Electron Microscopy Flashcards
Greater magnification than light microscope =
More spacing between crystals
Don’t need to produce thin sections (SEM), therefore EM is
Non destructive
Thin samples are needed for TEM, but not for SEM
Can be controlled by…..
Computer software
Provide information about …….. And ……… Of a sample
Topography and elemental composition
Uses a focused beam of electrons generated by a filament in the source …..
Filament is heated by an electric current to produce a cloud of electrons
Electrons escape filament surface by exceeding potential energy holding them, this is……
Thermionic emission
Electrons are accelerated towards the
Positive electron
Series of magnetic lenses focus electron cloud to produce
A thin beam known as the incident beam
The beam current (strength) is set by the analyst. All electrons have the same…….
Energy and wavelength
Beam is focused onto the sample. Samples may be under vacuum because it…..
Minimised the number of air molecules, thus reducing collisions
Difference between SEM and TEM?
SEM - interactions occur and sample surface
TEM - electrons pass through sample / scattered by sample atoms to produce back scattered electrons
Secondary electrons are produced by……
A second interaction between incident beam and sample.
Results in X-ray photon being produces as an electron from higher energy she’ll falls to fill the gap left behind from the secondary electron.
Greater magnification than….
Light microscopy.
Magnifies up to x 1’000’000
