2620217
Beschreibung
Karteikarten von Charlotte Hewson, aktualisiert more than 1 year ago
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Erstellt von Charlotte Hewson
vor mehr als 9 Jahre
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| Frage | Antworten |
| what are the two main advantages of an electron microscope? | -short wavelength so has high resolving power -electrons are negatively charged so beam con be focused using electromagnets |
| what is bad about electron microscopes? | electrons are absorbed by molecules in air so a near-vacuum must be created in the chamber of the microscope |
| what are the two types of electron microscope? | -Transmission electron microscope (TEM) -Scanning electron microscope (SEM) |
| How does a TEM work? | beam fired at sample, some passes through parts of the specimen so appears light but some parts absorb electrons so appears dark. |
| how is the image shown? | on a screen |
| what can this be photographed to produce? | a photomicrograph |
| what are 4 limitations of the TEM? | -needs a vacuum -complex staining process required and then is only black and white image -specimen must be extremely thin - may contain artefacts |
| how does an SEM work? | electron beam passed back and forth in a regular pattern. Electrons are scattered by specimen and pattern of this scattering depends on contours of specimen surface. Image built up on computer |
| what is the resolving power of an SEM compared to a TEM and a light microscope? | SEM = 20nm TEM = 0.1nm light = 0.2 um |
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