Search

Search Results

• 1. [Article] Towards p-Type Conductivity in SnO2Nanocrystals through Li Doping and Its Applications in Porous Diodes for Room Temperature Chlorine Gas Detection

  This work examined electrical transport properties and Li doping in SnO2synthesized by the sol–gel method. Solid-state 7Li-NMR line shapes revealed that Li ions occupy two distinct sites with differing ...

  Citation × Citation Citation Abstract Copy Title: Towards p-Type Conductivity in SnO2Nanocrystals through Li Doping and Its Applications in Porous Diodes for Room Temperature Chlorine Gas Detection Author: Chaparadza, Allen, Rananavare, Shankar Year: 2016 This work examined electrical transport properties and Li doping in SnO2synthesized by the sol–gel method. Solid-state 7Li-NMR line shapes revealed that Li ions occupy two distinct sites with differing dynamic mobilities. The chemical exchange rate between the two sites is, however, too slow for detection on the NMR timescale. Compressed nanoparticulate films of this doped semiconductor exhibited a positive Seebeck coefficient implying a p-type conductivity. A variable-temperature direct current conductivity, over a 25–350 °C temperature range, followed an Efros–Shklovskii variable range hopping (ES-VRH) conduction mechanism (ln(ρ) versus T−1/2) at temperatures below 100 °C with a crossover to 2D Mott variable range hopping (M-VRH) (ln(ρ) versus T−1/3) conduction at temperatures above 250 °C. In a transition region between these two limiting behaviors, direct current resistivity exhibited an anomalous temperature-independent plateau. We suggest that its origin may lie in a carrier inversion phenomenon wherein the majority carriers switch from holes to electrons due to Li ion expulsion from the crystalline core and creation of oxygen vacancies generated by loss of oxygen at elevated temperatures. Using a compression technique, porous diodes consisting of n-type (antimony doped SnO2) and the p-type (lithium-doped) nano-particulate films were prepared. Typical current-voltage curves of such devices resembled the behavior of a typical diode but for one key difference; owing to the porosity of the film, areas near the p-n interface and the p- and n-regions are accessible to gaseous analytes. This access is not possible in conventional diodes fabricated through contemporary planar technology. The gas sensing properties of the diodes were investigated by using Cl2, Br2, HCl, NO, NO2, CHCl3, NH3 and H2. Of all the gases tested, the sensor had very good sensitivity to Cl2 and had a response of 80 at 400 ppb of Cl2. The response time of the sensor was ~30 s at room temperature but the recovery time was temperature dependent. At room temperature the recovery time was 80s after 400 ppb chlorine exposure. The sensors were also found to recover quickly (~ 30 s) when the junctions were biased. Reverse biasing the diode provides a controllable band-bending at a p-n junction that could influence the electron-transfer rates from the adsorbates which create intra-band localized states. As a result reverse biasing can provide a means of desorbing the analyzed species. This approach eliminates the requirement to remove adsorbates by elevating the sensor temperature and hence improves on the energy efficiency of these types of sensors. Title: Towards p-Type Conductivity in SnO2Nanocrystals through Li Doping and Its Applications in Porous Diodes for Room Temperature Chlorine Gas Detection Author: Chaparadza, Allen, Rananavare, Shankar Year: 2016 This work examined electrical transport properties and Li doping in SnO2synthesized by the sol–gel method. Solid-state 7Li-NMR line shapes revealed that Li ions occupy two distinct sites with differing dynamic mobilities. The chemical exchange rate between the two sites is, however, too slow for detection on the NMR timescale. Compressed nanoparticulate films of this doped semiconductor exhibited a positive Seebeck coefficient implying a p-type conductivity. A variable-temperature direct current conductivity, over a 25–350 °C temperature range, followed an Efros–Shklovskii variable range hopping (ES-VRH) conduction mechanism (ln(ρ) versus T−1/2) at temperatures below 100 °C with a crossover to 2D Mott variable range hopping (M-VRH) (ln(ρ) versus T−1/3) conduction at temperatures above 250 °C. In a transition region between these two limiting behaviors, direct current resistivity exhibited an anomalous temperature-independent plateau. We suggest that its origin may lie in a carrier inversion phenomenon wherein the majority carriers switch from holes to electrons due to Li ion expulsion from the crystalline core and creation of oxygen vacancies generated by loss of oxygen at elevated temperatures. Using a compression technique, porous diodes consisting of n-type (antimony doped SnO2) and the p-type (lithium-doped) nano-particulate films were prepared. Typical current-voltage curves of such devices resembled the behavior of a typical diode but for one key difference; owing to the porosity of the film, areas near the p-n interface and the p- and n-regions are accessible to gaseous analytes. This access is not possible in conventional diodes fabricated through contemporary planar technology. The gas sensing properties of the diodes were investigated by using Cl2, Br2, HCl, NO, NO2, CHCl3, NH3 and H2. Of all the gases tested, the sensor had very good sensitivity to Cl2 and had a response of 80 at 400 ppb of Cl2. The response time of the sensor was ~30 s at room temperature but the recovery time was temperature dependent. At room temperature the recovery time was 80s after 400 ppb chlorine exposure. The sensors were also found to recover quickly (~ 30 s) when the junctions were biased. Reverse biasing the diode provides a controllable band-bending at a p-n junction that could influence the electron-transfer rates from the adsorbates which create intra-band localized states. As a result reverse biasing can provide a means of desorbing the analyzed species. This approach eliminates the requirement to remove adsorbates by elevating the sensor temperature and hence improves on the energy efficiency of these types of sensors. Close

