Electron Miscroscopy Flashcards
What is the definition of resolution?
Ability of the microscope to distinguish separate and distinct objects
What occurs to the resolution when the wavelength of light is small enough?
Two objects distinguishable as separate and distinct
What occurs to the resolution when the wavelength of light is too long?
Two objects not distinguishable as separate and distinct
What is the resolution of electron microscopy?
0.05-0.1nm
What is the resolution range of X-rays?
0.1-1nm
What is the resolution of light microscopes?
200nm
What is the resolution that visable light begins?
400nm
What is the definition of an electron microscope?
A microscope that uses electron beams, electrostatic and electromagnetic lenses to produce an enlarged image of very high magnification
What x of magnification can electron microscopy go to within the microscope?
100-1000x magnification
Who came up with the concept for electron microscopy?
- Louis de Broglie 1924
- Wanted to look at whether electrons could be diffracted in the same way as light properties
- He showed that electron beams behave similar to light waves
Who built the first electron microscope?
- Max Knoll and Ernst Ruska 1931
- Transmission microscope
- Built the first prototype
- At the time people knew there were small pathogenic diseases such as those causing polio
Who built the first scanning microscope?
- Max Knoll 1935
What are 7 components to the electron microscope?
- Electron gun
- Condenser lens
- Aperture
- Stage
- Objective lens
- Projector lens
- Viewing screen
What does the electron gun do and how?
- Traditionally a tungsten filament which is super-heated to 2700 degrees
- This generates electron admittance from the filament
What do the three lenses and the aperture do in the electron microscope?
Direct the bram through the column and focus onto the sample at the specific height where it is inserted on the stage
What happens at the viewing screen on a traditional EM and how are newer ones different?
- Image formation happens here
- Now have detectors in various places and imags are recorded onto these
What are two types of transmission EM?
- Single particle cryoEM
- Electron tomography
What are two types of scanning EM?
Serial blockface SEM
- FIB (focused ion beam) SEM
What does a scanning EM do?
Scans the surface of the specimen with an electron beam to produce a 3D-effect image
How does the SEM work?
- Electron beam rastered across the surface of the specimen using scanning coils in and X and Y motion
- Secondary electrons are bounced off the surface of the sample and are scattered and then picked up by the camera
What is a main preparation technique in SEM?
Put a conductive coating on the sample to prevent accumulation f charge and static electric fields
Usually a layer of gold
What are 3 advantages of SEM?
- 3D-effect surface visualisation
- Relatively quick
- Cheap
What is a downside of SEM?
The resolution is fairly low
What does a transmission EM do?
Transmits electron beam through the sample