Solution-Processable Graphene Oxide as an Efficient Hole Injection Layer for High Luminance Organic Light-Emitting Diodes

The application of solution-processable graphene oxide (GO) as hole injection layer in organic light-emitting diodes (OLEDs) is demonstrated. High luminance of over 53,000 cd m-2 is obtained at only 10 V. The results will unlock a route of applying GO in flexible OLEDs and other electrode applications.Comment: 14 pages, 3 figures, 1 tabl

Magnetism and structure of Ca3Co206 and Ca3Co409 thin films prepared by pulsed laser deposition

Cette thèse porte sur l'étude des propriétés structurales et magnétiques des couches minces de cobaltite de types Ca3C0206 et Ca3C0409 déposées par ablation laser pulsée sur des substrats d'AI20 3(OOl). Ce travail a d'abord consisté en l'élaboration de couches minces polycristallines de Ca3C0206 et épitaxiées de Ca3C0409. En ce qui concerne la cobaltite Ca3C0206, on a pu déterminer la valeur du gap optique et qui est en accord avec les valeurs obtenues par des études théoriques. Le résultat le plus original est qu'on a démontré que les propriétés magnétiques sont très sensibles à la taille des échantillons. On note que les plateaux d'aimantation observés à 2 K dans les couches minces de Ca3C0206 disparaissent pour les couches fines ayant une épaisseur inférieure à 60 nm. Cette disparition des plateaux d'aimantation est accompagnée de l'apparition d'une transition magnétique additionnelle vers 45 K. Nos résultats sont incompatibles avec l'effet tunnel quantique de l'aimantation comme mécanisme à l'origine des plateaux d'aimantation, et soutiennent les prédictions des modèles Monte-Carlo. Quant aux couches minces de Ca3C0409, on a déterminé la nature et l'origine des défauts structuraux qui sont souvent observés par microscopie électronique en transmission. Ces défauts correspondent à la formation de phase parasite de CaC020 4. La formation de cette phase parasite est due à la haute température de dépôt (750°C), à la grande pression appliquée par le substrat d'AI20 3(OOl) (5.5 GPa) à travers les contraintes et à une possible non stoechiométrie locale de la cible. Ces défauts structuraux influencent les propriétés magnétiques, en réduisant le champ coercitif et l'aimantation rémanente par rapport à ceux du Ca3C0409 massif.This thesis focuses on the study of structural and magne tic properties of Ca3C0206 and Ca3C0409 thin films deposited by pulsed laser deposition on Alz03(001) substrates. This work initially involved the elaboration of polycrystalline Ca3C0206 and epitaxial Ca3C0409 thin films. Regarding the Ca3C0206 cobaltite, we were able to determine the value of the optical band gap, which is in agreement with the values obtained by theoretical studies. More interestingly, we have demonstrated that the magnetic properties are very sensitive to sample size. The magnetization plateaus observed at 2 K in Ca3C0206 thin films disappear for thin films with a thickness below 60 nm. This disappearance of the magnetization steps is accompanied by the appearance of an additional magnetic transition around 45 K. Our results are inconsistent with the quantum tunneling of magnetization as a mechanism for the origin of magnetization plateaus, and support more the predictions of Monte Carlo based models. For the Ca3C0409 films, we have determined the nature and the origin of structural defects that are often observed by transmission electron microscopy. These defects are constituted of the CaC020 4 parasitic phase. The formation of this spurious phase is due to the high deposition temperature (750 oC), the high pressure applied by the AI20 3(OOl) substrate (5.5 GPa) and the possibility of a local non-stoichiometry of the target. These structural defects affect the magne tic properties, by reducing the coercivity and remanent magnetization with respect to those of the Ca3C0409 bulk samples

Magnetism and structure of Ca3Co206 and Ca3Co409 thin films prepared by pulsed laser deposition

Cette thèse porte sur l'étude des propriétés structurales et magnétiques des couches minces de cobaltite de types Ca3C0206 et Ca3C0409 déposées par ablation laser pulsée sur des substrats d'AI20 3(OOl). Ce travail a d'abord consisté en l'élaboration de couches minces polycristallines de Ca3C0206 et épitaxiées de Ca3C0409. En ce qui concerne la cobaltite Ca3C0206, on a pu déterminer la valeur du gap optique et qui est en accord avec les valeurs obtenues par des études théoriques. Le résultat le plus original est qu'on a démontré que les propriétés magnétiques sont très sensibles à la taille des échantillons. On note que les plateaux d'aimantation observés à 2 K dans les couches minces de Ca3C0206 disparaissent pour les couches fines ayant une épaisseur inférieure à 60 nm. Cette disparition des plateaux d'aimantation est accompagnée de l'apparition d'une transition magnétique additionnelle vers 45 K. Nos résultats sont incompatibles avec l'effet tunnel quantique de l'aimantation comme mécanisme à l'origine des plateaux d'aimantation, et soutiennent les prédictions des modèles Monte-Carlo. Quant aux couches minces de Ca3C0409, on a déterminé la nature et l'origine des défauts structuraux qui sont souvent observés par microscopie électronique en transmission. Ces défauts correspondent à la formation de phase parasite de CaC020 4. La formation de cette phase parasite est due à la haute température de dépôt (750°C), à la grande pression appliquée par le substrat d'AI20 3(OOl) (5.5 GPa) à travers les contraintes et à une possible non stoechiométrie locale de la cible. Ces défauts structuraux influencent les propriétés magnétiques, en réduisant le champ coercitif et l'aimantation rémanente par rapport à ceux du Ca3C0409 massif.This thesis focuses on the study of structural and magne tic properties of Ca3C0206 and Ca3C0409 thin films deposited by pulsed laser deposition on Alz03(001) substrates. This work initially involved the elaboration of polycrystalline Ca3C0206 and epitaxial Ca3C0409 thin films. Regarding the Ca3C0206 cobaltite, we were able to determine the value of the optical band gap, which is in agreement with the values obtained by theoretical studies. More interestingly, we have demonstrated that the magnetic properties are very sensitive to sample size. The magnetization plateaus observed at 2 K in Ca3C0206 thin films disappear for thin films with a thickness below 60 nm. This disappearance of the magnetization steps is accompanied by the appearance of an additional magnetic transition around 45 K. Our results are inconsistent with the quantum tunneling of magnetization as a mechanism for the origin of magnetization plateaus, and support more the predictions of Monte Carlo based models. For the Ca3C0409 films, we have determined the nature and the origin of structural defects that are often observed by transmission electron microscopy. These defects are constituted of the CaC020 4 parasitic phase. The formation of this spurious phase is due to the high deposition temperature (750 oC), the high pressure applied by the AI20 3(OOl) substrate (5.5 GPa) and the possibility of a local non-stoichiometry of the target. These structural defects affect the magne tic properties, by reducing the coercivity and remanent magnetization with respect to those of the Ca3C0409 bulk samples

