3.2 The electron microscope

Question 1

When was the electron microscope developed?

Answer 1

1931

Question 2

What is the best resolution on an electron microscope?

Answer 2

0.1nm (2000 times better than a light microscope)

Question 3

What are the two types of electron microscope?

Answer 3

Transmission electron microscope (TEM) and scanning electron microscope (SEM)

Question 4

How does the TEM produce photomicrographs?

Answer 4

Fires a beam of electrons from below, which focuses onto a specimen with an condenser electromagnet. Parts of the specimen absorb electrons and appear dark, so the parts that allow electrons through appear bright. An image is magnetically projected onto a screen.

Question 5

What are the main limitations of the TEM?

Answer 5

-whole system must be in a vacuum; living specimens cannot be observed
-the staining process is complex, and the final image isn’t even in colour
-specimen must be extremely thin
-the image may contain artefacts, which can be difficult to differentiate from the specimen

Question 6

What are the main limitations of the SEM?

Answer 6

-whole system must be in a vacuum; living specimens cannot be observed
-the staining process is complex, and the final image isn’t even in colour
-the image may contain artefacts, which can be difficult to differentiate from the specimen

Question 7

How does the SEM produce an image?

Answer 7

Fires a beam of electrons onto specimen from above, and passes the beam back and forth across a portion of the specimen. The electrons scatter according to the contours of the specimen and computers can analyse the scattering pattern, building a 3D image of the specimen.