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

Nanotube Functionalization Nitrobenzene Covalent-type functionalization binds to nanotube wall, converting sp 2 hybridization to sp 3 Destroys electronic structure and accordingly reduces conductivity Carbene Three bonding configurations O open is energetically preferred O open preserves sp 2 hybridization and conductivity Image from Lee and Marzari, Physical Review Letters 97:116801, 2007.

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

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

Room-Temperature Resistance Measurements Spread of many orders of magnitude in most samples Similarly-prepared samples show statistical dissimilarity, indicating variations in dispersion or deposition Close spacing of resistance values in some samples indicates high nanotube density; implies resistance values are meaningful

Single-Pad Temperature Variation Measurements The resistance of a set of pads was measured at 50 °C One of these pads measures while the sample was ramped from 50 to 200 °C and back, with measurements at 50 degree intervals. Each pad in the set was measured again at 50 °C. This was repeated until all pads in the set had been measured during a temperature cycle. A typical result is shown above, taken from a carbene sample. Top: Resistance as a function of temperature for ramp up (solid) and down (dashed), normalized to resistance at 50 °C. Bottom: Change in resistance as a function of the number of temperature cycles, normalized to initial baseline resistance. Resistance Ratio

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. The expected behavior is linearly increasing resistance with temperature, reversible upon decreasing the temperature. In carbene, the resistance-increasing effect of repeated cycling dominates the predicted linear temperature effect In pristine samples, some effect of the linear R-T dependence is still observed Top: Typical carbene (red), pristine (green), and nitrobenzene (blue) curves. Solid line indicates ramp up; dashed line, ramp down. Bottom: Change in baseline resistance with cycling. Resistance Ratio

Conclusions 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 a contamination effect which permanently increases resistance with temperature cycling –Expected linear response is difficult to confirm –Relative behavior of pristine and carbene is dominated by this effect and is difficult to analyze Carbene samples exhibit a general pristine-like behavior –Closely-spaced room-temperature resistance values indicate a relatively small but significant difference in conductivity, though much smaller than the pristine-nitrobenzene difference –Similar temperature response –However, the precise difference cannot be quantified from these data alone

References 1. Jeffrey Bahr and James Tour. Covalent chemistry of single-wall carbon nanotubes. Journal of Materials Chemistry, 12:1952–1958, Sarbajit Banerjee, Tirandai Hemraj-Benny, and Stanislaus S Wong. Covalent surface chemistry of single-walled carbon nanotubes. Advanced Materials, 17:17-29, 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, 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): , Hongjie Dai. Carbon nanotubes: Synthesis, integration, and properties. Accounts of Chemical Research, 35: , 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): , Cees Dekker. Carbon nanotubes as molecular quantum wires. Physics Today, 52:22-28, Christopher A. Dyke and James M. Tour. Unbundled and highly functionalized carbon nanotubes from aqueous reactions. Nano Letters, 3(9): , Young-Su Lee and Nicola Marzari. Cycloaddition functionalizations to preserve or control the conductance of carbon nanotubes. Physical Review Letters, 97:116801, R. Saito, G. Dresselhaus, and M. S. Dresselhaus. Physical Properties of Carbon Nanotubes, Imperial College Press: London, 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: , C. T. White and T. N. Todorov. Carbon nanotubes as long ballistic conductors. Nature, 393: , 1998.

AFM of Interdigitated Electrode

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

Room-Temperature Resistance Measurements

Single-Pad Temperature Variation Measurements: Carbene

Single-Pad Temperature Variation Measurements: Pristine

Single-Pad Temperature Variation Measurements: Nitrobenzene

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