Electron Microscopes

Question 1

How do transmission electron microscopes work

Answer 1

-electron beam takes the place of the light source
-electrons travel at much smaller wavelengths than visible light so can reveal much smaller details than what is possible with light
-electron microscopes use electromagnetic or electrostatic lenses which produce magnetic and electric fields that guide and focus the electrons
-sample very thin 0.1 micrometers
-special electron imaging devices convert the electron signal into a greyscale image where contrast corresponds to differences in sample thickness and density

Question 2

Is imagine from TEM 2D or 3D

Answer 2

2D

Question 3

How do scanning electron microscopes work

Answer 3

-scan a beam of electrons across a specimen which bounces off the surface of the specimen and the electrons are detected forming a 3D image that shows the surface of specimens
-since they can scan the outside surface the specimen viewed does not have to be thin
-the images they form are of a low resolution than TEMs

Question 4

What is resolution

Answer 4

Minimum distance between two objects that they can still be seen as two objects

Question 5

Is resolution higher in SEMs or TEMs

Answer 5

TEMs

Question 6

Disadvantages of electron microscopes

Answer 6

-interior of electron microscope is a vacuum meaning cannot be used to view living specimens
-requires very careful staining and specimen often has to be very thin
-can create artefacts (false images) due to staining