The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Lothar Ley - One of the best experts on this subject based on the ideXlab platform.
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Surface Conductivity induced by fullerenes on diamond: Passivation and thermal stability
Diamond and Related Materials, 2005Co-Authors: Paul Strobel, Jürgen Ristein, Lothar Ley, Konrad Seppelt, Ilya V. Goldt, Olga V. BoltalinaAbstract:Abstract The Surface Conductivity of hydrogen terminated diamond under atmospheric conditions is a well known phenomenon. Inspired by the Surface transfer doping model [F. Maier, M. Riedel, B. Mantel, J. Ristein, L. Ley, Phys. Rev. Lett. 85, (2000) 3472] we have recently investigated thin C60 layers as an alternative to atmospheric adsorbates. We could indeed show that C60 induces a sub-Surface accumulation layer that results in a Surface Conductivity comparable to the air induced one [P. Strobel, M. Riedel, J. Ristein, L. Ley, Nature 430, (2004) 439]. In the present work we investigate fluorinated fullerenes, namely C60F18, C60F36, and C60F48, as transfer dopants. The Surface Conductivity induced by fluorinated fullerenes increases with higher fluorination and achieves for C60F48 a level that exceeds that observed under atmospheric conditions by up to a factor of three. Furthermore, we study the thermal stability of the fullerene layers on diamond and their stabilisation by passivation with different dielectric films (SiO, CaF2, and Si3N4). In the case of fluorinated fullerenes we observe a significant improvement in thermal stability after passivation with dielectrics but the pristine Conductivity level cannot be kept. A different kind of stabilisation is achieved for C60. After the simultaneous exposure to oxygen, light, and temperature of about 150 °C the Surface Conductivity induced by C60 is stable up to 350 °C in vacuum with an undiminished doping efficiency. We ascribe this effect to an oxygen mediated polymerisation of the C60 layer.
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Electrochemical Surface Transfer Doping The Mechanism Behind the Surface Conductivity of Hydrogen-Terminated Diamond
Journal of The Electrochemical Society, 2004Co-Authors: Jürgen Ristein, M Riedel, Lothar LeyAbstract:Intrinsic diamond with a bandgap of 5.4 eV exhibits a Surface Conductivity (SC) of the order of 10 -5 Ω -1 when terminated by hydrogen. This Conductivity is carried by a hole-accumulation layer close to the Surface with an areal carrier concentration of about 10 13 cm -2 , and it has already been utilized for a unique kind of field effect transistor [H. Kawarada, Surf. Sci. Rep., 26, 205 (1996)]. Although the microscopic doping mechanism is still under debate. Based on the results of a variety of Surface-sensitive experiments we propose a new Surface-transfer doping mechanism by which electron transfer from the valence band to adsorbed, hydrated ionic species at the Surface creates the holes for the Surface Conductivity. In order to draw a complete picture of the Surface Conductivity concepts from Surface and semiconductor physics as well as electrochemistry have to be adopted.
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Surface band bending and Surface Conductivity of hydrogenated diamond
Physical Review B, 2003Co-Authors: D. Takeuchi, Jürgen Ristein, M Riedel, Lothar LeyAbstract:We establish a strict correlation between the total photoelectron yield spectra and the Surface Conductivity of hydrogenated diamond. The decomposition of the yield spectra into electron and exciton derived contributions requires an upward Surface band bending to accompany Surface Conductivity, while an essentially flat band or downward band bending is observed after removing the Surface Conductivity by annealing in vacuum. Between the two competing models proposed for Surface Conductivity with a sheet hole density of ${10}^{13}{\mathrm{cm}}^{\ensuremath{-}2},$ these results favor the Surface transfer-doping model strongly over the subSurface acceptor model.
