Scanning electron micrographs
You’ll be familiar with normal microscopes – tubes with lens at each end giving magnifcation of up to maybe 200x. What happens when that isn’t enough and we still can’t resolve the tiniest particles? Well we can move on to using electron microscopes, substituting eclectron beams for light beams. Here we show a few examples of Scanning electron micrographs . The dots on the left hand side give the scale for a length in microns [more accurately micrometres] of which there are 1000 in a single millimetre. The crystals in the top image are herefore about 0.01mm long.
Scanning electron microscopy (SEM) works by scanning a sample with electron beams. An electron ‘gun’ fires these beams, which then accelerate down the column of the scanning electron microscope, passing through a series of lenses and apertures, which act to focus it. All this takes place in a high vacuum which prevents and molecules or atoms already present in the microscope column from interacting with the electron beam. The sample is usually coated with gold to ensure complete conductivty of the electrons away from the impact point [preventing the sample from melting]. The electron beams scan the sample in a raster pattern, scanning the surface area in lines from side to side, top to bottom; secondary electrons are emitted from the sample building up a detailed pattern which is convereted into a visible image.
For the technically minded this catalog by a major supplier will illustrate some of the SEMs available!
This online book explain some of the uses of SEM in geology
The next few images come from John Conway’s PhD study of soil microstructure. the first at low magnification shows the general soil but highlights the existence of a very smooth surface on the root channel – this was then examined at much higher magnifciantion in order to identify what that smooth surface was composed of. This was revelaed to be clay particles aligned parallel to each other providing a smooth water proof lining which isolated the root from the rest of the soil. This soil came from Lleiniog near Beaumaris.
