arXiv subjects

Arnaud le Febvrier

Publications and source records attributed to Arnaud le Febvrier.

At least 19 recordsLinked to original sources

arXiv2026

A single platform with van der Pauw geometry for measurement of Seebeck coefficient, resistivity, and Hall effect of thin films

A modular thermoelectric properties measurement setup in van der Pauw configuration was developed for a straightforward and simultaneous measurement of electrical resistivity and Seebeck coefficient in an extensive temperature range of 25°C - 600°C and can also perform Hall measurements at room temperature. The setup is optimized for accurate measurement of voltages and temperatures gradients by minimizing possible errors from offset voltages, wire contributions and thermal contact resistances which helps getting reliable data. The setup is user friendly, and the measurements are fully automated and controlled using a LabVIEW program. The detachable modules make this setup quite versatile and provide an all-in-one (except thermal conductivity) solution for thermoelectric measurements.

physics.ins-det↗

arXiv2026

Atomistic mechanism and interface-structure-energetics of van der Waals epitaxy demonstrated by layered alpha-MoO3 growth on mica

Unlike conventional epitaxy, van der Waals epitaxy (vdWE) allows nearly stress-free growth of thick films with highly oriented crystals without dislocations even for large film-substrate lattice mismatches. Despite reports of vdWE in numerous materials systems, an atomistic understanding of film/substrate interface structure that explains and predicts vdWE has remained elusive. Here, we address this knowledge gap by unveiling atomistic interface mechanisms for vdWE of alpha-MoO3(0k0) on mica(001). X-ray diffraction and electron microscopy reveal alpha-MoO3(0k0) epilayers with large columnar crystals in three non-equivalent in-plane orientations. These results, together with negligible strain buildup in continuous epilayers, confirm vdWE. Ab initio computations showing interface energy minima for these orientations correlate with high cross-interface proximity between Mo atoms in alpha-MoO3 and K in mica conducive for maximal vdW attraction. These atomistic insights on interface structure and energetics provide a crucial framework for predicting vdWE for different film/substrate combinations and designing of stress-free and/or standalone epitaxial films of layered materials such as MoO3 on layered substrates such as f-mica.

cond-mat.mtrl-sci↗

arXiv2026

Questioning van der Waals Epitaxy of Non-Layered Materials on Mica: The Case of ScN

Growing stress-free epitaxial films by van der Waals epitaxy (vdWE) is of interest for realizing flexible optoelectronics and energy devices from freestanding epilayers. However, vdWE of non-layered materials is often presumed or claimed on layered substrates such as mica with inadequate experimental evidence. Here, we demonstrate that the growth of single-domain rocksalt ScN(111) films by sputter deposition on fluorophlogopite mica(001) occurs by conventional epitaxy. X-ray diffraction and electron microscopy reveal the film/substrate epitaxial relationship to be [-101](111)ScN||[010](001)mica. Our results indicating strain buildup seen from the dependence of (111) interplanar spacings, and strain relaxation by dislocation generation, question prior claims of vdWE of non-layered metal nitrides on mica. Our findings show that conventional epitaxy should be the default assumption for non-layered materials unless conditions for vdWE are explicitly established.

cond-mat.mtrl-sci↗

arXiv2026

Damage accumulation induced metal-insulator transition through ion implantation of ScN thin films

Ion implantation is a powerful approach for tuning the electrical properties of materials through controlled doping and defect engineering, with applications in thermoelectrics and microelectronics. Scandium nitride (ScN) is particularly sensitive to irradiation-induced disorder, with transport properties spanning several orders of magnitude and multiple conduction mechanisms involved. In this study, we investigate the evolution of electrical transport in epitaxial ScN thin films undergoing accumulated irradiation damage at an initial defect state. A phenomenological damage-accumulation model was successfully combined with temperature dependent resistivity and Hall effect measurements to elucidate the impact of defect buildup on electrical transport and to provide physically grounded, quantitative insight into the nature and accumulation of irradiation-induced defects. It reveals two distinct defects-generation regimes of electrically active defects. At low doses, direct-impact damage produces stable and isolated acceptor-type complex defects, (VSc-X) with VSc a scandium vacancy and X denoting residual impurities, leading to a gradual increase in resistivity. At higher doses, defect accumulation dominates through a multi-hit process, giving rise to point-defect buildup and carrier localization, resulting in hopping-dominated transport. This localized regime is thermally unstable and recovers upon low-temperature annealing. We further demonstrate that the residual defect landscape strongly influences both the critical dose for the metal-insulator transition and the localization strength: films grown on Al2O3 exhibit an earlier transition and weaker localization than those grown on MgO. These results highlight ion implantation as an effective route for engineering disorder-induced localization in ScN, with the initial film quality playing a decisive role.