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Surface Conductivity of nitrogen-doped diamond
Diamond and Related Materials, 2002Co-Authors: Jürgen Ristein, M Riedel, M. Stammler, B.f. Mantel, Lothar LeyAbstract:Abstract Synthetic type Ib diamond crystals with (001) Surfaces that expose growth sectors of different nitrogen content have been used to study the phenomenon of p-type Surface Conductivity upon plasma hydrogenation and upon overgrowth with thin epitaxial CVD diamond layers. We found that an unbiased microwave-driven hydrogen plasma leads to Surface Conductivity only on well-defined regions on the substrates that correlate with growth sectors of low nitrogen content; whereas no conductive layer is found on top of growth sectors with higher nitrogen concentrations in the range of 200 ppm. After growing a homoepitaxial intrinsic diamond layer of only 20 nm on top of the nitrogen doped diamond, these differences are no longer observed and Surface Conductivity is established homogeneously over the whole sample. The same effect can be achieved by exposing the Ib substrates to a pure hydrogen plasma provided the sample is biased with an additional DC voltage of −250 V. Both results can be understood in the framework of the Surface transfer doping model suggested earlier by Maier and colleagues when the compensation of nitrogen donors by Surface acceptors and their passivation by hydrogen is taken into account. The quantitative discussion shows that the doping capability of the Surface acceptors is exhausted at lateral concentrations of approximately 1×1013 cm−2, which also corresponds to the maximum hole concentration usually observed in hydrogen-induced p-type conductive layers.
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Surface Conductivity of Diamond as a Function of Nitrogen Doping
physica status solidi (a), 2001Co-Authors: Jürgen Ristein, Florian Maier, M Riedel, M. Stammler, B.f. Mantel, Lothar LeyAbstract:The Surface Conductivity of diamond has recently attracted a lot of interest since a number of electronic applications proposed for diamond are based on this effect. Nevertheless, its microscopic origin is still a matter of debate. We describe in the following experiments in which the impact of the bulk defect concentration of diamond on the Surface Conductivity is investigated. The experiments show that Surface Conductivity is suppressed in the presence of donor-like nitrogen defects although the Surfaces are clearly hydrogen (or deuterium) terminated. We suggest compensation of the Surface or Surface near acceptors to be the reason for this suppression. A quantitative discussion shows that the doping capability of the Surface acceptors is exhausted at lateral concentrations of about 3 × 10 13 cm -2 .
Philippe Leroy - One of the best experts on this subject based on the ideXlab platform.
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influence of Surface Conductivity on the apparent zeta potential of calcite
Journal of Colloid and Interface Science, 2016Co-Authors: Shuai Li, Philippe Leroy, Nicolas Devau, Damien Jougnot, Frank Heberling, Christophe ChiabergeAbstract:Zeta potential is a physicochemical parameter of particular importance in describing the Surface electrical properties of charged porous media. However, the zeta potential of calcite is still poorly known because of the difficulty to interpret streaming potential experiments. The Helmholtz-Smoluchowski (HS) equation is widely used to estimate the apparent zeta potential from these experiments. However, this equation neglects the influence of Surface Conductivity on streaming potential. We present streaming potential and electrical Conductivity measurements on a calcite powder in contact with an aqueous NaCl electrolyte. Our streaming potential model corrects the apparent zeta potential of calcite by accounting for the influence of Surface Conductivity and flow regime. We show that the HS equation seriously underestimates the zeta potential of calcite, particularly when the electrolyte is diluted (ionic strength ⩽ 0.01 M) because of calcite Surface Conductivity. The basic Stern model successfully predicted the corrected zeta potential by assuming that the zeta potential is located at the outer Helmholtz plane, i.e. without considering a stagnant diffuse layer at the calcite-water interface. The Surface Conductivity of calcite crystals was inferred from electrical Conductivity measurements and computed using our basic Stern model. Surface Conductivity was also successfully predicted by our Surface complexation model.
