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W I Milne - One of the best experts on this subject based on the ideXlab platform.
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influence of Ion Energy and substrate temperature on the optical and electronic properties of tetrahedral amorphous carbon ta c films
Journal of Applied Physics, 1997Co-Authors: Manish Chhowalla, J Robertson, G A J Amaratunga, S R P Silva, C A Davis, Chunwei Chen, W I MilneAbstract:The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum arc as a functIon of the Ion Energy and substrate temperature are reported. The sp3 fractIon was found to strongly depend on the Ion Energy, giving a highly sp3 bonded a-C denoted as tetrahedral amorphous carbon (ta-C) at Ion energies around 100 eV. The optical band gap was found to follow similar trends to other diamondlike carbon films, varying almost linearly with sp2 fractIon. The dependence of the electronic properties are discussed in terms of models of the electronic structure of a-C. The structure of ta-C was also strongly dependent on the depositIon temperature, changing sharply to sp2 above a transitIon temperature, T1, of ≈200 °C. Furthermore, T1 was found to decrease with increasing Ion Energy. Most film properties, such as compressive stress and plasmon Energy, were correlated to the sp3 fractIon. However, the optical and electrical properties were found to undergo a more gradual transitIon with the depositIon temperature which we attribute to the medium range order of sp2 sites. We attribute the variatIon in film properties with the depositIon temperature to diffusIon of interstitials to the surface above T1 due to thermal activatIon, leading to the relaxatIon of density in context of a growth model.
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properties of carbon Ion deposited tetrahedral amorphous carbon films as a functIon of Ion Energy
Journal of Applied Physics, 1996Co-Authors: B K Tay, S R P Silva, H S Tan, Li Zhong, W I MilneAbstract:Ion Energy, controlled by the substrate bias, is an important parameter in determining properties of films deposited by the filtered cathodic vacuum arc technique. The substrate bias determines the Ion Energy distributIon of the growth species. The Ion Energy is varied, while keeping the other depositIon conditIons constant, in order to study the effect of Ion Energy on the film properties. The films were characterized by their optical and mechanical parameters using an ellipsometer, surface profilometer, optical spectrometer, and nanoindenter. Electron Energy‐loss spectroscopy and Raman spectroscopy were used for structural analysis of the films.
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Ion Energy and plasma characterizatIon in a silicon filtered cathodic vacuum arc
Journal of Applied Physics, 1996Co-Authors: M M M Bilek, Manish Chhowalla, M Weiler, W I MilneAbstract:The plasma generated by a silicon filtered cathodic vacuum arc has been investigated using a Faraday cup and Langmuir probes. Ion Energy distributIons for arc currents ranging from 30 to 80 A were measured. Mean Ion energies were found to range from 8 to 18 eV. The Ion saturatIon current density varied from 0.1 to 1 mA/cm2 depending on both the arc and filter coil currents. The Energy distributIons were fitted by a sum of Gaussians spaced according to the gas dynamic model for Ion acceleratIon at the cathode spot.
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properties of filtered Ion beam deposited diamondlike carbon as a functIon of Ion Energy
Physical Review B, 1993Co-Authors: P J Fallon, J Robertson, G A J Amaratunga, W I Milne, C A Davis, V S Veerasamy, J KoskinenAbstract:A highly tetrahedrally bonded form on nonhydrogenated amorphous carbon (a-C) is produced by depositIon from filtered medium-Energy Ion beams. A range of such films was grown and the ${\mathit{sp}}^{3}$-bonded fractIons, plasmon energies, compressive stresses, and resistivities were measured as a functIon of Ion Energy. These properties are found to be strongly correlated and each to pass through a maximum at an Ion Energy of about 140 eV. The optimum Ion Energy is observed to depend on the type of carbon Ions deposited and, possibly, on the depositIon flux rate. The data are found to support depositIon models in which the ${\mathit{sp}}^{3}$ bonding arises from the subplantatIon of incident Ions, giving rise to a quenched increase in density and strain.
S S Bulanov - One of the best experts on this subject based on the ideXlab platform.
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radiatIon pressure acceleratIon the factors limiting maximum attainable Ion Energy
Physics of Plasmas, 2016Co-Authors: S S Bulanov, E Esarey, C B Schroeder, Zh T Esirkepov, M Kando, F Pegoraro, W P LeemansAbstract:RadiatIon pressure acceleratIon (RPA) is a highly efficient mechanism of laser-driven Ion acceleratIon, with near complete transfer of the laser Energy to the Ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable Ion Energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focused pulses and thin foils. However, in this case, finite spot size effects are important, and another limiting factor, the transverse expansIon of the target, may dominate over the group velocity effect. As the laser pulse diffracts after passing the focus, the target expands accordingly due to the transverse intensity profile of the laser. Due to this expansIon, the areal density of the target decreases, making it transp...
