Search

Search Results

• 1. [Article] Temperature dependence of dark current in a CCD

  We present data for dark current of a back-illuminated CCD over the temperature range of 222 to 291 K. Using an Arrhenius law, we found that the analysis of the data leads to the relation between the prefactor ...

  Citation × Citation Citation Abstract Copy Title: Temperature dependence of dark current in a CCD Author: Widenhorn, Ralf, Blouke, Morley M., Weber, Alexander, Rest, Armin, Bodegom, Erik Year: 2002 We present data for dark current of a back-illuminated CCD over the temperature range of 222 to 291 K. Using an Arrhenius law, we found that the analysis of the data leads to the relation between the prefactor and the apparent activation energy as described by the Meyer-Neldel rule. However, a more detailed analysis shows that the activation energy for the dark current changes in the temperature range investigated. This transition can be explained by the larger relative importance at high temperatures of the diffusion dark current and at low temperatures by the depletion dark current. The diffusion dark current, characterized by the band gap of silicon, is uniform for all pixels. At low temperatures, the depletion dark current, characterized by half the band gap, prevails, but it varies for different pixels. Dark current spikes are pronounced at low temperatures and can be explained by large concentrations of deep level impurities in those particular pixels. We show that fitting the data with the impurity concentration as the only variable can explain the dark current characteristics of all the pixels on the chip. Title: Temperature dependence of dark current in a CCD Author: Widenhorn, Ralf, Blouke, Morley M., Weber, Alexander, Rest, Armin, Bodegom, Erik Year: 2002 We present data for dark current of a back-illuminated CCD over the temperature range of 222 to 291 K. Using an Arrhenius law, we found that the analysis of the data leads to the relation between the prefactor and the apparent activation energy as described by the Meyer-Neldel rule. However, a more detailed analysis shows that the activation energy for the dark current changes in the temperature range investigated. This transition can be explained by the larger relative importance at high temperatures of the diffusion dark current and at low temperatures by the depletion dark current. The diffusion dark current, characterized by the band gap of silicon, is uniform for all pixels. At low temperatures, the depletion dark current, characterized by half the band gap, prevails, but it varies for different pixels. Dark current spikes are pronounced at low temperatures and can be explained by large concentrations of deep level impurities in those particular pixels. We show that fitting the data with the impurity concentration as the only variable can explain the dark current characteristics of all the pixels on the chip. Close

• 2. [Article] The Relationship Between Precipitation and Temperature Over the Contiguous United States

  The correlation between monthly total precipitation and monthly mean temperature over the 80-year period from 1905 to 1984 at nearly 1000 stations in the contiguous United States was calculated and analyzed. ...

  Citation × Citation Citation Abstract Copy Title: The Relationship Between Precipitation and Temperature Over the Contiguous United States Author: Zhao, Weining, Khalil, M. A. K. Year: 1993 The correlation between monthly total precipitation and monthly mean temperature over the 80-year period from 1905 to 1984 at nearly 1000 stations in the contiguous United States was calculated and analyzed. Both local and field significances were tested by using statistical methods. Areas of both negative and positive precipitation-temperature correlations were found. Over most of the United States, summer precipitation and temperature were negatively correlated, which indicates that warm summers tended to be dryer. This is particularly true in the central and southern Great Plains. The area south of the Great Lakes covering the eastern portion of the Corn Belt was the only major area where a significant positive correlation was found in winter. Title: The Relationship Between Precipitation and Temperature Over the Contiguous United States Author: Zhao, Weining, Khalil, M. A. K. Year: 1993 The correlation between monthly total precipitation and monthly mean temperature over the 80-year period from 1905 to 1984 at nearly 1000 stations in the contiguous United States was calculated and analyzed. Both local and field significances were tested by using statistical methods. Areas of both negative and positive precipitation-temperature correlations were found. Over most of the United States, summer precipitation and temperature were negatively correlated, which indicates that warm summers tended to be dryer. This is particularly true in the central and southern Great Plains. The area south of the Great Lakes covering the eastern portion of the Corn Belt was the only major area where a significant positive correlation was found in winter. Close

• 3. [Article] Optical properties of β″-(ET)2SF5CH2CF2SO3: A layered molecular superconductor with large discrete counterions

  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 ...

  Citation × Citation Citation Abstract Copy Title: Optical properties of β″-(ET)2SF5CH2CF2SO3: A layered molecular superconductor with large discrete counterions Author: Dong, J., Musfeldt, J. L., Schlueter, J. A., Williams, Jack M., Nixon, P. G., Winter, Rolf Walter, Gard, Gary L. Year: 1999 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 spectral weight. Vibronic features increase in intensity with decreasing temperature in the infrared, as expected. The temperature dependence of key anion vibrational modes are discussed in terms of intermolecular hydrogen bonding within the anion pocket. [S0163-1829(99)04330-1] Title: Optical properties of β″-(ET)2SF5CH2CF2SO3: A layered molecular superconductor with large discrete counterions Author: Dong, J., Musfeldt, J. L., Schlueter, J. A., Williams, Jack M., Nixon, P. G., Winter, Rolf Walter, Gard, Gary L. Year: 1999 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 spectral weight. Vibronic features increase in intensity with decreasing temperature in the infrared, as expected. The temperature dependence of key anion vibrational modes are discussed in terms of intermolecular hydrogen bonding within the anion pocket. [S0163-1829(99)04330-1] Close

• 4. [Article] Surface-enhanced Raman scattering at elevated temperatures

  The effect on surface-enhanced Raman scattering due to the increase in temperature of the metallic substrate is studied via a simple model for physisorbed molecules. Surface roughness is represented by ...