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The electrophoretic mobility of montmorillonite. Zeta potential and Surface Conductivity effects
Journal of Colloid and Interface Science, 2015Co-Authors: Philippe Leroy, Nicolas Devau, Christophe Tournassat, Olivier Bernard, Mohamed AzaroualAbstract:Clay minerals have remarkable adsorption properties because of their high specific Surface area and sur face charge density, which give rise to high electrochemical properties. These electrochemical properties cannot be directly measured, and models must be developed to estimate the electrostatic potential at the vicinity of clay mineral Surfaces. In this context, an important model prediction is the zeta potential which is thought to be representative of the electrostatic potential at the plane of shear. The zeta potential is usually deduced from electrophoretic measurements but for clay minerals, high Surface Conductivity decreases their mobility, thereby impeding straightforward interpretation of these measurements. By combining a Surface complexation, Conductivity and electrophoretic mobility model, we were able to reconcile zeta potential predictions with electrophoretic measurements on montmorillonite immerse in NaCl aqueous solutions. The electrochemical properties of the Stern and diffuse layers of the basal sur faces were computed by a triple-layer model. Computed zeta potentials have considerably higher amplitudes than measured zeta potentials calculated with the Smoluchowski equation. Our model successfully reproduced measured electrophoretic mobilities. This confirmed our assumptions that Surface Conductivity may be responsible for montmorillonite's low electrophoretic mobility and that the zeta potential mall be located at the beginning of the diffuse layer
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Influence of Surface Conductivity on the apparent zeta potential of homoionic montmorillonite particles
2015Co-Authors: Philippe Leroy, Nicolas Devau, Christophe Tournassat, Olivier BernardAbstract:Zeta potential is a physicochemical parameter of particular importance in describing ion adsorption and double layer interactions between charged particles [1]. However, for clay particles, the conversion of electrophoretic mobility measurements into zeta potentials is difficult. This is due to their lamellar form, their anisotropic Surface charge density distribution, but above all to their very high Surface electrical Conductivity, which is inversely proportional to the sizes of the particles [2]. When Surface Conductivity is similar to or higher than the electrical Conductivity of bulk water, it can significantly lower the electrophoretic mobility of the particles. It follows that the magnitude of the intrinsic zeta potential can be grossly underestimated if Surface Conductivity is not considered in the calculation of the zeta potential, in particularly when the aqueous solution is diluted (ionic strength typically < 0.1 M; [3]). We use a basic Stern model to describe the electrochemical properties and to calculate the intrinsic zeta potential of the basal planes of homoionic montmorillonites particles immersed in respectively NaCl, CaCl2 and MgCl2 aqueous solutions (10-5 to 1 M) (Fig. 1). Only the equilibrium constant of adsorption of Na+ ions on the basal plane of montmorillonite is adjusted by cation exchange capacity and electrophoretic mobility measurements [4] at fixed pH (pH = 6.5) and high salinity (1 M). Electrophoretic mobilities are then calculated by coupling our electrostatic Surface complexation model with Henry's electrophoretic mobility model that considers (1) the retardation force associated with Surface Conductivity of the Stern and diffuse layers and (2) the internal Conductivity of the clay aggregate. Our electrophoretic mobility model is also not restricted to low zeta potentials because the electrical potential distribution at the Surface of the particle is calculated by numerically solving the non-linear Poisson-Boltzmann equation. The very good agreement of calculated and measured electrophoretic mobilities confirms that the true zeta potential of the basal plane of montmorillonite particles may correspond to the electrical potential at the onset of the diffuse layer, i.e., at the outer Helmholtz plane (Fig. 2).
Jürgen Ristein - One of the best experts on this subject based on the ideXlab platform.
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Surface Conductivity induced by fullerenes on diamond: Passivation and thermal stability
Diamond and Related Materials, 2005Co-Authors: Paul Strobel, Jürgen Ristein, Lothar Ley, Konrad Seppelt, Ilya V. Goldt, Olga V. BoltalinaAbstract:Abstract The Surface Conductivity of hydrogen terminated diamond under atmospheric conditions is a well known phenomenon. Inspired by the Surface transfer doping model [F. Maier, M. Riedel, B. Mantel, J. Ristein, L. Ley, Phys. Rev. Lett. 85, (2000) 3472] we have recently investigated thin C60 layers as an alternative to atmospheric adsorbates. We could indeed show that C60 induces a sub-Surface accumulation layer that results in a Surface Conductivity comparable to the air induced one [P. Strobel, M. Riedel, J. Ristein, L. Ley, Nature 430, (2004) 439]. In the present work we investigate fluorinated fullerenes, namely C60F18, C60F36, and C60F48, as transfer dopants. The Surface Conductivity induced by fluorinated fullerenes increases with higher fluorination and achieves for C60F48 a level that exceeds that observed under atmospheric conditions by up to a factor of three. Furthermore, we study the thermal stability of the fullerene layers on diamond and their stabilisation by passivation with different dielectric films (SiO, CaF2, and Si3N4). In the case of fluorinated fullerenes we observe a significant improvement in thermal stability after passivation with dielectrics but the pristine Conductivity level cannot be kept. A different kind of stabilisation is achieved for C60. After the simultaneous exposure to oxygen, light, and temperature of about 150 °C the Surface Conductivity induced by C60 is stable up to 350 °C in vacuum with an undiminished doping efficiency. We ascribe this effect to an oxygen mediated polymerisation of the C60 layer.
