The magnetoelectrochemical switch

In the field of spintronics, the archetype solid-state two-terminal device is the spin valve, where the resistance is controlled by the magnetization configuration. We show here how this concept of spin-dependent switch can be extended to magnetic electrodes in solution, by magnetic control of their chemical environment. Appropriate nanoscale design allows a huge enhancement of the magnetic force field experienced by paramagnetic molecular species in solutions, which changes between repulsive and attractive on changing the electrodes' magnetic orientations. Specifically, the field gradient force created within a sub-100-nm-sized nanogap separating two magnetic electrodes can be reversed by changing the orientation of the electrodes' magnetization relative to the current flowing between the electrodes. This can result in a breaking or making of an electric nanocontact, with a change of resistance by a factor of up to 103. The results reveal how an external field can impact chemical equilibrium in the vicinity of nanoscale magnetic circuits

Evidence for Multiple Polytypes of Semiconducting Boron Carbide (C\u3csub\u3e2\u3c/sub\u3eB\u3csub\u3e10\u3c/sub\u3e) from Electronic Structure

Boron carbides fabricated via plasma enhanced chemical vapor deposition from different isomeric source compounds with the same C2B10H12 closo-icosa- hedral structure result in materials with very different direct (optical) band gaps. This provides compelling evidence for the existence of multiple polytypes of C2B10 boron carbide and is consistent with electron diffraction results

Etudes in situ des propriétés d'électronique de spin dans des nanocontacts magnétiques fabriqués via une technique Lab-on-chip

Cette thèse est consacrée à l'étude des propriétés électriques dépendent du spin de contacts magnétiques ayant une taille de quelques atomes seulement. Nous avons développé un montage original et sophistiqué permettant de fabriquer et mesurer le transport électrique au travers de ces matériaux nanométriques de tailles ultimes. Les échantillons ont été obtenus par une combinaison de techniques de fabrication 'top-down', avec une construction de type  bottom-up  l'électrochimie pour ramener la distance et la taille a des dimensions atteignant quelques atomes. Une approche de type Iab-on-chip , utilisant le microfluidique , permet de contrôler le flux et la présence de la solution électrolytique. Des contacts de tailles atomique ont été obtenus pour différents matériaux et les propriétés de magnétorésistance ont été systématiquement étudiées pour le Ni. Les mesures ont montré des propriétés d'anisotropie de la magnétorésistance, d'amplitude largement supérieure aux propriétés du bulk Ni. Le tiers des échantillons a montré un changement énorme de la résistance en fonctions de l'orientation du champ magnétique. En étudiant cet effet sous changement de l'environnement chimique de l'échantillon , nous avons pu irrévocablement identifier l'origine de cet effet, étant la présence des ions métalliques paramagnétiques en solution. Ceci éclaire d'un jour nouveau un débat dans la communauté, ayant exclu ce type d'observation en argumentant d'effet mécanique affectant les mesures. Des mesures complémentaires sur les contacts de Pt et sur des échantillons combinant des jonctions à brisure mécanique avec l'électrochimie, confirment le rôle particulier joué par l'environnement chimique.This thesis is dedicated to investigating spin-dependent electrical properties of magnetic contacts of a few atoms. New properties are expected when reducing the size of magnetic contacts down. We developed an original and sophisticated setup for fabricating and measuring electrical transport through such ultimate nano-sized materials. Samples were obtained by a combination of top down technologies related to patterning the initial 2 electrodes, with bottom-up construction, involving electrochemistry to close-up the distance and size down to atomic size values. We used a lab on chip approach, taking advantage of microfluidics to control the flow and presence of the electrolytic solution. This whole setup was inserted into an electromagnet. This allowed fast setting of magnetic field amplitude and orientation, under possible variable temperature environment. Atomic-size junctions were successfully obtained for several materials: Ag, Au , Ni Co, Pt, and magnetoresistance properties of Ni contacts were systematically investigated. Measurements revealed anisotropic magnetoresistance properties, of magnitudes much larger than bulk intrinsic values. One third of the samples exhibited huge change of resistance under applied magnetic field orientation. We unambiguously indentified the paramagnetic metal ions as the origin of this huge eftect. This provides novel insight into a debate in the community that had excluded this observation under the assumption that it is aftected by mechanical artifacts. Investigations on Pt contacts and on samples combining mechanical break junctions and electrochemistry junctions confirmed the peculiar role played by the electrochemical environment

