The electronic properties of single-walled carbon nanotubes are shown here to be extremely sensitive to the chemical environment. Exposure to air or oxygen dramatically influences the nanotubes' electrical resistance, thermoelectric power, and local density of states, as determined by transport measurements and scanning tunneling spectroscopy. These electronic parameters can be reversibly "tuned" by surprisingly small concentrations of adsorbed gases, and an apparently semiconducting nanotube can be converted into an apparent metal through such exposure. These results, although demonstrating that nanotubes could find use as sensitive chemical gas sensors, likewise indicate that many supposedly intrinsic properties measured on as-prepared nanotubes may be severely compromised by extrinsic air exposure effects.

https://science.sciencemag.org/content/sci/287/5459/1801.full.pdf

Extreme oxygen sensitivity of electronic properties of carbon nanotubes

Carbon nanotubes are unique tubular structures of nanometer diameter and large length/diameter ratio. The nanotubes may consist of one up to tens and hundreds of concentric shells of carbons with adjacent shells separation of ∼0.34 nm. The carbon network of the shells is closely related to the honeycomb arrangement of the carbon atoms in the graphite sheets. The amazing mechanical and electronic properties of the nanotubes stem in their quasi-one-dimensional (1D) structure and the graphite-like arrangement of the carbon atoms in the shells. Thus, the nanotubes have high Young’s modulus and tensile strength, which makes them preferable for composite materials with improved mechanical properties. The nanotubes can be metallic or semiconducting depending on their structural parameters. This opens the ways for application of the nanotubes as central elements in electronic devices including field-effect transistors (FET), single-electron transistors and rectifying diodes. Possibilities for using of the nanotubes as high-capacity hydrogen storage media were also considered. This report is intended to summarize some of the major achievements in the field of the carbon nanotube research both experimental and theoretical in connection with the possible industrial applications of the nanotubes.

Carbon nanotubes: properties and application

The Element Carbon Frank Hennrich, Valerie Moore, Marco Rolandi, and Mike O'Connell Allotropes of Carbon History Structure Progress of Single-Walled Carbon Nanotube Research toward Application References Synthesis of Carbon Nanotubes David Mann Introduction CNT Synthesis Methods Overview Specifics of CVD Growth Method Recent Advances in SWCNT Growth Control Conclusion References Carbon Nanotube Peapod Materials Satishkumar B. Chikkannanavar, Brian W. Smith, and David E. Luzzi Introduction and Historical Perspective C60@SWNT Beyond C60: Other Hierarchical Nanotube Materials Ordered Phases of Fullerenes in Larger Nanotubes Double-Wall Carbon Nanotubes Conclusions and Future Prospects Acknowledgments References Carbon Nanotube Electronics and Devices Marcus Freitag Metallic Carbon Nanotubes Semiconducting Carbon Nanotubes Outlook and Challenges References Magnetic Properties Junichiro Kono and Stephan Roche Introduction Theoretical Perspectives Experimental Results Acknowledgments References Raman Spectroscopy of Single-Walled Carbon Nanotubes: Probing Electronic and Chemical Behavior Stephen K. Doorn, Daniel Heller, Monica Usrey, Paul Barone, and Michael S. Strano Introduction Resonance Raman Studies of Carbon Nanotubes Raman Characterization of Nanotube Samples and Nanotube Reactivity Conclusions References Electromechanical Properties and Applications of Carbon Nanotubes Randal J. Grow Introduction Piezoresistance Theory of Strain-Induced Band-Gap Changes in Carbon Nanotubes Electrical Measurements of Strain-Induced Band-Gap Changes in Suspended Tubes Electrical Measurements of Strain-Induced Band-Gap Changes in Tubes on a Surface Conclusion of Piezoresistance of Nanotubes Electrostatic actuation Nanoelectromechanical systems Conclusion References Carbon Nanotube-Enabled Materials Han Gi Chae, Jing Liu, and Satish Kumar Introduction Dispersion and Processing Issues Characterization of Polymer/CNT Composites CNT Films and Fibers Polymer/CNT Composite Films and Fibers Crystallization, Wrapping, Interaction, and Intercalation Concluding Remarks Acknowledgment References Functionalized Carbon Nanotubes in Composites Christopher A. Dyke and James M. Tour Introduction SWNT Preparation and Characterization Functionalized SWNTs Carbon Nanotube-Modified Composites Conclusions Acknowledgments References Carbon Nanotube Tips for Scanning Probe Microscopy C. Patrick Collier Carbon nanotubes as AFM probes Fabrication of nanotube probe tips AFM imaging with nanotube probes Applications of carbon nanotube probes Future directions Acknowledgments References Index

Carbon Nanotubes: Properties and Applications

Dense, thick films of aligned single wall carbon nanotubes and nanotube ropes have been produced by filtration/deposition from suspension in strong magnetic fields. Electrical resistivity exhibits moderate anisotropy with respect to the alignment axis, while the thermopower is the same when measured parallel or perpendicular to this axis. Both parameters have identical temperature dependencies in the two orientations. Thermal conductivity in the parallel direction exceeds 200 W/mK, within a decade of graphite.

Electrical and thermal transport properties of magnetically aligned single wall carbon nanotube films

We have observed experimentally that the thermal conductance of a 2.76-μm-long individual suspended single-wall carbon nanotube (SWCNT) was very close to the calculated ballistic thermal conductance of a 1-nm-diameter SWCNT without showing signatures of phonon−phonon Umklapp scattering for temperatures between 110 and 300 K. Although the observed thermopower of the SWCNT can be attributed to a linear diffusion contribution and a constant phonon drag effect, there could be an additional contact effect.

Thermal conductance and thermopower of an individual single-wall carbon nanotube.

We have measured the temperature-dependent thermoelectric power (TEP) of crystalline ropes of single-walled carbon nanotubes. The TEP is large and holelike at high temperatures and approaches zero as T{r_arrow}0 . The results argue against the opening of a gap at low temperature in these materials. When derived from a simple band structure picture, the TEP of a single metallic nanotube is significantly lower than the measured TEP, strongly suggesting that the predicted electron-hole symmetry of metallic nanotubes is broken when the tubes self-assemble into ropes. Different models for the symmetry breaking are considered. {copyright} {ital 1998} {ital The American Physical Society}

/pdf/thermoelectric-power-of-single-walled-carbon-nanotubes-3c8reir34u.pdf

M. Muno

Papers

Thermoelectric Power of Single-Walled Carbon Nanotubes