3.2 The electron microscope

Question 1

What are the 2 types of electron microscopes?

Answer 1

1. transmission electron microscope (TEM)
2. scanning electron microscope (SEM)

Question 2

What are the advantages of electron microscopes?

Answer 2

1. the electron beam has a short wavelength so the microscope can resolve objects well
2. as electrons are negatively charged, the beam can be focused using electromagnets

Question 3

How does a TEM work?

Answer 3

Electromagnets are used to transmit a beam of electrons to specimen, and electrons penetrate the specimen from below.

Question 4

What are the limitations of TEM?

Answer 4

1. living specimen can’t be observed because the whole system must be in a vacuum
2. specimen must be stained
3. specimen must be very thin
4. image is in black and white
5. image may contain artefacts (人工製品)

Question 5

What is the resolving power of TEM?

Answer 5

0.1 nm

Question 6

How does a SEM work?

Answer 6

Electromagnets are used to transmit a beam of electrons to the surface of specimen from above.

Question 7

What are the limitations of SEM?

Answer 7

1. living specimen can’t be observed because the whole system must be in a vacuum
2. specimen must be stained
3. image is in black and white
4. image may contain artefacts (人工製品)