• 2. [Article] Nanosilver Rainbow: A Rapid and Facile Method to Tune Different Colours of Nanosilver Through the Controlled Synthesis of Stable Spherical Silver Nanoparticles

  A rapid and simple one-pot reaction to synthesize stable, spherically shaped silver nanoparticles (AgNps) of different sizes producing distinct optical properties in aqueous solution at ambient temperature ...

  Citation × Citation Citation Abstract Copy Title: Nanosilver Rainbow: A Rapid and Facile Method to Tune Different Colours of Nanosilver Through the Controlled Synthesis of Stable Spherical Silver Nanoparticles Author: Mendis, Pramujitha, de Silva, Rohini M., Nalin de Silva, K. M., Wijenayaka, Lahiru A., Jayawardana, Kalana, Yan, Mingdi Year: 2016 A rapid and simple one-pot reaction to synthesize stable, spherically shaped silver nanoparticles (AgNps) of different sizes producing distinct optical properties in aqueous solution at ambient temperature has been developed. Each system contains various sizes of silver nanoparticles showing rainbow colours with the peak wavelength of the absorption spectra ranging from 400 to 750 nm. Seven different colours of nano silver were developed through the controlled synthesis of spherical silver nanoparticles using silver nitrate as the metal precursor. Sodium borohydride was used as the main reducing agent and trisodium citrate and hydrazine sulphate were used as the stabilizing and auxiliary reducing agents respectively. The colour of the solution was controlled by varying the concentrations of reagents and the optimum conditions for all the colours are reported. Characterization of silver nanoparticles was carried out using UV-visible spectrophotometry and Transmission Electron Microscopy (TEM). Factors affecting the formation of different sizes of silver nanoparticles, such as silver nitrate concentration, reducing agent concentrations, reaction temperature and reaction pH are also reported. The stability of these coloured silver colloidal solutions was also investigated at different temperatures and the most stable temperature was found to be 4 °C, while the optimum pH to synthesize distinctively coloured silver nanoparticles was found to be in the range of 7–8. The outlined procedure provides a rapid, facile and reproducible synthetic route to spherical AgNps of varying size and ensuing optical properties. Thus, this method is certain to find value in the many applications where size tunability of AgNps is desired. Title: Nanosilver Rainbow: A Rapid and Facile Method to Tune Different Colours of Nanosilver Through the Controlled Synthesis of Stable Spherical Silver Nanoparticles Author: Mendis, Pramujitha, de Silva, Rohini M., Nalin de Silva, K. M., Wijenayaka, Lahiru A., Jayawardana, Kalana, Yan, Mingdi Year: 2016 A rapid and simple one-pot reaction to synthesize stable, spherically shaped silver nanoparticles (AgNps) of different sizes producing distinct optical properties in aqueous solution at ambient temperature has been developed. Each system contains various sizes of silver nanoparticles showing rainbow colours with the peak wavelength of the absorption spectra ranging from 400 to 750 nm. Seven different colours of nano silver were developed through the controlled synthesis of spherical silver nanoparticles using silver nitrate as the metal precursor. Sodium borohydride was used as the main reducing agent and trisodium citrate and hydrazine sulphate were used as the stabilizing and auxiliary reducing agents respectively. The colour of the solution was controlled by varying the concentrations of reagents and the optimum conditions for all the colours are reported. Characterization of silver nanoparticles was carried out using UV-visible spectrophotometry and Transmission Electron Microscopy (TEM). Factors affecting the formation of different sizes of silver nanoparticles, such as silver nitrate concentration, reducing agent concentrations, reaction temperature and reaction pH are also reported. The stability of these coloured silver colloidal solutions was also investigated at different temperatures and the most stable temperature was found to be 4 °C, while the optimum pH to synthesize distinctively coloured silver nanoparticles was found to be in the range of 7–8. The outlined procedure provides a rapid, facile and reproducible synthetic route to spherical AgNps of varying size and ensuing optical properties. Thus, this method is certain to find value in the many applications where size tunability of AgNps is desired. Close

• 3. [Article] The Discovery and Development of Metal-Free Arylation Reactions with Unsymmetrical Diaryliodonium Salts

  Functionalizing arenes and heteroarenes has been an active area of research since the 19th century, due to the presence of these molecular structures in many industrially important sectors. A tremendous ...

