Laser Synthesis of Single Wall Carbon Nanotubes

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Laser Synthesis of Single Wall
Carbon Nanotubes

• By Katie Chapin

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Topics of Discussion

• Carbon Nanotubes
• Definition
• Symmetries
• Zigzag
• Armchair
• Chiral
• Functions
• Laser Vaporization
• Experimental Process

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Topics of Discussion (cont.)

• Rochester Institute of Technology
• Problems with Experiment
• Target Pattern
• Coning
• Computer Program
• Target Pattern
• Overall Results

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Carbon Nanotubes

• Hexagonal network of carbon atoms
• Rolled up to form a cylinder
• Capped ends
• One nanometer wide by a few microns long
• Extremely strong
• Stronger than steel per unit weight

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Parameters for Carbon Nanotubes

• Chna1 ma2(n,m)
• Tt1a1 t2a2(t1,t2)
• t1(2mn)/d
• t2-((2nm)/d)
• where dgcd(n,m)
• cos? ((2nm)/(2sqrt((n2) (m2)nm)))

• Chiral vector (OA) is perpendicular to the
  nanotube axis
• Translational vector (OB) is parallel to the
  nanotube axis
• Chiral angle ? specifies the spiral symmetry

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Symmetries - Unit Cell
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Classification of Symmetries

• Zigzag nanotubes correspond to (n,0) or (0,m) and
  have a chiral angle of 0, armchair nanotubes
  have (n,n) and a chiral angle of 30, while
  chiral nanotubes have general (n,m) values and a
  chiral angle of between 0 and 30.

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Symmetries - Unit Cell (cont.)
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Functions of a Carbon Nanotube

• Semiconductor
• Zigzag and Chiral
• Metallic
• Armchair
• Storage
• Efficient light source
• High strength qualities

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Laser Vaporization
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Experimental Process

• Computer program
• Digitally controlled mirrors
• Laser beam
• Graphite target
• Quartz chamber filled with Argon gas
• Cooled collection probe

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Rochester Institute of Technology

• Dr. Thomas Gennett
• Chemistry professor at RIT
• National Renewable Energy Lab.
• Nanotechnology laboratory
• Varying over 55 different parameters to yield a
  productive rate of nanotubes (50mg/hr)

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Problems with Experiment

• Laser Pattern
• 50 overlap
• Develops cones

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Coning

• Heating of the target can reach temp. which cause
  the metal catalyst to melt in the local region
• Molten catalyst migrates to surface
• Cools causing large particles of metal to form at
  the surface
• Laser is unable to vaporize the larger particles,
  making that area of the target no longer active

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Coning (cont.)

• Production of nanotubes is inhibited and product
  yields decrease significantly
• Laser vaporizes the inhomogeneous material
• Cones can break off, contaminating soot

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Computer Program Comments

• Create vector program called a
• Command moves mirrors so laser hits point
  (1000,1000) in 10 tics. One tic is approximately
  23 milliseconds. The laser will repeatedly hit
  (1000,1000) for 10870 tics, 10870 allows the
  laser to hit the spot 5 times before moving. The
  program that was the most successful was a wait
  of 2500, one hit by the laser before moving.

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Computer Program

• createpgm 1 a
• slewxy 1000 1000 10 slewxy 1000 0
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• wait 10870 wait 10870
• wait 10870 wait 10870
• slewxy -100 1000 10 slewxy 0 -100
  10
• wait 10870 wait 10870
• wait 10870 wait 10870
  

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Target Pattern

• 50 overlap between adjacent spots
• Laser hits once and then moves

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Overall Results

• Production rates increased by up to 100
• Quality of material increased from 20w/w to
  40w/w b/c of the reduction of metal
• Diameters decreased
• (w/w means percent by weight)

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Overall Results (cont.)

• Graph depicts the different patterns and their
  affects on the diameter of nanotubes
• All data taken from lab results at RIT.

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Any Questions??