Galvanomagnetic properties and noise in a barely metallic film of V2O3

We have measured the magnetotransport properties of a strained metallic V2O3 thin film. Most of the properties are similar to V2O3 single crystals that have been submitted to a large pressure. In addition, resistance noise analysis indicates that conductivity fluctuations are freezing out at T\approx 10K. Examination of a range of measurements leads to the conclusion that spins-configuration fluctuations dominate in the low temperature regime.Comment: accepted for publication in Phys Rev

Examining Different Regimes of Ionization-Induced Damage in GaN Through Atomistic Simulations

Peer reviewe

Swift heavy ion-irradiated multi-phase calcium borosilicates: implications to molybdenum incorporation, microstructure, and network topology

Abstract: A series of calcium borosilicate glasses with varying [B2O3], [MoO3], and [CaO] were prepared and subjected to 92 MeV Xe ions used to simulate the damage from long-term α-decay in nuclear waste glasses. Modifications to the solubility of molybdenum, the microstructure of separated phases, and the Si–O–B network topology were investigated following five irradiation experiments that achieved doses between 5 × 1012 and 1.8 × 1014 Xe ions/cm2 in order to test the hypotheses of whether irradiation would induce, propagate, or anneal phase separation. Using electron microscopy, EDS analysis, Raman spectroscopy, and XRD, irradiation was observed to increase the integration of MoO42− by increasing the structural disorder within and between heterogeneous amorphous phases. This occurred through Si/B-O-Si/B bond breakage and reformation of boroxyl and 3/4-membered SiO4 rings. De-mixing of the Si–O–B network concurrently enabled cross directional Ca and Mo diffusion along defect created pathways, which were prevalent along the interface between phases. The initiation and extent of these changes was dependent primarily on the [SiO2]/[B2O3] ratio, with [MoO3] having a secondary effect on influencing the defect population with increasing dose. Microstructurally, these changes to bonding caused a reduction in heterogeneities between amorphous phases by reducing the size and increasing the spatial distribution of immiscible droplets. This general increase in structural disorder prevented crystallization in most cases, but where precipitation was initiated by radiation, it was re-amorphized with increasing dose. These outcomes suggest that internal radiation can alter phase separation tie lines, and can therefore be used as a tool to design certain structural environments for long-term encapsulation of radioisotopes

Unravelling the secrets of the resistance of GaN to strongly ionising radiation

GaN is the most promising upgrade to the traditional Si-based radiation-hard technologies. However, the underlying mechanisms driving its resistance are unclear, especially for strongly ionising radiation. Here, we use swift heavy ions to show that a strong recrystallisation effect induced by the ions is the key mechanism behind the observed resistance. We use atomistic simulations to examine and predict the damage evolution. These show that the recrystallisation lowers the expected damage levels significantly and has strong implications when studying high fluences for which numerous overlaps occur. Moreover, the simulations reveal structures such as point and extended defects, density gradients and voids with excellent agreement between simulation and experiment. We expect that the developed modelling scheme will contribute to improving the design and test of future radiation-resistant GaN-based devices. Gallium nitride is a wide bandgap semiconductor which is generally expected to replace some silicon-based technologies, despite some of its properties still requiring further investigation. Here, using a two-temperature model coupled to molecular dynamics simulations, the authors investigate and predict the effects of strongly ionising radiation in gallium nitride, revealing the mechanism behind its unusual resistance to radiation.Peer reviewe

Discovery of a maximum damage structure for Xe-irradiated borosilicate glass ceramics containing powellite

In order to increase the waste loading efficiency in nuclear waste glasses, alternate glass ceramic (GC) materials are sought that trap problematic molybdenum in a water-durable CaMoO4 phase within a borosilicate glass matrix. In order to test the radiation resistance of these candidate wasteforms, accelerated external radiation can be employed to replicate long-term damage. In this study, several glasses and GCs were synthesized with up to 10 mol% MoO3 and subjected to 92 MeV Xe ions with fluences ranging between 5 × 1012 to 1.8 × 1014 ions/cm2. The main mechanisms of modification following irradiation involve: (i) thermal and defect-assisted diffusion, (ii) relaxation from the ion's added energy, (iii) localized damage recovery from overlapping ion tracks, and (iv) the accumulation of point defects or the formation of voids that created significant strain and led to longer-range modifications. Most significantly, a saturation in alteration could be detected for fluences greater than 4 × 1013 ions/cm2, which represents an average structure that is representative of the maximum damage state from these competing mechanisms. The results from this study can therefore be used for long-term structural projections in the development of more complex GCs for nuclear waste applications