  Citation × Citation Citation Abstract Copy Title: Surface-enhanced Raman scattering at elevated temperatures Author: Leung, P.T., Hider, M. H., Sánchez, Erik J. Year: 1996 The effect on surface-enhanced Raman scattering due to the increase in temperature of the metallic substrate is studied via a simple model for physisorbed molecules. Surface roughness is represented by a spherical or spheroidal island, and the temperature effects on the surface plasmon are accounted for via a slightly modified Ujihara model. It is found that the enhancement ratio in general decreases as substrate temperature increases. For noble metals like silver, this temperature effect is particularly pronounced at scattering frequencies close to that of the surface-plasmon resonance; and for frequencies well below the surface plasmon frequency, the enhancement ratio is relatively insensitive to the change of substrate temperature. A tentative explanation is provided for our modeling results, and the implications from these results are discussed. Title: Surface-enhanced Raman scattering at elevated temperatures Author: Leung, P.T., Hider, M. H., Sánchez, Erik J. Year: 1996 The effect on surface-enhanced Raman scattering due to the increase in temperature of the metallic substrate is studied via a simple model for physisorbed molecules. Surface roughness is represented by a spherical or spheroidal island, and the temperature effects on the surface plasmon are accounted for via a slightly modified Ujihara model. It is found that the enhancement ratio in general decreases as substrate temperature increases. For noble metals like silver, this temperature effect is particularly pronounced at scattering frequencies close to that of the surface-plasmon resonance; and for frequencies well below the surface plasmon frequency, the enhancement ratio is relatively insensitive to the change of substrate temperature. A tentative explanation is provided for our modeling results, and the implications from these results are discussed. Close

• 5. [Article] Computation of dark frames in digital imagers

  Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm ...

  Citation × Citation Citation Abstract Copy Title: Computation of dark frames in digital imagers Author: Widenhorn, Ralf, Rest, Armin, Blouke, Morley M., Berry, Richard L., Bodegom, Erik Year: 2007 Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm that automatically corrects for dark current. It uses a calibration protocol to characterize the image sensor for different temperatures. For a given exposure time, the dark current of every pixel is characteristic of a specific temperature. The dark current of every pixel can therefore be used as an indicator of the temperature. Hot pixels have the highest signal-to-noise ratio and are the best temperature sensors. We use the dark current of a several hundred hot pixels to sense the chip temperature and predict the dark current of all pixels on the chip. Dark current computation is not a new concept, but our approach is unique. Some advantages of our method include applicability for poorly temperature-controlled camera systems and the possibility of ex post facto dark current correction. Title: Computation of dark frames in digital imagers Author: Widenhorn, Ralf, Rest, Armin, Blouke, Morley M., Berry, Richard L., Bodegom, Erik Year: 2007 Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm that automatically corrects for dark current. It uses a calibration protocol to characterize the image sensor for different temperatures. For a given exposure time, the dark current of every pixel is characteristic of a specific temperature. The dark current of every pixel can therefore be used as an indicator of the temperature. Hot pixels have the highest signal-to-noise ratio and are the best temperature sensors. We use the dark current of a several hundred hot pixels to sense the chip temperature and predict the dark current of all pixels on the chip. Dark current computation is not a new concept, but our approach is unique. Some advantages of our method include applicability for poorly temperature-controlled camera systems and the possibility of ex post facto dark current correction. Close

• 6. [Article] The surface plasmon enhancement effect on adsorbed molecules at elevated temperatures

  The surface plasmon enhancement effect on adsorbed molecules at elevated substrate temperatures is studied theoretically using surface enhanced Raman scattering (SERS) as an example. The surface structure ...

  Citation × Citation Citation Abstract Copy Title: The surface plasmon enhancement effect on adsorbed molecules at elevated temperatures Author: Leung, P.T., Chiang, Hai-Pang, Tse, W. S. Year: 1998 The surface plasmon enhancement effect on adsorbed molecules at elevated substrate temperatures is studied theoretically using surface enhanced Raman scattering (SERS) as an example. The surface structure is idealized to be a monodisperse spherical particle with its nonlocal dielectric response accounted for. The temperature effects are modeled using a temperature-dependent collision frequency in the Drude model. Numerical results show that only a small decrease in the SERS enhancement ratio occurs for temperatures up to the melting point of the substrate, even for scattering close to the surface plasmon resonance frequency of the metal. More definitive results are subjected to more realistic modeling as well as systematic experimental studies. The implication of this result to other surface photochemical processes is discussed. Title: The surface plasmon enhancement effect on adsorbed molecules at elevated temperatures Author: Leung, P.T., Chiang, Hai-Pang, Tse, W. S. Year: 1998 The surface plasmon enhancement effect on adsorbed molecules at elevated substrate temperatures is studied theoretically using surface enhanced Raman scattering (SERS) as an example. The surface structure is idealized to be a monodisperse spherical particle with its nonlocal dielectric response accounted for. The temperature effects are modeled using a temperature-dependent collision frequency in the Drude model. Numerical results show that only a small decrease in the SERS enhancement ratio occurs for temperatures up to the melting point of the substrate, even for scattering close to the surface plasmon resonance frequency of the metal. More definitive results are subjected to more realistic modeling as well as systematic experimental studies. The implication of this result to other surface photochemical processes is discussed. Close

• 7. [Article] Meyer-Neldel rule for dark current in charge-coupled devices

  We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from ...

