Alexander Kane

Hydrogen Sensing and Sensitivity of Palladium-Decorated Single-Walled Carbon Nanotubes with Defects

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 sites 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.

Graphitic Electrical Contacts to Metallic Single Walled Carbon Nanotubes Using Pt Electrodes

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.

Mechanism‐Guided Improvements to the Single Molecule Oxidation of Carbon Nanotube Sidewalls

Real-time monitoring of carbon nanotube conductance during electrochemical and chemical etching reveals the electronic signatures of individual bond alteration events on the nanotube sidewall. Tracking the conductance of multiple single-molecule experiments through different synthetic protocols supports putative mechanisms for sidewall derivatization. Insights gained from these mechanistic observations imply the formation of sidewall carboxylates, which are useful as handles for bioconjugation. We describe an electronic state required for efficacious chemical treatment. Such real-time monitoring can improve carboxylate yields to 45 % or more. The experiments illustrate the power of molecular nanocircuits to uncover and direct the mechanisms of chemical reactions.

High temperature resistance of small diameter, metallic single-walled carbon nanotube devices

The effects of high temperature cycling on the resistance of metallic single-walled carbon nanotube (SWCNT) devices is measured in situ. Individual, small-diameter SWCNTs contacted by palladium or titanium electrodes were measured from room temperature up to 1000K in ultrahigh vacuum. Upon the first thermal cycling, the device resistances fluctuate and generally decrease. Pd-contacted devices typically become stable by 450K, whereas Ti-contacted devices require higher treatments above 600K. Once these temperatures have been exceeded, subsequent thermal cycling has minimal effects. Heat-treated devices exhibit linear temperature dependences, with Pd and Ti contacts producing average temperature coefficients of −3×10−4∕K and 1.1×10−3∕K, respectively.