Do it with electrons ! Microscopy Structure determines properties We have discus

Do it with electrons ! Microscopy Structure determines properties We have discus www.phwiki.com

Do it with electrons ! Microscopy Structure determines properties We have discus

Edwards, Danny, Faculty Advisor has reference to this Academic Journal, PHwiki organized this Journal Do it with electrons ! Microscopy Structure determines properties We have discussed crystal structure (x-ray diffraction) But consider now different level of structure Microstructure ()- also affects properties Microscopy Structure determines properties We have discussed crystal structure (x-ray diffraction) But consider now different level of structure Microstructure – also affects properties Cemented WC () cutting tool

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Microscopy Structure determines properties We have discussed crystal structure (x-ray diffraction) But consider now different level of structure Microstructure – also affects properties Ferroelectric domains in BaTiO3 Microscopy Structure determines properties We have discussed crystal structure (x-ray diffraction) But consider now different level of structure Microstructure – also can be ‘art ()’ Electron microscopy SEM – scanning electron microscopy tiny electron beam scanned across surface of specimen backscattered () or secondary electrons () detected signal output to synchronized display

Electron microscopy SEM – scanning electron microscopy Magnification range 15x to 200,000x Resolution of 50 Å Excellent depth of focus Relatively easy sample prep SEM – scanning electron microscopy Electron gun Don’t make x-rays – use electrons directly Wavelength: NOT = hc/E (massless photons) = h/(2melectronqVo)1/2 (non-relativistic) = h/(2melectronqVo + q2Vo2/c2)1/2 (relativistic ()) SEM – scanning electron microscopy = h / (2melectronqVo + q2Vo2/c2)1/2 = 1.22639 / (Vo + 0.97845 · 10-6Vo2)1/2 (nm) & Vo(volts) 10 kV ——> 0.12 Å 100 kV ——> 0.037 Å

SEM – scanning electron microscopy SEM – scanning electron microscopy SEM – scanning electron microscopy

SEM – scanning electron microscopy Electron gun SEM – scanning electron microscopy Effects of increasing voltage in electron gun: Resolution increased ( decreased) Penetration increases Specimen charging increases (insulators) Specimen damage increases Image contrast decreases = h/(2melectronqVo + q2Vo2/c2))1/2 SEM – scanning electron microscopy Field emission electron source: High electric field at very sharp tip causes electrons to “tunnel” maybe

SEM – scanning electron microscopy Field emission electron source: High electric field at very sharp tip causes electrons to “tunnel” SEM – scanning electron microscopy Field emission electron source: High electric field at very sharp tip causes electrons to “tunnel” cool tip ——> smaller E in beam improved coherence many electrons from small tip ——> finer probe size, higher current densities (100X >) problems – high vacuum, more $$$, fussy SEM – scanning electron microscopy Lenses electrons focused by Lorentz as long as ce from electromagnetic field F = qv x B effectively same as optical lenses Lenses are ring-shaped coils generate magnetic field electrons pass thru hollow center lens focal length is continuously variable apertures control, limit beam

SEM – scanning electron microscopy Specimen Conducting – little or no preparation attach to mounting stub as long as insertion into instrument may need to provide conductive path with Ag paint Non-conducting – usually coat with conductive very thin layer (Au, C, Cr) SEM – scanning electron microscopy Specimen Can examine fracture surfaces electronic devices fibers coatings particles etc. SEM – scanning electron microscopy Specimen Can be tilted, translated Specimen size limited by size of sample chamber

SEM – scanning electron microscopy Specimen What comes from specimen Backscattered electrons Secondary electrons Fluorescent X-rays Brightness of regions in image increases as atomic number increases (less penetration gives more backscattered electrons) SEM – scanning electron microscopy Electron energy distribution SEM – scanning electron microscopy Backscattered electron detector – solid state detector electron energy up to 30-50 keV annular around incident beam repel secondary electrons with — biased mesh images are more sensitive to chemical composition (electron yield depends on atomic number) line of sight necessary

Edwards, Danny Renegade Rip Faculty Advisor www.phwiki.com

SEM – scanning electron microscopy Secondary electron detector – scintillation detector SEM – scanning electron microscopy Secondary electron detector – scintillation detector SEM – scanning electron microscopy Choose correct detector- topography example Fracture surface in iron backscattered electrons secondary electrons

SEM – scanning electron microscopy Composition – what elements present at a particular spot in specimen Use solid state detector Do energy scan as long as fluorescent X-rays SEM – scanning electron microscopy Composition mapping – x-ray fluorescence Use solid state detector set as long as X-ray energy as long as a particular element in specimen SEM – scanning electron microscopy Interaction volume Backscattered electrons come from whole volume (high energy) Secondary electrons come from neck only (low energy)

SEM – scanning electron microscopy Resolution Determined by probe size SEM – scanning electron microscopy Depth of field SEM – scanning electron microscopy Depth of field

Edwards, Danny Faculty Advisor

Edwards, Danny is from United States and they belong to Renegade Rip and they are from  Bakersfield, United States got related to this Particular Journal. and Edwards, Danny deal with the subjects like Local News; Student/Alumni Interest

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This Particular Journal got reviewed and rated by Jesuit School of Theology of Santa Clara University and short form of this particular Institution is CA and gave this Journal an Excellent Rating.