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Seunghyun Baik - One of the best experts on this subject based on the ideXlab platform.
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Electrical transport characteristics of Surface-Conductance-controlled, dielectrophoretically separated single-walled carbon nanotubes
Langmuir, 2007Co-Authors: Seunghyun Hong, Sehun Jung, Jaeboong Choi, Youngjin Kim, Seunghyun BaikAbstract:Alternating current dielectrophoresis has attracted considerable attention as a possible candidate to separate single-walled carbon nanotubes according to electronic types. Recently, the significant effect of Surface charge on the polarizability of semiconducting nanotubes was demonstrated using comparative Raman spectroscopic studies. Here we present electrical transport characteristics of Surface-charge-controlled, dielectrophoretically deposited nanotube arrays. The Surface charge was controlled using cationic/anionic surfactant mixtures. Complete separation between metallic and semiconducting species was achieved at the electric field frequency of 10 MHz only when the Surface charge of nanotubes was neutralized, which is consistent with previous Raman investigation. A theoretical analysis, using zeta potential information as input, further supported the experimental observation.
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dielectrophoresis of Surface Conductance modulated single walled carbon nanotubes using catanionic surfactants
Journal of Physical Chemistry B, 2006Co-Authors: Youngjin Kim, Sehun Jung, Jaeboong Choi, Seunghyun Hong, Michael S Strano, Seunghyun BaikAbstract:Dielectrophoresis has received considerable attention for separating nanotubes according to electronic types. Here we examine the effects of Surface conductivity of semiconducting single walled carbon nanotubes (SWNT), induced by ionic surfactants, on the sign of dielectrophoretic force. The crossover frequency of semiconducting SWNT increases rapidly as the conductivity ratio between the particle and medium increases, leading to an incomplete separation of ionic surfactant suspended SWNT at an electric field frequency of 10 MHz. To reduce the conductivity ratio, the Surface charge of SWNT is neutralized by an equimolar mixture of anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB), resulting in negative dielectrophoresis of semiconducting species at 10 MHz. A comparative Raman spectroscopy study shows a nearly complete separation of metallic SWNT.
Paul W J Glover - One of the best experts on this subject based on the ideXlab platform.
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nature of Surface electrical conductivity in natural sands sandstones and clays
Geophysical Research Letters, 1998Co-Authors: Andre Revil, Paul W J GloverAbstract:The electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from Surface conduction occurring at the fluid/grain interface. The nature of the Surface electrical conductivity of shaly and clean sands and sandstones is examined. Surface conduction is characterized by the specific Surface Conductance which is the sum of three contributions: (i) Conduction within the electrical diffuse layer, which makes a negligible contribution to the total specific Surface Conductance, (ii) Conduction in the Stern layer, which is shown to vary significantly with the salinity of the pore fluid at low salinities (10−6 to 10−3 mol 1−1), but becomes independent of salinity at higher salinities, (iii) A mechanism operating directly on the mineral Surface, independent of salinity, and perhaps associated with proton transfer. At salinities higher than 10−3 mol 1−1 and at 25°C, the specific Surface Conductance of quartz and clays is equal to 8.9×10−9 S and 2.5×10−9 S respectively. Equations describing the influence of Surface conductivity and microstructure upon the macroscopic electrical conductivity of sands, sandstones, and shales are also developed.
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theory of ionic Surface electrical conduction in porous media
Physical Review B, 1997Co-Authors: Andre Revil, Paul W J GloverAbstract:We present a model describing ionic electrical conduction in porous media, with particular emphasis given to Surface conduction. The porous medium is assumed to consist of an insulating matrix and an interconnected pore volume that is saturated with an electrolyte. When in contact with an electrolyte, mineral Surfaces get an excess of charge that is balanced by mobile ions in an electrical diffuse layer above the Surface. Electrical conduction in this diffuse layer can contribute substantially to the effective electrical conductivity of the porous medium. Our Surface conduction model is based on a description of Surface chemical reactions and electrical diffuse layer processes. For this purpose, we consider an amphoteric mineral Surface described by a five-site-type model. We derive the fractional occupancies of positive, negative, and neutral sites on the Surface, and the fractional ionic diffuse layer densities, as a function of the salinity and the pH. Finally, the specific Surface Conductance used to describe the Surface electrical conduction is related to the previously mentioned properties, via the electrical Surface potential, and is found to be dependent on the electrolyte concentration and pH.
