Macroscopic phase coherence in superconductors enables quantum interference and phase manipulatio... more Macroscopic phase coherence in superconductors enables quantum interference and phase manipulation at realistic device length scales. Numerous superconducting electronic devices are based on the modulation of the supercurrent in superconducting loops. While the overall behavior of symmetric superconducting loops has been studied, the effects of asymmetries in such devices remain under-explored and poorly understood. Here we report on an experimental and theoretical study of the flux modulation of the persistent current in a doubly connected asymmetric aluminum nanowire loop. A model considering the length and electronic cross-section asymmetries in the loop provides a quantitative account of the observations. Comparison with experiments give essential parameters such as persistent and critical currents as well as the amount of asymmetry which can provide feedback into the design of superconducting quantum devices.
Carbonate clumped isotope thermometry has been applied to fossil mollusk shells from Tibet to rec... more Carbonate clumped isotope thermometry has been applied to fossil mollusk shells from Tibet to reconstruct the paleoclimate and paleoelevation of the region. However, inferred paleoelevation and climatic conditions from this proxy are inconsistent with paleontological evidence. Here, we report new clumped isotope data from both modern and fossil (5−4 Ma) freshwater mollusk shells with the results of X-ray diffraction (XRD) analyses of fossil shells from the Himalayan-Tibetan Plateau. Although all of the fossil shells analyzed in this study appeared pristine based on visual inspection, XRD data reveal that more than half of these apparently “pristine” fossil shells contain trace amounts of calcite. Clumped isotope temperatures derived from the fossil shells display a large range of variation (>22 °C). Among the fossil shells analyzed, those containing traces of calcite have yielded temperatures that are on average ∼10 °C lower than those with no detectable calcite from the same str...
Agglomerates of polar molecules in nonpolar solvents are selectively heated by microwave radiatio... more Agglomerates of polar molecules in nonpolar solvents are selectively heated by microwave radiation. The magnitude of the selective heating was directly measured by using the temperature dependence of the intensities of the Stokes and anti-Stokes bands in the Raman spectra of p-nitroanisole (pNA) and mesitylene. Under dynamic heating conditions, a large apparent temperature difference (ΔT) of over 100 °C was observed between the polar pNA solute and the nonpolar mesitylene solvent. This represents the first direct measurement of the selective microwave heating process. The magnitude of the selective microwave heating was affected by the properties of the agglomerated pNA. As the concentration of the pNA increases, the magnitude of the selective heating of the pNA was observed to decrease. This is explained by the tendency of the pNA dipoles to orient in an antiparallel fashion in the aggregates as measured by the Kirkwood g value, which decreased with increasing concentration. This effect reduces the net dipole moment of the agglomerates, which decreases the microwave absorption. After the radiation was terminated, the effective temperature of the dipolar molecules returned slowly to that of the medium. The slow heat transfer was modeled successfully by treating the solutions as a biphasic solvent/solute system. Based on modeling and the fact that the agglomerate can be heated above the boiling temperature of the solvent, an insulating layer of solvent vapor is suggested to form around the heated agglomerate, slowing convective heat transfer out of the agglomerate. This is an effect unique to microwave heating.
We report the growth, via core transformation, of highly fluorescing, near-infrared-emitting bime... more We report the growth, via core transformation, of highly fluorescing, near-infrared-emitting bimetallic Au/Ag nanoclusters, which are capped with hydrophobic or hydrophilic monothiol-terminated ligands.