Exploring swift-heavy ion irradiation of InGaN/GaN multiple quantum wells for green-emitters: the use of Raman and photoluminescence to assess the irradiation effects on the optical and structural properties

N/

Etude multi-échelle de la transition métal-isolant de films minces du composé V2O3

Vanadium oxide V2O3, which is the prototype of strongly correlated electron systems, is isostructural to corundum α-Al2O3 and has a metallic paramagnetic phase at room temperature. Below 150K, a first-order metal-to-insulator transition is observed, and associated to a magnetic and structural transition. The objective of this thesis consists to grow and to characterize the structural and physical properties of V2O3 thin films, prepared by the pulsed laser deposition technique, on sapphire substrates (0001-Al2O3). The influence of the strains induced by the substrate and the thickness, upon the properties, was particularly studied. To achieve this goal, a multiscale study of the structure and the electronic transport properties was carried out. While preserving the R-3c structure of the bulk compound, it appears that the strains modify strongly the electrical behaviour of V2O3. The results highlight a surprising evolution with a critical thickness of 220Å. Consequently, the incompressible thick films are metallic on the whole range of temperature and the metal-to-insulator transition observed in bulk material is suppressed. On contrary, the very thin films exhibit a metal-to-insulator transition below 150K, as seen in the bulk. Using measurements on microbridges, we shown that a mesoscopic phase separation, can be used to explain the origin of the macroscopic evolution of the resistivity, and also its qualitative thickness-dependence.L'oxyde de vanadium V2O3, qui est le prototype des systèmes fortement corrélés, isostructural du corindon α-Al2O3, possède une phase métallique paramagnétique à la température ambiante. En dessous de 150K, une transition métal-isolant du premier ordre est observée et, est associée à une transition magnétique et structurale. L'objectif de ce travail de thèse consiste à synthétiser et à caractériser du point de vue structural et physique des films minces du composé V2O3, déposés par ablation laser pulsé, sur des substrats de saphir (0001-Al2O3). L'influence de la contrainte induite par le substrat et l'épaisseur, sur les propriétés du matériau a été particulièrement étudiée. Pour cela, une étude multi-échelle de la structure et des propriétés de transport électronique a été réalisée. Tout en conservant la structure R-3c du composé massif, il apparaît que les contraintes modifient fortement le comportement électrique de V2O3. Les résultats mettent en évidence une évolution surprenante autour de l'épaisseur critique 220Å. Ainsi, les films épais incompressibles, sont métalliques sur toute la gamme de température et la transition métal-isolant du composé massif est supprimée. En revanche, les films fins présentent une transition métal-isolant, comme le composé massif, en dessous de 150K. Grâce à des mesures sur des microponts, nous avons montré qu'une séparation de phases mésoscopiques permet d'expliquer l'origine de l'évolution macroscopique de la résistivité, ainsi que de la dépendance qualitative en épaisseur

Etude multi-échelle de la transition métal-isolant de films minces du composé V2O3

