RESUMEN

Using a model system of single, isolated carbon nanotubes loaded with high-capacitance metal-oxide films, we have quantitatively investigated electrochemical composites on the single-nanotube scale. Electrochemical charging and discharging of a model MnO2 storage material was used to probe interfacial charge transfer and surface impedances at the nanotube interface. We found that one single-walled carbon nanotube has an apparent surface resistivity of 30 mΩ cm(2), approximately 4 times smaller than for a multiwalled carbon nanotube and 50 times smaller than the 1.5 Ω cm(2) resistivity of Pt or graphite films. The improvement originates in the electrochemical-transport properties of microelectrodes shrunk to a nanotube's dimensions rather than any unique nanotube property like curvature, bandstructure, or surface chemistry. In explaining the enhanced performance of certain nanotube-containing composites, the results overturn widely held assumptions about nanotubes' roles while also providing guidelines for optimizing effective composites.

RESUMEN

Individual single-walled carbon nanotubes (SWCNTs) become sensitive to H(2) gas when their surfaces are decorated with Pd metal, and previous reports measure typical chemoresistive increases to be approximately 2-fold. Here, thousand-fold increases in resistance are demonstrated in the specific case where a Pd cluster decorates a SWCNT sidewall defect site. Measurements on single SWCNTs, performed both before and after defect incorporation, prove that defects have extraordinary consequences on the chemoresistive response, especially in the case of SWCNTs with metallic band structure. Undecorated defects do not contribute to H(2) chemosensitivity, indicating that this amplification is due to a specific but complex interdependence between a defect site's electronic transmission and the chemistry of the defect-Pd-H(2) system. Dosage experiments suggest a primary role is played by spillover of atomic H onto the defect site.

Asunto(s)

RESUMEN

We investigate electronic devices consisting of individual, metallic, single-walled carbon nanotubes contacted by Pt electrodes in a field effect transistor configuration, focusing on improvements to the metal-nanotube contact resistance as the devices are annealed in inert environments including ultrahigh vacuum. At moderate temperatures (T < 880 K), thermal processing results in high resistance contacts with thermally activated barriers. Higher temperatures (T > 880 K) achieve nearly transparent contacts. In the latter case, analytical surface measurements reveal the catalytic decomposition of hydrocarbons into graphene layers on the Pt surface, suggesting that improved electronic behavior is primarily due to the formation of an all-carbon nanotube-graphite interface rather than to the improvement of the nanotube-Pt one.

RESUMEN

Dual color four-wave-mixing (FWM) microscopy is used to spatially resolve the third-order optical response from individual carbon nanotubes. Good signal-to-noise is obtained from single-walled carbon nanotubes (SWNT) sitting on substrates, when the excitation beams are resonant with electronic transitions of the nanotube, by detecting the FWM response at the anti-Stokes frequency. Whereas the coherent anti-Stokes (CAS) signal is sensitive to both electronic and vibrational resonances of the material, it is shown that the signal from individual SWNTs is dominated by the electronic response. The CAS signal is strongly polarization dependent, with the highest signals found parallel with the enhanced electronic polarizibility along the long axis of the SWNT.