We describe the growth and characterization of highly fluorescing, near-infrared-emitting nanoclu... more We describe the growth and characterization of highly fluorescing, near-infrared-emitting nanoclusters made of bimetallic Au25-xAgx cores, prepared using various monothiol-appended hydrophobic and hydrophilic ligands. The reaction uses well-defined triphenylphosphine-protected Au11 clusters (as precursors), which are reacted with Ag(I)-thiolate complexes. The prepared nanoclusters are small (diameter…
Physical chemistry chemical physics : PCCP, Jan 9, 2018
We detail the characterization of atomically precise, luminescent silver and gold bimetallic nano... more We detail the characterization of atomically precise, luminescent silver and gold bimetallic nanoclusters (Ag and AgAuNCs) grown in the presence of bidentate lipoic acid (LA, the oxidized form) and dihydrolipoic acid (DHLA, the reduced form) ligands. We found that while doping AuNCs with Ag or Cu precursors using up to a 50% molar fraction (during growth) did not lead to any photoluminescence enhancement, doping of AgNCs with Au resulted in a six-fold enhancement of the PL emission compared to undoped AgNCs. The effect of doping is also reflected in the optical absorption and PL excitation spectra of the gold-doped NCs (AgAuNCs), where a clear blue shift in the absorbance features with respect to the pure AgNCs has been measured. Mass spectrometry measurements using ESI-MS showed that the AgNCs and Au-doped AgNCs had the compositions Ag29(DHLA)12 and Ag28Au(DHLA)12, respectively. The bimetallic nature of the AgAuNC cores was further supported by X-ray Photoelectron Spectroscopy (XPS...
ABSTRACTNiO-magnetite multilayers exhibit long range antiferromagnetic order with the magnetite f... more ABSTRACTNiO-magnetite multilayers exhibit long range antiferromagnetic order with the magnetite ferrimagnetic correlations confined to a single layer due to stacking faults of the spinel structure at the interfaces[l, 2, 3, 4]. A systematic study of the field-dependence of the interlayer coupling in a series of NiO-magnetite multilayers has been made using neutron diffraction. Both NiO and magnetite single thin films were included in the measurements for comparison. In the magnetite film, intensity changes with magnetic field are consistent with domain reorientation of the net ferrimagnetic moments, while in the NiO film there are essentially no intensity changes. There is no significant field dependence of the magnetic correlation lengths in either film. For multilayers where the ratio of NiO to magnetite layer thickness is far from unity, the field dependence approximates that of the bulk films. However, for a Fe3O4(68Å)|NiO(34Å) multilayer the NiO antiferromagnetic intensity decr...
As described by P. Xiong, J. Zhao, and co-workers on page 8043, surface adsorption of organic mol... more As described by P. Xiong, J. Zhao, and co-workers on page 8043, surface adsorption of organic molecules can lead to robust manipulation of ferromagnetism in (Ga,Mn)As and a surface-preparation protocol enables direct writing of nanopatterns of self-assembled organic monolayers on the surface of the (Ga,Mn). As by dip-pen nanolithography; arbitrary nanopatterns, such as the "GaMnAs" characters, can be created. These two breakthroughs point to a novel pathway of controlled nanoscale manipulation of magnetism in dilute magnetic semiconductors via surface molecular patterning, which may lead to a new paradigm for the flexible fabrication of erasable and reconfigurable magnetic nanostructures and devices.
A facile approach using click chemistry is demonstrated for immobilization of metalloporphyrins o... more A facile approach using click chemistry is demonstrated for immobilization of metalloporphyrins onto the surface of silica-coated iron oxide particles. Oleic-acid stabilized iron oxide nanocrystals were prepared by thermal decomposition of iron(III) acetylacetonate. Their crystallinity, morphology, and superparamagnetism were determined using X-ray diffraction, transmission electron microscopy, and a superconducting quantum interference device. Monodisperse core-shell particles were produced in the silica-coating of iron oxide via microemulsion synthesis. Surface modification of these particles was performed in two steps, which included the reaction of silica-coated iron oxide particles with 3-bromopropyltrichlorosilane, followed by azido-functionalization with sodium azide. Monoalkylated porphyrins were prepared using the Williamson ether synthesis of commercially available tetra(4-hydroxyphenyl) porphyrin with propargyl bromide in the presence of a base. (1)H NMR and matrix-assist...
Advanced materials (Deerfield Beach, Fla.), Jan 5, 2015
Surface adsorption of organic molecules provides a new method for the robust manipulation of ferr... more Surface adsorption of organic molecules provides a new method for the robust manipulation of ferromagnetism in (Ga,Mn)As. Electron acceptor and donor molecules yield significant enhancement and suppression, respectively, of ferromagnetism with modulation of the Curie temperature spanning 36 K. Dip-pen nanolithography is employed to directly pattern monolayers on (Ga,Mn)As, which is presented as a novel pathway toward producing magnetic nanostructures.