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radiatIon pressure acceleratIon the factors limiting maximum attainable Ion Energy
arXiv: Plasma Physics, 2016Co-Authors: S S Bulanov, E Esarey, C B Schroeder, Zh T Esirkepov, M Kando, F Pegoraro, W P LeemansAbstract:RadiatIon pressure acceleratIon (RPA) is a highly efficient mechanism of laser-driven Ion acceleratIon, with with near complete transfer of the laser Energy to the Ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable Ion Energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focused pulses and thin foils. However, in this case, finite spot size effects are important, and another limiting factor, the transverse expansIon of the target, may dominate over the group velocity effect. As the laser pulse diffracts after passing the focus, the target expands accordingly due to the transverse intensity profile of the laser. Due to this expansIon, the areal density of the target decreases, making it transparent for radiatIon and effectively terminating the acceleratIon. The off-normal incidence of the laser on the target, due either to the experimental setup, or to the deformatIon of the target, will also lead to establishing a limit on maximum Ion Energy.
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maximum attainable Ion Energy in the radiatIon pressure acceleratIon regime
Proceedings of SPIE, 2015Co-Authors: S S Bulanov, E Esarey, C B Schroeder, M Kando, F Pegoraro, Timur Zh Esirkepov, W P LeemansAbstract:The laser group velocity plays a crucial role in laser driven acceleratIon of electrons and Ions. In particular, a highly efficient mechanism of laser driven Ion acceleratIon, RadiatIon Pressure AcceleratIon, has a fundamental limit on the maximum attainable Ion Energy, which is determined by the group velocity of the laser. However there is another limiting factor that may shed the group velocity effects. It is due to the transverse expansIon of the target, which happens in the course of a tightly focused laser pulse interactIon with a thin foil. Transversely expanding targets become increasingly transparent for radiatIon thus terminating the acceleratIon. UtilizatIon of an external guiding structure for the accelerating laser pulse may provide a way of compensating for the group velocity and transverse expansIon effects.
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enhancement of maximum attainable Ion Energy in the radiatIon pressure acceleratIon regime using a guiding structure
Physical Review Letters, 2015Co-Authors: S S Bulanov, E Esarey, C B Schroeder, Zh T Esirkepov, M Kando, F Pegoraro, W P LeemansAbstract:RadiatIon pressure acceleratIon is a highly efficient mechanism of laser-driven Ion acceleratIon, with the laser Energy almost totally transferrable to the Ions in the relativistic regime. There is a fundamental limit on the maximum attainable Ion Energy, which is determined by the group velocity of the laser. In the case of tightly focused laser pulses, which are utilized to get the highest intensity, another factor limiting the maximum Ion Energy comes into play, the transverse expansIon of the target. Transverse expansIon makes the target transparent for radiatIon, thus reducing the effectiveness of acceleratIon. UtilizatIon of an external guiding structure for the accelerating laser pulse may provide a way of compensating for the group velocity and transverse expansIon effects.
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enhancement of maximum attainable Ion Energy in the radiatIon pressure acceleratIon regime using a guiding structure
arXiv: Plasma Physics, 2013Co-Authors: S S Bulanov, E Esarey, C B Schroeder, Zh T Esirkepov, M Kando, F Pegoraro, W P LeemansAbstract:RadiatIon Pressure AcceleratIon relies on high intensity laser pulse interacting with solid target to obtain high maximum Energy, quasimonoenergetic Ion beams. Either extremely high power laser pulses or tight focusing of laser radiatIon is required. The latter would lead to the appearance of the maximum attainable Ion Energy, which is determined by the laser group velocity and is highly influenced by the transverse expansIon of the target. Ion acceleratIon is only possible with target velocities less than the group velocity of the laser. The transverse expansIon of the target makes it transparent for radiatIon, thus reducing the effectiveness of acceleratIon. UtilizatIon of an external guiding structure for the accelerating laser pulse may provide a way of compensating for the group velocity and transverse expansIon effects.
Edmund Schungel - One of the best experts on this subject based on the ideXlab platform.