Vanadium oxide V2O3, which is the prototype of strongly correlated electron systems, is isostructural to corundum α-Al2O3 and has a metallic paramagnetic phase at room temperature. Below 150K, a first-order metal-to-insulator transition is observed, and associated to a magnetic and structural transition. The objective of this thesis consists to grow and to characterize the structural and physical properties of V2O3 thin films, prepared by the pulsed laser deposition technique, on sapphire substrates (0001-Al2O3). The influence of the strains induced by the substrate and the thickness, upon the properties, was particularly studied. To achieve this goal, a multiscale study of the structure and the electronic transport properties was carried out. While preserving the R-3c structure of the bulk compound, it appears that the strains modify strongly the electrical behaviour of V2O3. The results highlight a surprising evolution with a critical thickness of 220Å. Consequently, the incompressible thick films are metallic on the whole range of temperature and the metal-to-insulator transition observed in bulk material is suppressed. On contrary, the very thin films exhibit a metal-to-insulator transition below 150K, as seen in the bulk. Using measurements on microbridges, we shown that a mesoscopic phase separation, can be used to explain the origin of the macroscopic evolution of the resistivity, and also its qualitative thickness-dependence.L'oxyde de vanadium V2O3, qui est le prototype des systèmes fortement corrélés, isostructural du corindon α-Al2O3, possède une phase métallique paramagnétique à la température ambiante. En dessous de 150K, une transition métal-isolant du premier ordre est observée et, est associée à une transition magnétique et structurale. L'objectif de ce travail de thèse consiste à synthétiser et à caractériser du point de vue structural et physique des films minces du composé V2O3, déposés par ablation laser pulsé, sur des substrats de saphir (0001-Al2O3). L'influence de la contrainte induite par le substrat et l'épaisseur, sur les propriétés du matériau a été particulièrement étudiée. Pour cela, une étude multi-échelle de la structure et des propriétés de transport électronique a été réalisée. Tout en conservant la structure R-3c du composé massif, il apparaît que les contraintes modifient fortement le comportement électrique de V2O3. Les résultats mettent en évidence une évolution surprenante autour de l'épaisseur critique 220Å. Ainsi, les films épais incompressibles, sont métalliques sur toute la gamme de température et la transition métal-isolant du composé massif est supprimée. En revanche, les films fins présentent une transition métal-isolant, comme le composé massif, en dessous de 150K. Grâce à des mesures sur des microponts, nous avons montré qu'une séparation de phases mésoscopiques permet d'expliquer l'origine de l'évolution macroscopique de la résistivité, ainsi que de la dépendance qualitative en épaisseur

Etude multi-échelle de la transition métal-isolant de films minces du composé V2O3

L oxyde de vanadium V2O3, qui est le prototype des systèmes fortement corrélés, isostructural du corindon a-Al2O3, possède une phase métallique paramagnétique à la température ambiante. En dessous de 150K, une transition métal-isolant du premier ordre est observée et, associée à une transition magnétique et structurale.L objectif de ce travail de thèse consiste à synthétiser et à caractériser du point de vue structural et physique des films minces du composé V2O3, déposés par ablation laser pulsé, sur des substrats de saphir (0001-Al2O3). L influence de la contrainte induite par le substrat et l épaisseur, sur les propriétés du matériau a été particulièrement étudiée. Pour cela, une étude multi-échelle de la structure et des propriétés de transport électronique a été réalisée. Tout en conservant la structure R-3c du composé massif, il apparaît que les contraintes modifient fortement le comportement électrique de V2O3. Les résultats mettent en évidence une évolution surprenante autour de l épaisseur critique 220Å. Ainsi, les films épais incompressibles, sont métalliques sur toute la gamme de température et la transition métal-isolant du composé massif est supprimée. En revanche, les films fins présentent une transition métal-isolant, comme le composé massif, en dessous de 150K. Grâce à des mesures sur des microponts, nous avons montré qu une séparation de phases mésoscopiques permet d expliquer l origine de l évolution macroscopique de la résistivité, ainsi que de la dépendance qualitative en épaisseur.Vanadium oxide V2O3, which is the prototype of strongly correlated electron systems, is isostructural to corundum a-Al2O3 and has a metallic paramagnetic phase at room temperature. Below 150K, a first-order metal-to-insulator transition is observed, and associated to a magnetic and structural transition.The objective of this thesis consists to grow and to characterize the structural and physical properties of V2O3 thin films, prepared by the pulsed laser deposition technique, on sapphire substrates (0001-Al2O3). The influence of the strains induced by the substrate and the thickness, upon the properties, was particularly studied. To achieve this goal, a multiscale study of the structure and the electronic transport properties was carried out. While preserving the R-3c structure of the bulk compound, it appears that the strains modify strongly the electrical behaviour of V2O3. The results highlight a surprising evolution with a critical thickness of 220Å. Consequently, the incompressible thick films are metallic on the whole range of temperature and the metal-to-insulator transition observed in bulk material is suppressed. On contrary, the very thin films exhibit a metal-to-insulator transition below 150K, as seen in the bulk. Using measurements on microbridges, we showed that a mesoscopic phase separation can be used to explain the origin of the macroscopic evolution of the resistivity, and also its qualitative thickness-dependenceCAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Galvanomagnetic properties and noise in a barely metallic film of V2O3

International audienceWe have measured the magnetotransport properties of a strained metallic V2O3 thin film. Most of the properties are similar to V2O3 single crystals that have been submitted to a large pressure. In addition, the resistance noise analysis indicates that conductivity fluctuations are freezing out at T approximate to 10 K. Examination of a range of measurements leads to the conclusion that spins-configuration fluctuations dominate in the low-temperature regime