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Isabel Montero - One of the best experts on this subject based on the ideXlab platform.
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dynamic secondary Electron Emission in rough composite materials
Scientific Reports, 2019Co-Authors: Leandro Olano, Petronilo Martiniglesias, J R Dennison, Isabel MonteroAbstract:The interaction of ionizing radiation with matter is of critical importance in numerous areas of science and technology like space and vacuum technology and even medicine and biotechnology. Secondary Electron Emission is a consequence of Electron irradiation on materials. We achieve extremely low secondary Electron Emission yield values smaller than 0.2, even up to incident Electron energies ~1 keV, due to an undocumented synergy between neighbouring metal and dielectric domains in composite samples. To investigate this experimental discovery, we propose a simple 3D model where the dielectric and metallic domains are arranged in parallel and interleaved. The proposed surface profile has a triangular shape to model the surface roughness. We obtain a continuous equation to describe the electric field that arises between grounded conductors and charged dielectrics domains. The calculated trajectories of secondary Electrons in this 3D geometry are used to predict dynamic secondary Emission yield, which strongly depends on the charge accumulated in the dielectric domains. This research paves the way to design new materials of low secondary Emission yield, addressing the technological problem not yet resolved to inhibit the Electron avalanche in RF equipment that limit their maximum working power.
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secondary Electron Emission under Electron bombardment from graphene nanoplatelets
Applied Surface Science, 2014Co-Authors: Isabel Montero, Lydya Aguilera, María E. Dávila, L. Galán, Valentin Nistor, David Raboso, Luis A Gonzalez, R FerrittoAbstract:Abstract We present novel strategies for obtaining materials with low secondary Electron Emission under Electron beam irradiation for advanced technological applications. Apart from the promising low secondary Electron Emission yield (SEY) of amorphous carbon coatings deposited on rough surfaces, graphene nanoplatelets are shown to be very effective in reducing the SEY even over flat substrates. Here, we report very low SEY from coatings of graphene platelets exposed to the air, indicating a 60% reduction of the SEY respect to the uncoated flat surfaces. The shape of the SEY curve as a function of primary energy looks like the inverted image of a typical SEY curve.
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CuO nanowires for inhibiting secondary Electron Emission
Journal of Physics D: Applied Physics, 2013Co-Authors: Lydya Aguilera, Isabel Montero, María E. Dávila, A. Ruiz, L. Galán, Valentin Nistor, David Raboso, F. Javier Palomares, F. SoriaAbstract:Copper oxide nanowires (NWs) grown on copper to avoid the secondary Electron Emission were investigated. Optimal temperatures for NW growth were found to be in the range 700–800 K. NW surface coverage of 102 µm−2 is required to strongly reduce the secondary Electron yield. A total secondary Electron Emission coefficient below 1 was obtained for NW aspect ratio higher than 103.
Yevgeny Raitses - One of the best experts on this subject based on the ideXlab platform.