Seunghyun Hong - One of the best experts on this subject based on the ideXlab platform.
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Electrical transport characteristics of Surface-Conductance-controlled, dielectrophoretically separated single-walled carbon nanotubes
Langmuir, 2007Co-Authors: Seunghyun Hong, Sehun Jung, Jaeboong Choi, Youngjin Kim, Seunghyun BaikAbstract:Alternating current dielectrophoresis has attracted considerable attention as a possible candidate to separate single-walled carbon nanotubes according to electronic types. Recently, the significant effect of Surface charge on the polarizability of semiconducting nanotubes was demonstrated using comparative Raman spectroscopic studies. Here we present electrical transport characteristics of Surface-charge-controlled, dielectrophoretically deposited nanotube arrays. The Surface charge was controlled using cationic/anionic surfactant mixtures. Complete separation between metallic and semiconducting species was achieved at the electric field frequency of 10 MHz only when the Surface charge of nanotubes was neutralized, which is consistent with previous Raman investigation. A theoretical analysis, using zeta potential information as input, further supported the experimental observation.
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dielectrophoresis of Surface Conductance modulated single walled carbon nanotubes using catanionic surfactants
Journal of Physical Chemistry B, 2006Co-Authors: Youngjin Kim, Sehun Jung, Jaeboong Choi, Seunghyun Hong, Michael S Strano, Seunghyun BaikAbstract:Dielectrophoresis has received considerable attention for separating nanotubes according to electronic types. Here we examine the effects of Surface conductivity of semiconducting single walled carbon nanotubes (SWNT), induced by ionic surfactants, on the sign of dielectrophoretic force. The crossover frequency of semiconducting SWNT increases rapidly as the conductivity ratio between the particle and medium increases, leading to an incomplete separation of ionic surfactant suspended SWNT at an electric field frequency of 10 MHz. To reduce the conductivity ratio, the Surface charge of SWNT is neutralized by an equimolar mixture of anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB), resulting in negative dielectrophoresis of semiconducting species at 10 MHz. A comparative Raman spectroscopy study shows a nearly complete separation of metallic SWNT.
Dennis D Baldocchi - One of the best experts on this subject based on the ideXlab platform.
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interannual variability of evapotranspiration and energy exchange over an annual grassland in california
Journal of Geophysical Research, 2008Co-Authors: Dennis D Baldocchi, Ted HehnAbstract:[1] We report on the interannual variability of evapotranspiration (E) and energy exchange of an annual grassland in the Mediterranean climate zone of California. They were measured directly with the eddy covariance technique over a 6-year period that spanned between July 2001 and June 2007 and experienced a large range in precipitation (376 mm to 888 mm). Despite a two-fold range in precipitation, annual E ranged much less, between 266 mm and 391 mm. We found that pronounced energy-limited and water-limited periods occurred within the same year. In the water-limited period, monthly integrated E scaled negatively with solar radiation and was restrained by precipitation. In the energy-limited period, on the other hand, the majority of E scaled positively with solar radiation (Rg) and was confined by potential E (Ep). E was most sensitive to the availability of soil moisture during the transition to the senescence period rather than onset of the greenness period, causing annual E to be strongly modulated by growing season length. Bulk Surface Conductance scaled consistently with Priestley-Taylor α coefficient regardless of interannual and seasonal variability of precipitation, E, and solar radiation.
