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Articles 1 - 30 of 30
Full-Text Articles in Physics
Td-Dft Spin-Adiabats With Analytic Nonadiabatic Derivative Couplings, Nicole Bellonzi, Ethan Alguire, Shervin Fatehi, Yihan Shao, Joseph E. Subotnik
Td-Dft Spin-Adiabats With Analytic Nonadiabatic Derivative Couplings, Nicole Bellonzi, Ethan Alguire, Shervin Fatehi, Yihan Shao, Joseph E. Subotnik
Chemistry Faculty Publications and Presentations
Wepresent an algorithm for efficient calculation of analytic nonadiabatic derivative couplings between spin-adiabatic, time-dependent density functional theory states within the Tamm-Dancoff approximation. Our derivation is based on the direct differentiation of the Kohn-Sham pseudowavefunction using the framework of Ou et al. Our implementation is limited to the case of a system with an even number of electrons in a closed shell ground state, and we validate our algorithm against finite difference at an S1/T2 crossing of benzaldehyde. Through the introduction of a magnetic field spin-coupling operator, we break time-reversal symmetry to generate complex valued nonadiabatic derivative couplings. Although the nonadiabatic …
Communication: Visualization And Spectroscopy Of Defects Induced By Dehydrogenation In Individual Silicon Nanocrystals, Dmitry A. Kislitsyn, Jon M. Mills, Vancho Kocevski, Sheng-Kuei Chiu, William J.I. Debenedetti, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin
Communication: Visualization And Spectroscopy Of Defects Induced By Dehydrogenation In Individual Silicon Nanocrystals, Dmitry A. Kislitsyn, Jon M. Mills, Vancho Kocevski, Sheng-Kuei Chiu, William J.I. Debenedetti, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin
Chemistry Faculty Publications and Presentations
We present results of a scanning tunneling spectroscopy (STS) study of the impact of dehydrogenation on the electronic structures of hydrogen-passivated silicon nanocrystals (SiNCs) supported on the Au(111)surface. Gradual dehydrogenation is achieved by injecting high-energy electrons into individual SiNCs, which results, initially, in reduction of the electronic bandgap, and eventually produces midgap electronic states. We use theoretical calculations to show that the STS spectra of midgap states are consistent with the presence of silicon dangling bonds, which are found in different charge states. Our calculations also suggest that the observed initial reduction of the electronic bandgap is attributable to the …
Mapping Of Defects In Individual Silicon Nanocrystals Using Real- Space Spectroscopy, Dmitry A. Kislitsyn, Vancho Kocevski, Jon M. Mills, Sheng-Kuei Chiu, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin
Mapping Of Defects In Individual Silicon Nanocrystals Using Real- Space Spectroscopy, Dmitry A. Kislitsyn, Vancho Kocevski, Jon M. Mills, Sheng-Kuei Chiu, Christian F. Gervasi, Benjamen N. Taber, Ariel E. Rosenfield, Olle Eriksson, Ján Rusz, Andrea Mitchell Goforth, George V. Nazin
Chemistry Faculty Publications and Presentations
The photophysical properties of silicon semiconductor nanocrystals (SiNCs) are extremely sensitive to the presence of surface chemical defects, many of which are easily produced by oxidation under ambient conditions. The diversity of chemical structures of such defects and the lack of tools capable of probing individual defects continue to impede understanding of the roles of these defects in SiNC photophysics. We use scanning tunneling spectroscopy to study the impact of surface defects on the electronic structures of hydrogen-passivated SiNCs supported on the Au(111) surface. Spatial maps of the local electronic density of states (LDOS) produced by our measurements allowed us …
Aqueous Red-Emitting Silicon Nanoparticles For Cellular Imaging: Consequences Of Protecting Against Surface Passivation By Hydroxide And Water For Stable Red Emission, Sheng-Kuei Chiu, Beth Ann Manhat, William J.I. Debenedetti, Anna L. Brown, Katye Fichter, Tania Vu, Micah Eastman, Jun Jiao, Andrea Mitchell Goforth
