Post on 28-Dec-2015
OU NanoLab/NSF NUE/Bumm & Johnson
Microscopy & Resolution
Magnification: Image size/Object size
Resolution: The fineness of detail that can be distinguished in an image.
Highest Typical ResolutionOptical Microscope ~200 nmElectron Microscope ~0.1 nm
OU NanoLab/NSF NUE/Bumm & Johnson
Definitions
• Acceptance angle θ
• Numerical Aperture NA = n sinθ
• Rayleigh resolution criterion for a circular aperture Δx = 0.61 λ/NA
θ
OU NanoLab/NSF NUE/Bumm & Johnson
OPTICAL MICROSCOPESImage construction for a simple biconvex lens
OU NanoLab/NSF NUE/Bumm & Johnson
Rayleigh criterion for resolution
www.microscopy.fsu.edu ; www.imb-jena.de See more interactive tutorials at www.microscopy.fsu.edu
Numerical Aperature Resolution Rayleigh Criterion
OU NanoLab/NSF NUE/Bumm & Johnson
ComparisonBright-Field
Dark-Field
• Full apertureis illuminated
• A central obstruction blocks the central cone.
OU NanoLab/NSF NUE/Bumm & Johnson
www.microscopy.fsu.edu
Dark-FieldOptical Microscopy•A central obstruction blocks the central cone.
•The sample is only illuminated by the marginal rays.
•These marginal rays must be at angles too large for the objective lens to collect.
•Only light scattered by the object is collected by the lens.
OU NanoLab/NSF NUE/Bumm & Johnson
www.microscopy.fsu.edu
Dark-FieldOpticalMicroscopy
OU NanoLab/NSF NUE/Bumm & Johnson
THE ELECTRON MICROSCOPEThe wavelength of the electron can be tuned by changing the accelerating voltage.
de Broglie : λ = h/mv λ: wavelength associated with the particle h: Plank’s constant 6.63×10-34 Js; mv: momentum of the particle me= 9.1×10-31 kg; e = 1.6×10-19 coulomb
P.E eV = ½mv2 λ = h/(2meV) = 12.3/V (for V in KV, λ in Å)V of 60 kV, λ = 0.05 Å Δx ~ 2.5 Å
Microscopes using electrons as illuminating radiation
TEM & SEM
OU NanoLab/NSF NUE/Bumm & Johnson
OU NanoLab/NSF NUE/Bumm & Johnson
Components of the TEM
1. Electron Gun: Filament, Anode/Cathode2. Condenser lens system and its apertures3. Specimen chamber4. Objective lens and apertures5. Projective lens system and apertures6. Correctional facilities (Chromatic, Spherical, Astigmatism)
7. Desk consol with CRTs and camera
Transformers: 20-100 kV; Vacuum pumps: 10-6 – 10-10 Torr
OU NanoLab/NSF NUE/Bumm & Johnson
Schematic of E Gun & EM lens
Magnification: 10,000 – 100,000; Resolution: 1 - 0.2 nm
www.udel.edu
OU NanoLab/NSF NUE/Bumm & Johnson
TEM IMAGES
www.udel.edu ; www.nano-lab. com ; www.thermo.com