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the effect of secondary electrons on the separate control of Ion Energy and flux in dual frequency capacitively coupled radio frequency discharges
Applied Physics Letters, 2010Co-Authors: Z Donko, Julian Schulze, Peter Hartmann, Ihor Korolov, Uwe Czarnetzki, Edmund SchungelAbstract:Dual-frequency capacitive discharges are used to separately control the mean Ion Energy, e¯Ion, and flux, ΓIon, at the electrodes. We study the effect of secondary electrons on this separate control in argon discharges driven at 2+27 MHz at different pressures using Particle in Cell simulatIons. For secondary yield γ≈0, ΓIon decreases as a functIon of the low frequency voltage amplitude due to the frequency coupling, while it increases at high γ due to the effective multiplicatIon of secondary electrons inside the sheaths. Therefore, separate control is strongly limited. e¯Ion increases with γ, which might allow an in situ determinatIon of γ-coefficients.
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the electrical asymmetry effect in capacitively coupled radio frequency discharges measurements of dc self bias Ion Energy and Ion flux
Journal of Physics D, 2009Co-Authors: Julian Schulze, Edmund Schungel, Uwe CzarnetzkiAbstract:The recently theoretically predicted electrical asymmetry effect (EAE) (Heil et al 2008 IEEE Trans. Plasma Sci. 36 1404, Heil et al 2008 J. Phys. D: Appl. Phys. 41 165202, Czarnetzki et al 2009 J. Phys.: Conf. Ser. at press) in capacitively coupled radio frequency (CCRF) discharges and the related separate control of Ion Energy and flux via the EAE (Czarnetzki et al 2009 J. Phys.: Conf. Ser. at press, Donk´ o et al 2008 J. Phys. D: Appl. Phys. 42 025205) are tested experimentally for the first time. A geometrically symmetric CCRF discharge (equal electrode surface areas) operated at 13.56 and 27.12MHz with variable phase angle between the harmonics is operated in argon at different pressures. The dc self bias, the Energy as well as the flux of Ions at the grounded electrode, and the space and phase resolved optical emissIon are measured. The results verify the predictIons of models and simulatIons: via the EAE a dc self bias is generated as an almost linear functIon of the phase. This variable dc self bias allows separate control of Ion Energy and flux in an almost ideal way under various discharge conditIons. (Some figures in this article are in colour only in the electronic versIon)
Julian Schulze - One of the best experts on this subject based on the ideXlab platform.
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the effect of secondary electrons on the separate control of Ion Energy and flux in dual frequency capacitively coupled radio frequency discharges
Applied Physics Letters, 2010Co-Authors: Z Donko, Julian Schulze, Peter Hartmann, Ihor Korolov, Uwe Czarnetzki, Edmund SchungelAbstract:Dual-frequency capacitive discharges are used to separately control the mean Ion Energy, e¯Ion, and flux, ΓIon, at the electrodes. We study the effect of secondary electrons on this separate control in argon discharges driven at 2+27 MHz at different pressures using Particle in Cell simulatIons. For secondary yield γ≈0, ΓIon decreases as a functIon of the low frequency voltage amplitude due to the frequency coupling, while it increases at high γ due to the effective multiplicatIon of secondary electrons inside the sheaths. Therefore, separate control is strongly limited. e¯Ion increases with γ, which might allow an in situ determinatIon of γ-coefficients.
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the electrical asymmetry effect in capacitively coupled radio frequency discharges measurements of dc self bias Ion Energy and Ion flux
Journal of Physics D, 2009Co-Authors: Julian Schulze, Edmund Schungel, Uwe CzarnetzkiAbstract:The recently theoretically predicted electrical asymmetry effect (EAE) (Heil et al 2008 IEEE Trans. Plasma Sci. 36 1404, Heil et al 2008 J. Phys. D: Appl. Phys. 41 165202, Czarnetzki et al 2009 J. Phys.: Conf. Ser. at press) in capacitively coupled radio frequency (CCRF) discharges and the related separate control of Ion Energy and flux via the EAE (Czarnetzki et al 2009 J. Phys.: Conf. Ser. at press, Donk´ o et al 2008 J. Phys. D: Appl. Phys. 42 025205) are tested experimentally for the first time. A geometrically symmetric CCRF discharge (equal electrode surface areas) operated at 13.56 and 27.12MHz with variable phase angle between the harmonics is operated in argon at different pressures. The dc self bias, the Energy as well as the flux of Ions at the grounded electrode, and the space and phase resolved optical emissIon are measured. The results verify the predictIons of models and simulatIons: via the EAE a dc self bias is generated as an almost linear functIon of the phase. This variable dc self bias allows separate control of Ion Energy and flux in an almost ideal way under various discharge conditIons. (Some figures in this article are in colour only in the electronic versIon)
W P Leemans - One of the best experts on this subject based on the ideXlab platform.