Aqueous Red-Emitting Silicon Nanoparticles For Cellular Imaging: Consequences Of Protecting Against Surface Passivation By Hydroxide And Water For Stable Red Emission, Sheng-Kuei Chiu, Beth Ann Manhat, William J.I. Debenedetti, Anna L. Brown, Katye Fichter, Tania Vu, Micah Eastman, Jun Jiao, Andrea Mitchell Goforth
Chemistry Faculty Publications and Presentations
Stable, aqueous, red-to-near infrared emission is critical for the use of silicon nanoparticles (Si NPs) in biological fluorescence assays, but such Si NPs have been difficult to attain. We report a synthesis and surface modification strategy that protects Si NPs and preserves red photoluminescence (PL) in water for more than 6 mo. The Si NPs were synthesized via high temperature reaction, liberated from an oxide matrix, and functionalized via hydrosilylation to yield hydrophobic particles. The hydrophobic Si NPs were phase transferred to water using the surfactant cetyltrimethylammonium bromide (CTAB) with retention of red PL. CTAB apparently serves a double role …
Synthesis And Characterization Of N- And P- Doped Tin Oxide Nanowires, Hoang Tran, Shankar B. Rananavare
Synthesis And Characterization Of N- And P- Doped Tin Oxide Nanowires, Hoang Tran, Shankar B. Rananavare
Chemistry Faculty Publications and Presentations
Bulk-scale synthetic methods for preparing doped tin oxide (SnO2) nanowires (NWs) are presented. n-and p-doping is achieved through insertion of Antimony and Lithium in tin oxide lattice, respectively. We also present a comparison of the structural and optical properties of SnO2 nanoparticles (NPs), and SnO2 NWs. Both n-type and p- type NWs display a characteristic red shift in their photoluminescence (PL) spectra. Surface plasmons observed in these systems imply high carrier concentrations. These corrosion resistant materials are useful in fabricating ultra-sensitive gas detectors and transparent electronics.
Bis Photobase Generator, Hoang Tran, Shankar B. Rananavare
Bis Photobase Generator, Hoang Tran, Shankar B. Rananavare
Chemistry Faculty Publications and Presentations
The extension of 193nm technology is desirable due to the magnitude of past investments. Since “optical” advancements are increasingly difficult, there is a strong demand for more sophisticated “smart” resists to increase pattern density. Many studies have proven double pattering can be used for the extension of 193nm lithography. In this study, a new class of two stage photo base generators will be introduced along with the synthetic procedure and molecular characterization. The characterizations for exposure study by NMR have shown typical characteristics to stage decomposition under the exposure of 254nm light as well as promising pitch division. GCMS was …
Bandwidth Tuning Triggers Interplay Of Charge Order And Superconductivity In Two-Dimensional Organic Materials, S. Kaiser, M. Dressel, Y. Sun, A. Greco, J. A. Schlueter, Gary L. Gard, N. Drichko
Bandwidth Tuning Triggers Interplay Of Charge Order And Superconductivity In Two-Dimensional Organic Materials, S. Kaiser, M. Dressel, Y. Sun, A. Greco, J. A. Schlueter, Gary L. Gard, N. Drichko
Chemistry Faculty Publications and Presentations
We observe charge-order fluctuations in the quasi-two-dimensional organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃, both by means of vibrational spectroscopy, locally probing the fluctuating charge order, and by investigating the in-plane dynamical response by infrared reflectance spectroscopy. The decrease of the effective electronic interaction in an isostructural metal suppresses both charge-order fluctuations and superconductivity, pointing to their interplay. We compare the results of our experiments with calculations on the extended Hubbard model.