cond-mat.mtrl-sci↗

arXiv2025

Robust Superconductivity and High Upper Critical Fields in Epitaxial cubic W2N Thin Films

Transition Metal Nitrides are a versatile class of materials, combining chemical robustness, high hardness, and superconducting behaviour with critical temperatures between 2 to 10 K. While several binary TMNs have been explored, superconductivity in stoichiometric W2N has remained largely unexplored. Here, we report on superconducting thin films of stoichiometric W2N, demonstrating a distinctly high upper critical field of 8.5 T, uncommon among binary TMNs. This robust superconducting response under high magnetic fields highlights the technological relevance of W2N for integrated quantum and cryogenic electronic platforms. Overall, these results position stoichiometric W2N as a promising addition to the TMN superconducting landscape, opening new avenues for functional materials design based on chemically stable and mechanically resilient nitrides.

cond-mat.supr-con↗

arXiv2025

Lattice Mismatch Driven In Plane Strain Engineering for Enhanced Upper Critical Fields in Mo2N Superconducting Thin Films

Transition metal nitrides are a fascinating class of hard coating material that provide an excellent platform for investigating superconductivity and fundamental electron phonon interactions. In this work the structural morphological and superconducting properties have been studied for Mo2N thin films deposited via direct current magnetron sputtering on cplane Al2O3 and MgO substrates to elucidate the effect of internal strain on superconducting properties. High resolution X Ray diffraction and time of flight elastic recoil detection analysis confirms the growth of single phase Mo2N thin films exhibiting epitaxial growth with twin domain structure. Low temperature electrical transport measurements reveal superconducting transitions at 5.2 K and 5.6 K with corresponding upper critical fields of 5 T and 7 T for the films deposited on Al2O3 and MgO, respectively. These results indicate strong type II superconductivity and the observed differences in superconducting properties are attributed to substrate induced strain which leads to higher e ph coupling for the film on MgO substrate. These findings highlight the tunability of superconducting properties in Mo2N films through strategic substrate selection.

cond-mat.supr-con↗

arXiv2025

Phase selection and texturing in molybdenum oxide films grown by reactive magnetron sputtering

Molybdenum oxide films offer a rich variety of properties for diverse applications, but exclusive synthesis of desired phases is a major challenge. Here, we demonstrate that oxygen flow ratio fO2 = [O2]/[Ar+O2] is crucial not only for phase selection of non-layered monoclinic MoO2 and layered orthorhombic alpha-MoO3 but also for controlling grain size and preferred orientation. Both mica and sapphire support exclusive MoO2 formation in the 0.15 < fO2 < 0.25 window at deposition temperatures Tdep = 400 and 500 degree C and alpha-MoO3 formation in the 0.35 < fO2 < 0.5 window at 400 degree C. Within fO2 windows favoring exclusive phase formation, high fO2 fosters large grains with out-of-plane 0k0 texture, except for MoO2 films on c-sapphire that show no systematic trends. These findings provide a framework for rational synthesis of phase-pure monoclinic MoO2 and orthorhombic MoO3 with control over texture and microstructure to access desired properties.

cond-mat.mtrl-sci↗

arXiv2025

Electron-phonon interactions and tensor analysis in topological insulator bismuth telluride using angle resolved polarized Raman spectroscopy

We report on the angle-resolved polarized Raman spectroscopy and estimation of the Raman tensor elements using both classical and quantum treatments to analyse the polarized Raman spectra of single crystal Bismuth Telluride. The observed polar patterns and systematic variations in the relative intensities of four characteristic Raman active modes indicate a higher differential polarizability along the c-axis, accompanied by anisotropic photon-phonon interactions. This interplay of electron-photon-phonon interactions is crucial for understanding the lattice dynamics of Bismuth Telluride, which underpin its thermoelectric performance and topological properties.