  Citation × Citation Citation Abstract Copy Title: Meyer-Neldel rule for dark current in charge-coupled devices Author: Widenhorn, Ralf, Mündermann, Lars, Rest, Armin, Bodegom, Erik Year: 2001 We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from a linear behavior in the form of continuous bending. However, as a first approximation, the dark current, D, can be expressed as: D=Dₒ exp(−ΔE/kT),where ΔE is the activation energy, k is Boltzmann’s constant, and T the absolute temperature. It was found that ΔE and the exponential prefactor Dₒ follow the Meyer–Neldel rule (MNR) for all of the more than 222,000 investigated pixels. The isokinetic temperature, Tₒ, for the process was found as 294 K. However, measurements at 313 K did not show the predicted inversion in the dark current. It was found that the dark current for different pixels merged at temperatures higher than Tₒ. A model is presented which explains the nonlinearity and the merging of the dark current for different pixels with increasing temperature. Possible implications of this finding regarding the MNR are discussed. Title: Meyer-Neldel rule for dark current in charge-coupled devices Author: Widenhorn, Ralf, Mündermann, Lars, Rest, Armin, Bodegom, Erik Year: 2001 We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from a linear behavior in the form of continuous bending. However, as a first approximation, the dark current, D, can be expressed as: D=Dₒ exp(−ΔE/kT),where ΔE is the activation energy, k is Boltzmann’s constant, and T the absolute temperature. It was found that ΔE and the exponential prefactor Dₒ follow the Meyer–Neldel rule (MNR) for all of the more than 222,000 investigated pixels. The isokinetic temperature, Tₒ, for the process was found as 294 K. However, measurements at 313 K did not show the predicted inversion in the dark current. It was found that the dark current for different pixels merged at temperatures higher than Tₒ. A model is presented which explains the nonlinearity and the merging of the dark current for different pixels with increasing temperature. Possible implications of this finding regarding the MNR are discussed. Close

• 8. [Article] Approximate Equations of State in Two-Temperature Plasma Mixtures

  Approximate thermodynamic state relations for multicomponent atomic and molecular gas mixtures are often constructed by artificially partitioning the mixture into its constituent materials and requiring ...

  Citation × Citation Citation Abstract Copy Title: Approximate Equations of State in Two-Temperature Plasma Mixtures Author: Ramshaw, John D., Cook, Andrew W. Year: 2014 Approximate thermodynamic state relations for multicomponent atomic and molecular gas mixtures are often constructed by artificially partitioning the mixture into its constituent materials and requiring the separated materials to be in temperature and pressure equilibrium. Iterative numerical algorithms have been employed to enforce this equilibration and compute the resulting approximate state relations in single-temperature mixtures. In partially ionized gas mixtures, there is both theoretical and empirical evidence that equilibrating the chemical potentials, number densities, or partial pressures of the free electrons is likely to produce more accurate results than equilibrating the total pressures. Moreover, in many situations of practical interest the free electrons and heavy particles have different temperatures. In this paper, we present a generalized algorithm for equilibrating the heavy-particle and electron temperaturesand a third user-specified independent thermodynamic variable in a two-temperature plasmamixture. Test calculations based on the equilibration of total pressure vs. electron pressure are presented for three different mixtures. Title: Approximate Equations of State in Two-Temperature Plasma Mixtures Author: Ramshaw, John D., Cook, Andrew W. Year: 2014 Approximate thermodynamic state relations for multicomponent atomic and molecular gas mixtures are often constructed by artificially partitioning the mixture into its constituent materials and requiring the separated materials to be in temperature and pressure equilibrium. Iterative numerical algorithms have been employed to enforce this equilibration and compute the resulting approximate state relations in single-temperature mixtures. In partially ionized gas mixtures, there is both theoretical and empirical evidence that equilibrating the chemical potentials, number densities, or partial pressures of the free electrons is likely to produce more accurate results than equilibrating the total pressures. Moreover, in many situations of practical interest the free electrons and heavy particles have different temperatures. In this paper, we present a generalized algorithm for equilibrating the heavy-particle and electron temperaturesand a third user-specified independent thermodynamic variable in a two-temperature plasmamixture. Test calculations based on the equilibration of total pressure vs. electron pressure are presented for three different mixtures. Close

• 9. [Article] Mechanisms of Methane Transport Through Trees

  Although the dynamics of methane (CH4) emission from croplands and wetlands have been fairly well investigated, the contribution of trees to global methane emission and the mechanisms of tree transport ...

  Citation × Citation Citation Abstract Copy Title: Mechanisms of Methane Transport Through Trees Author: Kutschera, Ellynne Marie Year: 2013 Although the dynamics of methane (CH4) emission from croplands and wetlands have been fairly well investigated, the contribution of trees to global methane emission and the mechanisms of tree transport are relatively unknown. Methane emissions from the common wetland tree species Populus trichocarpa (black cottonwood) native to the Pacific Northwest were measured under hydroponic conditions in order to separate plant transport mechanisms from the influence of soil processes. Roots were exposed to methane enriched water and canopy emissions of methane were measured using a canopy enclosure. Methane accumulation in the canopy was generally linear and the average canopy methane flux was 3.0 ± 2.6 μg CH4 min-1. Flux magnitudes from stem experiments scaled to the area of the main tree stem are comparable to whole-canopy flux values, indicating that the majority of methane emitted from the tree leaves through the stem. Samples for stable carbon isotope composition were taken during the canopy experiments. Compared to the isotopic composition of root water methane, canopy methane was depleted in 13C on average by 8.6 ± 3.3 permil; this indicates that methane moving through the tree is not following a purely bulk flow pathway (where no depletion would occur), but is instead subject to at least one fractionating mechanism. When temperature was varied, the flux at the coolest temperature was significantly different from the higher flux at the warmest temperature (p-value less than 0.02). The calculated Q10 for methane flux was 2.4, which indicates a positive feedback with temperature increase. Analysis of δ13C values of emitted CH4 in the temperature experiments shows increasing depletion with cooler temperatures and lower flux. This indicates that not only does the magnitude of flux vary with temperature, but the actual dominant transport mechanism changes as well. Title: Mechanisms of Methane Transport Through Trees Author: Kutschera, Ellynne Marie Year: 2013 Although the dynamics of methane (CH4) emission from croplands and wetlands have been fairly well investigated, the contribution of trees to global methane emission and the mechanisms of tree transport are relatively unknown. Methane emissions from the common wetland tree species Populus trichocarpa (black cottonwood) native to the Pacific Northwest were measured under hydroponic conditions in order to separate plant transport mechanisms from the influence of soil processes. Roots were exposed to methane enriched water and canopy emissions of methane were measured using a canopy enclosure. Methane accumulation in the canopy was generally linear and the average canopy methane flux was 3.0 ± 2.6 μg CH4 min-1. Flux magnitudes from stem experiments scaled to the area of the main tree stem are comparable to whole-canopy flux values, indicating that the majority of methane emitted from the tree leaves through the stem. Samples for stable carbon isotope composition were taken during the canopy experiments. Compared to the isotopic composition of root water methane, canopy methane was depleted in 13C on average by 8.6 ± 3.3 permil; this indicates that methane moving through the tree is not following a purely bulk flow pathway (where no depletion would occur), but is instead subject to at least one fractionating mechanism. When temperature was varied, the flux at the coolest temperature was significantly different from the higher flux at the warmest temperature (p-value less than 0.02). The calculated Q10 for methane flux was 2.4, which indicates a positive feedback with temperature increase. Analysis of δ13C values of emitted CH4 in the temperature experiments shows increasing depletion with cooler temperatures and lower flux. This indicates that not only does the magnitude of flux vary with temperature, but the actual dominant transport mechanism changes as well. Close