Fermiology And Superconductivity At High Magnetic Fields In A Completely Organic Cation Radical Salt, J. S. Brooks, V. Williams, E. Choi, D. Graf, M. Tokumoto, S. Uji, F. Zuo, J. Wosnitza, J. A. Schlueter, H. David, Rolf Walter Winter, Gary L. Gard, K. Storr
Fermiology And Superconductivity At High Magnetic Fields In A Completely Organic Cation Radical Salt, J. S. Brooks, V. Williams, E. Choi, D. Graf, M. Tokumoto, S. Uji, F. Zuo, J. Wosnitza, J. A. Schlueter, H. David, Rolf Walter Winter, Gary L. Gard, K. Storr
Chemistry Faculty Publications and Presentations
We report specialized interplane magnetoresistance (MR) measurements on the organic superconducting compound β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) in both the superconducting (Tc ∼ 5K) and normal states versus magnetic field direction. In the normal state, detailed angular-dependent magnetoresistance oscillation (AMRO) studies reveal peculiar features of the Fermi surface topology of this compound, and very high magnetic field studies further support the unusual nature of the electronic structure. In the superconducting state we investigate, through detailedAMRO measurements, the anomalous MR peak that appears within the superconducting field-temperature phase diagram. Our results reveal a direct connection between the superconducting state determined from …
The Reno Aerosol Optics Study: An Evaluation Of Aerosol Absorption Measurement Methods, Patrick J. Sheridan, W. Patrick Arnott, John A. Ogren, Elisabeth Andrews, Dean B. Atkinson, David S. Covert, Hans Moosmüller, Andreas Petzold, Beat Schmid, Anthony W. Strawa, Ravi Varma, Aki Virkkula
The Reno Aerosol Optics Study: An Evaluation Of Aerosol Absorption Measurement Methods, Patrick J. Sheridan, W. Patrick Arnott, John A. Ogren, Elisabeth Andrews, Dean B. Atkinson, David S. Covert, Hans Moosmüller, Andreas Petzold, Beat Schmid, Anthony W. Strawa, Ravi Varma, Aki Virkkula
Chemistry Faculty Publications and Presentations
The Reno Aerosol Optics Study (RAOS) was designed and conducted to compare the performance of many existing and new instruments for the in situ measurement of aerosol optical properties with a focus on the determination of aerosol light absorption. For this study, simple test aerosols of black and white particles were generated and combined in external mixtures under low relative humidity conditions and delivered to each measurement system. The aerosol mixing and delivery system was constantly monitored using particle counters and nephelometers to ensure that the same aerosol number concentration and amount reached the different instruments. The aerosol light-scattering measurements …
Pressure-Induced Insulating State In An Organic Superconductor, Gary L. Gard, Javid Mohtasham, J. A. Schlueter, C. Pfleiderer, J. Wosnitza, J. Hagel
Pressure-Induced Insulating State In An Organic Superconductor, Gary L. Gard, Javid Mohtasham, J. A. Schlueter, C. Pfleiderer, J. Wosnitza, J. Hagel
Chemistry Faculty Publications and Presentations
The electronic-transport properties of the quasi-two-dimensional organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated in magnetic fields up to 15 T and under hydrostatic pressure up to about 14 kbars. Shubnikov–de Haas data reveal a nonmonotonic pressure dependence of the holelike Fermi surface, a roughly linear increase of the electron g factor, and an approximately linear decrease of the cyclotron effective mass. By assuming that the latter reflects the pressure-induced reduction of the superconducting coupling parameter λ the rapid reduction of the superconducting transition temperature Tc(p) can be reasonably well described by the modified McMillan equation. Above …
Enhanced Magnetic Quantum Oscillations In The Mixed State Of A Two-Dimensional Organic Superconductor, J. Wosnitza, J. Hagel, P. J. Meeson, D. Bintley, J. A. Schlueter, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard
Enhanced Magnetic Quantum Oscillations In The Mixed State Of A Two-Dimensional Organic Superconductor, J. Wosnitza, J. Hagel, P. J. Meeson, D. Bintley, J. A. Schlueter, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard
Chemistry Faculty Publications and Presentations
We report on de Haas–van Alphen (dHvA) oscillations observed in the mixed state of the organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene) utilizing the field-modulation technique and torque magnetometry. At low temperatures (30 mK), the dHvA signal persists down to 1.4 T well below the upper critical field Bc2≈3.6T. Contrary to most theoretical predictions and previous experimental findings, no additional damping of the dHvA-oscillation amplitude, but a reduced damping of the dHvA signal is found. This highly unusual effect might indicate a reduced quasiparticle scattering rate or an additional oscillatory contribution in the superconducting state.
