The Electron Microscope Flashcards
When was the electron microscope developed?
1930s
What does an electron microscope use instead of light?
A beam of electrons.
Why does the microscope have a higher resolving power than a light microscope?
It has a much shorter wavelength.
What is the beam focused with and why?
Electromagnets, as electrons are negatively charged.
What has to be created for the microscope to work effectively and why?
A near-vacuum, as electrons are absorbed or deflected by molecules in the air.
What are the two types of electron microscope?
The transmission electron microscope (TEM) and the scanning electron microscope (SEM).
What does a TEM consist of?
An electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet.
Why do parts of the specimen appear dark and other parts appear bright?
Parts absorb electrons and other parts (thin parts) allow the electrons to pass through.
What is the resolving power of a TEM?
0.1 nanometres.
Why can the resolving power of a TEM not always be achieved?
Difficulties in preparing the specimen limit the resolution, or a higher energy electron beam is required.
What are the main limitations of a TEM?
Living specimens cannot be observed, a complex staining process is required, the image is not in colour, the specimen must be very thin, and the image may contain artefacts.
Why must the specimens be really thin in a TEM?
To allow electrons to penetrate.
What is the result of a TEM if the specimen must be really thin?
A flat, 2D image.
What are photomicrographs?
The image produced on a microscope screen that can be photographed.
How can we overcome the problem of the image being 2D on a TEM?
We use a SEM.
