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I G Madiba - One of the best experts on this subject based on the ideXlab platform.
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effect of neutron Irradiation on the structural electrical and optical properties evolution of rpld vo2 films
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2019Co-Authors: I G Madiba, Nicolas Emond, M Chaker, B S Khanyile, S I Tadadjeu, Peter Zolliker, M Izerrouken, Nolubabalo MatiniseAbstract:Abstract This study reports on the effect of neutron Irradiation at different fluences on the properties of VO2 thin films. The Irradiations were performed at NUR research reactor, Algiers at a temperature of about 40 °C, with fast neutron fluence (En > 1 MeV) up to 1.9 × 1018 n.cm−2. The induced defects have been investigated using structural, optical and electrical measurements. Both bulk sensitive characterization techniques, Raman and grazing incident angle X-ray diffraction (GIXRD) analysis, show that no structural transformation is induced by neutron Irradiation, although strain induced defect production are generated throughout the films while surface sensitive techniques, X-ray photoelectron spectroscopy (XPS) and work function measurements, show that the charge carrier (electron) concentration at room temperature decreases after Irradiation. Potentially due to fast neutron Irradiation induced defects, mainly in the form of Frenkel pairs, swelling and color center formation occurs in VO2 thin films without amorphization. This is further corroborated by an increase of the room temperature resistivity through the irradiated films. Temperature-dependent electrical and optical transmission measurements confirm that the characteristic semiconductor-to-metal transition of the VO2 films is preserved upon Irradiation. We therefore conclude that VO2 is an excellent candidate for thermal shielding and thermal management of small satellites.
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effects of gamma Irradiations on reactive pulsed laser deposited vanadium dioxide thin films
Applied Surface Science, 2017Co-Authors: I G Madiba, Nicolas Emond, M Chaker, S I Tadadjeu, F T Thema, U Muller, Peter ZollikerAbstract:Abstract Vanadium oxide films are considered suitable coatings for various applications such as thermal protective coating of small spacecrafts because of their thermochromic properties. While in outer space, such coating will be exposed to cosmic radiations which include γ-rays. To study the effect of these γ-rays on the coating properties, we have deposited vanadium dioxide (VO2) films on silicon substrates and subjected them to extensive γ-Irradiations with typical doses encountered in space missions. The prevalent crystallographic phase after Irradiation remains the monoclinic VO2 phase but the films preferential orientation shifts to lower angles due to the presence of disordered regions caused by radiations. Raman spectroscopy measurements also evidences that the VO2 structure is slightly affected by gamma Irradiation. Indeed, increasing the gamma rays dose locally alters the crystalline and electronic structures of the films by modifying the V–V inter-dimer distance, which in turns favours the presence of the VO2 metallic phase. From the XPS measurements of V2p and O1s core level spectra, an oxidation of vanadium from V4+ towards V5+ is revealed. The data also reveal a hydroxylation upon Irradiation which is corroborated by the vanishing of a low oxidation state peak near the Fermi energy in the valence band. Our observations suggest that gamma radiations induce the formation of Frenkel pairs. Moreover, THz transmission measurements show that the long range structure of VO2 remains intact after Irradiation whilst the electrical measurements evidence that the coating resistivity decreases with gamma Irradiation and that their transition temperature is slightly reduced for high gamma ray doses. Even though gamma rays are only one of the sources of radiations that are encountered in space environment, these results are very promising with regards to the potential of integration of such VO2 films as a protective coating for spacecrafts.
S I Tadadjeu - One of the best experts on this subject based on the ideXlab platform.
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effect of neutron Irradiation on the structural electrical and optical properties evolution of rpld vo2 films
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2019Co-Authors: I G Madiba, Nicolas Emond, M Chaker, B S Khanyile, S I Tadadjeu, Peter Zolliker, M Izerrouken, Nolubabalo MatiniseAbstract:Abstract This study reports on the effect of neutron Irradiation at different fluences on the properties of VO2 thin films. The Irradiations were performed at NUR research reactor, Algiers at a temperature of about 40 °C, with fast neutron fluence (En > 1 MeV) up to 1.9 × 1018 n.cm−2. The induced defects have been investigated using structural, optical and electrical measurements. Both bulk sensitive characterization techniques, Raman and grazing incident angle X-ray diffraction (GIXRD) analysis, show that no structural transformation is induced by neutron Irradiation, although strain induced defect production are generated throughout the films while surface sensitive techniques, X-ray photoelectron spectroscopy (XPS) and work function measurements, show that the charge carrier (electron) concentration at room temperature decreases after Irradiation. Potentially due to fast neutron Irradiation induced defects, mainly in the form of Frenkel pairs, swelling and color center formation occurs in VO2 thin films without amorphization. This is further corroborated by an increase of the room temperature resistivity through the irradiated films. Temperature-dependent electrical and optical transmission measurements confirm that the characteristic semiconductor-to-metal transition of the VO2 films is preserved upon Irradiation. We therefore conclude that VO2 is an excellent candidate for thermal shielding and thermal management of small satellites.