High-Field Magnetic Resonant Properties Of Β’–(Et)2sf5cf2so3, Gary L. Gard, Rolf Walter Winter, J. A. Schlueter, Brian H. Ward, E. Jobiliong, A. P. Reyes, P. Kuhns, J. Krzystek, J. S. Brooks, S. A. Zvyagin, B. Rutel
High-Field Magnetic Resonant Properties Of Β’–(Et)2sf5cf2so3, Gary L. Gard, Rolf Walter Winter, J. A. Schlueter, Brian H. Ward, E. Jobiliong, A. P. Reyes, P. Kuhns, J. Krzystek, J. S. Brooks, S. A. Zvyagin, B. Rutel
Chemistry Faculty Publications and Presentations
The charge transfer salt β′-(ET)₂SF₅CF₂SO₃, which has previously been considered a spin-Peierls material with a TSP;33 K, is examined using high-resolution high-field sub-millimeter/millimeter wave electron spin resonance (ESR), and nuclear magnetic resonance (NMR) techniques. A peak in the nuclear spin-lattice relaxation behavior in fields of 8 T, accompanied by a broadening and paramagnetic shift of the resonance line, indicates a phase transition at Tc~20 K. A pronounced change in the high-field ESR excitation spectra at ~24 T, observed at Tc~20 K, may indicate the onset of antiferromagnetic (AFM) correlations of the low temperature phase in β′-(ET)₂SF₅CF₂SO₃. Peculiarities of the low-temperature …
Coherent Vs Incoherent Interlayer Transport In Layered Metals, Gary L. Gard, J. Wosnitza, J. Hagel, J. S. Qualls, J. S. Brooks, E. Balthes, D. Schweitzer, J. A. Schlueter, U. Geiser, Javid Mohtasham, Rolf Walter Winter
Coherent Vs Incoherent Interlayer Transport In Layered Metals, Gary L. Gard, J. Wosnitza, J. Hagel, J. S. Qualls, J. S. Brooks, E. Balthes, D. Schweitzer, J. A. Schlueter, U. Geiser, Javid Mohtasham, Rolf Walter Winter
Chemistry Faculty Publications and Presentations
The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For k -BEDT-TTF)₂I₃, where BEDTTTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at Q590°(field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃. This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal.
Thermal Activation Between Landau Levels In The Organic Superconductor Β″-(Bedt-Ttf)2sf5ch2cf2so3, Gary L. Gard, M. S. Nam, A. Ardavan, J. A. Symington, J. Singleton, N. Harrison, C. H. Mielke, J. A. Schlueter, Rolf Walter Winter
Thermal Activation Between Landau Levels In The Organic Superconductor Β″-(Bedt-Ttf)2sf5ch2cf2so3, Gary L. Gard, M. S. Nam, A. Ardavan, J. A. Symington, J. Singleton, N. Harrison, C. H. Mielke, J. A. Schlueter, Rolf Walter Winter
Chemistry Faculty Publications and Presentations
We show that Shubnikov–de Haas oscillations in the interlayer resistivity of the organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ become very pronounced in magnetic fields ~60T. The conductivity minima exhibit thermally activated behavior that can be explained simply by the presence of a Landau gap, with the quasi-one-dimensional Fermi surface sheets contributing negligibly to the conductivity. This observation, together with complete suppression of chemical potential oscillations, is consistent with an incommensurate nesting instability of the quasi-one-dimensional sheets.
Shubnikov–De Haas Effect In The Superconducting State Of An Organic Superconductor, J. Wosnitza, S. Wanka, J. Hagel, R. Häussler, H. V. Löhneysen, J. A. Schlueter, U. Geiser, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Shubnikov–De Haas Effect In The Superconducting State Of An Organic Superconductor, J. Wosnitza, S. Wanka, J. Hagel, R. Häussler, H. V. Löhneysen, J. A. Schlueter, U. Geiser, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Chemistry Faculty Publications and Presentations
We report the observation of Shubnikov–de Haas (SdH) oscillations in the mixed state of the organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (Tc≈4.4K). At low temperatures the SdH oscillations persist clearly below the upper critical field Bc₂(0)≈3.6 T almost down to the field where the resistivity vanishes. Rather unusually, no additional damping of the SdH-signal amplitude — as well as of the de Haas–van Alphen amplitude — is observed in the superconducting state. This indicates that the damping in the vortex state of this quasi-two-dimensional superconductor is different in character to that observed for most three-dimensional materials.
