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ECE_220A_Lecture-16_Nov_15_2011_slides

ECE_220A_Lecture-16_Nov_15_2011_slides - SEM...

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SEM
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http://research.amnh.org/pbi/description/imaging.html
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electron microscope image of a fruit fly’s compound eye http://arstechnica.com/science/news/2009/03/looking-at-the-worlds-tiniest-dumbbells.ars
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Feather
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http://commons.wikimedia.org/wiki/File:AFM_%28used%29_cantilever_in_Scanning_Electron_Microscope,_magnification_1000x.GIF
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Electron column EDS detector Sample entry Pumps Image EDS data secondary electron detector
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secondary electron <50 eV Backscattered electron >50 eV up to incident energy Interaction volume Electrons incident upon you sample
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secondary electron <50 eV Backscattered electron >50 eV up to incident energy Interaction volume Electrons incident upon you sample
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Topological Contrast
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Topological Contrast
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Backscattered electron yield vs Z Electron yield vs energy Secondary electrons are more surface sensitive
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Atomic Number Contrast: backscattered electron image
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SEM Optics The condenser lenses demagnify the objective (the image of the beam source- filament) The objective lens focuses on the specimen as well as demagnifies
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Working Distance: Specimen to lens Specimen must be moved closer to be in focus
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Smaller beam diameter Beam Size
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Lens Aberrations Spherical aberration (d s ) (aperture- beam current, diffraction limit (d d ) minimum size) Chromatic aberration (d c ) (Energy spread of electron source) Actual Probe Size = (d p 2 + d s 2 + d d 2 + d c 2 ) 1/2
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