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Our Research Using a Raster Electron Microscope |
But how do you do photos with a raster electron microscope?
First the objects we wanted to see had to be prepared. This means the
antenna, foot and pieces of the wing were laid on a small, round plate covered
with sticky tape.
Then the whole thing was covered with a very thin gold layer. This was done with
the help of high voltage.
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| The objects are covered with a gold layer. Liquid nitrogen is used for cooling. |
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| Here are the objects covered with the gold layer. |
The principle of the raster electron microscope is to send a ray of primary electrons on the object to cause a ray of secondary electrons which are caught by a detector and worked into a picture.
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First the electrons are sped up and pushed into the wanted direction to hit the object in a particular point. This happens in the tube. When the ray of primary electrons hits a point of the object’s surface, secondary electrons are thrown out by the object’s surface. The number of electrons thrown out depends on the angle incidence of the primary electrons, in other words of the angle of the surface. The secondary electrons are "sucked off" by an anode (detector) which is charged positively and therefore attracts electrons (negative charge).
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| ...and here it is |
The electronic signal of the secondary electrons hitting the detector is transformed into a point of a picture on the screen of a picture tube. The brightness of this point on the screen depends on the number of secondary electrons.
To show the whole surface of the object the ray of primary electrons is lead
over the object in a line-scanning pattern. So a stereoscopic picture appears on
the screen.
This picture can be photographed by a camera attached to the microscope.
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| On the left you can see the tube where the electrons hit the object. On the right are the monitors and buttons to adjust the microscope. |
