Electron Microscopy Flashcards
What are the main components of an electron microscope?
The gun The Objective Lens The Intermediate Lens Te Projector Lens The Apertures The camera
What are the most common types of electron guns?
Thermionic and field emission guns
What are the lenses composed of?
Magnetic coils tuned to focus and directa passing electron beam
What is the main function of the objective lens?
1st step in magnification and focussing
What is the function of the intermediate lens?
It controls the positioning and strength of the image
What are the different types of electron guns?
Heated Tungsten
Lanthanium Hexaboride (LAB6)
Field Emission Gun (FEG)
How does a field emission gun work?
Electrons are expelle by appling a very powerful electric field very close to the filament tip causing the electrons to tunnel out of the electron reservoir
What are the two types of coherence?
Spatial and temporal
What is spatial coherence?
If the electrons all stay close to parallel then the beam will remain together for as long as possible thus increasing brightness.
How is an image created using an EM?
It is based upon the electrons which bounce elastically. From their energy loss it can be calculated where they hit the object.
How is contrast formed?
It comes from interference between the electrons coming in from different angles
What are grids?
Small copper discs witha fine mesh, atop which a thin layer of carbon is deposited.
How is Carbon made hydrophillic?
Glow discharging
What is a holey grid?
When the C is deposited in such wa as to create holes of a desired size. Prevents C creating noise in the image
How is carbon evaporation performed?
A sheet of freshly covered mica is placed within an avacuated chamber that has a sall graphite rod connected to a high voltage circuit. Current is applied and carbon is evaporated onto the mica. the Mica is lowered into a small water tank on filter paper and the the c film slides off