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effects of gamma Irradiations on reactive pulsed laser deposited vanadium dioxide thin films
Applied Surface Science, 2017Co-Authors: I G Madiba, Nicolas Emond, M Chaker, S I Tadadjeu, F T Thema, U Muller, Peter ZollikerAbstract:Abstract Vanadium oxide films are considered suitable coatings for various applications such as thermal protective coating of small spacecrafts because of their thermochromic properties. While in outer space, such coating will be exposed to cosmic radiations which include γ-rays. To study the effect of these γ-rays on the coating properties, we have deposited vanadium dioxide (VO2) films on silicon substrates and subjected them to extensive γ-Irradiations with typical doses encountered in space missions. The prevalent crystallographic phase after Irradiation remains the monoclinic VO2 phase but the films preferential orientation shifts to lower angles due to the presence of disordered regions caused by radiations. Raman spectroscopy measurements also evidences that the VO2 structure is slightly affected by gamma Irradiation. Indeed, increasing the gamma rays dose locally alters the crystalline and electronic structures of the films by modifying the V–V inter-dimer distance, which in turns favours the presence of the VO2 metallic phase. From the XPS measurements of V2p and O1s core level spectra, an oxidation of vanadium from V4+ towards V5+ is revealed. The data also reveal a hydroxylation upon Irradiation which is corroborated by the vanishing of a low oxidation state peak near the Fermi energy in the valence band. Our observations suggest that gamma radiations induce the formation of Frenkel pairs. Moreover, THz transmission measurements show that the long range structure of VO2 remains intact after Irradiation whilst the electrical measurements evidence that the coating resistivity decreases with gamma Irradiation and that their transition temperature is slightly reduced for high gamma ray doses. Even though gamma rays are only one of the sources of radiations that are encountered in space environment, these results are very promising with regards to the potential of integration of such VO2 films as a protective coating for spacecrafts.
Erin Patrick - One of the best experts on this subject based on the ideXlab platform.
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enhancement of algan gan high electron mobility transistor off state drain breakdown voltage via backside proton Irradiation
Proceedings of SPIE, 2015Co-Authors: Ya His Hwang, S J Pearton, Erin PatrickAbstract:Proton Irradiation from the backside of the samples were employed to enhance off-state drain breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs) grown on Si substrates. Via holes were fabricated directly under the active area of the HEMTs by etching through the Si substrate for subsequent backside proton Irradiation. By taking the advantage of the steep drop at the end of proton energy loss profile, the defects created by the proton Irradiation from the backside of the sample could be precisely placed at specific locations inside the AlGaN/GaN HEMT structure. There were no degradation of drain current nor enhancement of off-state drain voltage breakdown voltage observed for the irradiated AlGaN/GaN HEMTs with the proton energy of 225 or 275 keV, for which the defects created by the proton Irradiations were intentionally placed in the GaN buffer. HEMTs with defects placed in the 2 dimensional electron gas (2DEG) channel region and AlGaN barrier using 330 or 340 keV protons not only showed degradation of drain current, but also exhibited improvement of the off-state drain breakdown voltage. FLOODS TCAD finite-element simulations were performed to confirm the hypothesis of a virtual gate formed around the 2DEG region to reduce the peak electric field around the gate edges and increase the off-state drain breakdown voltage.
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enhancement of algan gan high electron mobility transistors off state drain breakdown voltage via backside proton Irradiation
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials Processing Measurement and Phenomena, 2014Co-Authors: Shun Li, Yahsi Hwang, Yuehling Hsieh, S J Pearton, Erin Patrick, Camilo Velez Cuervo, D SmithAbstract:Proton Irradiation from the backside of the samples were employed to enhance off-state drain breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs) grown on Si substrates. Via holes were fabricated directly under the active area of the HEMTs by etching through the Si substrate for subsequent backside proton Irradiation. By taking the advantage of the steep drop at the end of proton energy loss profile, the defects created by the proton Irradiation from the backside of the sample could be precisely placed at specific locations inside the AlGaN/GaN HEMT structure. There were no degradation of drain current nor enhancement of off-state drain voltage breakdown voltage observed for the irradiated AlGaN/GaN HEMTs with the proton energy of 225 or 275 keV, for which the defects created by the proton Irradiations were intentionally placed in the GaN buffer. HEMTs with defects placed in the two dimensional electron gas (2DEG) channel region and AlGaN barrier using 330 or 340 keV protons not only ...
