This document discusses microscopy techniques and their resolutions. Optical microscopes have a resolution of around 200 nm while electron microscopes can achieve resolutions as low as 0.1 nm. It explains the Rayleigh resolution criterion and how numerical aperture affects resolution. Dark-field optical microscopy is described as using marginal rays and blocking the central cone to only image scattered light. Components of transmission electron microscopes are outlined, noting they use electrons rather than light for higher resolutions down to 1-0.2 nm.

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Microscopy & Resolution
Magnification: Image size/Object size
Resolution: The fineness of detail that can be
distinguished in an image.
Highest Typical Resolution
Optical Microscope ~200 nm
Electron Microscope ~0.1 nm

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Definitions
• Acceptance angle θ
• Numerical Aperture
NA = n sinθ
• Rayleigh resolution criterion for a circular
aperture Δx = 0.61 λ/NA
θ

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OPTICAL MICROSCOPES
Image construction for a simple biconvex lens

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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

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Comparison
Bright-
Field
Dark-
Field
• Full
aperture
is
illuminated
• A central
obstruction blocks
the central cone.

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Dark-Field
Optical 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.

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Dark-Field
Optical
Microscopy

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THE ELECTRON MICROSCOPE
The 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

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Components of the TEM
1. Electron Gun: Filament, Anode/Cathode
2. Condenser lens system and its apertures
3. Specimen chamber
4. Objective lens and apertures
5. Projective lens system and apertures
6. Correctional facilities (Chromatic, Spherical, Astigmatism)
7. Desk consol with CRTs and camera
Transformers: 20-100 kV; Vacuum pumps: 10-6 – 10-10 Torr

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Schematic of E Gun & EM lens
Magnification: 10,000 – 100,000; Resolution: 1 - 0.2 nm
www.udel.edu

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TEM IMAGES
www.udel.edu ; www.nano-lab. com ; www.thermo.com