a piece of sample. You can get some cracking in the vacuum⁵ so you actually get cracks forming in your sample which are not there, they’ve been caused by the microscope. Sometimes the coating can cause artefacts. If you coat too thickly, you can start to see the metal⁶ particles, and of course, if you’re looking for small particles, they can look just like your sample might look like.

Charging artefact is probably the most common thing we’ll get in the SEM. What that means is the sample isn’t conducting as well as it should be, so we get the electrons building up within the sample forming a little charge. A charging artefact can look really, really different in different samples. So this is a carbon fibre⁷ sample that is charging quite badly. All these black and white areas are artefacts – they’re not actually there, but they create quite a nice cool colourful image. So what you can get is smears across your image, you can get lines, you can get black halos, white halos, all kinds of things. Usually the way to tell if something’s an artefact is just from experience, so spending a lot of time looking at a whole lot of different samples, you’ll see these things continually appearing.

electron microscope: A microscope that uses a focused beam of electrons, rather than visible light, to magnify objects. Electron microscopes use electromagnetic coils to focus the electron beam (instead of the glass lenses used to focus light in optical microscopes). Traditional light microscopes magnify images 1000-2000 times, electron microscopes can magnify 300,000 times or more.
microscope: An instrument that uses a lens or a series of lenses to magnify small objects.
condition: An existing state or situation; a mode or state of being.
artefact: 1. A product of human art and workmanship. 2. An object remaining from a particular period. 3. In the context of the international prototype kilogram (IPK), a 1 kilogram cylinder of platinum-iridium alloy was manufactured in France in the 1880s to serve as the mass standard. 4. Something observed during a scientific investigation that is not naturally present but has been introduced as a result of the experimental procedure. Artefacts are commonly introduced during preparation of specimens for microscopy.
vacuum: An absence of matter. In practice, a space that contains a very low density of matter (very low pressure) is often referred to as a vacuum.
metal: Any of a category of elements that usually have a shiny surface, are generally good conductors of heat and electricity and can be melted or fused, hammered into thin sheets or drawn into wires (for example, copper).
carbon fibre: A material consisting of thin strong crystalline filaments of carbon often used as a strengthening material in composites.

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A microscope that uses a focused beam of electrons, rather than visible light, to magnify objects. Electron microscopes use electromagnetic coils to focus the electron beam (instead of the glass lenses used to focus light in optical microscopes). Traditional light microscopes magnify images 1000-2000 times, electron microscopes can magnify 300,000 times or more.

1. A product of human art and workmanship.

2. An object remaining from a particular period.

3. In the context of the international prototype kilogram (IPK), a 1 kilogram cylinder of platinum-iridium alloy was manufactured in France in the 1880s to serve as the mass standard.

4. Something observed during a scientific investigation that is not naturally present but has been introduced as a result of the experimental procedure. Artefacts are commonly introduced during preparation of specimens for microscopy.

A material consisting of thin strong crystalline filaments of carbon often used as a strengthening material in composites.

An instrument that uses a lens or a series of lenses to magnify small objects.

An absence of matter. In practice, a space that contains a very low density of matter (very low pressure) is often referred to as a vacuum.

An existing state or situation; a mode or state of being.

Any of a category of elements that usually have a shiny surface, are generally good conductors of heat and electricity and can be melted or fused, hammered into thin sheets or drawn into wires (for example, copper).

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