Peter Zolliker - One of the best experts on this subject based on the ideXlab platform.
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effect of neutron Irradiation on the structural electrical and optical properties evolution of rpld vo2 films
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2019Co-Authors: I G Madiba, Nicolas Emond, M Chaker, B S Khanyile, S I Tadadjeu, Peter Zolliker, M Izerrouken, Nolubabalo MatiniseAbstract:Abstract This study reports on the effect of neutron Irradiation at different fluences on the properties of VO2 thin films. The Irradiations were performed at NUR research reactor, Algiers at a temperature of about 40 °C, with fast neutron fluence (En > 1 MeV) up to 1.9 × 1018 n.cm−2. The induced defects have been investigated using structural, optical and electrical measurements. Both bulk sensitive characterization techniques, Raman and grazing incident angle X-ray diffraction (GIXRD) analysis, show that no structural transformation is induced by neutron Irradiation, although strain induced defect production are generated throughout the films while surface sensitive techniques, X-ray photoelectron spectroscopy (XPS) and work function measurements, show that the charge carrier (electron) concentration at room temperature decreases after Irradiation. Potentially due to fast neutron Irradiation induced defects, mainly in the form of Frenkel pairs, swelling and color center formation occurs in VO2 thin films without amorphization. This is further corroborated by an increase of the room temperature resistivity through the irradiated films. Temperature-dependent electrical and optical transmission measurements confirm that the characteristic semiconductor-to-metal transition of the VO2 films is preserved upon Irradiation. We therefore conclude that VO2 is an excellent candidate for thermal shielding and thermal management of small satellites.
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effects of gamma Irradiations on reactive pulsed laser deposited vanadium dioxide thin films
Applied Surface Science, 2017Co-Authors: I G Madiba, Nicolas Emond, M Chaker, S I Tadadjeu, F T Thema, U Muller, Peter ZollikerAbstract:Abstract Vanadium oxide films are considered suitable coatings for various applications such as thermal protective coating of small spacecrafts because of their thermochromic properties. While in outer space, such coating will be exposed to cosmic radiations which include γ-rays. To study the effect of these γ-rays on the coating properties, we have deposited vanadium dioxide (VO2) films on silicon substrates and subjected them to extensive γ-Irradiations with typical doses encountered in space missions. The prevalent crystallographic phase after Irradiation remains the monoclinic VO2 phase but the films preferential orientation shifts to lower angles due to the presence of disordered regions caused by radiations. Raman spectroscopy measurements also evidences that the VO2 structure is slightly affected by gamma Irradiation. Indeed, increasing the gamma rays dose locally alters the crystalline and electronic structures of the films by modifying the V–V inter-dimer distance, which in turns favours the presence of the VO2 metallic phase. From the XPS measurements of V2p and O1s core level spectra, an oxidation of vanadium from V4+ towards V5+ is revealed. The data also reveal a hydroxylation upon Irradiation which is corroborated by the vanishing of a low oxidation state peak near the Fermi energy in the valence band. Our observations suggest that gamma radiations induce the formation of Frenkel pairs. Moreover, THz transmission measurements show that the long range structure of VO2 remains intact after Irradiation whilst the electrical measurements evidence that the coating resistivity decreases with gamma Irradiation and that their transition temperature is slightly reduced for high gamma ray doses. Even though gamma rays are only one of the sources of radiations that are encountered in space environment, these results are very promising with regards to the potential of integration of such VO2 films as a protective coating for spacecrafts.
Alain Barbu - One of the best experts on this subject based on the ideXlab platform.
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single and dual beam in situ Irradiations of high purity iron in a transmission electron microscope effects of heavy ion Irradiation and helium injection
Acta Materialia, 2014Co-Authors: D Brimbal, B Decamps, J Henry, E Meslin, Alain BarbuAbstract:In order to study the effects of 14 MeV neutron Irradiation on materials used in the first walls of future fusion reactors, high-purity iron was ion-irradiated with and without helium in the JANNuS facility. Thin foils of high-purity iron were dual-beam irradiated in situ in a transmission electron microscope using 1 MeV Fe+ and 15 keV He+ ions. Several important results regarding dislocation loops and helium bubbles were obtained. For example, it was demonstrated that dislocation loops with a0 〈0 1 0〉 type Burgers vectors are glissile and can move and eliminate at the surface of the thin foil at 500 °C. A comparison of Irradiations with and without helium showed that helium atoms reduce the mobility of dislocation loops in pure iron irradiated at 500 °C. Also, we demonstrated that the heterogeneous formation of bubbles inside dislocation loops found previously is also present for helium implantation rates of ∼80 atomic parts per million (appm) He/displacements per atom (dpa).