• 10. [Article] Temperature dependence of optical properties for amorphous silicon at wavelengths of 632.8 and 752 nm

  The temperature dependence of the optical properties for amorphous silicon is studied at wavelengths of 632.8 and 752 nm. Both the refractive index and extinction coefficient increase linearly with temperature ...

  Citation × Citation Citation Abstract Copy Title: Temperature dependence of optical properties for amorphous silicon at wavelengths of 632.8 and 752 nm Author: Leung, P.T., Do, Nhan, Yavas, Oguz, Tam, Andrew C., Leung, Wing P., Park, Hee K., Grigoropoulos, Costas P., Boneberg, Johannes, Leiderer, Paul Year: 1993 The temperature dependence of the optical properties for amorphous silicon is studied at wavelengths of 632.8 and 752 nm. Both the refractive index and extinction coefficient increase linearly with temperature for 752 nm, while the refractive index decreases and the extinction coefficient increases for 632.8 nm. The rate of increase of the extinction coefficient at 632.8 nm is twice as much as that for 752 nm. Title: Temperature dependence of optical properties for amorphous silicon at wavelengths of 632.8 and 752 nm Author: Leung, P.T., Do, Nhan, Yavas, Oguz, Tam, Andrew C., Leung, Wing P., Park, Hee K., Grigoropoulos, Costas P., Boneberg, Johannes, Leiderer, Paul Year: 1993 The temperature dependence of the optical properties for amorphous silicon is studied at wavelengths of 632.8 and 752 nm. Both the refractive index and extinction coefficient increase linearly with temperature for 752 nm, while the refractive index decreases and the extinction coefficient increases for 632.8 nm. The rate of increase of the extinction coefficient at 632.8 nm is twice as much as that for 752 nm. Close

• 11. [Article] Anomalous low-temperature and high-field magnetoresistance in the organic superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3

  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 ...

  Citation × Citation Citation Abstract Copy Title: Anomalous low-temperature and high-field magnetoresistance in the organic superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3 Author: Zuo, F., Su, X., Zhang, P., Brooks, J. S., Wosnitza, J., Schlueter, J. A., Williams, Jack M., Nixon, P. G., Winter, Rolf Walter, Gard, Gary L. Year: 1999 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] Title: Anomalous low-temperature and high-field magnetoresistance in the organic superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3 Author: Zuo, F., Su, X., Zhang, P., Brooks, J. S., Wosnitza, J., Schlueter, J. A., Williams, Jack M., Nixon, P. G., Winter, Rolf Walter, Gard, Gary L. Year: 1999 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] Close

• 12. [Article] Hydrodynamic Theory of Multicomponent Diffusion and Thermal Diffusion in Multitemperature Gas Mixtures

  A phenomenological theory is developed for multicomponent diffusion, including thermal diffusion, in gas mixtures in which the components may have different temperatures. The theory is based on the hydrodynamic ...

  Citation × Citation Citation Abstract Copy Title: Hydrodynamic Theory of Multicomponent Diffusion and Thermal Diffusion in Multitemperature Gas Mixtures Author: Ramshaw, John D. Year: 1993 A phenomenological theory is developed for multicomponent diffusion, including thermal diffusion, in gas mixtures in which the components may have different temperatures. The theory is based on the hydrodynamic approach of Maxwell and Stefan, as extended and elaborated by Furry [1] and Williams [2]. The present development further extends these earlier treatments to multiple temperatures and multicomponent thermal diffusion. The resulting diffusion fluxes obey generalized Stefan-Maxwell relations which include the effects of ordinary, forced, pressure, and thermal diffusion. When thermal diffusion is neglected, these relations have the same form as the usual single-temperature ones, except that mole fractions are replaced by pressure fractions (i.e., ratios of partial pressures to total pressure). The binary and thermal diffusion coefficients are given in terms of collision integrals. Single-temperature systems and binary systems are treated as special cases of the general theory. A self-consistent effective binary diffusion approximation for multitemperature systems is presented. Title: Hydrodynamic Theory of Multicomponent Diffusion and Thermal Diffusion in Multitemperature Gas Mixtures Author: Ramshaw, John D. Year: 1993 A phenomenological theory is developed for multicomponent diffusion, including thermal diffusion, in gas mixtures in which the components may have different temperatures. The theory is based on the hydrodynamic approach of Maxwell and Stefan, as extended and elaborated by Furry [1] and Williams [2]. The present development further extends these earlier treatments to multiple temperatures and multicomponent thermal diffusion. The resulting diffusion fluxes obey generalized Stefan-Maxwell relations which include the effects of ordinary, forced, pressure, and thermal diffusion. When thermal diffusion is neglected, these relations have the same form as the usual single-temperature ones, except that mole fractions are replaced by pressure fractions (i.e., ratios of partial pressures to total pressure). The binary and thermal diffusion coefficients are given in terms of collision integrals. Single-temperature systems and binary systems are treated as special cases of the general theory. A self-consistent effective binary diffusion approximation for multitemperature systems is presented. Close