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angular temperature and impurity effects on secondary Electron Emission from ni 110
Journal of Applied Physics, 2018Co-Authors: M I Patino, Yevgeny Raitses, Richard E Wirz, Bruce E KoelAbstract:The secondary Electron Emission from a temperature-controlled Ni(110) sample was examined for 50–1500 eV Electrons impacting at 0°–35°, 50°, and 78°. Measurements showed a non-cosine dependence on an Electron incidence angle: the yield has a maximum at 0°, minima at ±12°, and increases at larger angles up to 35°. This trend in angular dependence is characteristic of single crystal materials and is due to increased secondary Electron generation when primary Electrons are directed along a close-packed direction. For example, compared to polycrystalline nickel, the yield for Ni(110) from primary Electrons at 0° (i.e., along the [110] direction) is up to 36% larger. Additionally, secondary Electron yields are highly sensitive to incident Electron energy (most notably between 0 and 500 eV) and to the presence of adsorbed carbon monoxide [with an up to 25% decrease compared to clean Ni(110)]. However, yields are independent of sample temperature between 300 and 600 K and of exposure to deuterium ions leading to formation of subsurface hydrogen. These results reaffirm the unique secondary Electron Emission properties of single crystals materials and highlight the importance of crystal orientation. Results are important for plasma-enhanced chemistry applications that utilize Ni(110) catalysts, since larger secondary Electron Emission may facilitate reactions of adsorbed species.The secondary Electron Emission from a temperature-controlled Ni(110) sample was examined for 50–1500 eV Electrons impacting at 0°–35°, 50°, and 78°. Measurements showed a non-cosine dependence on an Electron incidence angle: the yield has a maximum at 0°, minima at ±12°, and increases at larger angles up to 35°. This trend in angular dependence is characteristic of single crystal materials and is due to increased secondary Electron generation when primary Electrons are directed along a close-packed direction. For example, compared to polycrystalline nickel, the yield for Ni(110) from primary Electrons at 0° (i.e., along the [110] direction) is up to 36% larger. Additionally, secondary Electron yields are highly sensitive to incident Electron energy (most notably between 0 and 500 eV) and to the presence of a...
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application of auger spectroscopy for measurement of secondary Electron Emission from conducting material for electric propulsion devices
2013Co-Authors: M I Patino, Yevgeny Raitses, Bruce E Koel, Richard E WirzAbstract:A facility utilizing Auger Electron spectroscopy was developed to measure secondary Electron Emission from conducting materials. Both the total secondary Electron Emission yield and the energy distribution of the emitted Electrons were measured for graphite for primary Electron beam energies of 50 to 500eV. The total yield calculated using two different techniques - with the secondary Electron Emission calculated from current measurements of the sample and from a hemispherical collector - were found to agree well with each other and with a semi-empirical equation for the energies at which the measurements were taken.
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kinetic simulation of secondary Electron Emission effects in hall thrusters
Physics of Plasmas, 2006Co-Authors: D Sydorenko, A I Smolyakov, Igor D Kaganovich, Yevgeny RaitsesAbstract:The particle-in-cell code has been developed for kinetic simulations of Hall thrusters with a focus on plasma-wall interaction. It is shown that the effect of secondary Electron Emission on wall losses is different from predictions of previous fluid and kinetic studies. In simulations, the Electron velocity distribution function is strongly anisotropic, depleted at high energy, and nonmonotonic. Secondary Electrons form two beams propagating between the walls of a thruster channel in opposite radial directions. The beams produce secondary Electron Emission themselves depending on their energy at the moment of impact with the wall, which is defined by the electric and magnetic fields in the thruster as well as by the Electron transit time between the walls. The condition for the space-charge-limited secondary Electron Emission depends not only on the energy of bulk plasma Electrons but also on the energy of beam Electrons. The contribution of the beams to the particles and energy wall losses may be much larger than that of the plasma bulk Electrons. Recent experimental studies may indirectly support the results of these simulations, in particular, with respect to the Electron temperature saturation and the channel width effect on the thruster discharge.
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secondary Electron Emission from dielectric materials of a hall thruster with segmented electrodes
Other Information: PBD: 12 Feb 2003, 2003Co-Authors: A. Dunaevsky, Yevgeny Raitses, Nathaniel J FischAbstract:The discharge parameters in Hall thrusters depend strongly on the yield of secondary Electron Emission from channel walls. Comparative measurements of the yield of secondary Electron Emission at low energies of primary Electrons were performed for several dielectric materials used in Hall thrusters with segmented electrodes. The measurements showed that at low energies of primary Electrons the actual energetic dependencies of the total yield of secondary Electron Emission could differ from fits, which are usually used in theoretical models. The observed differences might be caused by Electron backscattering, which is dominant at lower energies and depends strongly on surface properties. Fits based on power or linear laws are relevant at higher energies of primary Electrons, where the bulk material properties play a decisive role.