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seasonal variation of energy and water vapor exchange rates above and below a boreal jack pine forest canopy
Journal of Geophysical Research, 1997Co-Authors: Dennis D Baldocchi, Christoph A Vogel, Brad HallAbstract:Fluxes of energy and water vapor over boreal forest stands are expected to vary during the growing season due to temporal variations in solar energy, soil and air temperature, soil moisture, photosynthetic capacity, and leaf area. To investigate this hypothesis, we measured fluxes of energy balance components (solar, latent and sensible heat, and soil and canopy heat storage) over and under a boreal jack pine forest in central Canada during the 1994 growing season. Temporal trends of daily-integrated energy fluxes were significant during a 117 day period between spring and autumn. Mean fluxes of net radiation and latent heat peaked near the summer solstice. By the autumnal equinox their magnitudes were half of their peak values. On a day-to-day basis the presence or absence of clouds modulated solar energy fluxes, while evaporation rates were dependent on whether the canopy was dry or wet. When the canopy was dry, daily evaporation was generally less than 2.5 mm d−1. This amount was less than one-half the rate of equilibrium evaporation and was low compared to evaporation from vegetation in temperate zones. When the canopy was wet, daily evaporation approached 3 mm d−1 and exceeded predicted rates of equilibrium evaporation. Evaporation from the dry forest was weakly coupled to available energy and was restricted by the canopy AEs low-Surface Conductance. Biotic factors limiting the forest AEs Surface Conductance include the forest AEs low-leaf area index and partial stomatal closure. Abiotic and physiological factors restricting stomatal opening included a scarce supply of soil moisture, limiting vapor pressure deficits and the low photosynthetic capacity of the needles. The fluxes of solar energy and latent and sensible heat at the floor of the forest were a significant portion of energy exchange between the forest and the atmosphere. Typically, 20 to 40% of the total energy exchange by the jack pine stand originated at the understory. Since a substantial amount of energy occurs under the forest, two-layer, not a big-leaf AE, evaporation models are recommended as a tool for estimating water vapor fluxes from this open forest stand.
Youngjin Kim - One of the best experts on this subject based on the ideXlab platform.
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Electrical transport characteristics of Surface-Conductance-controlled, dielectrophoretically separated single-walled carbon nanotubes
Langmuir, 2007Co-Authors: Seunghyun Hong, Sehun Jung, Jaeboong Choi, Youngjin Kim, Seunghyun BaikAbstract:Alternating current dielectrophoresis has attracted considerable attention as a possible candidate to separate single-walled carbon nanotubes according to electronic types. Recently, the significant effect of Surface charge on the polarizability of semiconducting nanotubes was demonstrated using comparative Raman spectroscopic studies. Here we present electrical transport characteristics of Surface-charge-controlled, dielectrophoretically deposited nanotube arrays. The Surface charge was controlled using cationic/anionic surfactant mixtures. Complete separation between metallic and semiconducting species was achieved at the electric field frequency of 10 MHz only when the Surface charge of nanotubes was neutralized, which is consistent with previous Raman investigation. A theoretical analysis, using zeta potential information as input, further supported the experimental observation.
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dielectrophoresis of Surface Conductance modulated single walled carbon nanotubes using catanionic surfactants
Journal of Physical Chemistry B, 2006Co-Authors: Youngjin Kim, Sehun Jung, Jaeboong Choi, Seunghyun Hong, Michael S Strano, Seunghyun BaikAbstract:Dielectrophoresis has received considerable attention for separating nanotubes according to electronic types. Here we examine the effects of Surface conductivity of semiconducting single walled carbon nanotubes (SWNT), induced by ionic surfactants, on the sign of dielectrophoretic force. The crossover frequency of semiconducting SWNT increases rapidly as the conductivity ratio between the particle and medium increases, leading to an incomplete separation of ionic surfactant suspended SWNT at an electric field frequency of 10 MHz. To reduce the conductivity ratio, the Surface charge of SWNT is neutralized by an equimolar mixture of anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB), resulting in negative dielectrophoresis of semiconducting species at 10 MHz. A comparative Raman spectroscopy study shows a nearly complete separation of metallic SWNT.