Etudes in situ des propriétés d'électronique de spin dans des nanocontacts magnétiques fabriqués via une technique Lab-on-chip

Cette thèse est consacrée à l'étude des propriétés électriques dépendent du spin de contacts magnétiques ayant une taille de quelques atomes seulement. Nous avons développé un montage original et sophistiqué permettant de fabriquer et mesurer le transportThis thesis is dedicated to investigating spin-dependent electrical properties of magnetic contacts of a few atoms. New properties are expected when reducing the size of magnetic contacts down. We developed an original and sophisticated setup for fabrica

Etudes in situ des propriétés d'électronique de spin dans des nanocontacts magnétiques fabriqués via une technique Lab-on-chip

Cette thèse est consacrée à l'étude des propriétés électriques dépendent du spin de contacts magnétiques ayant une taille de quelques atomes seulement. Nous avons développé un montage original et sophistiqué permettant de fabriquer et mesurer le transport électrique au travers de ces matériaux nanométriques de tailles ultimes. Les échantillons ont été obtenus par une combinaison de techniques de fabrication 'top-down', avec une construction de type bottom-up l'électrochimie pour ramener la distance et la taille a des dimensions atteignant quelques atomes. Une approche de type Iab-on-chip , utilisant le microfluidique , permet de contrôler le flux et la présence de la solution électrolytique. Des contacts de tailles atomique ont été obtenus pour différents matériaux et les propriétés de magnétorésistance ont été systématiquement étudiées pour le Ni. Les mesures ont montré des propriétés d'anisotropie de la magnétorésistance, d'amplitude largement supérieure aux propriétés du bulk Ni. Le tiers des échantillons a montré un changement énorme de la résistance en fonctions de l'orientation du champ magnétique. En étudiant cet effet sous changement de l'environnement chimique de l'échantillon , nous avons pu irrévocablement identifier l'origine de cet effet, étant la présence des ions métalliques paramagnétiques en solution. Ceci éclaire d'un jour nouveau un débat dans la communauté, ayant exclu ce type d'observation en argumentant d'effet mécanique affectant les mesures. Des mesures complémentaires sur les contacts de Pt et sur des échantillons combinant des jonctions à brisure mécanique avec l'électrochimie, confirment le rôle particulier joué par l'environnement chimique.This thesis is dedicated to investigating spin-dependent electrical properties of magnetic contacts of a few atoms. New properties are expected when reducing the size of magnetic contacts down. We developed an original and sophisticated setup for fabricating and measuring electrical transport through such ultimate nano-sized materials. Samples were obtained by a combination of top down technologies related to patterning the initial 2 electrodes, with bottom-up construction, involving electrochemistry to close-up the distance and size down to atomic size values. We used a lab on chip approach, taking advantage of microfluidics to control the flow and presence of the electrolytic solution. This whole setup was inserted into an electromagnet. This allowed fast setting of magnetic field amplitude and orientation, under possible variable temperature environment. Atomic-size junctions were successfully obtained for several materials: Ag, Au , Ni Co, Pt, and magnetoresistance properties of Ni contacts were systematically investigated. Measurements revealed anisotropic magnetoresistance properties, of magnitudes much larger than bulk intrinsic values. One third of the samples exhibited huge change of resistance under applied magnetic field orientation. We unambiguously indentified the paramagnetic metal ions as the origin of this huge eftect. This provides novel insight into a debate in the community that had excluded this observation under the assumption that it is aftected by mechanical artifacts. Investigations on Pt contacts and on samples combining mechanical break junctions and electrochemistry junctions confirmed the peculiar role played by the electrochemical environment.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Mercury and C\u3csub\u3e2\u3c/sub\u3eB\u3csub\u3e10\u3c/sub\u3e Icosahedra Interaction