R. Abrams - One of the best experts on this subject based on the ideXlab platform.
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Secondary Electron Emission studies
Applied Surface Science, 1997Co-Authors: A. Shih, C. Hor, J. Yater, R. AbramsAbstract:Secondary-Electron-Emission processes under Electron bombardment play an important role in the performance of a variety of Electron devices. While in some devices, the anode and the grid require materials that suppress the secondary-Electron-generation process, the crossed-field amplifier (CFA) is an example where the cathode requires an efficient secondary-Electron-Emission material. Secondary-Electron-Emission processes will be discussed by a three-step process: penetration of the primary Electrons, transmission of the secondary Electrons through the material, and final escape of the secondary Electrons over the vacuum barrier. The transmission of the secondary Electrons is one of the critical factors in determining the magnitude of the secondary-Electron yield. The wide band-gap in an insulator prevents low-energy secondary Electrons from losing energy through Electron-Electron collisions, thereby resulting in a large escape depth for the secondary Electrons and a large secondary-Electron yield. In general, insulating materials have high secondary-Electron yields, but a provision to supply some level of electrical conductivity is necessary in order to replenish the Electrons lost in the secondary-Electron-Emission process. Our secondary-Emission study of diamond demonstrates that the vacuum barrier height can have a strong effect on the total yield. The combined effect of a large escape depth of the secondary Electrons and a low vacuum-barrier height is responsible for the extraordinarily high secondary-Electron yields observed on hydrogen-terminated diamond samples.
Eun Ha Choi - One of the best experts on this subject based on the ideXlab platform.
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Work function of MgO single crystals from ion-induced secondary Electron Emission coefficient
Journal of Applied Physics, 2003Co-Authors: Jae Yong Lim, Jae Won Cho, Seung Oun Kang, Guangsup Cho, Han Sup Uhm, Eun Ha ChoiAbstract:The work functions φω of MgO single crystals with its respective orientation (111), (200), and (220) have been investigated from their ion-induced secondary Electron Emission coefficient γ, respectively, using various ions with different ionization energies in a γ-focused ion beam system. The work function φω for MgO single crystal with (111) orientation has the lowest value, 4.22 eV, whereas it is 4.94 eV for (200) and the highest value is 5.07 eV for (220). These work functions of MgO single crystals can explain the nonzero values of the ion-induced secondary Electron Emission coefficient γ for Xe+ ions, whose ionization energy is 12.13 eV.
Lydya Aguilera - One of the best experts on this subject based on the ideXlab platform.
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secondary Electron Emission under Electron bombardment from graphene nanoplatelets
Applied Surface Science, 2014Co-Authors: Isabel Montero, Lydya Aguilera, María E. Dávila, L. Galán, Valentin Nistor, David Raboso, Luis A Gonzalez, R FerrittoAbstract:Abstract We present novel strategies for obtaining materials with low secondary Electron Emission under Electron beam irradiation for advanced technological applications. Apart from the promising low secondary Electron Emission yield (SEY) of amorphous carbon coatings deposited on rough surfaces, graphene nanoplatelets are shown to be very effective in reducing the SEY even over flat substrates. Here, we report very low SEY from coatings of graphene platelets exposed to the air, indicating a 60% reduction of the SEY respect to the uncoated flat surfaces. The shape of the SEY curve as a function of primary energy looks like the inverted image of a typical SEY curve.
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CuO nanowires for inhibiting secondary Electron Emission
Journal of Physics D: Applied Physics, 2013Co-Authors: Lydya Aguilera, Isabel Montero, María E. Dávila, A. Ruiz, L. Galán, Valentin Nistor, David Raboso, F. Javier Palomares, F. SoriaAbstract:Copper oxide nanowires (NWs) grown on copper to avoid the secondary Electron Emission were investigated. Optimal temperatures for NW growth were found to be in the range 700–800 K. NW surface coverage of 102 µm−2 is required to strongly reduce the secondary Electron yield. A total secondary Electron Emission coefficient below 1 was obtained for NW aspect ratio higher than 103.