Application of Nanotubes

1
Application of Nanotubes

• E Antony

2
Common Applications

• Field Emission (LED, etc)
• Conductive plastics
• Conductive adhesives Connectors
• Molecular electronics
• Energy storage
• Thermal materials (conduct or insulate)
• Structural composites (Boeing 787,buildings,etc)
• Catalytic biomedical supports
• others

3
What caught my interest?

• The thermal similarity of the different types of
  nanotubes and
• The electrical differences between the different
  types of nanotubes

4
Common Applications

• Field Emission (LED, etc)
• Conductive plastics
• Conductive adhesives Connectors
• Molecular electronics
• Energy storage
• Thermal materials (conduct or insulate)
• Structural composites (Boeing 787)
• Catalytic biomedical supports
• others

5
Y?

• I am interested in the relationship between
  bonding, structure and properties of substances.
  
• So, why do the different forms have similar
  properties in some cases but different properties
  in other cases? These are contrary to most
  substances which are typically conductors of both
  heat and electricity or neither.

6
Thoughts on what I wanted to develop

• A tube which will conduct heat (sand) but not
  electricity (colored sand) and a second tube
  which will conduct both.
• A means of relating these properties to the
  molecular shapes.
• A way of demonstrating at least one application
  which uses these properties.

7
Designs

• Tube 1 Zig-Zag
• Consists of 2 nested PVC pipes each containing
  straws which have been glued in place. The
  straws are continuous between the two sets of
  pipes so that in one position, sand can pass
  through easily representing heat transfer.
  Rotation of the pipes constricts the straws and
  prevents sand from passing through easily-a
  semi-conductor. The pipes are of different
  lengths such that the lower of the outer pipes
  covers the lower inner pipe and a portion of the
  upper, inner pipe.

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Zig-Zag
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Designs

• Tube 2 Armchair
• Like tube 1 except the straws have been cut
  between the two sets of pipes so that rotation of
  the pipes does not constrict the straws and
  allows sand to pass through easily-a conductor of
  heat or electricity. Again the pipes are of
  different length such that the lower of the outer
  pipes covers the lower inner pipe and a portion
  of the upper, inner pipe.
• Each pipe contains a diagram of the structure.

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Armchair
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Additional Visual Aids

• Models of Zig-Zag and Armchair nanotubes have
  been built using sp2 plastic models and
  connectors. Along one side of each model, the
  trigonal planar sp2 has been replaced with
  trigonal bipyramidal sp3d with a plastic
  connector attached to the outer axial position.
  This demonstrates the position of the orbital
  involved in pi bonding and allows the student to
  see why the Armchair is well suited for
  electrical conduction while the Zig-Zag is not.

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Orbital Model Armchair
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Orbital Model Armchair
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Larger view Zig-Zag
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Orbital Diagram Zig-Zag
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An Introduction to Nanotubes

• Open the website, https//www.ccs.uky.edu/ernst/c
  arbontubes/TubeApplet.html (this can be accessed
  through the Favorites icon.
• Move your cursor to the lower picture, click on
  the figure and practice rotating or otherwise
  manipulating the image. View the tube from
  various perspectives so that you form a clear
  mental image of the structure.
• The box labeled Nanotube Indices will allow you
  to change the type of nanotube being viewed as
  well as the size (circumference) of the tube.
  You will notice that the default tube has indices
  (6,6). These indices are commonly referred to as
  n and m (n,m). the default indices are typical
  of one type of tube, known as an armchair
  nanotube, where nm. Try other indices where nm
  (suggestion, large values increase the
  calculation time so I would suggest using values
  of 4 to 20). I would also suggest that you
  observe the tube with the open ends vertical.
  This will provide a consistent perspective to
  assist you in seeing similarities and
  differences. What do the tubes have in common?
• Repeat 3 using indices where m0, i.e. (4,0),
  (7,0), etc. What do these have in common and how
  are they different from the armchair tubes?
  These are known as zig zag nanotubes.
• Repeat 3 using combinations where n is not equal
  to m or zero. These are known as chiral
  nanotubes. (I would suggest using n values which
  are similar to m, although it is not necessary.)
•  
• Pick up the handout which was adapted from The
  Science Teacher and an overhead transparency
  showing a molecule of graphene. Review the
  origin of the indices and how they describe the
  nanotube. Practice rolling the graphene
  overhead to produce the nanotube structure.
•  

