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November 14, 2005 EEBE 512/ENEL 619.15 Dr. KE Jones
Lecture 22: Chapter 4: Surface Characterization in Biomaterials and Tissue Engineering
Really just a bunch of Microscopy.
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
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It’s from the Greek, mikros (small) and skopeo (look at).
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Objectives
Starting from the de Broglie equation, demonstrate that TEM resolution depends on the voltage of the accelerating field
Describe the principle and sample preparation for: TEM, SEM, 2 modes of STM & SFM, XPS, AES, SIMS, ISS,
FT-IR, ATR, FTIR-ATR
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Outline
TEM SEM
Electron Microscope
STM SFM
Scanning Probe Microscope
Surface Topography
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Why EM?
The topography of biomaterials we are interested in are very small.
• ceramics
• composites
• metals
• polymers
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
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EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
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Why electrons?
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It all started with light, but even with better lenses, oil immersion and short wavelengths, resolution was only about 0.2 mm/1000x = 0.2 micrometers.
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
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EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
TEM invented in 1931Dr. Ernst Ruska at the University of Berlin.
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EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Fig 4.4 (a) TEM
Condenser
Objective
Projector
Sample
Fluorescent screen
Electron source
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• e- can “scatter” or pass thru sample (i.e. slide projector)• transmitted e- (no scat) produce image• The denser parts of the sample scatter more e- > less e- transmitted > appears darker
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
TEM cont’
1. Chemical (fixation, washing, dehydration, infiltration with solvents & resins, embedding and curing)
2. Ultamicrotomy: 30 - 60 nm
3. Stained with e- dense material
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
TEM (the end)
• Only unscattered e- are visualized.
• No 3D, can’t see surface (although
shadowing)
• Can’t cut everything small enough.
Materials Sciences Division—Lawrence Berkeley National Laboratory
Four images, each taken at 60 second intervals, portray the rightward march of indium atoms along a carbon nantoube under an applied bias of 2 volts. The ends of the nanotube, where the electrical contacts are made, are out of view to the left and right. Reversing the direction of the voltage reverses the direction of motion.
Carbon Nanotubes as Nanoscale Mass ConveyorsAtom Transport at the Nanoscale
A. Zettl , 04-5
100 nm
Model depiction of the motion of atoms along a single-walled carbon nanotube. In principle, this phenomenon could be the basis for arrays of nano-sized conveyor belts delivering mass to specific locations atom-by-atom or picking up material at one site and delivering it to another.
Image created by K. Jensen.
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Scanning Electron Microscope
First true SEM, 1942, resolution 50 nm, magnification 8000x.Now, 1 nm & 400 000x.
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Fig. 4.4 (b) SEM
Condenser
Condenser
Condenser
Sample
Electron source
Deflector
CRT
Detector
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• uses e- that interactinteract with sample• detector• production of 2ndary e- > detector > more 2ndary e- in dense areas• 3D-image of surface features
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
SEM cont’
1. Dry and stable in vacuum
2. Apply a thin metal coating to specimen to make it conductive
3. Bunch of other stuff not mentioned in text.
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
UofA Electron Microscope Facility
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http://www.ualberta.ca/~mingchen/index.htm
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
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Butterfly wing surface
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
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EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
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Origami crane folded by Dr. Ming Chen
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Where are we…
TEM SEM
Electron Microscope
STM SFM
Scanning Probe Microscope
Surface Topography
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Scanning Tunneling Microscope
• uses e- tunneling effect• apply voltage between probe tip and sample surface• tunneling current develops
• measures mech &/or elec properties at atomic level• images from voltage, current and/or probe position
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
STM cont’
Two Modes
Constant current:
• bumpy surface
• feedback through high gain voltage amps, keeps tunneling current constant by moving probe
• voltage & 3d position
Constant height:
• flat surface
• current & 2d position
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Scanning Force Microscope
• also Atomic Force Microscope (AFM)• measures atomic forces between probe and sample surface
• van der Waals (attactive, dominate @ large dist)• exclusion principle (repulsive, dominate @ near dist)
• piezoelectric element controls movement
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
STM cont’
Two Modes
Constant force:
• feedback of force controls piezoscanner that controls sample position
• piezoscanner position
Constant height:
• sample at constant height
• measure deflection of cantilever (optical)
• contact or not (shear force problem)
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
STM cont’
Laser
Lens
Sample
Piezoscanner
Two-segment photodetector
Mirror Cantilever
Fig 4.9 Optical lever
EEBE 512/ENEL 619.15 Dr. KE JonesNovember 14, 2005
Objectives
Starting from the de Broglie equation, demonstrate that TEM resolution depends on the voltage of the accelerating field
Describe the principle and sample preparation for: TEM, SEM, 2 modes of STM & SFM, XPS, AES, SIMS, ISS,
FT-IR, ATR, FTIR-ATR