cond-mat.mtrl-sci↗

arXiv2024

Effects of W alloying on the electronic structure, phase stability and thermoelectric power factor in epitaxial CrN thin films

CrN-based alloy thin films are of interest as thermoelectric materials for energy harvesting. Ab initio calculations show that dilute alloying of CrN with 3 at.% W substituting Cr, induce flat electronic bands and push the Fermi level EF into the conduction band, while retaining dispersive Cr 3d bands. These features are conducive for both high electrical conductivity σand high Seebeck coefficient α, and hence the thermoelectric power factor α^2σ. To investigate this possibility, epitaxial CrWxNz films were grown on c-plane sapphire by dc-magnetron sputtering. However, even films with the lowest W concentration (x = 0.03) in our study contained metallic h-Cr2N, which is not conducive for a high α. Nevertheless, the films exhibit a sizeable power factor of α^2σ~ 4.7 x 10-4 Wm-1K-2 due to high σ~ 700 Scm-1, and a moderate α~ -25 ~{^^^^00b5}V/K. Increasing h-Cr2N fractions in the 0.03 < x \le 0.19 range monotonically increases σ, but severely diminishes αleading to two orders of magnitude decrease in α^2σ. This trend continues with x > 0.19 due to W precipitation. These findings indicate that dilute W additions below its solubility limit in CrN is important for realizing high thermoelectric power factor in CrWxNz alloy films.

cond-mat.mtrl-sci↗

arXiv2024

Electronic structure and thermoelectric properties of epitaxial Sc1-xVxNy thin films grown on MgO(001)

The electronic structure of Sc1-xVxNy epitaxial films with different alloying concentrations of V are investigated with respect to effects on thermoelectric properties. Band structure calculations on Sc0.75V0.25N indicate that V 3d states lie in the band gap of the parent ScN compound in the vicinity of the Fermi level. Thus, theoretically the presence of light (dispersive) bands at the Γ-point with band multiplicity is expected to lead to lower electrical resistivity while flat (heavy) bands at X-W-K symmetry points are associated with higher Seebeck coefficient than that of ScN. With this aim, epitaxial Sc1-xVxNy thin film samples were deposited on MgO(001) substrates. All the samples showed N substoichiometry and pseudocubic crystal structure. The N-vacancy-induced states were visible in the Sc 2p XAS spectra. The reference ScN and Sc1-xVxNy samples up to x = 0.12 were n type, exhibiting carrier concentration of 1021 cm-3, typical for degenerate semiconductors. For the highest V alloying of x = 0.15, holes became the majority charge carrier as indicated by the positive Seebeck coefficient. The underlying electronic structure and bonding mechanism in Sc1-xVxNy influence the electrical resistivity, Seebeck coefficient, and Hall effect. Thus, the work contributes to the fundamental understanding of the correlated defects and thermoelectric properties to the electronic structure in Sc-N system with V alloying.

cond-mat.mtrl-sci↗

arXiv2024

Enhanced Thermoelectric Properties By Embedding Fe Nanoparticles Into CrN Films For Energy Harvesting Applications

Nanostructured materials and nanocomposites have shown great promise for improving the efficiency of thermoelectric materials. Herein, Fe nanoparticles were imbedded into a CrN matrix by combining two physical vapor deposition approaches, namely high-power impulse magnetron sputtering and a nanoparticle gun. The combination of these techniques allowed the formation of nanocomposites in which the Fe nanoparticles remained intact without intermixing with the matrix. The electrical and thermal transport properties of the nanocomposites were investigated and compared to a monolithic CrN film. The measured thermoelectric properties revealed an increase in the Seebeck coefficient, with a decrease of hall carrier concentration and an increase of the electron mobility which could be explained by energy filtering by internal phases created at the NP/matrix interface. The thermal conductivity of the final nanocomposite was reduced from 4.8 W m-1K-1 to a minimum of 3.0 W m-1K-1 W. This study shows prospects for the nanocomposite synthesis process using nanoparticles and its use in improving the thermoelectric properties of coatings.

cond-mat.mtrl-sci↗

arXiv2023

Thermoelectric properties and electronic structure of Cr(Mo,V)Nx thin films studied by synchrotron and lab-based X-ray spectroscopy