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radiatIon pressure acceleratIon the factors limiting maximum attainable Ion Energy
Physics of Plasmas, 2016Co-Authors: S S Bulanov, E Esarey, C B Schroeder, Zh T Esirkepov, M Kando, F Pegoraro, W P LeemansAbstract:RadiatIon pressure acceleratIon (RPA) is a highly efficient mechanism of laser-driven Ion acceleratIon, with near complete transfer of the laser Energy to the Ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable Ion Energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focused pulses and thin foils. However, in this case, finite spot size effects are important, and another limiting factor, the transverse expansIon of the target, may dominate over the group velocity effect. As the laser pulse diffracts after passing the focus, the target expands accordingly due to the transverse intensity profile of the laser. Due to this expansIon, the areal density of the target decreases, making it transp...
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radiatIon pressure acceleratIon the factors limiting maximum attainable Ion Energy
arXiv: Plasma Physics, 2016Co-Authors: S S Bulanov, E Esarey, C B Schroeder, Zh T Esirkepov, M Kando, F Pegoraro, W P LeemansAbstract:RadiatIon pressure acceleratIon (RPA) is a highly efficient mechanism of laser-driven Ion acceleratIon, with with near complete transfer of the laser Energy to the Ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable Ion Energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focused pulses and thin foils. However, in this case, finite spot size effects are important, and another limiting factor, the transverse expansIon of the target, may dominate over the group velocity effect. As the laser pulse diffracts after passing the focus, the target expands accordingly due to the transverse intensity profile of the laser. Due to this expansIon, the areal density of the target decreases, making it transparent for radiatIon and effectively terminating the acceleratIon. The off-normal incidence of the laser on the target, due either to the experimental setup, or to the deformatIon of the target, will also lead to establishing a limit on maximum Ion Energy.
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maximum attainable Ion Energy in the radiatIon pressure acceleratIon regime
Proceedings of SPIE, 2015Co-Authors: S S Bulanov, E Esarey, C B Schroeder, M Kando, F Pegoraro, Timur Zh Esirkepov, W P LeemansAbstract:The laser group velocity plays a crucial role in laser driven acceleratIon of electrons and Ions. In particular, a highly efficient mechanism of laser driven Ion acceleratIon, RadiatIon Pressure AcceleratIon, has a fundamental limit on the maximum attainable Ion Energy, which is determined by the group velocity of the laser. However there is another limiting factor that may shed the group velocity effects. It is due to the transverse expansIon of the target, which happens in the course of a tightly focused laser pulse interactIon with a thin foil. Transversely expanding targets become increasingly transparent for radiatIon thus terminating the acceleratIon. UtilizatIon of an external guiding structure for the accelerating laser pulse may provide a way of compensating for the group velocity and transverse expansIon effects.
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enhancement of maximum attainable Ion Energy in the radiatIon pressure acceleratIon regime using a guiding structure
Physical Review Letters, 2015Co-Authors: S S Bulanov, E Esarey, C B Schroeder, Zh T Esirkepov, M Kando, F Pegoraro, W P LeemansAbstract:RadiatIon pressure acceleratIon is a highly efficient mechanism of laser-driven Ion acceleratIon, with the laser Energy almost totally transferrable to the Ions in the relativistic regime. There is a fundamental limit on the maximum attainable Ion Energy, which is determined by the group velocity of the laser. In the case of tightly focused laser pulses, which are utilized to get the highest intensity, another factor limiting the maximum Ion Energy comes into play, the transverse expansIon of the target. Transverse expansIon makes the target transparent for radiatIon, thus reducing the effectiveness of acceleratIon. UtilizatIon of an external guiding structure for the accelerating laser pulse may provide a way of compensating for the group velocity and transverse expansIon effects.
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enhancement of maximum attainable Ion Energy in the radiatIon pressure acceleratIon regime using a guiding structure
arXiv: Plasma Physics, 2013Co-Authors: S S Bulanov, E Esarey, C B Schroeder, Zh T Esirkepov, M Kando, F Pegoraro, W P LeemansAbstract:RadiatIon Pressure AcceleratIon relies on high intensity laser pulse interacting with solid target to obtain high maximum Energy, quasimonoenergetic Ion beams. Either extremely high power laser pulses or tight focusing of laser radiatIon is required. The latter would lead to the appearance of the maximum attainable Ion Energy, which is determined by the laser group velocity and is highly influenced by the transverse expansIon of the target. Ion acceleratIon is only possible with target velocities less than the group velocity of the laser. The transverse expansIon of the target makes it transparent for radiatIon, thus reducing the effectiveness of acceleratIon. UtilizatIon of an external guiding structure for the accelerating laser pulse may provide a way of compensating for the group velocity and transverse expansIon effects.