Using neutron diffraction, x-ray scattering, and bulk-magnetization methods, we have characterize... more Using neutron diffraction, x-ray scattering, and bulk-magnetization methods, we have characterized the magnetic structure for Fe3O4/NiO superlattices grown by molecular-beam epitaxy. The antiferromagnetic NiO order extends through several superlattice bilayers, even though the intervening Fe3O4 layers are ferrimagnetic. The structural and magnetic coherence of the Fe3O4 is limited by interfacial stacking faults between adjacent layers resulting from symmetry differences between the NiO rocksalt and Fe3O4 spinel unit cell. The diffraction data manifest this interfacial disorder via a broadening of selected reflections. Using a structure-factor model based upon a Hendricks-Teller description of the random-stacking sequence, we have separated the magnetic order parameters of the Fe3O4 and NiO interlayers. The NiO appears to order at temperatures larger than TN for bulk (520 K) due to coupling to the Fe3O4 layers (TC=858 K). The dependence of this enhancement on the relative NiO composition is qualitatively consistent with the predictions of mean-field theory.
We present the first spin-resolving electron spectroscopic studies of thin film magnetite (Fe_3O_... more We present the first spin-resolving electron spectroscopic studies of thin film magnetite (Fe_3O_4)(001) surface, focusing on spin- resolved AES and EELS. A unique angle-, energy-, and spin-resolved electron spectrometer has been designed and built for the study of magnetic surface systems, based on a tandem configuration of energy- dispersive energy analyzer and Mott spin-polarimeter. Spin-resolved secondary emission spectroscopy reflects semi-metallic band structure of Fe_3O_4. The measured polarization plateau, at (29.8%), correlates well with average 3-d band polarization of stoichiometric Fe_3O4 (34.2%). Enhancement of polarization at low energies is observed, contradicting the Mauri model. Spin-resolved AES of the films show correlation effects in valence-valence transitions. Suppressed intensity and polarization of M_23M_45M_45 peaks relative to M_1M_45M_45 are observed, as well as strong resonant emission with shake-up. No spin polarization was detected in oxygen Auger featu...
Macroscopic phase coherence in superconductors enables quantum interference and phase manipulatio... more Macroscopic phase coherence in superconductors enables quantum interference and phase manipulation at realistic device length scales. Numerous superconducting electronic devices are based on the modulation of the supercurrent in superconducting loops. While the overall behavior of symmetric superconducting loops has been studied, the effects of asymmetries in such devices remain under-explored and poorly understood. Here we report on an experimental and theoretical study of the flux modulation of the persistent current in a doubly connected asymmetric aluminum nanowire loop. A model considering the length and electronic cross-section asymmetries in the loop provides a quantitative account of the observations. Comparison with experiments give essential parameters such as persistent and critical currents as well as the amount of asymmetry which can provide feedback into the design of superconducting quantum devices.
Carbonate clumped isotope thermometry has been applied to fossil mollusk shells from Tibet to rec... more Carbonate clumped isotope thermometry has been applied to fossil mollusk shells from Tibet to reconstruct the paleoclimate and paleoelevation of the region. However, inferred paleoelevation and climatic conditions from this proxy are inconsistent with paleontological evidence. Here, we report new clumped isotope data from both modern and fossil (5−4 Ma) freshwater mollusk shells with the results of X-ray diffraction (XRD) analyses of fossil shells from the Himalayan-Tibetan Plateau. Although all of the fossil shells analyzed in this study appeared pristine based on visual inspection, XRD data reveal that more than half of these apparently “pristine” fossil shells contain trace amounts of calcite. Clumped isotope temperatures derived from the fossil shells display a large range of variation (>22 °C). Among the fossil shells analyzed, those containing traces of calcite have yielded temperatures that are on average ∼10 °C lower than those with no detectable calcite from the same str...
