1. Temperature Effects on the Electronic Conductivity of Carbon Nanotubes
Mark Mascaro
Department of Materials Science and Engineering
Advisor Francesco Stellacci
May 10, 2007

2. Carbene Functionalization
Image from Lee and Marzari, Physical Review Letters 97:116801, 2007.
Three bonding configurations
O open is energetically preferred
O open preserves sp2 hybridization, and therefore conductivity

3. Electrode Fabrication
25 nm palladium electrodes
Prepared by electron beam lithography (fingers) and optical lithography (pads)
Large contact pad to accommodate destructive testing

4. Room-Temperature Resistance Measurements
Four-point probe measurements were conducted across pairs of contact pads. A typical result is shown above.

5. Room-Temperature Resistance Measurements
Spread of many orders of magnitude in most samples
Similarly-prepared samples show statistical dissimilarity, indicating uneven dispersion
Tight spacing of resistance values in Carbene Prior, Pristine Prior, etc. indicates high nanotube density; implies significant resistance values

6. Point-Dwell Test for Equilibration
The predicted linear behavior is observed
Random scattering of resistance values sampled immediately after chuck reached target temperature indicates sample likely equilibrates near-instantaneously

7. Single-Pad Temperature Variation Measurements
The resistance of a set of pads was measured at 50 °C
One of these pads was ramped from 50 to 200 °C and back, with measurements at 50 degree intervals.
The set was measured again at 50 °C.
This was repeated until all pads in the set had been ramped.
A typical result is shown above.
Left: Resistance as a function of temperature for ramp up (red) and down (blue), normalized to resistance at 50 °C.
Right: Change in resistance as a function of the number of temperature cycles, normalized to initial resistance at 50 °C.

8. Single-Pad Temperature Variation Measurements
The expected behavior is linearly increasing resistance with increasing temperature, reversible upon decreasing the temperature.
Carbene and pristine show the same general behavior, while nitrobenzene displays a noisy response
All samples show an increase in resistance with repeated cycling.
In carbene, the resistance-increasing effect of repeated cycling dominates the predicted linear temperature effect
In pristine samples, decreasing resistance during the ramp down is still observed
Above: Typical carbene (red), pristine (green), and nitrobenzene (blue) curves. Solid line indicates ramp up; dashed line, ramp down.
Right: Change in baseline resistance with cycling using the same color scheme.

9. Single-Pad Temperature Variation Measurements
The expected behavior is linearly increasing resistance with increasing temperature, reversible upon decreasing the temperature.
Carbene and pristine show the same general behavior, while nitrobenzene displays a noisy response
All samples show an increase in resistance with repeated cycling.
In carbene, the resistance-increasing effect of repeated cycling dominates the predicted linear temperature effect
In pristine samples, decreasing resistance during the ramp down is still observed
Above: Typical carbene (red), pristine (green), and nitrobenzene (blue) curves. Solid line indicates ramp up; dashed line, ramp down.
Right: Change in baseline resistance with cycling using the same color scheme.

10. Conclusions Carbene samples exhibit pristine-like behavior
Closely-spaced room-temperature resistance values indicate a possible one-order difference
Similar temperature response
However, the precise difference cannot be quantified from this data alone
This measurement technique is extremely sensitive to sample preparation
Dispersion cannot be measured or controlled for
Statistical methods were inconclusive: significant variation within identical samples made absolute comparison difficult
There is evidence of a contamination effect which permanently increases resistance in these samples upon temperature cycling

11. References
Jeffrey Bahr and James Tour. Covalent chemistry of single-wall carbon nanotubes. Journal of Materials Chemistry, 12:1952–1958, 2002.
Sarbajit Banerjee, Tirandai Hemraj-Benny, and Stanislaus S Wong. Covalent surface chemistry of single-walled carbon nanotubes. Advanced Materials, 17:17-29, 2005.
Robert Chen, Sarunya Bangsaruntip, Katerina Drouvalakis, Nadine Wong Shi Kam, Moonsub Shim, Yiming Li, Woong Kim, Paul Utz, and Hongjie Dai. Noncovalent functionalization of carbon nanotubes for highly specific electronic biosensors. Proc. Nat. Acad. Sci. USA, 100:4894, 2003.
Y. Chen, R. C. Haddon, S. Fang, A. M. Rao, P. C. Eklund, W. H. Lee, E. C. Dickey, E. A. Grulke, J. C. Pendergrass, A. Chavan, B. E. Haley, and R. E. Smalley. Chemical attachment of organic functional groups to single-walled carbon nanotube material. Journal of Materials Research, 13(9): , 1998.
Hongjie Dai. Carbon nanotubes: Synthesis, integration, and properties. Accounts of Chemical Research, 35: , 2002.
Hongjie Dai, Jason H. Hafner, Andrew G. Rinzler, Daniel T. Colbert, and Richard E. Smalley. Nanotubes as nanoprobes in scanning probe microscopy. Nature, 384(6605): , 1996.
Cees Dekker. Carbon nanotubes as molecular quantum wires. Physics Today, 52:22-28, 1999.
Christopher A. Dyke and James M. Tour. Unbundled and highly functionalized carbon nanotubes from aqueous reactions. Nano Letters, 3(9): , 2003.
Young-Su Lee and Nicola Marzari. Cycloaddition functionalizations to preserve or control the conductance of carbon nanotubes. Physical Review Letters, 97:116801, 2006.
R. Saito, G. Dresselhaus, and M. S. Dresselhaus. Physical Properties of Carbon Nanotubes, Imperial College Press: London, 1998.
Sander J. Tans, Michel H. Devoret, Hongjie Dai, Andreas Thess, Richard E. Smalley, L. J. Geerligs, and Cees Dekker. Individual single-wall carbon nanotubes as quantum wires. Nature, 386: , 1997.
C. T. White and T. N. Todorov. Carbon nanotubes as long ballistic conductors. Nature, 393: , 1998.

12. AFM of Interdigitated Electrode

13. Room-Temperature Resistance Measurements

14. Single-Pad Temperature Variation Measurements: Carbene

15. Single-Pad Temperature Variation Measurements: Pristine

16. Single-Pad Temperature Variation Measurements: Nitrobenzene

17. Single-Pad Temperature Variation Measurements
Carbene and pristine show the same general behavior, while nitrobenzene displays a noisy response
All samples show an increase in resistance with repeated cycling.
In carbene, the resistance-increasing effect of repeated cycling dominates the predicted reversible, linear temperature effect
In pristine samples, decreasing resistance during the ramp down is still observed