Vaikunth R. Khalap

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.

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 probes 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. For example, a phenolic type of covalent defect is revealed to produce a tunnel barrier 0.1 eV high and 0.5 nm wide.

Sensitivity of point defects in one dimensional nanocircuits

When tailored to contain a single resistive defect, one dimensional nanocircuits can realize high dynamic range, high bandwidth transduction of single molecule chemical events. The physical mechanisms behind this sensitive transduction, however, remain poorly understood. Here, we complement ongoing sensing measurements with scanning probe characterization of the electronic properties of defects. The high sensitivity of defect sites is directly probed, and is found to be in excellent agreement with a finite element model containing realistic device parameters for the defect sites. The model illuminates the most likely sensing mechanisms of these single molecule circuits, and fully supports the premise that further tailoring of the defect sites could enable the chemically selective interrogation of a wide range of complex molecular interactions.