3.2 The electron microscope Flashcards
Advantage of an electron microscope?
The electron beam has a very short wavelength and therefore resolve objects well
Electrons are negatively charged so the beam can be focused using electromagnets
How do electron microscopes work?
Electrons are absorbed or deflected by the molecules in the air
What types of electron microscopes are there?
The transmission electron microscope and Scanning electron microscope
How does a TEM work?
An electron gun produces an electron beam that passes through the specimen
Some electrons get absorbed making the area dark, some go through and become bright
What image can be produced when TEM photographed?
A photomicrograph
Resolution of TEM?
0.1nm
Limitations of TEM?
Whole system must be in a vacuum therefore no living specimens can be observed
Complex ‘staining’ process which still results in a colourless image
Specimen must be extremely thin
Images can contain artefacts (stuff that can appear on the photomicrograph from preparation etc)
What is the SEM?
Similar to TEM, but electrons bounce back and forth in a regular pattern to contour the specimen surface
Build a 3D image
Advantage of SEM?
Specimen does not have to be extremely thin as electrons don’t penetrate
Resolution of SEM?
20nm (less than TEM but better than light)
Why do specimens have to be kept in a near-vacuum to work efficiently?
Electrons can get absorbed by the molecules in the air and present a false image