Chromium-based nitrides are used in hard, resilient coatings, and show promise for thermoelectric applications due to their combination of structural, thermal, and electronic properties. Here, we investigated the electronic structures and chemical bonding correlated to the thermoelectric properties of epitaxially grown chromium-based multicomponent nitride Cr(Mo,V)Nx thin films. Due to minuscule N vacancies, finite population of Cr 3d and N 2p states appear at the Fermi level and diminishes the band opening for Cr0.51N0.49. Incorporating holes by alloying V in N deficient CrN matrix results in enhanced thermoelectric power factor with marginal change in the charge transfer of Cr to N compared to Cr0.51N0.49. Further alloying Mo isoelectronic to Cr increases the density of states across the Fermi level due to hybridization of the (Cr, V) 3d and Mo 4d-N 2p states in Cr(Mo,V)Nx. The hybridization effect with reduced N 2p states off from stoichiometry drives the system towards metal like electrical resistivity and reduction in Seebeck coefficient compensating the overall power factor still comparable to Cr0.51N0.49. The N deficiency also depicts a critical role in reduction of the charge transfer from metal to N site. The present work envisages ways for enhancing thermoelectric properties through electronic band engineering by alloying and competing effects of N vacancies.

cond-mat.mtrl-sci↗

arXiv2023

Valence electron concentration- and N vacancy-induced elasticity in cubic early transition metal nitrides

Motivated by frequently reported deviations from stoichiometry in cubic transition metal nitride (TMNx) thin films, the effect of N-vacancy concentration on the elastic properties of cubic TiNx, ZrNx, VNx, NbNx, and MoNx (0.72<x<1.00) is systematically studied by density functional theory (DFT) calculations. The predictions are validated experimentally for VNx (0.77<x<0.97). The DFT results indicate that the elastic behavior of the TMNx depends on both the N-vacancy concentration and the valence electron concentration (VEC) of the transition metal: While TiNx and ZrNx exhibit vacancy-induced reductions in elastic modulus, VNx and NbNx show an increase. These trends can be rationalized by considering vacancy-induced changes in elastic anisotropy and bonding. While introduction of N-vacancies in TiNx results in a significant reduction of elastic modulus along all directions and a lower average bond strength of Ti-N, the vacancy-induced reduction in [001] direction of VNx is overcompensated by the higher stiffness along [011] and [111] directions, resulting in a higher average bond strength of V-N. To validate the predicted vacancy-induced changes in elasticity experimentally, close-to-single-crystal VNx (0.77<x<0.97) are grown on MgO(001) substrates. As the N-content is reduced, the relaxed lattice parameter a0, as probed by X-ray diffraction, decreases from 4.128 A to 4.096 A. This reduction in lattice parameter is accompanied by an anomalous 11% increase in elastic modulus, as determined by nanoindentation. As the experimental data agree with the predictions, the elasticity enhancement in VNx upon N-vacancy formation can be understood based on the concomitant changes in elastic anisotropy and bonding.

cond-mat.mtrl-sci↗

arXiv2022

Phase formation in CrFeCoNi nitride thin films

As a single-phase alloy, CrFeCoNi is a face centered cubic (fcc) material related to the archetypical high-entropy Cantor alloy CrFeCoNiMn. For thin films, CrFeCoNi of approximately equimolar composition tends to assume an fcc structure when grown at room temperature by magnetron sputtering. However, the single-phase solid solution state is typically not achieved for thin films grown at higher temperatures. The same holds true for Cantor alloy-based ceramics (nitrides and oxides), where phase formation is extremely sensitive to process parameters such as the amount of reactive gas. This study combines theoretical and experimental methods to understand the phase formation in nitrogen-containing CrFeCoNi thin films. Density functional theory calculations considering three competing phases (CrN, Fe-Ni and Co) show that the free energy of mixing, delta G of (CrFeCoNi)1-xNx solid solutions has a maximum at x = 0.20-0.25, and delta G becomes lower when x less than 0.20, greater than 0.25. Thin films of (CrFeCoNi)1-xNx (x = 0.14-0.41) grown by magnetron sputtering show stabilization of the metallic fcc when x lesser than or equal to 0.22 and the stabilization of the NaCl B1 structure when x is greater than 0.33, consistent with the theoretical prediction. In contrast, films with intermediate amounts of nitrogen (x = 0.22) grown at higher temperatures show segregation into multiple phases of CrN, Fe-Ni-rich and Co. These results offer an explanation for the requirement of kinetically limited growth conditions at low temperature for obtaining single-phase CrFeCoNi Cantor-like nitrogen-containing thin films and are of importance for understanding the phase-formation mechanisms in multicomponent ceramics.

