We present results from two approaches to probe the connection between atomic-scale structure and/or defects and functional electronic properties in carbon nanotube-based devices. The effect of defects on electron transport in carbon nanotube field effect transistors (CNFETs) is measured by combined scanning gate microscopy (SGM) and scanning impedance microscopy (SIM). The Fermi energy of individual defects is quantified from SGM images with varying tip bias voltage. Three regimes of transport are identified as the back gate voltage is used to increase the carrier density within the CNFET: defect-limited transport at low carrier density, a diffusion-like regime at intermediate density, and a nearly ballistic regime at high carrier density. In a second set of experiments, we have developed a new chip-based platform for simultaneous transport measurement and transmission electron microscopy of active nanotube devices.
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