Agglomerates of polar molecules in nonpolar solvents are selectively heated by microwave radiatio... more Agglomerates of polar molecules in nonpolar solvents are selectively heated by microwave radiation. The magnitude of the selective heating was directly measured by using the temperature dependence of the intensities of the Stokes and anti-Stokes bands in the Raman spectra of p-nitroanisole (pNA) and mesitylene. Under dynamic heating conditions, a large apparent temperature difference (ΔT) of over 100 °C was observed between the polar pNA solute and the nonpolar mesitylene solvent. This represents the first direct measurement of the selective microwave heating process. The magnitude of the selective microwave heating was affected by the properties of the agglomerated pNA. As the concentration of the pNA increases, the magnitude of the selective heating of the pNA was observed to decrease. This is explained by the tendency of the pNA dipoles to orient in an antiparallel fashion in the aggregates as measured by the Kirkwood g value, which decreased with increasing concentration. This effect reduces the net dipole moment of the agglomerates, which decreases the microwave absorption. After the radiation was terminated, the effective temperature of the dipolar molecules returned slowly to that of the medium. The slow heat transfer was modeled successfully by treating the solutions as a biphasic solvent/solute system. Based on modeling and the fact that the agglomerate can be heated above the boiling temperature of the solvent, an insulating layer of solvent vapor is suggested to form around the heated agglomerate, slowing convective heat transfer out of the agglomerate. This is an effect unique to microwave heating.
We report the growth, via core transformation, of highly fluorescing, near-infrared-emitting bime... more We report the growth, via core transformation, of highly fluorescing, near-infrared-emitting bimetallic Au/Ag nanoclusters, which are capped with hydrophobic or hydrophilic monothiol-terminated ligands.
We describe the growth and characterization of highly fluorescing, near-infrared-emitting nanoclu... more We describe the growth and characterization of highly fluorescing, near-infrared-emitting nanoclusters made of bimetallic Au25-xAgx cores, prepared using various monothiol-appended hydrophobic and hydrophilic ligands. The reaction uses well-defined triphenylphosphine-protected Au11 clusters (as precursors), which are reacted with Ag(I)-thiolate complexes. The prepared nanoclusters are small (diameter…
Physical chemistry chemical physics : PCCP, Jan 9, 2018
We detail the characterization of atomically precise, luminescent silver and gold bimetallic nano... more We detail the characterization of atomically precise, luminescent silver and gold bimetallic nanoclusters (Ag and AgAuNCs) grown in the presence of bidentate lipoic acid (LA, the oxidized form) and dihydrolipoic acid (DHLA, the reduced form) ligands. We found that while doping AuNCs with Ag or Cu precursors using up to a 50% molar fraction (during growth) did not lead to any photoluminescence enhancement, doping of AgNCs with Au resulted in a six-fold enhancement of the PL emission compared to undoped AgNCs. The effect of doping is also reflected in the optical absorption and PL excitation spectra of the gold-doped NCs (AgAuNCs), where a clear blue shift in the absorbance features with respect to the pure AgNCs has been measured. Mass spectrometry measurements using ESI-MS showed that the AgNCs and Au-doped AgNCs had the compositions Ag29(DHLA)12 and Ag28Au(DHLA)12, respectively. The bimetallic nature of the AgAuNC cores was further supported by X-ray Photoelectron Spectroscopy (XPS...
ABSTRACTNiO-magnetite multilayers exhibit long range antiferromagnetic order with the magnetite f... more ABSTRACTNiO-magnetite multilayers exhibit long range antiferromagnetic order with the magnetite ferrimagnetic correlations confined to a single layer due to stacking faults of the spinel structure at the interfaces[l, 2, 3, 4]. A systematic study of the field-dependence of the interlayer coupling in a series of NiO-magnetite multilayers has been made using neutron diffraction. Both NiO and magnetite single thin films were included in the measurements for comparison. In the magnetite film, intensity changes with magnetic field are consistent with domain reorientation of the net ferrimagnetic moments, while in the NiO film there are essentially no intensity changes. There is no significant field dependence of the magnetic correlation lengths in either film. For multilayers where the ratio of NiO to magnetite layer thickness is far from unity, the field dependence approximates that of the bulk films. However, for a Fe3O4(68Å)|NiO(34Å) multilayer the NiO antiferromagnetic intensity decr...