• 13. [Article] Optical, electronic, and thermodynamic properties of layered mixed anion compounds

  Mixed anion compounds that form ZrCuSiAs-type crystal structures exhibit remarkable properties such as superconductivity at low temperatures, hole conduction with optical transparency in the visible region, ...

  Citation × Citation Citation Abstract Copy Title: Optical, electronic, and thermodynamic properties of layered mixed anion compounds Author: Vielma, Jason Michael Mixed anion compounds that form ZrCuSiAs-type crystal structures exhibit remarkable properties such as superconductivity at low temperatures, hole conduction with optical transparency in the visible region, and exciton absorption at room temperature. In this thesis, properties of a selected group of materials out of the very large set of mixed anion compounds with the ZrCuSiAs-type structure are investigated by computational first principles methods. The discovery of superconductivity in LaFePO (T[subscript C] ~ 4 K) and LaFeAsO[subscript 1-x]F[subscript x] (T[subscript C] ~ 26 K) naturally led to the speculation that LaFeSbO is possibly a superconductor with an even higher transition temperature. However, all attempts to synthesize LaFeSbO failed. We performed a theoretical chemical stability analysis based on ab initio density functional theory (DFT) and determined that LaFeSbO is not stable with respect to all synthesis conditions. Instead La₂SbO₂ is found with most synthesis conditions and indeed this was found experimentally. A local stability analysis for LaFeSbO based on the calculation of the phonon dispersion curves from DFT supercells calculations reveals that LaFeSbO is potentially metastable, which opens up the possible synthesis by a non-equilibrium process. Layered oxychalcogenides LaCuChO (Ch = {S,Se,Te}) and isostructural layered fluorochalcogenides BaCuChF have drawn much interest in recent years as p-type wide bandgap semiconductors with applications in transparent electronics and photovoltaics. Previous experimental and computational studies concluded for both LaCuChO, with bandgaps between 2.4-3.1 eV, and BaCuChF, with optical bandgaps between 2.8-3.5 eV, that p-type conductivity is primarily due to copper vacancies. But, until now no quantitative defect analysis has been performed for LaCuChO. Furthermore, members of both materials show strong excitonic absorption features, which are observable at room and higher temperatures. However, disagreement exists in the literature on the origin and nature of the room temperature excitons in the respective families of materials, attributing the room temperature excitonic absorption in LaCuChO to 2 dimensional quantum confinement of hole carriers in the layered structure, and room temperature excitonic absorption in BaCuChF is described by a 3 dimensional Wannier-Mott excitonic model. A comparative ab initio computational study of the defect physics and optical properties including the excitonic effects for both families of materials has been conducted. Point defects and defect complexes are taken into account and previously omitted corrections have been included, while accurate chemical potential stability diagrams and formation energies are calculated using recently improved methods. The optical properties are calculated using the Bethe-Salpeter equation in the GW approximation. Title: Optical, electronic, and thermodynamic properties of layered mixed anion compounds Author: Vielma, Jason Michael Mixed anion compounds that form ZrCuSiAs-type crystal structures exhibit remarkable properties such as superconductivity at low temperatures, hole conduction with optical transparency in the visible region, and exciton absorption at room temperature. In this thesis, properties of a selected group of materials out of the very large set of mixed anion compounds with the ZrCuSiAs-type structure are investigated by computational first principles methods. The discovery of superconductivity in LaFePO (T[subscript C] ~ 4 K) and LaFeAsO[subscript 1-x]F[subscript x] (T[subscript C] ~ 26 K) naturally led to the speculation that LaFeSbO is possibly a superconductor with an even higher transition temperature. However, all attempts to synthesize LaFeSbO failed. We performed a theoretical chemical stability analysis based on ab initio density functional theory (DFT) and determined that LaFeSbO is not stable with respect to all synthesis conditions. Instead La₂SbO₂ is found with most synthesis conditions and indeed this was found experimentally. A local stability analysis for LaFeSbO based on the calculation of the phonon dispersion curves from DFT supercells calculations reveals that LaFeSbO is potentially metastable, which opens up the possible synthesis by a non-equilibrium process. Layered oxychalcogenides LaCuChO (Ch = {S,Se,Te}) and isostructural layered fluorochalcogenides BaCuChF have drawn much interest in recent years as p-type wide bandgap semiconductors with applications in transparent electronics and photovoltaics. Previous experimental and computational studies concluded for both LaCuChO, with bandgaps between 2.4-3.1 eV, and BaCuChF, with optical bandgaps between 2.8-3.5 eV, that p-type conductivity is primarily due to copper vacancies. But, until now no quantitative defect analysis has been performed for LaCuChO. Furthermore, members of both materials show strong excitonic absorption features, which are observable at room and higher temperatures. However, disagreement exists in the literature on the origin and nature of the room temperature excitons in the respective families of materials, attributing the room temperature excitonic absorption in LaCuChO to 2 dimensional quantum confinement of hole carriers in the layered structure, and room temperature excitonic absorption in BaCuChF is described by a 3 dimensional Wannier-Mott excitonic model. A comparative ab initio computational study of the defect physics and optical properties including the excitonic effects for both families of materials has been conducted. Point defects and defect complexes are taken into account and previously omitted corrections have been included, while accurate chemical potential stability diagrams and formation energies are calculated using recently improved methods. The optical properties are calculated using the Bethe-Salpeter equation in the GW approximation. Close

• 14. [Article] Measurements of the Mössbauer Fraction in Chromium

  Precision measurements of the Mossbauer fraction of Fe57 in chromium were made using the black absorber technique over a range of temperatures from 78K to 792K. Because of uncertainty in corrections at ...