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Electrochemical Surface Transfer Doping The Mechanism Behind the Surface Conductivity of Hydrogen-Terminated Diamond
Journal of The Electrochemical Society, 2004Co-Authors: Jürgen Ristein, M Riedel, Lothar LeyAbstract:Intrinsic diamond with a bandgap of 5.4 eV exhibits a Surface Conductivity (SC) of the order of 10 -5 Ω -1 when terminated by hydrogen. This Conductivity is carried by a hole-accumulation layer close to the Surface with an areal carrier concentration of about 10 13 cm -2 , and it has already been utilized for a unique kind of field effect transistor [H. Kawarada, Surf. Sci. Rep., 26, 205 (1996)]. Although the microscopic doping mechanism is still under debate. Based on the results of a variety of Surface-sensitive experiments we propose a new Surface-transfer doping mechanism by which electron transfer from the valence band to adsorbed, hydrated ionic species at the Surface creates the holes for the Surface Conductivity. In order to draw a complete picture of the Surface Conductivity concepts from Surface and semiconductor physics as well as electrochemistry have to be adopted.
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Surface band bending and Surface Conductivity of hydrogenated diamond
Physical Review B, 2003Co-Authors: D. Takeuchi, Jürgen Ristein, M Riedel, Lothar LeyAbstract:We establish a strict correlation between the total photoelectron yield spectra and the Surface Conductivity of hydrogenated diamond. The decomposition of the yield spectra into electron and exciton derived contributions requires an upward Surface band bending to accompany Surface Conductivity, while an essentially flat band or downward band bending is observed after removing the Surface Conductivity by annealing in vacuum. Between the two competing models proposed for Surface Conductivity with a sheet hole density of ${10}^{13}{\mathrm{cm}}^{\ensuremath{-}2},$ these results favor the Surface transfer-doping model strongly over the subSurface acceptor model.
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Surface Conductivity of nitrogen-doped diamond
Diamond and Related Materials, 2002Co-Authors: Jürgen Ristein, M Riedel, M. Stammler, B.f. Mantel, Lothar LeyAbstract:Abstract Synthetic type Ib diamond crystals with (001) Surfaces that expose growth sectors of different nitrogen content have been used to study the phenomenon of p-type Surface Conductivity upon plasma hydrogenation and upon overgrowth with thin epitaxial CVD diamond layers. We found that an unbiased microwave-driven hydrogen plasma leads to Surface Conductivity only on well-defined regions on the substrates that correlate with growth sectors of low nitrogen content; whereas no conductive layer is found on top of growth sectors with higher nitrogen concentrations in the range of 200 ppm. After growing a homoepitaxial intrinsic diamond layer of only 20 nm on top of the nitrogen doped diamond, these differences are no longer observed and Surface Conductivity is established homogeneously over the whole sample. The same effect can be achieved by exposing the Ib substrates to a pure hydrogen plasma provided the sample is biased with an additional DC voltage of −250 V. Both results can be understood in the framework of the Surface transfer doping model suggested earlier by Maier and colleagues when the compensation of nitrogen donors by Surface acceptors and their passivation by hydrogen is taken into account. The quantitative discussion shows that the doping capability of the Surface acceptors is exhausted at lateral concentrations of approximately 1×1013 cm−2, which also corresponds to the maximum hole concentration usually observed in hydrogen-induced p-type conductive layers.
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Diamond Surface Conductivity experiments and photoelectron spectroscopy
Diamond and Related Materials, 2001Co-Authors: Jürgen Ristein, Florian Maier, M Riedel, M. StammerAbstract:A unique feature of diamond Surfaces is a highly conductive p-type layer which is usually observed when the Surfaces are hydrogen terminated. We present a combination of Conductivity and photoelectron yield measurements on a variety of different diamond samples in order to elucidate the role of hydrogen and adsorbates for this phenomenon. The experiments show that hydrogen termination is a necessary but not a sufficient condition for the appearance of the Surface Conductivity. Additionally, adsorbates from the atmosphere are needed. On the basis of the experiments an electrochemical model is developed which can explain the effect of the hydrogen termination and also shows why hydrogen terminated diamond is the only semiconductor with p-type Surface Conductivity.
Richard B Jackman - One of the best experts on this subject based on the ideXlab platform.
