Nanoscience

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Nanoscience Microscopies SEM, AFM STM
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Block Diagram of E-beam
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SEM Picts
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SEM Picts
Dendritic Growth
Ostrinium Nubilialis
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Miami Research Results
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STM

• Scanning tunneling microscope

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Outside the Barrier
Wavefunction extends outside of well edge for a
finite square well
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Two finite wells at a distance

• The electron wavefunctions extend
• into space between finite wells

http//www.chembio.uoguelph.ca/educmat/chm729/STMp
age/stmdet.htm
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Two finite wells at close approachcan look like
a barrier to the electrons!

• Electrons can tunnel into or through barriers
  depending on

http//phys.educ.ksu.edu/vqm/html/qtunneling.html
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Two finite wells at close approach

• Electron wavefunctions can overlap

http//www.chembio.uoguelph.ca/educmat/chm729/STMp
age/stmdet.htm
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• This is the STM image of Si(111)-7x7 surface, the
  white spots represents the position of the atoms.

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Scanning --

• Constant Current Mode
• Constant Height Mode
• http//www.surfaces.lsu.edu/STMoverview.html

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www.surfaces.lsu.edu/STMoverview.html
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Modes of Operation

• Constant Current
• Constant
• Height

userpage.chemie.fu-berlin.de/.../html/node5.htm
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Use of STM- Chemical Constrast
The surface of alloys may differ in several
respects from the corresponding bulk structure.
The surface may also exhibit a chemical order
different from the one in the bulk of the
material. This influences processes such as gas
adsorption and catalysis, since adsorbed
molecules often prefer a certain chemical
environment of substrate atoms. It all started
with an (111) oriented surface of a PtNi alloy
(bulk composition 25 Pt, 75 Ni surface
approx. 50 of each). We found that we can
distinguish between Pt and Ni atoms on this
surface with the STM!Since Pt and Ni are about
50 of the surface atoms each, the brighter
species is Ni. The white blobs in the image are
impurities of unknown nature.
http//www.iap.tuwien.ac.at/www/surface/STM_Galler
y/chemical_resolution.html
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Use of STM

• Excitation of different vibrational modes
  depending on species (C2H2 vs. C2D2)
• Science, 280, 1715 (1998).
• Single molecule chemical reactions
• Science News, 158, 215 (2000).

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Researchers usually compare "before" and "after"
pictures of typical regions of a material to see
how it changes during a phase transition. This
is now see on an atomic scale.
As the lead atoms in this 20 x 13 nanometer
region are warmed from 40 to 136 Kelvin, they
switch from the corrugated to the flat
arrangement at the transition temperature of 86
Kelvin . Vienna University of Technology
Phys. Rev. Lett. 94, 046101
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Downside to STM?

• Requires electrical path for tunneling
• Gives information of heights of electron clouds
  above surface eg. graphite structure
• Some questions cannot be explored

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Other cool sites

• http//www.almaden.ibm.com/vis/stm (Interesting
  STM images)
• http//www.nobel.se/physics/educational/microscope
  s/scanning/ (Interesting STM images)

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Atomic Force Microscopy
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AFM

• Cantilever structure on end on end of wafer
  holds the pyramidal tip
• Light from a diode laser bounces of tip and
  strikes a split photodetector
• Motion is detected by differences in intensity
  on the detector portions

http//www.stolaf.edu/depts/physics/afm/diagram.ht
ml
Lets also look at http//www.weizmann.ac.il/Chem
ical_Research_Support/surflab/peter/afmworks/
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Wafer TIP

• Si or SiN 10 nm at end 100 atoms

Electron micrograph of two 100 µm long V-shaped
cantilevers (by Jean-Paul Revel, Caltech
cantilevers from Park Scientific Instruments,
Sunnyvale, CA).

• Three common types of AFM tip.
• normal tip (3 µm tall) (b) supertip (c)
  Ultralever (also 3 µm tall).
• Electron micrographs by Jean-Paul Revel, Caltech.

http//stm2.nrl.navy.mil/how-afm/how-afm.html
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General Schematic
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AFM Modes

• Contact
• Low and High Gain
• Low gain drag tip across sample see
  deflection which is OK for relatively flat
  surfaces
• High gain tries to push down on sample to
  maintain a particular height which is OK for more
  bumpy surfaces, but not for soft surfaces
• - Tapping mode
• Good for local surface distortions to measure
  friction and spring forces on surfaces
• Non-contact
• Requires a frequency modulation technique which
  is good for biological samples- repulsive forces
  from surface

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Metrology -- Fabrication

• AFM can be used to study the success of e-beam
  lithography and subsequent processing steps.

Nanotechnology, 13 659 (2002).
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AFM DNA studies
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Results
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Tobacco Mosaic Virus
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Non-Contact Mode SolidLipid Nanoparticles
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STM AFM

• Microscopic techniques which give us resolutions
  in angstroms or nanometers
• Used for fabrication, chemical and biological
  studies
• A definite force in the nanoworld !