As described by P. Xiong, J. Zhao, and co-workers on page 8043, surface adsorption of organic mol... more As described by P. Xiong, J. Zhao, and co-workers on page 8043, surface adsorption of organic molecules can lead to robust manipulation of ferromagnetism in (Ga,Mn)As and a surface-preparation protocol enables direct writing of nanopatterns of self-assembled organic monolayers on the surface of the (Ga,Mn). As by dip-pen nanolithography; arbitrary nanopatterns, such as the "GaMnAs" characters, can be created. These two breakthroughs point to a novel pathway of controlled nanoscale manipulation of magnetism in dilute magnetic semiconductors via surface molecular patterning, which may lead to a new paradigm for the flexible fabrication of erasable and reconfigurable magnetic nanostructures and devices.
A facile approach using click chemistry is demonstrated for immobilization of metalloporphyrins o... more A facile approach using click chemistry is demonstrated for immobilization of metalloporphyrins onto the surface of silica-coated iron oxide particles. Oleic-acid stabilized iron oxide nanocrystals were prepared by thermal decomposition of iron(III) acetylacetonate. Their crystallinity, morphology, and superparamagnetism were determined using X-ray diffraction, transmission electron microscopy, and a superconducting quantum interference device. Monodisperse core-shell particles were produced in the silica-coating of iron oxide via microemulsion synthesis. Surface modification of these particles was performed in two steps, which included the reaction of silica-coated iron oxide particles with 3-bromopropyltrichlorosilane, followed by azido-functionalization with sodium azide. Monoalkylated porphyrins were prepared using the Williamson ether synthesis of commercially available tetra(4-hydroxyphenyl) porphyrin with propargyl bromide in the presence of a base. (1)H NMR and matrix-assist...
Advanced materials (Deerfield Beach, Fla.), Jan 5, 2015
Surface adsorption of organic molecules provides a new method for the robust manipulation of ferr... more Surface adsorption of organic molecules provides a new method for the robust manipulation of ferromagnetism in (Ga,Mn)As. Electron acceptor and donor molecules yield significant enhancement and suppression, respectively, of ferromagnetism with modulation of the Curie temperature spanning 36 K. Dip-pen nanolithography is employed to directly pattern monolayers on (Ga,Mn)As, which is presented as a novel pathway toward producing magnetic nanostructures.
Using neutron diffraction, x-ray scattering, and bulk-magnetization methods, we have characterize... more Using neutron diffraction, x-ray scattering, and bulk-magnetization methods, we have characterized the magnetic structure for Fe3O4/NiO superlattices grown by molecular-beam epitaxy. The antiferromagnetic NiO order extends through several superlattice bilayers, even though the intervening Fe3O4 layers are ferrimagnetic. The structural and magnetic coherence of the Fe3O4 is limited by interfacial stacking faults between adjacent layers resulting from symmetry differences between the NiO rocksalt and Fe3O4 spinel unit cell. The diffraction data manifest this interfacial disorder via a broadening of selected reflections. Using a structure-factor model based upon a Hendricks-Teller description of the random-stacking sequence, we have separated the magnetic order parameters of the Fe3O4 and NiO interlayers. The NiO appears to order at temperatures larger than TN for bulk (520 K) due to coupling to the Fe3O4 layers (TC=858 K). The dependence of this enhancement on the relative NiO composition is qualitatively consistent with the predictions of mean-field theory.
We present the first spin-resolving electron spectroscopic studies of thin film magnetite (Fe_3O_... more We present the first spin-resolving electron spectroscopic studies of thin film magnetite (Fe_3O_4)(001) surface, focusing on spin- resolved AES and EELS. A unique angle-, energy-, and spin-resolved electron spectrometer has been designed and built for the study of magnetic surface systems, based on a tandem configuration of energy- dispersive energy analyzer and Mott spin-polarimeter. Spin-resolved secondary emission spectroscopy reflects semi-metallic band structure of Fe_3O_4. The measured polarization plateau, at (29.8%), correlates well with average 3-d band polarization of stoichiometric Fe_3O4 (34.2%). Enhancement of polarization at low energies is observed, contradicting the Mauri model. Spin-resolved AES of the films show correlation effects in valence-valence transitions. Suppressed intensity and polarization of M_23M_45M_45 peaks relative to M_1M_45M_45 are observed, as well as strong resonant emission with shake-up. No spin polarization was detected in oxygen Auger featu...
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