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Surface Conductivity on hydrogen terminated diamond
Semiconductor Science and Technology, 2003Co-Authors: Oliver Aneurin Williams, Richard B JackmanAbstract:Hydrogen terminated diamond exhibits Surface Conductivity of a p-type character. However, hydrogen termination itself is not sufficient to promote this effect and it has been shown by various authors that an aqueous layer containing adsorbates of a particular electronegativity is required to promote electron out diffusion from the Surface, thus creating a population of holes in the vicinity of the Surface. This paper describes detailed electrical measurements on this Surface conductive layer in various environments. The stability of this transport mechanism with particular attention to device applications is discussed.
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Influence of the postplasma process conditions on the Surface Conductivity of hydrogenated diamond Surfaces
Journal of Applied Physics, 2003Co-Authors: E. Snidero, Oliver Aneurin Williams, Dominique Tromson, Christine Mer, P. Bergonzo, John S. Foord, Christoph E. Nebel, Richard B JackmanAbstract:It is a common observation that diamond Surface Conductivity rises after exposure to hydrogen plasmas. Hydrogenation treatments are known to induce a p-type conductive layer, which is not present on non-hydrogenated samples. However, the particular mechanisms predominant in the plasma treatment process are still controversial, and several antagonist conditions have been reported to be of importance, such as sample temperature (500 °C to 800 °C), duration (a few seconds to 1 h), and microwave (MW) power density, etc. Further, the post-plasma step is also crucial, especially since the Surface Conductivity has been reported to be affected by the presence of an adsorbate layer on the diamond Surface. By setting up the arrangement to enable the in situ measurement of the Surface Conductivity after treatment, we have been able to control all parameters that could affect the Surface Conductivity, in order to determine those of importance. Among the parameters studied, we were able to analyze the influence of the...
Jose A. Garrido - One of the best experts on this subject based on the ideXlab platform.
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Diamond Surface Conductivity: Properties, devices, and sensors
Mrs Bulletin, 2014Co-Authors: Christopher Ian Pakes, Jose A. Garrido, Hiroshi KawaradaAbstract:Hydrogen termination of diamond lowers its ionization energy, driving electron transfer from the valence band into an adsorbed water layer or to a strong molecular acceptor. This gives rise to p -type Surface Conductivity with holes confined to a subSurface layer of a few nanometers thickness. The transfer doping mechanism, the electronic behavior of the resulting hole accumulation layer, and the development of robust field-effect transistor (FET) devices using this platform are reviewed. An alternative method of modulating the hole carrier density has been developed based upon an electrolyte-gate architecture. The operation of the resulting “solution-gated” FET architecture in two contemporary applications will be described: the charge state control of nitrogen-vacancy centers in diamond and biosensing. Despite 25 years of work in this area, our knowledge of Surface Conductivity of diamond continues to develop.
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Low dimensionality of the diamond Surface Conductivity
Physical Review B, 2014Co-Authors: Moritz V. Hauf, Martin Stutzmann, Patrick Simon, Max Seifert, Alexander W. Holleitner, Jose A. GarridoAbstract:Undoped diamond, a remarkable bulk electrical insulator, exhibits a high Surface Conductivity in air when the Surface is hydrogen terminated. Although theoretical models have claimed that a two-dimensional hole gas is established as a result of Surface energy-band bending, no definitive experimental demonstration has been reported so far. Here, we prove the two-dimensional character of the Surface Conductivity by low-temperature characterization of diamond in-plane gated field-effect transistors that enable the lateral confinement of the transistor's drain-source channel to nanometer dimensions. In these devices, we observe Coulomb blockade effects of multiple quantum islands varying in size with the gate voltage. The charging energy and thus the size of these zero-dimensional islands exhibit a gate-voltage dependence which is the direct result of the two-dimensional character of the conductive channel formed at hydrogen-terminated diamond Surfaces.
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The Surface Conductivity at the diamond/aqueous electrolyte interface.
Journal of the American Chemical Society, 2008Co-Authors: Jose A. Garrido, Andreas Härtl, Markus Dankerl, Andreas Reitinger, Martin Eickhoff, Andreas Helwig, Gerhard Müller, Martin StutzmannAbstract:We investigate the origin of the Surface Conductivity of H-terminated diamond films immersed in aqueous electrolyte. We demonstrate that in contrast to the in air situation, charge transfer across the diamond interface does not govern the Surface Conductivity in aqueous electrolyte when a gate electrode controls the diamond/electrolyte interfacial potential. Instead, this almost ideally polarizable interface allows the capacitive charging of the Surface. This description resolves the observed disagreement of the pH sensitivity of the diamond Surface Conductivity in air and in aqueous electrolyte.