Comparative Thermal-Expansion Study Of Β″-(Et)2sf5ch2cf2so3 And Κ-(Et)2cu(Ncs)2: Uniaxial Pressure Coefficients Of Tc And Upper Critical Fields, J. Müller, M. Lang, F. Steglich, J. A. Schlueter, A. M. Kini, U. Geiser, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard, T. Sasaki, N. Toyota
Comparative Thermal-Expansion Study Of Β″-(Et)2sf5ch2cf2so3 And Κ-(Et)2cu(Ncs)2: Uniaxial Pressure Coefficients Of Tc And Upper Critical Fields, J. Müller, M. Lang, F. Steglich, J. A. Schlueter, A. M. Kini, U. Geiser, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard, T. Sasaki, N. Toyota
Chemistry Faculty Publications and Presentations
We report high-resolution measurements of the coefficient of thermal expansion, α=l⁻¹ x (δl/δΤ), on single crystals of the organic superconductors β″-(ET)₂SF₅CH₂CF₂SO₃ and κ-(ET)₂Cu(NCS)₂. For both salts we find large and highly anisotropic phase-transition anomalies at Tc. Combining these data with literature results on the specific heat via the Ehrenfest relation, the uniaxial pressure coefficients of Tc can be determined. Most remarkably, a strikingly similar in-plane vs out-of-plane anisotropy is found for both compounds: the strong suppression of Tc observed in hydrostatic-pressure experiments is dominated by a huge negative uniaxial stress effect perpendicular to the conducting planes. Therefore we expect that …
Two-Dimensional Fermi Liquid With Fixed Chemical Potential, J. Wosnitza, S. Wanka, J. Hagel, E. Balthes, N. Harrison, J. A. Schlueter, A. M. Kini, U. Geiser, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard
Two-Dimensional Fermi Liquid With Fixed Chemical Potential, J. Wosnitza, S. Wanka, J. Hagel, E. Balthes, N. Harrison, J. A. Schlueter, A. M. Kini, U. Geiser, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard
Chemistry Faculty Publications and Presentations
de Haas-van Alphen measurements made on the organic metal β″-(ET)₂SF₅CH₂CF₂SO₃ reveal the existence of an ideal two-dimensional (2D) Fermi surface, but rather than having the conventional sawtooth wave form that is normally observed in all other 2D electron gases, instead, an ‘‘inverse sawtooth’’ wave form is observed, which is to be expected when the chemical potential is pinned at a constant value. While this proves the existence of the theoretically predicted quasi-one-dimensional band, it further implies that this band has an exceptionally large density of states.