  Citation × Citation Citation Abstract Copy Title: The Discovery and Development of Metal-Free Arylation Reactions with Unsymmetrical Diaryliodonium Salts Author: Sundalam, Sunil Kumar Year: 2017 Functionalizing arenes and heteroarenes has been an active area of research since the 19th century, due to the presence of these molecular structures in many industrially important sectors. A tremendous amount of research has been published in achieving these chemical transformations using stoichiometric reagents and transition metal-catalyzed reactions. However, challenges still remain. An alternative and comparable methodology to metal-catalyzed reactions to overcome the drawbacks will advance this particular area of research is desirable. Hypervalent iodine compounds offer a promising approach to metal-free arylation reactions. These mild, air and moisture stable compounds have showed significant success as non-toxic and metal-free reagents for the arylation reactions. In particular, unsymmetrical diaryliodonium salts offer functionalization of complex arene structure in an efficient and sustainable pathway. A base-mediated coupling reaction for the metal-free synthesis of alkyl-aryl ethers by using unsymmetrical diaryliodonium salts and aliphatic alcohols is described. This method shows broad substrate scope with respect to both of the coupling partners to produce industrially useful alkyl-aryl ethers in moderate to excellent yields. The reaction is operationally simple, proceeds at mild temperature, and is atom-economical. Sustainability and synthetic utility of this reaction is demonstrated by the use of unsymmetrical aryl(mesityl)iodonium salts as the arylating agents. A limitation of poor reactivity of electron rich unsymmetrical diaryliodonium salts was overcome by designing 2nd generation conditions and using trimethoxy benzene (TMP) as the auxiliary group. Additionally discovery and development of an efficient method to access highly functionalized arynes from unsymmetrical aryl(mesityl)iodonium tosylate salts is presented. The aryne intermediates are generated by ortho C-H deprotonation of aryl(mesityl)iodonium salt with an amide base and subsequently trapped in a cycloaddition reaction with furan in moderate to good yields. Selective iodonium moiety elimination is discussed and the effect of auxiliary and temperature to reduce the regioisomeric ratio is demonstrated. Finally, additional coupling partner including benzyl azide and aliphatic amines are presented to show further utility of this methodology. Also, mechanistic investigations leading to the moderate reactivity of some electron rich unsymmetrical diaryliodonium salts is discussed. Title: The Discovery and Development of Metal-Free Arylation Reactions with Unsymmetrical Diaryliodonium Salts Author: Sundalam, Sunil Kumar Year: 2017 Functionalizing arenes and heteroarenes has been an active area of research since the 19th century, due to the presence of these molecular structures in many industrially important sectors. A tremendous amount of research has been published in achieving these chemical transformations using stoichiometric reagents and transition metal-catalyzed reactions. However, challenges still remain. An alternative and comparable methodology to metal-catalyzed reactions to overcome the drawbacks will advance this particular area of research is desirable. Hypervalent iodine compounds offer a promising approach to metal-free arylation reactions. These mild, air and moisture stable compounds have showed significant success as non-toxic and metal-free reagents for the arylation reactions. In particular, unsymmetrical diaryliodonium salts offer functionalization of complex arene structure in an efficient and sustainable pathway. A base-mediated coupling reaction for the metal-free synthesis of alkyl-aryl ethers by using unsymmetrical diaryliodonium salts and aliphatic alcohols is described. This method shows broad substrate scope with respect to both of the coupling partners to produce industrially useful alkyl-aryl ethers in moderate to excellent yields. The reaction is operationally simple, proceeds at mild temperature, and is atom-economical. Sustainability and synthetic utility of this reaction is demonstrated by the use of unsymmetrical aryl(mesityl)iodonium salts as the arylating agents. A limitation of poor reactivity of electron rich unsymmetrical diaryliodonium salts was overcome by designing 2nd generation conditions and using trimethoxy benzene (TMP) as the auxiliary group. Additionally discovery and development of an efficient method to access highly functionalized arynes from unsymmetrical aryl(mesityl)iodonium tosylate salts is presented. The aryne intermediates are generated by ortho C-H deprotonation of aryl(mesityl)iodonium salt with an amide base and subsequently trapped in a cycloaddition reaction with furan in moderate to good yields. Selective iodonium moiety elimination is discussed and the effect of auxiliary and temperature to reduce the regioisomeric ratio is demonstrated. Finally, additional coupling partner including benzyl azide and aliphatic amines are presented to show further utility of this methodology. Also, mechanistic investigations leading to the moderate reactivity of some electron rich unsymmetrical diaryliodonium salts is discussed. Close

• 4. [Article] Gold Tris(carboxyphenyl)corroles as Multifunctional Materials: Room Temperature Near-IR Phosphorescence and Applications to Photodynamic Therapy and Dye-Sensitized Solar Cells

  Two amphiphilic corroles—5,10,15-tris(3-carboxyphenyl)corrole (H3[mTCPC]) and 5,10,15-tris(4-carboxyphenyl)corrole (H3[pTCPC])—and their gold complexes have been synthesized, and their photophysical properties ...

