Characterization Techniques

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Characterization Techniques
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Transmission Electron Microscopy (TEM)
illumination device
condensing lens
specimen
objective lens
projection lens
viewing plane
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TEM Formation of the Image
Contrast comes from diffraction atomic number
Z contrast sample thickness
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TEM sample preparation
no stain sample must have inherent contrast and
beam resistance negative stain heavy metal
non-selectively coats sample resulting in high Z
contrast positive stain heavy metal selectively
coats sample resulting in high Z
contrast vitreous ice cryo-TEM aqueous sample
are rapidly frozen protecting the organic
material. Allows for viewing native conditions
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High resolution TEM image (twin boundary)
5 Å2
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PTA negative staining agent for TEM
PTA phosphotungstic acid H3PW12O40
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TEM image of T4 bacteriophage (negatively stained
with PTA)
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Uranyl acetate negative staining agent for TEM
(UO2(CH3COO)2)22H2O
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TEM image of earthworm hemoglobin (negatively
stained with UA)
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(No Transcript)
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Negative vs Positive staining in TEM
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Microphase separation of block copolymers in
solid state
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Organization of gold particles by block copolymer
lamellar structure
annealing
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TEM transmission electron microscopy
Pros Can visualize structures down about
2Å. Excellent lateral resolution. Can be
used in combination with spectroscopic
techniques such as EELS and XPS. Can acquire
diffraction pattern and image from the same
sample. Cons Electron beam may be
destructive to organic assemblies. Purely
organic samples often need to be
stained. Expensive instrumentation
(gt2M) Difficult technique to learn. 2D
projection of 3D objects. difficult sample
preparation
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Scanning Electron Microscopy (SEM)
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SEM images
Molybdenum trioxide crystals
Radiolarian (magnification X 750)
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SEM images of graphite polyhedral crystals
Gogotsi et al. Science 2000, 290, 317
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SEM image of white blood cell with HIV budding
from the cell surface
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SPM Scanning Probe Microscopy
Includes AFM Atomic Force Microscopy STM
Scanning Tunneling Microscopy In some cases can
image individual molecules - Å level
resolution Fraught with peril - many artifacts
are possible! Some limitations on the types of
samples that may be imaged. Relatively
inexpensive (50K-200K) easy to learn
difficult to master
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AFM Atomic Force Microscopy
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AFM Tips
Typical radius of curvature is 10-15 nm
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Atomic Force Microscopy (AFM)
AFM instrument maintains constant force between
the tip and the surface.
(FS) Force Sensor - The force sensor measures the
force between the probe and the sample by
monitoring the deflection of a cantilever.
(ZP) Z piezoelectric Ceramic - Moves the force
sensor in the vertical direction to the surface
as the probe is scanned with the X and Y
piezoelectric transducers.
(FCU) Feedback control unit - The feedback
control unit takes in the signal from the light
lever force sensor and outputs the voltage that
drives the Z piezoelectric ceramic. This voltage
refers to the voltage that is required to
maintain a constant deflection of the cantilever
while scanning.
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AFM images of graft copolymers (bottle-brushes)
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AFM images of graft copolymers (bottle-brushes)
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STM Scanning Tunneling Microscopy
Same general concept as AFM in that you raster
a tip over the surface of a sample to image
it. Method of imaging is based on the
tunneling current formed between platinum tip and
the sample. Sample should be at least
minimally conductive Extremely high resolution
images are attainable
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Scanning Tunneling Microscopy (STM)
1 - piezo-electric tube
2 - sharp metallic tip (probe)
3 conducting surface (specimen)

• STM measures tunneling current between 2 and 3
  (tip-surface distance 3Å)

• Tunneling current strongly (exponentially)
  depends on tip-surface distance
• That dependence provides an extremely high
  resolution (as low as 0.01 Å)

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High resolution STM images
Misfit dislocation loop at the Au/Ni
(111) Interface (45x50 Å2)
Palladium nanocrystal on Al2O3 (50x50 Å)
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High resolution STM image of CNT
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STM images of individual atoms
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Moving and Assembling Individual Atoms