Lecture 7 Flashcards
How does a light sensitive device work?
It is a matrix of light sensitive points. When one is hit the matrix switch 1 is opened, then switch 2 etc until it reaches the end.
How does a CCD work?
All the switches open at once, passing the information onto a final pixel. This is much quicker.
What is the problem with using a CCD?
Only 99.999% is passed on each time, this adds up.
What is the standard amount of pixels?
1024 x 1024
What is a scintillator?
A material that flouresces when struck by a charged particle or high energy photon
Why do we have a sciintillator ?
A CCD can not capture the high energy electron directly
What is the scintillator made of?
Fine grain powder mixed with acetone or ethanol than put ina supersonic path creating a milky solution. This is poured onto the substrate and left to dry.
How does the scintillator work?
Electrons come in and hit the scintillator, where intrinsic amplification occurs as many photons are released. Each photon is confined to that section by glass fibres, ensuring it is released where the electron hit the scintillator.
How can the broadened beam created by a scintallator be avoided?
Depositing an Aluminium cover of 10-50nm atop the scintillator and keeping the scintillator as thin as possible
How does an imaging plate work?
It is a sheet of plastic that directly detects the electrons and is read by a laser disc reader.
What are weiß domains?
Every magnetic material consists of a sub-pattern of different magnetic domains.
What is the Lorentz force?
The force exerted on a charged partcile moving with velocity through an alectric and magnetic field
What are the experimental requirements for Lorentz imaging?
Must have a special lens
Eveything must have ferromagnetic shielding
In the upper pole piece there must be another set of coils - condensor lens
In the lower pole piece there must be two coils
What is the purpose of Lorentz imaging?
To see magnetisation and orientation
How does electron holography work?
It works by splitting the beam into two, the reference beam and the object wave. So a coherent electron beam is emitted from the electron gun. One side passes through the sample and is altered by this. There is then an electron biprism which brings the two waves to overlap on a lower plane creating an interference pattern.