Magnetism and structure of Ca3Co206 and Ca3Co409 thin films prepared by pulsed laser deposition

Cette thèse porte sur l'étude des propriétés structurales et magnétiques des couches minces de cobaltite de types Ca3C0206 et Ca3C0409 déposées par ablation laser pulsée sur des substrats d'AI20 3(OOl). Ce travail a d'abord consisté en l'élaboration de coThis thesis focuses on the study of structural and magne tic properties of Ca3C0206 and Ca3C0409 thin films deposited by pulsed laser deposition on Alz03(001) substrates. This work initially involved the elaboration of polycrystalline Ca3C0206 and epitax

Magnetostrictive properties of amorphous SmCo thin films with imprinted anisotropy

We examine the magnetostriction in amorphous SmCo thin films with a composition in the range 4-27 at.% Sm. The magnetostriction increases significantly with increasing Sm content but is small compared to terbium-based ferromagnetic compounds, despite the large imprinted anisotropy. The magnetostriction and anisotropy both increase approximately linearly as the temperature is reduced. The magnetoelastic energy is found to be far smaller than the anisotropy energy so the magnetoelastic atomic displacements during growth cannot be the origin of the imprinted anisotropy. The anisotropy is only slightly altered by the application of large tensile stresses, indicating that the local strain fields involved in magnetostriction are not equivalent to the global strain produced by mechanical bending

Giant magnetic domains in amorphous SmCo thin films

The potential for tuning of magnetic properties and the exceptional uniformity are among the features that make amorphous magnetic materials attractive for technology. Here it is shown that the magnetization reversal in amorphous SmCo thin films takes place through the formation of giant magnetic domains, over a centimeter across. The domain structure is found to be dictated by the direction of the imprinted in-plane easy axis and the film boundaries. This is a consequence of the size of the anisotropy and the structural uniformity of the films, which also allows the movement of millimeter-long domain walls over distances of several millimeters. The results demonstrate the possibility of tailoring the magnetic domain structure in amorphous magnets over a wide range of length scales, up to centimeters. Moreover, they highlight an important consequence of the structural perfection of amorphous films

Thickness-dependent optical band gap in one-dimensional Ca3Co2O6 nanometric films

Recent studies on the physical properties of Ca3CO2O6 nanometric samples have shown that their properties are significantly different from those of the bulk samples. The origin of this change is not trivial. We have carried out optical measurements on Ca3CO2O6 thin films with different thicknesses in order to characterize their electronic structure using optical spectroscopy measurements. The absorption spectra show a dependence on the film thickness that is correlated to the grain size in the polycrystalline layers. We found that the optical band gap increases from 1.3 to 1.55 eV when the thickness changes from 35 to 100 nm. The change in the band gap evolution with the film thickness is discussed in terms of both the amorphous effect and the grain size in the Ca3CO2O6 thin films. Finally, we show that these results are consistent with recent measurements concerning magnetic and electrical properties of Ca3Co2O6 nanometric samples. (C) 2011 Elsevier B.V. All rights reserved

Soft Room-Temperature Ferromagnetism of Carbon-Implanted Amorphous Fe93Zr7 Films

We report on the effect of carbon implantation on the structural, electronic, and magnetic properties of Fe93Zr7 (FeZr) amorphous films. Extended X-ray absorption fine structure measurements on (FeZr)(100-x)C-x (x = 0, 5.5, and 11) indicate the incorporation of carbon in the FeZr matrix, with an increase of the Fe-Fe distance by implanting carbon. X-ray photoelectron spectroscopy measurements reveal the creation of Fe-C bonds after implantation. A significant enhancement of the Curie temperature and decrease of the coercivity are observed in the carbon-implanted films. Moreover, the non collinear ferromagnetism of the as-grown FeZr film diminishes upon carbon implantation. (c) 2013 The Japan Society of Applied Physic