17
Tube Identification and Labeling Activity

• The previous computer activity helped you
  identify three different structures of carbon
  nanotubes (CNTs). This activity will help
  clarify the labeling (indices) of the tubes.
• You have before you a transparency with a model
  of a portion of a graphene molecule. Graphene is
  a single sheet of graphite which we have looked
  at several times this year. A nanotube can be
  viewed as a rolled sheet of graphene. There are
  three ways to do this create each by rolling your
  transparency sheet. Note that the direction of
  the tube is shown by the direction of the
  cylinder being formed. Does this agree with what
  you saw on the computer screen? If not, you may
  wish to return to the program and compare the
  figures.
• For CNTs, the direction in which the graphene
  sheet is rolled can be identified by counting the
  number of carbon atoms it takes to move to an
  equivalent position (see Figure 1 below). Since
  graphene is a 2 Dimensional lattice, there are
  only 2 counting directions (identified as a1 and
  a2) in which this can be done. Starting from an
  arbitrary atom, the a1 and a2 vectors point
  toward the nearest equivalent atoms (Figure 1).
  The nanotube type is determined by counting how
  many atoms in the a1 direction (n) and how many
  in the a2 direction (m) are needed to
  circumscribe the tube and return to the original
  position. Create a few CNTs using your
  transparency and determine n and m for each.
  Then create the tube on the computer screen. Are
  the two images consistent? (note that lengths
  will vary due to the number of cells shown on the
  screen). Compare your results to the figures
  below
•  
• Figures and terminology for this sheet are from
  The Structures and Properties of Carbon, The
  Science Teacher, Castellini, et.al, December
  2006, Pages 36-41.

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Figures for Tube ID and Zig Zag
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Armchair
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• Now return to the website. Focus on the graphic
  on the upper right side of the display,
  specifically on the green lines. The green lines
  are directed along the tube when the tube is
  aligned vertically. When one of these lines
  passes directly through a vertex, the tube acts
  like a metal in that it is a conductor of
  electricity. (We say that it is a metallic
  conductor. In fact it conducts much better than
  a metal by a process called ballistic
  conductivity and is nearly a superconductor.)
  However, when no line passes through a vertex,
  the tube is a semiconductor, under what
  conditions is a tube metallic? (hint, use the
  indices to systematically check out each type of
  tube) your discoveries have a solid basis in
  mathematics, but the math is beyond the scope of
  this course).
•  
• After you have reached your conclusions, we will
  demonstrate the phenomena.

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Conductivity Demonstration

• To demonstrate the thermal and electrical
  conductivity of the tubes you should have the two
  tubes and two containers of colored sand
  available as well as vessels for collecting the
  sand as it is poured.
•  
•  
• Starting with the Armchair model in the Thermal
  position, hold the tube over a receiving
  container and pour the sand. (Comment-red hot,
  blue hot, etc) Note that the tube is an
  excellent conductor of heat. Those interested
  in this process should first read about phonons
  as the conductivity results from phonon waves)
•  
• Repeat the process with the Zig Zag model.
  Again, the nanotube is an excellent conductor of
  heat.
•   
• Now move the nanotube positions to Electrical
  and add the second color sand to the Armchair
  model. It is an excellent conductor of
  electricity as well as heat.
• Repeat the process with the Zig Zag model. Note
  that the electricity passes through but very
  slowly. Most Zig Zag tubes are semiconductors.
•  
• At this point students may point out that,
  according to the computer animation, some of the
  Zig Zag tubes did conduct electricity.
  Specifically those for which n/3 is a whole
  number are metallic. You should acknowledge that
  they are correct and that this model, like all
  models, has limitations and that they just found
  one of them.
•  