  Citation × Citation Citation Abstract Copy Title: Measurements of the Mössbauer Fraction in Chromium Author: Brace, B. Frederick, Jr. Year: 1972 Precision measurements of the Mossbauer fraction of Fe57 in chromium were made using the black absorber technique over a range of temperatures from 78K to 792K. Because of uncertainty in corrections at high temperatures, only the data collected from 78K to 600K was used in analyzing the results. The f values were analyzed in terms of a Debye approximmation. This analysis of the data yielded a theoretical fit which was based on two adjustable parameters (a Debye temperature of 438K and an anharmonicity parameter of 2 x 10-4K-1). The f measurements were also analyzed using a theory proposed by Mannheim in 1968. Two different phonon density of states functions (Feldman, Muhlestein) were applied to Mannheim’s theory, and the resulting theoretical fits to experimental values showed a decrease in the force constant as a result of introducing an impurity into the chromium. Feldman’s phonon spectrum yielded a force constant ratio of 1.30±.07 and an anharmoncity parameter of ℇ=2.5(±.5) x 10-4K-1. Title: Measurements of the Mössbauer Fraction in Chromium Author: Brace, B. Frederick, Jr. Year: 1972 Precision measurements of the Mossbauer fraction of Fe57 in chromium were made using the black absorber technique over a range of temperatures from 78K to 792K. Because of uncertainty in corrections at high temperatures, only the data collected from 78K to 600K was used in analyzing the results. The f values were analyzed in terms of a Debye approximmation. This analysis of the data yielded a theoretical fit which was based on two adjustable parameters (a Debye temperature of 438K and an anharmonicity parameter of 2 x 10-4K-1). The f measurements were also analyzed using a theory proposed by Mannheim in 1968. Two different phonon density of states functions (Feldman, Muhlestein) were applied to Mannheim’s theory, and the resulting theoretical fits to experimental values showed a decrease in the force constant as a result of introducing an impurity into the chromium. Feldman’s phonon spectrum yielded a force constant ratio of 1.30±.07 and an anharmoncity parameter of ℇ=2.5(±.5) x 10-4K-1. Close

• 15. [Article] The Meyer-Neldel rule for diodes in forward bias

  We analyzed the temperature dependence of the forward current of a silicon diode. Instead of representing the data in the ordinarily used current versus voltage graph, the currents are plotted for different ...

  Citation × Citation Citation Abstract Copy Title: The Meyer-Neldel rule for diodes in forward bias Author: Widenhorn, Ralf, Fitzgibbons, Michael, Bodegom, Erik Year: 2004 We analyzed the temperature dependence of the forward current of a silicon diode. Instead of representing the data in the ordinarily used current versus voltage graph, the currents are plotted for different voltages as a function of the inverse temperature. The constant voltage curves can be fitted linearly and the extrapolations of the fits seem to merge to one common focal point. Hence, we demonstrate that a real diode follows the Meyer-Neldel rule (MNR). It is shown that the MNR is due to a shift of the current from ideal-diode to high-injection-diode behavior. We will argue that the merging of the different Arrhenius plots toward one focal point, and hence a MNR, can be the result of various mechanisms. The general requirements to observe a MNR are not very restrictive. It is therefore not surprising that the MNR has been observed in a multitude of systems. The origin that gives rise to the MNR can be manifold and allows for different models to explain its occurrence. Title: The Meyer-Neldel rule for diodes in forward bias Author: Widenhorn, Ralf, Fitzgibbons, Michael, Bodegom, Erik Year: 2004 We analyzed the temperature dependence of the forward current of a silicon diode. Instead of representing the data in the ordinarily used current versus voltage graph, the currents are plotted for different voltages as a function of the inverse temperature. The constant voltage curves can be fitted linearly and the extrapolations of the fits seem to merge to one common focal point. Hence, we demonstrate that a real diode follows the Meyer-Neldel rule (MNR). It is shown that the MNR is due to a shift of the current from ideal-diode to high-injection-diode behavior. We will argue that the merging of the different Arrhenius plots toward one focal point, and hence a MNR, can be the result of various mechanisms. The general requirements to observe a MNR are not very restrictive. It is therefore not surprising that the MNR has been observed in a multitude of systems. The origin that gives rise to the MNR can be manifold and allows for different models to explain its occurrence. Close

• 16. [Article] Geophysical strain and tilt : measurement methodology and analysis of data

  Tilt and strain meters were installed on the Portland State University campus in the summer of 1982 and data was collected for 4 months. Instrument selection, operation, installation and performance are ...