  Citation × Citation Citation Abstract Copy Title: Gold Tris(carboxyphenyl)corroles as Multifunctional Materials: Room Temperature Near-IR Phosphorescence and Applications to Photodynamic Therapy and Dye-Sensitized Solar Cells Author: Alemayehu, Abraham B., Day, Nicholas U., Mani, Tomoyasu, Rudine, Alexander B., Thomas, Kolle E., Gederaas, Odrun A., Vinogradov, Sergei A., Wamser, Carl C., Ghosh, Abhik Year: 2016 Two amphiphilic corroles—5,10,15-tris(3-carboxyphenyl)corrole (H3[mTCPC]) and 5,10,15-tris(4-carboxyphenyl)corrole (H3[pTCPC])—and their gold complexes have been synthesized, and their photophysical properties and photovoltaic behavior have been investigated. Like other nonpolar gold corroles, Au[mTCPC] and Au[pTCPC] were both found to exhibit room temperature phosphorescence in deoxygenated solutions with quantum yields of ∼0.3% and triplet lifetimes of ∼75 μs. Both compounds exhibited significant activity as dyes in photodynamic therapy experiments and in dye-sensitized solar cells. Upon irradiation at 435 nm, both Au corroles exhibited significant phototoxicity against AY27 rat bladder cancer cells while the free-base corroles proved inactive. Dye-sensitized solar cells constructed using the free bases H3[mTCPC] and H3[pTCPC] exhibited low efficiencies (≪1%), well under that obtained with 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin, H2[pTCPP] (1.9%, cf. N719 9.5%). Likewise, Au[pTCPC] proved inefficient, with an efficiency of ∼0.2%. By contrast, Au[mTCPC] proved remarkably effective, exhibiting an open-circuit voltage (Voc) of 0.56 V, a short-circuit current of 8.7 mA cm–2, a fill factor of 0.72, and an efficiency of 3.5%. Title: Gold Tris(carboxyphenyl)corroles as Multifunctional Materials: Room Temperature Near-IR Phosphorescence and Applications to Photodynamic Therapy and Dye-Sensitized Solar Cells Author: Alemayehu, Abraham B., Day, Nicholas U., Mani, Tomoyasu, Rudine, Alexander B., Thomas, Kolle E., Gederaas, Odrun A., Vinogradov, Sergei A., Wamser, Carl C., Ghosh, Abhik Year: 2016 Two amphiphilic corroles—5,10,15-tris(3-carboxyphenyl)corrole (H3[mTCPC]) and 5,10,15-tris(4-carboxyphenyl)corrole (H3[pTCPC])—and their gold complexes have been synthesized, and their photophysical properties and photovoltaic behavior have been investigated. Like other nonpolar gold corroles, Au[mTCPC] and Au[pTCPC] were both found to exhibit room temperature phosphorescence in deoxygenated solutions with quantum yields of ∼0.3% and triplet lifetimes of ∼75 μs. Both compounds exhibited significant activity as dyes in photodynamic therapy experiments and in dye-sensitized solar cells. Upon irradiation at 435 nm, both Au corroles exhibited significant phototoxicity against AY27 rat bladder cancer cells while the free-base corroles proved inactive. Dye-sensitized solar cells constructed using the free bases H3[mTCPC] and H3[pTCPC] exhibited low efficiencies (≪1%), well under that obtained with 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin, H2[pTCPP] (1.9%, cf. N719 9.5%). Likewise, Au[pTCPC] proved inefficient, with an efficiency of ∼0.2%. By contrast, Au[mTCPC] proved remarkably effective, exhibiting an open-circuit voltage (Voc) of 0.56 V, a short-circuit current of 8.7 mA cm–2, a fill factor of 0.72, and an efficiency of 3.5%. Close

• 5. [Article] Synthesis, Characterization, and Electrical Properties of ([SnSe]1+δ)m(NbSe2)3 Ferecrystalline Compounds

  29 pages. A thesis presented to the Department of Chemistry and Biochemistry, and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor ...

  Citation × Citation Citation Abstract Copy Title: Synthesis, Characterization, and Electrical Properties of ([SnSe]1+δ)m(NbSe2)3 Ferecrystalline Compounds Author: Ta, Phuong Kim Year: 2015 29 pages. A thesis presented to the Department of Chemistry and Biochemistry, and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2015. Title: Synthesis, Characterization, and Electrical Properties of ([SnSe]1+δ)m(NbSe2)3 Ferecrystalline Compounds Author: Ta, Phuong Kim Year: 2015 29 pages. A thesis presented to the Department of Chemistry and Biochemistry, and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2015. Close

• 6. [Article] Thermal Effects of Microinverter Placement on the Performance of Silicon Photovoltaics

  Typical installation of a microinverter in a plane parallel position on the back side of a monocrystalline silicon photovoltaic (PV) panel can lead to differential heating of the PV cells immediately above ...

