The Electron Microscope

Question 1

What are the advantages of an electron microscope?

Answer 1

The electron beam has a smaller wavelength, so can resolve objects well. Electrons are negatively charged so the beam can be focussed using electromagnets.

Question 2

What are the components of a Transmission Electron Microscope?

Answer 2

Electron gun produces beam of electrons. The beam is focussed onto the specimen by a condenser electromagnet.

Question 3

What creates the resulting image from the microscope?

Answer 3

Parts of the specimen absorbs electrons, therefore appearing dark. Other parts f the specimen allow electrons to pass through, so appear bright.

Question 4

Why might the 0.1nm resolving power not always be achieved?

Answer 4

• Difficulties preparing specimen limit resolution that can be achieved.
• A higher energy electron beam is required which may kill the specimen.

Question 5

What are the limitations of the TEM?

Answer 5

• System must be in vacuum so living specimens cannot be observed.
• ‘Staining’ process is required.
• Specimen must be extremely thin.
• The image may contain artefacts.

Question 6

What is the image like produced form the TEM?

Answer 6

Flat, 2-D.

Question 7

What are the advantages of the SEM?

Answer 7

• Specimens do not need to be extremely thin as electrons do not penetrate.
• 3-D image can be built up.

Question 8

How does the SEM work?

Answer 8

SEM directs a beam of electrons on to the specimen from above. The beam passes back and forth and electrons are scattered depending on contours of specimen surface.