We contrast the interaction of mercury with adsorbed orthocarborane films and semiconducting (dehydrogenated) boron carbide. Photoemission spectra reveal small shifts in orthocarborane (C2B10H12) molecular orbital binding energies as well as the shift in mercury 5d5/2 shallow core level binding energies, suggesting only small interaction between mercury and the molecular film. Mercury does, however, interact with decomposed orthocarboranes i.e. semiconducting boron carbide

Invisible electronics: Metastable Cu-vacancies chain defects for highly conductive p-type transparent oxide

International audienceNon-stoichiometric copper chromium delafossite has lately attracted a high interest in the community of oxide materials due to its high p-type electrical conductivity and adequate transparency in the visible range. This study reports record electrical conductivity of Cu0.66Cr1.33O2 thin films deposited by chemical vapour deposition and investigates their properties. As-deposited samples show conductivities greater than 100 S cm−1 and carrier concentrations around 1021 cm−3, highest reported value for any non-intrinsically doped delafossite system. A new structural defect consisting in Cu-vacancies chains is identified. This defect, never observed or presumed before, heals upon annealing at 900 °C under argon environment, resulting in an electrical conductivity's reduction of six orders of magnitude. Through a wide-range of structural, chemical and transport measurement techniques, a structure-defect-property correlation of this system is established and the metastability of the non-stoichiometry induced defects is investigated. The possibility of manipulating the defects and carrier concentrations through high-temperature annealing and the outstanding electrical properties associated with the large-scale deposition technique and moderate deposition temperature could be of great technological interest. This material could find important applications as hole injection or extraction layer in all-oxide photovoltaic and light emitting devices

Structural, morphological, and optical properties of Bi2O3 thin films grown by reactive sputtering

Bi2O3 thin films were grown using reactive RF sputtering from a metallic Bi target. The influence of various deposition parameters (substrate temperature, applied power on target and oxygen content in the working gas) on the morphology, structure and optical properties of films was investigated. Depending on the O-2/(Ar + O-2) ratio of the working gas, bismuth, delta-Bi2O3, alpha-Bi2O3 or a mixture of these phases can be deposited, with a narrow window for growth of [111]-oriented delta-Bi2O3 thin films. The delta-Bi2O3 phase is stable from room temperature up to 350 degrees C (in air), where an irreversible transition to alpha-Bi2O3 occurs. This phase transformation is also shown to occur during TEM sample preparation, because of the inherent heating from the ion-milling process, unless liquid -nitrogen cooling is used. (C) 2017 Published by Elsevier B.V.Funding Agencies|Swedish Foundation for Strategic Research (Future Research Leaders 5); Nordforsk [9046]; Nordic Innovation Centre [09046]; European Research Council (ERC) under the European Communitys Seventh Framework Programme (FP)/ERC [335383]; Swedish Research Council (VR) [2012-4430]</p

Ultra-low-energy catalytic degradation of ozone by off-stoichiometric delafossite Cu–Cr–O for highly selective low-temperature solid-state O3 sensors

Off-stoichiometric copper-chromium delafossite featuring giant catalytic degradation of ozone is demonstrated for the very first time. This leads to the reversible low-temperature detection of ozone onto resistive thin-film devices to values as low as 50 ppb. The selectivity when compared with molecular oxygen is also evidenced. Near-Atmospheric Pressure X-Ray Photoelectron Spectroscopy led to the understanding of the ozone - Cu0·66Cr1·33O2 surface reaction. The partial oxidation of copper into Cu2+ dependence on the ozone concentration is for the first time revealed. The apparition of a new peak associated with chemisorbed oxygen proves that the specific sub-stochiometric copper sites of the delafossite phase are driving the efficient and selective catalytic decomposition of ozone into monoatomic oxygen at the neat surface of thin films. The sensing response in ambient air is not limited by ozone decomposition but by the number of available adsorption sites. This work discloses pioneering results for the sensing networks integration of competitive ozone sensors based on Cu0·66Cr1·33O2