  Citation × Citation Citation Abstract Copy Title: Thermal Effects of Microinverter Placement on the Performance of Silicon Photovoltaics Author: Day, Nicholas U., Reinhart, Chase C., DeBow, Shaun, Smith, Matthew K., Sailor, David J., Johansson, Erik, Wamser, Carl C. Year: 2016 Typical installation of a microinverter in a plane parallel position on the back side of a monocrystalline silicon photovoltaic (PV) panel can lead to differential heating of the PV cells immediately above the microinverter by as much as 4 °C. Rotation of the microinverter to a perpendicular position allows the microinverter itself to run cooler by about 4 °C and completely removes the distinctive heat signature on the panels. Because the thermal effects of the microinverters are significant for only two of the 72 cells on the panel, changes in DC power output from the panels are not detectable. However, lower microinverter temperatures increase microinverter efficiency by about 0.65%, such that overall AC power production is increased by about 0.09%. In addition to these small improvements to be gained by the repositioning of microinverters, there are also potential long-term concerns that nonuniform heating may lead to accelerated degradation in the affected area of the panel. Title: Thermal Effects of Microinverter Placement on the Performance of Silicon Photovoltaics Author: Day, Nicholas U., Reinhart, Chase C., DeBow, Shaun, Smith, Matthew K., Sailor, David J., Johansson, Erik, Wamser, Carl C. Year: 2016 Typical installation of a microinverter in a plane parallel position on the back side of a monocrystalline silicon photovoltaic (PV) panel can lead to differential heating of the PV cells immediately above the microinverter by as much as 4 °C. Rotation of the microinverter to a perpendicular position allows the microinverter itself to run cooler by about 4 °C and completely removes the distinctive heat signature on the panels. Because the thermal effects of the microinverters are significant for only two of the 72 cells on the panel, changes in DC power output from the panels are not detectable. However, lower microinverter temperatures increase microinverter efficiency by about 0.65%, such that overall AC power production is increased by about 0.09%. In addition to these small improvements to be gained by the repositioning of microinverters, there are also potential long-term concerns that nonuniform heating may lead to accelerated degradation in the affected area of the panel. Close

• 7. [Article] Copper Nanowires Synthesis and Self-Assembly for Interconnect Applications

  One-dimensional (1D) nanomaterial self-assembly offers an excellent approach to the fabrication of highly complex nanodevices. Despite considerable effort and research, precisely controlling the orientation ...

  Citation × Citation Citation Abstract Copy Title: Copper Nanowires Synthesis and Self-Assembly for Interconnect Applications Author: Darmakkolla, Srikar Rao Year: 2017 One-dimensional (1D) nanomaterial self-assembly offers an excellent approach to the fabrication of highly complex nanodevices. Despite considerable effort and research, precisely controlling the orientation and positioning of nanowires (NWs) on a large-scale area and assembling into a functional device is still a state of the art problem. This thesis focuses on the dimensionally controlled copper nanowires (Cu NWs) synthesis, and magnetic field assisted self-assembly of cupronickel nanowires (Cu/Ni NWs) into interconnect structures on a carbon doped silicon dioxide (CDO) wafer. CDO is a low dielectric constant (k) material used for copper interconnects in multilayered complex integrated circuits (ICs). Here, a strong affinity of copper (Cu) and nickel (Ni) to thiol (-SH) functional groups were exploited to strongly adhere the nanowires (Cu/Ni NWs) onto the CDO substrate. Thiol (-SH) functionalization of the CDO surface was achieved via a series of reactions involving (1) esterification of the surface exposed ≡Si-OH functional group to its triflate (≡Si-O-Tf), (2) reduction of triflate to ≡Si-H using DIBAL-H, and (3) hydrosilylation of ≡Si-H using 2-propene thiol (≡Si-(CH2)3-SH) in a photochemical reaction. The thiol functionalization of CDO surface enhances the interaction of Cu/Ni NWs with strong chemical bonds. The same reaction scheme was also used in the functionalization of the hydrophilic (Si-OH) surface to the hydrophobic long alkyl chain derivatized (≡Si-CH2-(CH2)16-CH3) surface. This long alkyl chain modified surface acts as an excellent moisture resistant film, which helps to maintain the low-k value of CDO. The dimensionally controlled Cu NWs were synthesized by a wet chemical approach. Optimization of the reducing agent, hydrazine (N2H4), controlled the surface morphology of