22
Assignment for day 2

• Assignment for tomorrow Reflect on possible
  applications of nanotubes. How could we use
  them?
• Investigate and be ready to report on an actual
  application on carbon nanotubes including
• What is the application?
• What does that mean (provide a working
  definition, not a textbook definition).
• What are the advantages provided by the nanotube
  compared to conventional materials?
• Is the application based on the property
  investigated today? If not, what other useful
  property of nanotubes was instrumental in their
  inclusion?
• Citation of your source (Be thorough but you need
  not adhere to a particular format such as APA).

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Instructor Notes for Day 2 

• List some of the applications and summarize key
  properties of nanotubes based upon the results of
  the student assignments.
•  
• Discuss why some of these are expected based upon
  the structure of the tubes.
•  
•  
•  
•  
•   
• Demonstrate the advantage of the fine tip using
  the demonstration device 2 and/or the simplified
  model.
• Show the images of the nanotube being used as the
  detecting tip on STM, AFM, etc and as
  nanotweezers.

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Demonstrations of the Importance of Tip Size

• Demonstration 1
•  
• This is a very simple demonstration yet it
  clearly shows the significance of tip size on
  probe sensitivity.
• Preparation of materials
• Using a material which is about 1/8 inch thick
  (Cardboard, stir stick for paint, etc), create an
  edge with an irregular surface. This surface
  should have some slowly sloping areas and some
  narrow, deep (1/2 inch). Next, remove the cap
  from a SharpieR pen and carefully cut off the
  closed end of the cap such that only the very tip
  of the pen is exposed. Verify that it can write
  when in a vertical position.
•  
• Place a sheet of clean paper under the surface.
  Using the SharpieR, trace along the edge of the
  surface. Place the cut cap on the pen and again
  trace the surface. Show the results. It should
  be clear that the wide probe was able to detect
  slow changes along the surface but could not
  provide significant information about crevices,
  etc, while the fine tip yielded a much better
  representation of the surface.
•  
• Show the students the picture of the nanotube
  mounted on a conventional AFM tip (below). A
  picture of a folded protein or similar structure
  would provide additional discussion for the
  class.
•  
•  
•  

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AFM tip with nanotube
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• Demonstration 2
•  
• This demonstration shows both the significance of
  tip size and the magnification of a signal. This
  magnification is mechanical as opposed to an
  instrument which uses electrical amplification.
•  
• Completing the Demonstration
•  
• Mount a pen in the Pen Holder and a fresh sheet
  of paper on the clipboard (our recording device).
  Place the probe on the upper end of the surface
  to be scanned and slowly slide the clipboard so
  that it pulls the sample upwards. You may have
  to relieve the tension if the probe becomes
  stuck in one of the grooves in the sample.
  When the scan is complete, replace the probe tip
  and repeat, preferably with a different color
  pen. Compare the two scans. Again, the fine
  tip will yield a truer image and one with more
  detail. If you wish, you may measure the depth
  of the crevices as well as the height of the peak
  it produced. Then compare the distance from the
  fulcrum to the pen and from the fulcrum to the
  probe. Compare the two ratios. Discuss both the
  advantages and disadvantages of magnification (a
  major disadvantage being the increase in noise
  which is also evident in the trace).

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Nanotweezers
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Thank yous and Acknowledgements

• Greta Zenner
• Jen Ehrlich, Farrell Rogers and Sue Whitsett,
• George Lisensky, Wendy Crone and Mike Condren
• Katie Cadwell, Angela Johnson, Ken Gentry and
  Dana Horoszewski
• Andrew Greenberg
• Mark Eriksson and Ernst Richter