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Electron Irradiation
for the Production of Junctions
(a) Initial Configuration
- Virtual support plate
- absolutely inert and does not interact with the
nanotubes or the e-beam
- Kinetic energy assigned via the primary knock-on atom
(PKA) approximation is 10 eV
- corresponds to "head on" collisions with an
approximately 50 keV electron beam
(b) Simulation Details
- Carbon nanotube pairs considered: (5,5)+(5,5),
(10,0)+(10,0), (8,3)+(8,3), and (5,5)+(10,0)
- System temperature: 300 K
- Imitation of electron collision
- Periodically assigning a velocity to the PKA
- One electron collision every 10 MD steps for 2 ps; 1
ps of cooling with no collisions
- Total of 20 irradiation-cooling cycles
- Annealing at 600 K after finishing irradiation; cool
down to 300 K
(c) Final Welded Structures
i) Percentage of different carbon bonding for each
pair before and after annealing
| |
(5,5)+(5,5) |
(10,0)+(10,0) |
(8,3)+(8,3) |
(5,5)+(10,0) |
| Annealing |
Before |
After |
Before |
After |
Before |
After |
Before |
After |
| sp3 |
1.9 |
3.2 |
2.4 |
4.5 |
3.3 |
1.9 |
2.4 |
3.0 |
| sp2 |
86.2 |
85.9 |
90.2 |
89.7 |
97.0 |
88.6 |
86.2 |
87.3 |
| sp |
10.3 |
10.3 |
6.7 |
5.5 |
8.9 |
9.1 |
10.8 |
9.2 |
| Terminal |
1.6 |
0.6 |
0.7 |
0.2 |
0.8 |
0.3 |
0.3 |
0.3 |
(d) Mechanical Properties
| Tension |
Compression |
 |
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(e) Electronic Properties
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1) Ideal (5,5)-(5,5) Junction
- Tight-binding molecular dynamics (TBMD) method
used to produce relaxed, ideal junction between two coplanar (5,5)
carbon nanotubes.
- Density of states (DOS) (full curve) and
eigenvalue participation ratio (histogram) around the Fermi level
(shifted at E=0). Ohmic behavior predicted to occur.
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2) (5,5)-(5,5) Junction by
Electron Irradiation
- TBMD used to produce the relaxed atomic
structure of the junction produced by electron-beam irradiation of two
overlayed (5,5) carbon nanotubes.
- DOS (full curve) and eigenvalue participation
ratio (histogram) around the Fermi level (shifted at E=0). Weak
localization and energy quantization predicted to occur. → quantum dots!
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(f) Conclusions
- Electron irradiation can produce nanotube junctions
with unique electronic properties that are mechanically robust.
- These simulations suggest that nanomanipulation +
electron irradiation of nanotubes = arrays of all-carbon-based quantum
dots as small as 1 nm connected to ballistic conductors.
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