nanowires (NWs). Interestingly, the high concentration of reducing agent produced particle decorated and/or with a rough NW surface, and conversely decreasing its concentration resulted in a comparatively thin, particle-free and smooth surface. The reaction temperature affected the aspect ratio (Length/Diameter) of the NWs. As the reaction temperature increased from 60 to 90 °C, the aspect ratio decreased from 140 to 21. Controlling the orientation of Cu NWs in a magnetic field was accomplished by coating them with a thin layer (~20 nm) of ferromagnetic nickel (Ni). This Ni-coated NWs showed an excellent degree of alignment (half-width ≈10 degrees) in the direction of an applied magnetic field over a large surface area at field strength as low as 2500 Gauss. Also, the Ni coating helped in protecting the copper core from oxidation resulting in better electrical wire-to-wire contacts. A nanowire-based interconnect channel was fabricated by combining magnetic field assisted alignment and deposition of aligned NWs on a thiol-modified and photolithography patterned CDO substrate. The NWs, deposited in the trenches, strongly bonded to the thiol-derivatized CDO substrate while an acetone wash removed loosely bound NWs on the photoresist surface. In electrical characterization, the directionally well-aligned Cu/Ni NWs channel displayed surprisingly two-fold higher conductivity than randomly arranged NWs channel. Title: Copper Nanowires Synthesis and Self-Assembly for Interconnect Applications Author: Darmakkolla, Srikar Rao Year: 2017 One-dimensional (1D) nanomaterial self-assembly offers an excellent approach to the fabrication of highly complex nanodevices. Despite considerable effort and research, precisely controlling the orientation and positioning of nanowires (NWs) on a large-scale area and assembling into a functional device is still a state of the art problem. This thesis focuses on the dimensionally controlled copper nanowires (Cu NWs) synthesis, and magnetic field assisted self-assembly of cupronickel nanowires (Cu/Ni NWs) into interconnect structures on a carbon doped silicon dioxide (CDO) wafer. CDO is a low dielectric constant (k) material used for copper interconnects in multilayered complex integrated circuits (ICs). Here, a strong affinity of copper (Cu) and nickel (Ni) to thiol (-SH) functional groups were exploited to strongly adhere the nanowires (Cu/Ni NWs) onto the CDO substrate. Thiol (-SH) functionalization of the CDO surface was achieved via a series of reactions involving (1) esterification of the surface exposed ≡Si-OH functional group to its triflate (≡Si-O-Tf), (2) reduction of triflate to ≡Si-H using DIBAL-H, and (3) hydrosilylation of ≡Si-H using 2-propene thiol (≡Si-(CH2)3-SH) in a photochemical reaction. The thiol functionalization of CDO surface enhances the interaction of Cu/Ni NWs with strong chemical bonds. The same reaction scheme was also used in the functionalization of the hydrophilic (Si-OH) surface to the hydrophobic long alkyl chain derivatized (≡Si-CH2-(CH2)16-CH3) surface. This long alkyl chain modified surface acts as an excellent moisture resistant film, which helps to maintain the low-k value of CDO. The dimensionally controlled Cu NWs were synthesized by a wet chemical approach. Optimization of the reducing agent, hydrazine (N2H4), controlled the surface morphology of nanowires (NWs). Interestingly, the high concentration of reducing agent produced particle decorated and/or with a rough NW surface, and conversely decreasing its concentration resulted in a comparatively thin, particle-free and smooth surface. The reaction temperature affected the aspect ratio (Length/Diameter) of the NWs. As the reaction temperature increased from 60 to 90 °C, the aspect ratio decreased from 140 to 21. Controlling the orientation of Cu NWs in a magnetic field was accomplished by coating them with a thin layer (~20 nm) of ferromagnetic nickel (Ni). This Ni-coated NWs showed an excellent degree of alignment (half-width ≈10 degrees) in the direction of an applied magnetic field over a large surface area at field strength as low as 2500 Gauss. Also, the Ni coating helped in protecting the copper core from oxidation resulting in better electrical wire-to-wire contacts. A nanowire-based interconnect channel was fabricated by combining magnetic field assisted alignment and deposition of aligned NWs on a thiol-modified and photolithography patterned CDO substrate. The NWs, deposited in the trenches, strongly bonded to the thiol-derivatized CDO substrate while an acetone wash removed loosely bound NWs on the photoresist surface. In electrical characterization, the directionally well-aligned Cu/Ni NWs channel displayed surprisingly two-fold higher conductivity than randomly arranged NWs channel. Close

