Transcript Microscopy as a means for Nano

Microscopy as a Means for
Nano-Characterization
By Thomas Williams
Phys 3500
What is Microscopy?
 Microscopy is any technique for producing
visible images of structures or details too
small to otherwise be seen by the human
eye.
What is Nano Characterization?
 What does it look like?
• Dimensions, structure,
What is it made of?
• Molecules, elemental proportions
What are it’s properties?
•Physical, chemical, electromagnetic
Why Microscopy?
 In order to effectively study something or
build something it is important to see
exactly what it is we’re doing.
 As the things we are interested in get
smaller and smaller we need more better,
meaning more powerful microscopy.
 Eventually this will necessitate advances in
the physics.
The Origens of Microscopy
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In the first century AD Romans invented glass
and began experimenting with various shapes,
stumbling upon the converging lens.
In approx. 1590 Dutch eyeglass makers Hans
and Zacharias Jensonn makes a compound
microscope.
Mid 17th century Anton Van Leeuwenhoek uses
an improved single lens microscope to view and
describe bacteria, protozoan, etc.
http://www.cas.muohio.edu/~mbi-ws/microscopes/history.html
Age of the
Optical Microscope
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In the late 17th century Robert Hooke added a
third lens, greatly improving contrast issues and
comfort.
Over the next two hundred years optical
microscopy revolutionizes science, especially
biology.
During this time improvements are continually
made, including corrections for chromatic
spherical aberrations.
In the late 19th century, Ernst Abbe showed that
the improvement of the magnification of optical
microscopes was fundamentally limited by the
wavelength of light.
http://www.microscope-microscope.org/images/BWScope.jpg
History of Electron Microscopy
 1931- Ernst Ruska co-invents the electron microscope.
• 1938- 10nm resolution reached.
• 1940- 2.4 nm resolution.
• 1945- 1.0nm resolution achieved.
 1981- Gerd Binning and Heinrich Rohrer invent the scanning
tunneling electron microscope (STM).
 1986- The Atomic Force Microscope was developed in collaboration
between IBM and Stanford University.
Transmission Electron
Microscope (TEM)
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Same principle as optical
microscope but with electrons.
Condenser aperture stops high
angle electrons, first step in
improving contrast.
The objective aperture and
selected area aperture are
optional but can enhance
contrast by blocking high angle
diffracted electrons
Advantages: we can look at non
conducting samples, i.e.
polymers, ceramics, and
biological samples.
http://www.unl.edu/CMRAcfem/temoptic.htm
TEM Images
http://www.abdn.ac.uk/emunit/emunit/temcells/index.htm
Scanning Electron Microscope
(SEM)
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The SEM functions much like an
optical microscope but uses
electrons instead of visible light
waves.
The SEM uses a series a series of
EM coils as lenses to focus and
manipulate the electron beam.
Samples must be dehydrated and
made conductive.
Images are back and white.
http://www.mos.org/sln/SEM/works/slideshow/semmov.html
SEM Images
http://www.mos.org/sln/SEM/works.html
Scanning Tunneling
Electron Microscope (STM)
 Basic principle is tunneling.
 Tunneling current flows
between tip and sample when
separated by less than 100nm.
 The tunneling current gives
us atomic information about
the surface as the tip scans.
http://www.iap.tuwien.ac.at/www/surface/STM_Gallery/index.htmlx
What is tunneling?
 The probability that the electron
will exist outside the barrier in
the vacuum is non zero.
 If these leak-out waves overlap
and a small bias voltage is
applied between the tip and the
sample, a tunneling current
flows.
 The magnitude of this tunneling
current does not give the
nuclear position directly, but is
directly proportional to the
electron density of the sample
at a point.
http://www.chembio.uoguelph.ca/educmat/chm729/STMpage/stmdet.htm
What does piezo-electric mean?
 In 1880 Pierre Curie discovered that by applying a
pressure to certain crystals he could induce a
potential across the crystal.
 The STM reverses this process. Thus, by applying
a voltage across a piezoelectric crystal, it will
elongate or compress.
 A typical piezoelectric material used in an STM is
Lead Zirconium Titanate.
QuickTime™ and a
GIF decompressor
are needed to see this picture.
http://www.iap.tuwien.ac.at/www/surface/STM_Gallery/index.htmlx
STM Images
http://www.almaden.ibm.com/vis/stm/gallery.html
Atomic Force Microscopy
(AFM)
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AFM is performed by scanning a sharp tip on the end of a flexible cantilever across the
sample while maintaining a small force.
Typical tip radii are on the order of 1nm to 10nm.
AFM has two modes, tapping mode and contact mode.
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In scanning mode, constant cantilever deflection is maintained.
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In tapping mode, the cantilever is oscillated at its resonance frequency.
http://www.nanoscience.com/education/AFM.html
http://www.azom.com/details.asp?ArticleID=3278
AFM Images
http://www.azom.com/details.asp?ArticleID=3278
http://www.nanoscience.com/index.html
AFM Video
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
http://www.nanoscience.com/education/gallery.html
Future / Conclusions
 We still have a long way to go before we’ve
exhausted the limits of electron wavelength
resolution limit.
 The wave length of a high energy electron is on
the order of .001nm or 1.0pm, our current best
resolution with an STM is only approximately
.1nm.
 Limiting factors include, aberations, contrast,
References
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Wikipedia - http://en.wikipedia.org/wiki/Main_Page
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History of the Microscope - http://www.cas.muohio.edu/~mbi-ws/microscopes/history.html
Molecular Expressions -
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http://microscopy.fsu.edu/primer/museum/hornyolddissecting1920.html
Dictionary.com - http://dictionary.reference.com/
Micro-bus -http://www.microscope-microscope.org/microscope-home.html
BBC H2G2 - http://www.bbc.co.uk/dna/h2g2/
About.com - http://about.com/
MOS - http://www.mos.org/sln/SEM/works/slideshow/semmov.html
UNL - http://www.unl.edu/CMRAcfem/temoptic.htm
IBM - http://www.ibm.com/us/
AZOM.com - http://www.azom.com/default.asp
Nanonscience Instruments - http://www.nanoscience.com/index.html
Special Thanks
 Dr. Tapas Kar & the Fall 06 NanoChemistry Crew.
 Google, and their amazing database of
resources.
 Utah State, for seeing the growing need to
offer classes in nanotechnology.