Scanning gate spectroscopy and its application to carbon nanotube defects.

A variation of scanning gate microscopy (SGM) is demonstrated in which this imaging mode is extended into an electrostatic spectroscopy. Continuous variation of the SGM probe's electrostatic potential is used to directly resolve the energy spectrum of localized electronic scattering in functioning, molecular scale devices. The technique is applied to the energy-dependent carrier scattering that occurs at defect sites in carbon nanotube transistors, and fitting energy-resolved experimental data to a simple transmission model determines the electronic character of each defect site.

Atomistic oxidation mechanism of a carbon nanotube in nitric acid.

Motivated by recent experiments, we investigate how NO3-SWNT interactions become energetically favorable with varying oxidation state of a single-walled carbon nanotube (SWNT) using first-principles calculations. Chemisorption becomes less endothermic with respect to physisorption when the SWNT oxidation state is elevated. Importantly, the dissociative incorporation of an oxygen atom into the SWNT sidewall becomes highly favorable when the SWNT oxidation state is elevated from electron density depletion in the vicinity, as caused experimentally using electrochemical potential.

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.

Conductance-controlled point functionalization of single-walled carbon nanotubes.

We used covalent attachments to single-walled carbon nanotubes (SWNTs) to fabricate single-molecule electronic devices. The technique does not rely on submicrometer lithography or precision mechanical manipulation, but instead uses circuit conductance to monitor and control covalent attachment to an electrically connected SWNT. Discrete changes in the circuit conductance revealed chemical processes happening in real time and allowed the SWNT sidewalls to be deterministically broken, reformed, and conjugated to target species.