• 8. [Article] Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence

  While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible ...

  Citation × Citation Citation Abstract Copy Title: Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence Author: Radlinger, Christine Marie Year: 2017 While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible photoluminescence (PL) from nanocrystalline silicon in 1990 triggered many ensuing research efforts to optimize PL from nanocrystalline silicon for optical applications. Currently, use of photoluminescent silicon nanoparticles (Si NPs) is commercially limited by: 1) the instability of the energy and intensity of the PL, and 2) the low quantum yield of interband PL from Si NPs. Herein, red-emitting, hydrogen-passivated silicon nanoparticles (H-Si NPs) were synthesized by thermally-induced disproportionation of a HSiCl3-derived (HSiO1.5)n polymer. The H-Si NPs produced by this method were then subjected to various chemical and physical environments to assess the long-term stability of the optical properties as a function of changing surface composition. This dissertation is intended to elucidate correlations between the reported PL instability and the observed changes in the Si NP surface chemistry over time and as a function of environment. First, the stability of the H-Si NP surface at slightly elevated temperatures towards reactivity with a simple alkane was probed. The H-Si NPs were observed by FT-IR spectroscopy to undergo partial hydrosilylation upon heating in refluxing hexane, in addition to varying degrees of surface oxidation. The unexpected reactivity of the Si surface in n-hexane supports the unstable nature of the H-Si NP surface, and furthermore implicates the presence of highly-reactive Si radicals on the surfaces of the Si NPs. We propose that reaction of alkene impurities with the Si surface radicals is largely responsible for the observed surface alkylation. However, we also present an alternate mechanism by which Si surface radicals could react with alkanes to result in alkylation of the surface. Next, the energy and intensity stability of the interband PL from H-Si NPs in the presence of a radical trap was probed. Upon addition of (2,2,6,6,-tetramethyl-piperidin-1-yl)oxyl (TEMPO), the energy and intensity of the interband transition was observed to change over time, dependent on the reaction conditions. First, when the reaction occurred at 4ºC with minimal light exposure, the interband transition exhibited a gradual hypsochromic shift to between 595 nm and 655 nm, versus the λmax of the original low energy emission peak at 700 nm, depending on the amount of TEMPO in the sample. Second, when the reaction proceeded at room temperature with frequent exposure to 360 nm irradiation, the original interband transition at 660 nm was quenched while a new peak at 575 nm developed. Based on all the data collected and analyzed, we assign the 595 -- 655 nm transition as due to interband exciton recombination from Si NPs with reduced diameters relative to the original Si NPs. We furthermore assign the 575 nm transition as due to an oxide-related defect state resulting from rapid oxidation of photo-excited Si NPs. Title: Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence Author: Radlinger, Christine Marie Year: 2017 While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible photoluminescence (PL) from nanocrystalline silicon in 1990 triggered many ensuing research efforts to optimize PL from nanocrystalline silicon for optical applications. Currently, use of photoluminescent silicon nanoparticles (Si NPs) is commercially limited by: 1) the instability of the energy and intensity of the PL, and 2) the low quantum yield of interband PL from Si NPs. Herein, red-emitting, hydrogen-passivated silicon nanoparticles (H-Si NPs) were synthesized by thermally-induced disproportionation of a HSiCl3-derived (HSiO1.5)n polymer. The H-Si NPs produced by this method were then subjected to various chemical and physical environments to assess the long-term stability of the optical properties as a function of changing surface composition. This dissertation is intended to elucidate correlations between the reported PL instability and the observed changes in the Si NP surface chemistry over time and as a function of environment. First, the stability of the H-Si NP surface at slightly elevated temperatures towards reactivity with a simple alkane was probed. The H-Si NPs were observed by FT-IR spectroscopy to undergo partial hydrosilylation upon heating in refluxing hexane, in addition to varying degrees of surface oxidation. The unexpected reactivity of the Si surface in n-hexane supports the unstable nature of the H-Si NP surface, and furthermore implicates the presence of highly-reactive Si radicals on the surfaces of the Si NPs. We propose that reaction of alkene impurities with the Si surface radicals is largely responsible for the observed surface alkylation. However, we also present an alternate mechanism by which Si surface radicals could react with alkanes to result in alkylation of the surface. Next, the energy and intensity stability of the interband PL from H-Si NPs in the presence of a radical trap was probed. Upon addition of (2,2,6,6,-tetramethyl-piperidin-1-yl)oxyl (TEMPO), the energy and intensity of the interband transition was observed to change over time, dependent on the reaction conditions. First, when the reaction occurred at 4ºC with minimal light exposure, the interband transition exhibited a gradual hypsochromic shift to between 595 nm and 655 nm, versus the λmax of the original low energy emission peak at 700 nm, depending on the amount of TEMPO in the sample. Second, when the reaction proceeded at room temperature with frequent exposure to 360 nm irradiation, the original interband transition at 660 nm was quenched while a new peak at 575 nm developed. Based on all the data collected and analyzed, we assign the 595 -- 655 nm transition as due to interband exciton recombination from Si NPs with reduced diameters relative to the original Si NPs. We furthermore assign the 575 nm transition as due to an oxide-related defect state resulting from rapid oxidation of photo-excited Si NPs. Close

• 9. [Article] Solvent Chemistry in the Electronic Cigarette Reaction Vessel

  Knowledge of the mechanism of formation, levels and toxicological profiles of the chemical products in the aerosols (i.e., vapor plus particulate phases) of e-cigarettes is needed in order to better inform ...

  Citation × Citation Citation Abstract Copy Title: Solvent Chemistry in the Electronic Cigarette Reaction Vessel Author: Jensen, Robert Paul, Strongin, Robert M., Peyton, David H. Year: 2017 Knowledge of the mechanism of formation, levels and toxicological profiles of the chemical products in the aerosols (i.e., vapor plus particulate phases) of e-cigarettes is needed in order to better inform basic research as well as the general public, regulators, and industry. To date, studies of e-cigarette emissions have mainly focused on chromatographic techniques for quantifying and comparing the levels of selected e-cigarette aerosol components to those found in traditional cigarettes. E-cigarettes heat and aerosolize the solvents propylene glycol (PG) and glycerol (GLY), thereby affording unique product profiles as compared to traditional cigarettes. The chemical literature strongly suggests that there should be more compounds produced by PG and GLY than have been reported in e-cigarette aerosols to date. Herein we report an extensive investigation of the products derived from vaporizing PG and GLY under mild, single puff conditions. This has led to the discovery of several new compounds produced under vaping conditions. Prior reports on e-cigarette toxin production have emphasized temperature as the primary variable in solvent degradation. In the current study, the molecular pathways leading to enhanced PG/GLY reactivity are described, along with the most impactful chemical conditions promoting byproduct production. Title: Solvent Chemistry in the Electronic Cigarette Reaction Vessel Author: Jensen, Robert Paul, Strongin, Robert M., Peyton, David H. Year: 2017 Knowledge of the mechanism of formation, levels and toxicological profiles of the chemical products in the aerosols (i.e., vapor plus particulate phases) of e-cigarettes is needed in order to better inform basic research as well as the general public, regulators, and industry. To date, studies of e-cigarette emissions have mainly focused on chromatographic techniques for quantifying and comparing the levels of selected e-cigarette aerosol components to those found in traditional cigarettes. E-cigarettes heat and aerosolize the solvents propylene glycol (PG) and glycerol (GLY), thereby affording unique product profiles as compared to traditional cigarettes. The chemical literature strongly suggests that there should be more compounds produced by PG and GLY than have been reported in e-cigarette aerosols to date. Herein we report an extensive investigation of the products derived from vaporizing PG and GLY under mild, single puff conditions. This has led to the discovery of several new compounds produced under vaping conditions. Prior reports on e-cigarette toxin production have emphasized temperature as the primary variable in solvent degradation. In the current study, the molecular pathways leading to enhanced PG/GLY reactivity are described, along with the most impactful chemical conditions promoting byproduct production. Close