  Citation × Citation Citation Abstract Copy Title: Geophysical strain and tilt : measurement methodology and analysis of data Author: MacKay, Robert Year: 1983 Tilt and strain meters were installed on the Portland State University campus in the summer of 1982 and data was collected for 4 months. Instrument selection, operation, installation and performance are discussed. Suggestions that could enhance data quality and data collection efficiency are presented. An analysis procedure is suggested and an example of this procedure for an interval of data is discussed. The influence of the temperature, pressure, rainfall and solid earth tides on the signal is investigated, as well as the correlation between similar channels of the different tilt instruments. The temperature, rainfall and solid earth tides were all determined to have an influence on the instruments. A statistical test of the influence of the barometric pressure on the signal revealed no significant influence. A very low correlation between similar components of the different tilt instruments was observed aside from their thermal dependence. It was concluded that in order to obtain high quality data for the use in quantitative calculations, the temperature influence on the raw record must be minimized. Title: Geophysical strain and tilt : measurement methodology and analysis of data Author: MacKay, Robert Year: 1983 Tilt and strain meters were installed on the Portland State University campus in the summer of 1982 and data was collected for 4 months. Instrument selection, operation, installation and performance are discussed. Suggestions that could enhance data quality and data collection efficiency are presented. An analysis procedure is suggested and an example of this procedure for an interval of data is discussed. The influence of the temperature, pressure, rainfall and solid earth tides on the signal is investigated, as well as the correlation between similar channels of the different tilt instruments. The temperature, rainfall and solid earth tides were all determined to have an influence on the instruments. A statistical test of the influence of the barometric pressure on the signal revealed no significant influence. A very low correlation between similar components of the different tilt instruments was observed aside from their thermal dependence. It was concluded that in order to obtain high quality data for the use in quantitative calculations, the temperature influence on the raw record must be minimized. Close

• 17. [Article] Approximate Thermodynamic State Relations in Partially Ionized Gas Mixtures

  Thermodynamic state relations for mixtures of partially ionized nonideal gases are often approximated by artificially partitioning the mixture into compartments or subvolumes occupied by the pure partially ...

  Citation × Citation Citation Abstract Copy Title: Approximate Thermodynamic State Relations in Partially Ionized Gas Mixtures Author: Ramshaw, John D. Year: 2004 Thermodynamic state relations for mixtures of partially ionized nonideal gases are often approximated by artificially partitioning the mixture into compartments or subvolumes occupied by the pure partially ionized constituent gases, and requiring these subvolumes to be in temperature and pressure equilibrium. This intuitively reasonable procedure is easily shown to reproduce the correct thermal and caloric state equations for a mixture of neutral nonionized ideal gases. The purpose of this paper is to point out that (a) this procedure leads to incorrect state equations for a mixture of partially ionized ideal gases, whereas (b) the alternative procedure of requiring that the subvolumes all have the same temperature and free electron density reproduces the correct thermal and caloric state equations for such a mixture. These results readily generalize to the case of partially degenerate and/or relativistic electrons, to a common approximation used to represent pressure ionization effects, and to two-temperature plasmas. This suggests that equating the subvolume electron number densities or chemical potentials instead of pressures is likely to provide a more accurate approximation in nonideal plasma mixtures. Title: Approximate Thermodynamic State Relations in Partially Ionized Gas Mixtures Author: Ramshaw, John D. Year: 2004 Thermodynamic state relations for mixtures of partially ionized nonideal gases are often approximated by artificially partitioning the mixture into compartments or subvolumes occupied by the pure partially ionized constituent gases, and requiring these subvolumes to be in temperature and pressure equilibrium. This intuitively reasonable procedure is easily shown to reproduce the correct thermal and caloric state equations for a mixture of neutral nonionized ideal gases. The purpose of this paper is to point out that (a) this procedure leads to incorrect state equations for a mixture of partially ionized ideal gases, whereas (b) the alternative procedure of requiring that the subvolumes all have the same temperature and free electron density reproduces the correct thermal and caloric state equations for such a mixture. These results readily generalize to the case of partially degenerate and/or relativistic electrons, to a common approximation used to represent pressure ionization effects, and to two-temperature plasmas. This suggests that equating the subvolume electron number densities or chemical potentials instead of pressures is likely to provide a more accurate approximation in nonideal plasma mixtures. Close

• 18. [Article] Mössbauer studies of stable interstitial and substitutional sites of cobalt in gold

  Precision measurements of the Debye-Waller factor of Fe57 in Au using the wide black absorber technique have been made in the temperature range from room temperature to 830 K. The major source of error ...

  Citation × Citation Citation Abstract Copy Title: Mössbauer studies of stable interstitial and substitutional sites of cobalt in gold Author: Steen, Charles Freeland Year: 1971 Precision measurements of the Debye-Waller factor of Fe57 in Au using the wide black absorber technique have been made in the temperature range from room temperature to 830 K. The major source of error arises from Au Ly x-rays which are unresolved by the radiation detection system from the 14.4 KeV gamma ray. The K absorption edge of Br has been used to correct for the presence of x-rays. These measurements have revealed the existence of two nonequivalent lattice sites which the Co57 impurity (parent of Fe57) may occupy. One of the sites has been populated by quenching the source from temperatures greater than 1150 K and has been identified as a substitutional lattice site. From an analysis of the Mössbauer spectrum it is concluded that some of the substitutional sites may be in the vicinity of dislocations. It has been determined that the impurity-host force constant for Fe57 atoms in the substitutional site is about the same as the host-host force constant; the experimental value of the anharmonicity parameter ɛ (-2) for Fe57 in the Au is nearly the same as calculated values of ɛ (-2) for pure Au. The second site forms very slowly upon annealing the source at intermediate temperatures and has been identified as being interstitial in character. The slow rate of formation of the interstitial site indicates that diffusion is a primary mechanism in its formation. The second site must therefore be more complicated than an ordinary interstitial. It is proposed that this site is a split, or dumbbell, interstitial formed by substituting two impurity atoms for one of the Au atoms. Title: Mössbauer studies of stable interstitial and substitutional sites of cobalt in gold Author: Steen, Charles Freeland Year: 1971 Precision measurements of the Debye-Waller factor of Fe57 in Au using the wide black absorber technique have been made in the temperature range from room temperature to 830 K. The major source of error arises from Au Ly x-rays which are unresolved by the radiation detection system from the 14.4 KeV gamma ray. The K absorption edge of Br has been used to correct for the presence of x-rays. These measurements have revealed the existence of two nonequivalent lattice sites which the Co57 impurity (parent of Fe57) may occupy. One of the sites has been populated by quenching the source from temperatures greater than 1150 K and has been identified as a substitutional lattice site. From an analysis of the Mössbauer spectrum it is concluded that some of the substitutional sites may be in the vicinity of dislocations. It has been determined that the impurity-host force constant for Fe57 atoms in the substitutional site is about the same as the host-host force constant; the experimental value of the anharmonicity parameter ɛ (-2) for Fe57 in the Au is nearly the same as calculated values of ɛ (-2) for pure Au. The second site forms very slowly upon annealing the source at intermediate temperatures and has been identified as being interstitial in character. The slow rate of formation of the interstitial site indicates that diffusion is a primary mechanism in its formation. The second site must therefore be more complicated than an ordinary interstitial. It is proposed that this site is a split, or dumbbell, interstitial formed by substituting two impurity atoms for one of the Au atoms. Close

