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Author Dube, I.; Jiménez, D.; Fedorov, G.; Boyd, A.; Gayduchenko, I.; Paranjape, M.; Barbara, P.
Title Understanding the electrical response and sensing mechanism of carbon-nanotube-based gas sensors Type Journal Article
Year 2015 Publication Carbon Abbreviated Journal Carbon
Volume 87 Issue Pages 330-337
Keywords carbon nanotubes, CNT detectors, field effect transistors, FET
Abstract Gas sensors based on carbon nanotube field effect transistors (CNFETs) have outstanding sensitivity compared to existing technologies. However, the lack of understanding of the sensing mechanism has greatly hindered progress on calibration standards and customization of these nano-sensors. Calibration requires identifying fundamental transistor parameters and establishing how they vary in the presence of a gas. This work focuses on modeling the electrical response of CNTFETs in the presence of oxidizing (NO2) and reducing (NH3) gases and determining how the transistor characteristics are affected by gas-induced changes of contact properties, such as the Schottky barrier height and width, and by the doping level of the nanotube. From the theoretical fits of the experimental transfer characteristics at different concentrations of NO2 and NH3, we find that the CNTFET response can be modeled by introducing changes in the Schottky barrier height. These changes are directly related to the changes in the metal work function of the electrodes that we determine experimentally, independently, with a Kelvin probe. Our analysis yields a direct correlation between the ON – current and the changes in the electrode metal work function. Doping due to molecules adsorbed at the carbon-nanotube/metal interface also affects the transfer characteristics.
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ISSN 0008-6223 ISBN Medium
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Notes Approved no
Call Number Serial 1778
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Author Yang, Y.; Fedorov, G.; Shafranjuk, S. E.; Klapwijk, T. M.; Cooper, B. K.; Lewis, R. M.; Lobb, C. J.; Barbara, P.
Title Electronic transport and possible superconductivity at Van Hove singularities in carbon nanotubes Type Journal Article
Year 2015 Publication Nano Lett. Abbreviated Journal Nano Lett.
Volume 15 Issue 12 Pages 7859-7866
Keywords carbon nanotubes, CNT, tunable superconductivity, van Hove singularities
Abstract Van Hove singularities (VHSs) are a hallmark of reduced dimensionality, leading to a divergent density of states in one and two dimensions and predictions of new electronic properties when the Fermi energy is close to these divergences. In carbon nanotubes, VHSs mark the onset of new subbands. They are elusive in standard electronic transport characterization measurements because they do not typically appear as notable features and therefore their effect on the nanotube conductance is largely unexplored. Here we report conductance measurements of carbon nanotubes where VHSs are clearly revealed by interference patterns of the electronic wave functions, showing both a sharp increase of quantum capacitance, and a sharp reduction of energy level spacing, consistent with an upsurge of density of states. At VHSs, we also measure an anomalous increase of conductance below a temperature of about 30 K. We argue that this transport feature is consistent with the formation of Cooper pairs in the nanotube.
Address Department of Physics, Georgetown University , Washington, District of Columbia 20057, United States
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ISSN 1530-6984 ISBN Medium
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Notes PMID:26506109; Suuplementary info (attached to pdf) DOI: 10.1021/acs.nanolett.5b02564 Approved no
Call Number Serial 1782
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