Anomalous Low-Temperature And High-Field Magnetoresistance In The Organic Superconductor Β″-(Bedt-Ttf)2sf5ch2cf2so3, F. Zuo, X. Su, P. Zhang, J. S. Brooks, J. Wosnitza, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Anomalous Low-Temperature And High-Field Magnetoresistance In The Organic Superconductor Β″-(Bedt-Ttf)2sf5ch2cf2so3, F. Zuo, X. Su, P. Zhang, J. S. Brooks, J. Wosnitza, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Chemistry Faculty Publications and Presentations
We report direct observations of anomalous magnetic-field and temperature dependences of the Shubnikov–de Haas oscillations in the organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃. Unlike other BEDT-TTF based organic superconductors, a nonmetallic temperature dependence of the background magnetoresistance is clearly observed. It is speculated that the nonmetallic behavior may arise from a partial nesting of the open orbits, similar to the field-induced density wave in the quasi-one-dimensional systems or a charge localization. The analysis of the magnetoresistance oscillations are found to deviate from the conventional Lifshitz-Kosevich description at high field and low temperatures. [S0163-1829(99)05433-8]
Optical Properties Of Β″-(Et)2sf5ch2cf2so3: A Layered Molecular Superconductor With Large Discrete Counterions, J. Dong, J. L. Musfeldt, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Optical Properties Of Β″-(Et)2sf5ch2cf2so3: A Layered Molecular Superconductor With Large Discrete Counterions, J. Dong, J. L. Musfeldt, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Chemistry Faculty Publications and Presentations
We report the polarized infrared and optical reflectance of β″-(ET)₂SF₅CH₂CF₂SO₃ as a function of temperature. This fully organic superconductor displays weakly metallic behavior over the entire temperature range of our investigation. The electronic properties present several unusual features including the lack of a conventional free carrier (Drude) response at low temperature, infrared localization phenomena, and an unexpected temperature dependence of the oscillator strength. Similar behavior is observed in other β and β″ superconductors above Tc, suggesting that this class of compounds is very close to a metal→insulator transition where electronic correlations are important and the Drude response carries very little …
Anisotropic Magnetoresistance In The Organic Superconductor Β″–(Bedt-Ttf)2sf5ch2cf2so3, X. Su, F. Zuo, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Anisotropic Magnetoresistance In The Organic Superconductor Β″–(Bedt-Ttf)2sf5ch2cf2so3, X. Su, F. Zuo, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Chemistry Faculty Publications and Presentations
In this paper, we report transport measurements of interlayer magnetoresistance with field parallel and perpendicular to the current direction in an all organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃. For H∥I, the isothermal magnetoresistance R(H) at low temperatures (T
Specific Heat And Critical Fields Of The Organic Superconductor Β″–(Bedt-Ttf)2sf5ch2cf2so3, S. Wanka, J. Hagel, D. Beckmanm, J. Wosnitza, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Specific Heat And Critical Fields Of The Organic Superconductor Β″–(Bedt-Ttf)2sf5ch2cf2so3, S. Wanka, J. Hagel, D. Beckmanm, J. Wosnitza, J. A. Schlueter, Jack M. Williams, P. G. Nixon, Rolf Walter Winter, Gary L. Gard
Chemistry Faculty Publications and Presentations
We report on specific-heat, magnetization, and ac-susceptibility measurements of β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, an organic superconductor with Tc=4.5 K, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. The jump of the specific heat C at Tc and the exact form of the specific heat difference between C in the superconducting (B=0 T) and in the normal (B=3.5 T) state can be well described by BCS theory with strong coupling. We estimate an electron-phonon coupling parameter λ≈1.1. From measurements of C in magnetic fields we extract the upper critical field Bc₂(T). Low-field dc-magnetization measurements were used to determine the temperature dependence of the lower critical field Bc₁. …
Structure, Dynamics, And Phase Transitions In The Fullerene Derivatives C_{60}O And C_{61}H_{2}, C. Meingast, G. Roth, L. Pintschovius, R. H. Michel, C. Stoermer, M. M. Kappes, Paul A. Heiney, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii
Structure, Dynamics, And Phase Transitions In The Fullerene Derivatives C_{60}O And C_{61}H_{2}, C. Meingast, G. Roth, L. Pintschovius, R. H. Michel, C. Stoermer, M. M. Kappes, Paul A. Heiney, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii
Chemistry Faculty Publications and Presentations