• 19. [Article] The Effect of Plasma on Graphene Quality in an Inductively Couple Plasma Chemical Vapor Deposition Reactor

  Despite continued interest in research and application development, full scale graphene production is still limited by many factors including prohibitively high growth temperature requirements. Extremely ...

  Citation × Citation Citation Abstract Copy Title: The Effect of Plasma on Graphene Quality in an Inductively Couple Plasma Chemical Vapor Deposition Reactor Author: Coyne, Brendan Year: 2017 Despite continued interest in research and application development, full scale graphene production is still limited by many factors including prohibitively high growth temperature requirements. Extremely high quality graphene growth is possible at high temperatures using chemical vapor deposition (CVD). Use of an inductively coupled plasma chemical vapor deposition (ICP CVD) reactor with the benefit of precursor gas decomposition through plasma generation, may provide possibility to reduce growth temperature. Herein, we report plasma’s effects on graphene growth by comparing growths of increasing power supplied to plasma generation and changes in precursor gas ratios. Plasma composition was characterized by ultraviolet and visible light spectroscopy; graphene was characterized by Raman spectroscopy. Plasma was observed to change gradually and in a threshold shift. Gradual changes in plasma resulted in changes in graphene quality, both defect density and number of layers. The shift produced sudden changes in graphene quality. Further, increasing power before and after the shift produced opposite correlated trends. Finally, reduced hydrogen to acetylene gas ratios produced plasma associated with higher powers at a higher gas ratio. Though the comparative plasma spectra between the two reduced gas ratio growths were very similar, the quality of graphene was different. Additionally, both lower gas ratio growths produced quality different than what was expected by the trends suggested by the higher gas ratio growths. Though plasma demonstrated a role in graphene quality, a more detailed understand of its driving mechanisms must be developed in conjunction with other growth mechanisms if it is to be utilized to substantially reduce growth temperature. Title: The Effect of Plasma on Graphene Quality in an Inductively Couple Plasma Chemical Vapor Deposition Reactor Author: Coyne, Brendan Year: 2017 Despite continued interest in research and application development, full scale graphene production is still limited by many factors including prohibitively high growth temperature requirements. Extremely high quality graphene growth is possible at high temperatures using chemical vapor deposition (CVD). Use of an inductively coupled plasma chemical vapor deposition (ICP CVD) reactor with the benefit of precursor gas decomposition through plasma generation, may provide possibility to reduce growth temperature. Herein, we report plasma’s effects on graphene growth by comparing growths of increasing power supplied to plasma generation and changes in precursor gas ratios. Plasma composition was characterized by ultraviolet and visible light spectroscopy; graphene was characterized by Raman spectroscopy. Plasma was observed to change gradually and in a threshold shift. Gradual changes in plasma resulted in changes in graphene quality, both defect density and number of layers. The shift produced sudden changes in graphene quality. Further, increasing power before and after the shift produced opposite correlated trends. Finally, reduced hydrogen to acetylene gas ratios produced plasma associated with higher powers at a higher gas ratio. Though the comparative plasma spectra between the two reduced gas ratio growths were very similar, the quality of graphene was different. Additionally, both lower gas ratio growths produced quality different than what was expected by the trends suggested by the higher gas ratio growths. Though plasma demonstrated a role in graphene quality, a more detailed understand of its driving mechanisms must be developed in conjunction with other growth mechanisms if it is to be utilized to substantially reduce growth temperature. Close

• 20. [Article] Cryogenic thin-film electron emitters

  Thin‐film electron emitters are described, which operate below 200°K and below a limiting critical applied voltage (νc) in a stable temperature‐independent regime. Current‐voltage characteristics and normal ...

  Citation × Citation Citation Abstract Copy Title: Cryogenic thin-film electron emitters Author: Smejtek, Pavel, Onn, David G., Silver, M. Year: 1974 Thin‐film electron emitters are described, which operate below 200°K and below a limiting critical applied voltage (νc) in a stable temperature‐independent regime. Current‐voltage characteristics and normal electron energy distributions are presented. Fabrication and operation criteria are outlined. Comparison with temperature‐dependent emitters is made, and possible conduction mechanisms discussed briefly. Title: Cryogenic thin-film electron emitters Author: Smejtek, Pavel, Onn, David G., Silver, M. Year: 1974 Thin‐film electron emitters are described, which operate below 200°K and below a limiting critical applied voltage (νc) in a stable temperature‐independent regime. Current‐voltage characteristics and normal electron energy distributions are presented. Fabrication and operation criteria are outlined. Comparison with temperature‐dependent emitters is made, and possible conduction mechanisms discussed briefly. Close