OU NanoLab/NSF NUE/Bumm & Johnson Microscopy & Resolution Magnification:Image size/Object size...

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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 Resolution Optical Microscope ~200 nm Electron Microscope ~0.1 nm

Transcript of OU NanoLab/NSF NUE/Bumm & Johnson Microscopy & Resolution Magnification:Image size/Object size...

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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 ResolutionOptical Microscope ~200 nmElectron 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 MICROSCOPESImage construction for a simple biconvex lens

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ComparisonBright-Field

Dark-Field

• Full apertureis illuminated

• A central obstruction blocks the central cone.

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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.

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www.microscopy.fsu.edu

Dark-FieldOpticalMicroscopy

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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

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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

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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