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Signatures of Chemical Defects in Carbon Nanotube Electronic Devices Brett Goldsmith Collins Lab Department of Physics and Astronomy A broad look at defects Types of Devices (all CVD SWCNT): •pristine nanotube with nearly ballistic conduction •Growth defects in unmodified nanotubes •Mild oxidation (no missing carbon) •Harsh oxidation (missing carbon) Tools to Study CNT Defects •Scanning Tunneling Microscopy Ishigashi, PRL. November, 2004 •Chemical Labeling Fan, Nature Materials. December, 2005 •Scanning Gate Microscopy Bachtold, PRL. June, 2000 •Kelvin Force Microscopy Bachtold, PRL. June, 2000 Fan, Nature Materials. December, 2005 Scanning Probe Microscopy - KFM Source Drain VSD VF Vtip Kelvin Force Microscopy (KFM): • Records forces between tip and sample • Measures Surface Potential • Allows indirect measurement of local resistance Source Drain Scanning Probe Microscopy - SGM Source Drain VSD VF Scanned Gate Microscopy (SGM): • Records current through the nanotube circuit • Measures local field sensitivity • Shows where the device is “gate sensitive” Vtip topography topography + SGM Growth Defects - KFM Ballistic Nanotube Nanotube with Growth Defects Growth Defects – KFM detail Ballistic Nanotube Nanotube with Growth Defects: Growth Defects - SGM topography topography + SGM Defect Creation on Nanotubes WE RE CE Vg Many ways to create defects: •Mechanical •Chemical •Irradiation •Electrochemical Jaan Mannik V18.7 Basic Effects of Oxidation Current (nanoAmps) 6000 Pristine Nanotube 4000 2000 0 -2000 -4000 -6000 -0.50 -0.25 0.00 Voltage 0.25 0.50 Basic Effects of Oxidation Current (nano Amps) 200 Weak Defect Weak Oxidation 100 0 -100 -200 -0.50 -0.25 0.00 Voltage 0.25 0.50 Basic Effects of Strong Oxidation Current (nanoAmps) 4 Strong Defect Strong Oxidation 2 0 -2 -4 -0.50 -0.25 0.00 Voltage 0.25 0.50 Mild Oxidation - SGM topography topography + SGM One SWNT after Progressively Harsh Treatments Surface Potential along as-grown CNT: Surface Potential after mild oxidation: Surface Potential after strong oxidation: Weak Defects - KFM Ballistic Nanotube Mildly Oxidized Nanotube Summary Dr. Yuwei Fan Dr. Jaan Mannik Brett Goldsmith Alex Kane Derek Kingrey Bucky Khalap Kevin Loutherback Fatima Alim Yasser Elliasal UCI Integrated Nanosystems Research Facility Engineering the Microworld at The University of California, Irvine ACS-PRF Microscopy techniques such as KFM and SGM show that oxidation and growth defects have similar effects on CNT circuits.