The effect of perturbing the icosohedral symmetry of C60 by the addition of the side groups -O and -CH2 upon orientational order-disorder and glass transitions in solid C60 has been studied by a combination of high-resolution capacitance dilatometry and single-crystal x-ray and powder inelastic neutron scattering. Both fullerene derivatives C60O (epoxide) and C61H2 (6,5-annulene) are shown to undergo a sequence of transitions similar to that found in pure C60, i.e., a first-order orientational ordering transition just below room temperature followed by an orientational glass transition at lower temperatures. Although the …
Structure And Phase Transition Of The 6,5-Annulene Isomer Of C_{61}H_{2}, Andrea N. Lommen, Paul A. Heiney, Gavin B. M. Vaughan, Peter W. Stephens, Dengfa Liu, Dayin Li, Allan L. Smith, Andrew R. Mcghie, Robert M. Strongin, Laurent Brard, Amos B. Smith Iii
Structure And Phase Transition Of The 6,5-Annulene Isomer Of C_{61}H_{2}, Andrea N. Lommen, Paul A. Heiney, Gavin B. M. Vaughan, Peter W. Stephens, Dengfa Liu, Dayin Li, Allan L. Smith, Andrew R. Mcghie, Robert M. Strongin, Laurent Brard, Amos B. Smith Iii
Chemistry Faculty Publications and Presentations
We have used differential scanning calorimetry and x-ray diffraction to study the crystalline phases of the 6,5-annulene isomer of C61H2. At 308 K the methylenated fullerenes are orientationally disordered in a face-centered cubic lattice with lattice parameter 14.19±0.02 Å. Below Tc=290 K the symmetry is lowered to Pa3¯, a simple-cubic structure. At 20 K the lattice parameter is 14.06±0.02 Å, with substantial statistical disorder remaining. The transition temperature in C61H2 is slightly higher than in C60O and higher still than in C60, but the three compounds exhibit orientationally …
Orientational Phase Transition In Na_{X}C_{60} (1, T. Yildirim, J. E. Fischer, A. B. Harris, Peter W. Stephens, Dengfa Liu, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii
Orientational Phase Transition In Na_{X}C_{60} (1, T. Yildirim, J. E. Fischer, A. B. Harris, Peter W. Stephens, Dengfa Liu, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii
Chemistry Faculty Publications and Presentations
X-ray diffraction and calorimetry data on cubic NaxC60(1<x60, e.g., Tm(x=1.3)=325 K. The ordered phases are the same as in pure C60: simple cubic, space group Pa3¯, but the orientations in the disordered phase are more restricted. We explain how Na stabilizes the ordered phase to rather high T, while K and Rb do not, in terms of Coulomb interactions between C60 molecules and and Na ions which we calculate from the local charge density of C60.
Existence Of High-Order Superlattices In Orientationally Ordered C_{60}, J. E. Fischer, D. E. Luzzi, K. Kniaź, A. R. Mcghie, D. A. Ricketts-Foot, W. R. Romanow, Gavin B. M. Vaughan, Dayin Li, Allan L. Smith, Robert M. Strongin, M. A. Cichy, Laurent Bard, Amos B. Smith Iii
Existence Of High-Order Superlattices In Orientationally Ordered C_{60}, J. E. Fischer, D. E. Luzzi, K. Kniaź, A. R. Mcghie, D. A. Ricketts-Foot, W. R. Romanow, Gavin B. M. Vaughan, Dayin Li, Allan L. Smith, Robert M. Strongin, M. A. Cichy, Laurent Bard, Amos B. Smith Iii
Chemistry Faculty Publications and Presentations
We correlate the presence or absence of high-order modulated structures in solid C60 with the differential scanning calorimetry signature of the orientational ordering transition and other diagnostic data. We have searched for, but not observed, the 2a face-centered cubic structure recently observed in low-temperature electron and single-crystal x-ray diffraction. We conclude that the intrinsic ground state is the previously reported simple cubic structure [space groupPa3¯, a(14 K)=14.06 Å], and that other structures may be stabilized by defects or impurities.
Coherence Peak And Superconducting Energy Gap In Rb_{3}C_{60} Observed By Muon Spin Relaxation, R. F. Kiefl, W. A. Macfarlane, K. H. Chow, S. Dunsiger, T. L. Duty, T. M. S. Johnston, J. W. Schneider, J. Sonier, Laurent Brard, Robert M. Strongin, J. E. Fischer, Amos B. Smith Iii
Coherence Peak And Superconducting Energy Gap In Rb_{3}C_{60} Observed By Muon Spin Relaxation, R. F. Kiefl, W. A. Macfarlane, K. H. Chow, S. Dunsiger, T. L. Duty, T. M. S. Johnston, J. W. Schneider, J. Sonier, Laurent Brard, Robert M. Strongin, J. E. Fischer, Amos B. Smith Iii
Chemistry Faculty Publications and Presentations
Muon spin relaxation resulting from spin exchange scattering of endohedral muonium (μ+e-) with thermal electronic excitations has been observed in the fullerene superconductor Rb3C60. The temperature dependence of T1-1 shows a coherence peak just below Tc and can be fit to the conventional Hebel-Slichter theory for spin relaxation in a superconductor with a broadened BCS density of states. The average energy gap for electronic excitations, Δ/kB=53(4) K or 2Δ/ kBTc=3.6(3), is consistent with the BCS weak coupling limit.
