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• 1. [Article] Neutron-Scattering Study of Librations and Intramolecular Phonons in Rb_{2.6}K_{0.4}C_{60}

  We report the results of inelastic neutron-scattering measurements on Rb2.6K0.4C60. Librational modes were observed as broad peaks with maxima between 4.1 and 4.7 meV, as the temperature is lowered from ...

  Citation × Citation Citation Abstract Copy Title: Neutron-Scattering Study of Librations and Intramolecular Phonons in Rb_{2.6}K_{0.4}C_{60} Author: Reznik, D., Kamitakahara, W. A., Neumann, D. A., Copley, J. R. D., Fischer, J. E., Strongin, Robert M., Cichy, M. A., Smith, Amos B., III Year: 1994 We report the results of inelastic neutron-scattering measurements on Rb2.6K0.4C60. Librational modes were observed as broad peaks with maxima between 4.1 and 4.7 meV, as the temperature is lowered from 300 to 12 K. As in K3C60, no change in the width or position of the librational peak was observed when the sample was cooled through the superconducting transition. Thus any coupling of the librations to electronic states is small. The magnitude of the orientational potential barrier was estimated from the librational peak frequency. A flat background observed in the low-energy inelastic-scattering spectra is ascribed to two-phonon scattering. The density of states of intramolecular modes is similar to that of previously studied M3C60 compounds; modes at 53 and 66 meV in pure C60 are not observed in Rb2.6K0.4C60. Title: Neutron-Scattering Study of Librations and Intramolecular Phonons in Rb_{2.6}K_{0.4}C_{60} Author: Reznik, D., Kamitakahara, W. A., Neumann, D. A., Copley, J. R. D., Fischer, J. E., Strongin, Robert M., Cichy, M. A., Smith, Amos B., III Year: 1994 We report the results of inelastic neutron-scattering measurements on Rb2.6K0.4C60. Librational modes were observed as broad peaks with maxima between 4.1 and 4.7 meV, as the temperature is lowered from 300 to 12 K. As in K3C60, no change in the width or position of the librational peak was observed when the sample was cooled through the superconducting transition. Thus any coupling of the librations to electronic states is small. The magnitude of the orientational potential barrier was estimated from the librational peak frequency. A flat background observed in the low-energy inelastic-scattering spectra is ascribed to two-phonon scattering. The density of states of intramolecular modes is similar to that of previously studied M3C60 compounds; modes at 53 and 66 meV in pure C60 are not observed in Rb2.6K0.4C60. Close

• 2. [Article] One-Dimensional Nanostructure and Sensing Applications: Tin Dioxide Nanowires and Carbon Nanotubes

  The key challenge for a nanomaterial based sensor is how to synthesize in bulk quantity and fabricate an actual device with insightful understanding of operational mechanisms during performance. I report ...

  Citation × Citation Citation Abstract Copy Title: One-Dimensional Nanostructure and Sensing Applications: Tin Dioxide Nanowires and Carbon Nanotubes Author: Tran, Hoang Anh Year: 2016 The key challenge for a nanomaterial based sensor is how to synthesize in bulk quantity and fabricate an actual device with insightful understanding of operational mechanisms during performance. I report here effective, controllable methods that exploit the concepts of the "green approach" to synthesize two different one-dimensional nanostructures, including tin oxide nanowires and carbon nanotubes. The syntheses are followed by product characterization and sensing device fabrications as well as sensor performance understanding at the molecular level. Sensor-analyte response and recovery kinetics are also presented. The first part of the thesis describes bulk-scale synthesis and characterization of tin oxide nanowires by the molten salt synthetic method and the nanowire doping with antimony (n-types) and lithium. The work builds on the success of using n-doped SnO2 nanoparticles to selectively detect chlorine gas at room temperature. Replacing n-doped nanoparticles with n-doped nanowires reduces the number of inter-particle electron hops between sensing electrodes. The nanowire based sensors show unprecedented 5 ppb detectability of corrosive Cl2 gas concentration in air. At the higher range, 10 ppm of Cl2 gas leads to a 250 fold increase in the device resistance. During sensor recovery, FT-IR studies show that dichlorine monoxide (Cl2O) and chlorine dioxide (ClO2) are the desorbing species. Long term stability of devices is affected by lattice oxygen vacancies replaced by chlorine atoms. Bulk-scale synthesis of multiwall carbon nanotube (MWCNTs) was achieved by a novel inexpensive synthetic method. The green chemistry method uses the non-toxic and easy to handle solid carbon source naphthalene. The synthesis is carried out by simply heating naphthalene and organometallic precursors as catalysts in a sealed glass tube. Synthesis at 610º C leads to MWCNTs of 50 nm diameter and lengths exceeding well over microns. MWCNT doping is attempted with nitrogen (n-type) and boron (p-type) precursors. Palladium nanoparticles decorated on as-synthesized MWCNTs are employed for specific detection of explosive hydrogen gas with concentrations far below the explosive concentration limits. During performance, the sensor exhibits abnormal response behaviors at hydrogen gas concentrations higher than 1%. A model of charge carrier inversion, brought about by reduction of MWCNT by hydrogen molecules dissociated by Pd nanoparticles is proposed. Title: One-Dimensional Nanostructure and Sensing Applications: Tin Dioxide Nanowires and Carbon Nanotubes Author: Tran, Hoang Anh Year: 2016 The key challenge for a nanomaterial based sensor is how to synthesize in bulk quantity and fabricate an actual device with insightful understanding of operational mechanisms during performance. I report here effective, controllable methods that exploit the concepts of the "green approach" to synthesize two different one-dimensional nanostructures, including tin oxide nanowires and carbon nanotubes. The syntheses are followed by product characterization and sensing device fabrications as well as sensor performance understanding at the molecular level. Sensor-analyte response and recovery kinetics are also presented. The first part of the thesis describes bulk-scale synthesis and characterization of tin oxide nanowires by the molten salt synthetic method and the nanowire doping with antimony (n-types) and lithium. The work builds on the success of using n-doped SnO2 nanoparticles to selectively detect chlorine gas at room temperature. Replacing n-doped nanoparticles with n-doped nanowires reduces the number of inter-particle electron hops between sensing electrodes. The nanowire based sensors show unprecedented 5 ppb detectability of corrosive Cl2 gas concentration in air. At the higher range, 10 ppm of Cl2 gas leads to a 250 fold increase in the device resistance. During sensor recovery, FT-IR studies show that dichlorine monoxide (Cl2O) and chlorine dioxide (ClO2) are the desorbing species. Long term stability of devices is affected by lattice oxygen vacancies replaced by chlorine atoms. Bulk-scale synthesis of multiwall carbon nanotube (MWCNTs) was achieved by a novel inexpensive synthetic method. The green chemistry method uses the non-toxic and easy to handle solid carbon source naphthalene. The synthesis is carried out by simply heating naphthalene and organometallic precursors as catalysts in a sealed glass tube. Synthesis at 610º C leads to MWCNTs of 50 nm diameter and lengths exceeding well over microns. MWCNT doping is attempted with nitrogen (n-type) and boron (p-type) precursors. Palladium nanoparticles decorated on as-synthesized MWCNTs are employed for specific detection of explosive hydrogen gas with concentrations far below the explosive concentration limits. During performance, the sensor exhibits abnormal response behaviors at hydrogen gas concentrations higher than 1%. A model of charge carrier inversion, brought about by reduction of MWCNT by hydrogen molecules dissociated by Pd nanoparticles is proposed. Close