• 10. [Article] Controlling Water Exchange Kinetics and Improving ParaCEST Imaging

  Generating MR image contrast from exogenous contrast media though chemical exchange saturation transfer (CEST) offers several exciting new possibilities, such as multicolored imaging, the interleaving ...

  Citation × Citation Citation Abstract Copy Title: Controlling Water Exchange Kinetics and Improving ParaCEST Imaging Author: Slack, Jacqueline R. Year: 2017 Generating MR image contrast from exogenous contrast media though chemical exchange saturation transfer (CEST) offers several exciting new possibilities, such as multicolored imaging, the interleaving of pre- and post-contrast images, and the potential to perform ratiometric metabolic imaging. The major limitation of the deployment of CEST imaging is the comparatively high detection limits of exogenous agents and particularly at the low B1 power levels required to meet SAR requirements. The large chemical shifts afforded by paramagnetic (paraCEST) agents permit more rapid exchange kinetics and therefore potentially more effective contrast agents. Despite comparatively large chemical shifts, many Ln3+ DOTA-tetraamide (DOTAM) chelates traditionally investigated as CEST agents are predicted to have exchange kinetics that are considerably faster than optimal at very low B1 powers. This work explores two methodologies for slowing water exchange kinetics in Ln3+ DOTAM chelates and improving CEST imaging: structural manipulation and encapsulation. In the first method, rigid Ln3+ NB-DOTAM chelates with hydrophobic amide substituents was thoroughly studied using NMR spectroscopy techniques in order to assess their ability to produce CEST contrast at low B1 power levels. NMR techniques utilized included 1H NMR, variable temperature, COSY, and CEST experiments. The phenyl amide substituent in the pseudo-axial position afforded chelates with considerably slow water proton exchange rates and appreciably more CEST contrast than isomeric chelates with the amide substituent in the pseudo-equatorial position. The second method involved characterizing a vesicle system to be used for encapsulating a Ln3+ DOTAM chelate. The vesicles prepared were analyzed using the following NMR techniques: 1H NMR, T1, shift reagent, and CEST experiments. The vesicle system chosen for study did not afford slow water exchange kinetics to enhance CEST contrast. A second vesicle system was attempted but the vesicle synthesis was difficult, parameters studied were not optimized, and the second system did not exhibit slow water exchange with the limited amount of experiments run and data collected. Title: Controlling Water Exchange Kinetics and Improving ParaCEST Imaging Author: Slack, Jacqueline R. Year: 2017 Generating MR image contrast from exogenous contrast media though chemical exchange saturation transfer (CEST) offers several exciting new possibilities, such as multicolored imaging, the interleaving of pre- and post-contrast images, and the potential to perform ratiometric metabolic imaging. The major limitation of the deployment of CEST imaging is the comparatively high detection limits of exogenous agents and particularly at the low B1 power levels required to meet SAR requirements. The large chemical shifts afforded by paramagnetic (paraCEST) agents permit more rapid exchange kinetics and therefore potentially more effective contrast agents. Despite comparatively large chemical shifts, many Ln3+ DOTA-tetraamide (DOTAM) chelates traditionally investigated as CEST agents are predicted to have exchange kinetics that are considerably faster than optimal at very low B1 powers. This work explores two methodologies for slowing water exchange kinetics in Ln3+ DOTAM chelates and improving CEST imaging: structural manipulation and encapsulation. In the first method, rigid Ln3+ NB-DOTAM chelates with hydrophobic amide substituents was thoroughly studied using NMR spectroscopy techniques in order to assess their ability to produce CEST contrast at low B1 power levels. NMR techniques utilized included 1H NMR, variable temperature, COSY, and CEST experiments. The phenyl amide substituent in the pseudo-axial position afforded chelates with considerably slow water proton exchange rates and appreciably more CEST contrast than isomeric chelates with the amide substituent in the pseudo-equatorial position. The second method involved characterizing a vesicle system to be used for encapsulating a Ln3+ DOTAM chelate. The vesicles prepared were analyzed using the following NMR techniques: 1H NMR, T1, shift reagent, and CEST experiments. The vesicle system chosen for study did not afford slow water exchange kinetics to enhance CEST contrast. A second vesicle system was attempted but the vesicle synthesis was difficult, parameters studied were not optimized, and the second system did not exhibit slow water exchange with the limited amount of experiments run and data collected. Close