Unusual Thermal Stability Of A Site-Ordered Mc60 Rocksalt Structure (M=K, Rb, Or Cs), Q. Zhu, O. Zhou, J. E. Fischer, Andrew R. Mcghie, W. R. Romanow, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii
Unusual Thermal Stability Of A Site-Ordered Mc60 Rocksalt Structure (M=K, Rb, Or Cs), Q. Zhu, O. Zhou, J. E. Fischer, Andrew R. Mcghie, W. R. Romanow, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii
Chemistry Faculty Publications and Presentations
X-ray diffraction and differential scanning calorimetry of MxC60, with x∼1 and M=K, Rb, or Cs, reveal an unusual T-dependent phase sequence. A low-symmetry ground state is found, while the high-T limit is an ordered rocksalt structure in which only the octahedral sites are occupied. The unusual high-T stability of this ordered phase is attributed to the entropy of molecular orientational disorder and/or thermal disorder of the alkali-metal ions within the octahedral sites. Unique to KxC60 with x≥1.4, we find at intermediate temperatures an fcc site-disordered lattice gas …
Pressure Dependence Of Ozone Interference In The Laser Fluorescence Measurement Of Oh In The Atmosphere [Comment], Thomas M. Hard, C. Y. Chan, A. A. Mehrabzadeh, Robert J. O'Brien
Pressure Dependence Of Ozone Interference In The Laser Fluorescence Measurement Of Oh In The Atmosphere [Comment], Thomas M. Hard, C. Y. Chan, A. A. Mehrabzadeh, Robert J. O'Brien
Chemistry Faculty Publications and Presentations
The authors comment on the paper by Shirinzadeh et al. (Applied Optics, vol. 26, p. 2102, 1987). They point out three errors which caused the overprediction of spurious HO data.
Discharge Suppression System For A Double Focusing, Atmospheric Pressure Ionization Mass Spectrometer, Andrew H. Grange, Robert J. O'Brien, Douglas F. Barofsky
Discharge Suppression System For A Double Focusing, Atmospheric Pressure Ionization Mass Spectrometer, Andrew H. Grange, Robert J. O'Brien, Douglas F. Barofsky
Chemistry Faculty Publications and Presentations
An electrical discharge suppression system for a medium throughput (∼2 l/s) pumping line has been devised that works up to potentials of ±15 kV. This device permits atmospheric pressure ionization sources to be interfaced to high-resolution, magnetic sector mass spectrometers with source potentials of 6-10 kV
Pressure Dependence Of Fluorescent And Photolytic Interferences In Ho Detection By Laser-Excited Fluorescence, Thomas M. Hard, Robert J. O'Brien, T. B. Cook
Pressure Dependence Of Fluorescent And Photolytic Interferences In Ho Detection By Laser-Excited Fluorescence, Thomas M. Hard, Robert J. O'Brien, T. B. Cook
Chemistry Faculty Publications and Presentations
In the measurement of HO concentrations by laser-excited fluorescence, expansion of the sampled air offers a way to reduce fluorescent and photolytic interference by other species. The decrease in [HO] upon expansion is balanced by an increase in HO fluorescence yield over a wide range of pressures. Background air fluorescence is reduced if the responsible species have fluorescence yields higher than those of HO. Preliminary experiments indicate that most of the fluorescence observed in laboratory air is due to such species. Upon expansion, the suppression of fluorescent interference can be no greater than the reduction in pressure, whereas the suppression …