cond-mat.mtrl-sci↗

arXiv2022

Solid-state Janus nanoprecipitation enables amorphous-like heat conduction in crystalline Mg3Sb2-based thermoelectric materials

Solid-state precipitation can be used to tailor materials properties, ranging from ferromagnets and catalysts to mechanical strengthening and energy storage. Thermoelectric properties can be modified by precipitation to enhance phonon scattering while retaining charge-carrier transmission. Here, we uncover unconventional dual Janus-type nanoprecipitates in Mg3Sb1.5Bi0.5 formed by side-by-side Bi- and Ge-rich appendages, in contrast to separate nanoprecipitate formation. These Janus nanoprecipitates result from local co-melting of Bi and Ge during sintering, enabling an amorphous-like lattice thermal conductivity. A precipitate size effect on phonon scattering is observed due to the balance between alloy-disorder and nanoprecipitate scattering. The thermoelectric figure-of-merit ZT reaches 0.6 near room temperature and 1.6 at 773 K. The Janus nanoprecipitation can be introduced into other materials and may act as a general property-tailoring mechanism.

cond-mat.mtrl-sci↗

arXiv2022

P-type behavior of CrN thin films by control of point defects

We report the results of a combined experimental and theoretical study on nonstoichiometric CrN1+d thin films grown by reactive magnetron sputtering on c-plane sapphire, MgO (100) and LaAlO3 (100) substrates in a Ar/N2 gas mixture using different percentage of N2. There is a transition from n-type to p-type behavior in the layers as a function of nitrogen concentration varying from 48 at. % to 52 at. % in CrN films. The compositional change follows a similar trend for all substrates, with a N/Cr ratio increasing from approximately 0.7 to 1.06-1.10 by increasing percentage of N2 in the gas flow ratio. As a result of the change in stoichiometry, the lattice parameter and the Seebeck coefficient increase together with the increase of N in CrN1+d; in particular, the Seebeck value coefficient transitions from -50 uV.K-1 for CrN0.97 to +75 uV.K-1 for CrN1.1. Density functional theory calculations show that Cr vacancies can account for the change in Seebeck coefficient, since they push the Fermi level down in the valence band, whereas N interstitial defects in the form of N2 dumbbells are needed to explain the increasing lattice parameter. Calculations including both types of defects, which have a strong tendency to bind together, reveal a slight increase in the lattice parameter and a simultaneous formation of holes in the valence band. To explain the experimental trends, we argue that both Cr vacancies and N2 dumbbells, possibly in combined configurations, are present in the films. We demonstrate the possibility of controlling the semiconducting behavior of CrN with intrinsic defects from n- to p-type, opening possibilities to integrate this compound in energy-harvesting thermoelectric devices.

cond-mat.mtrl-sci↗

arXiv2021

An upgraded ultra-high vacuum magnetron-sputtering system for high-versatility and software-controlled deposition

Magnetron sputtering is a widely used physical vapor deposition technique. Reactive sputtering is used for the deposition of, e.g, oxides, nitrides and carbides. In fundamental research, versatility is essential when designing or upgrading a deposition chamber. Furthermore, automated deposition systems are the norm in industrial production, but relatively uncommon in laboratory-scale systems used primarily for fundamental research. Combining automatization and computerized control with the required versatility for fundamental research constitutes a challenge in designing, developing, and upgrading laboratory deposition systems. The present article provides a detailed description of the design of a lab-scale deposition chamber for magnetron sputtering used for the deposition of metallic, oxide, nitride and oxynitride films with automated controls, dc or pulsed bias, and combined with a coil to enhance the plasma density near the substrate. LabVIEW software (provided as Supplementary Information) has been developed for a high degree of computerized or automated control of hardware and processes control and logging of process details.

physics.app-ph↗

arXiv2018

Effect of impurities on morphology and growth mode of (111) and (001) epitaxial-like ScN films

ScN material is an emerging semiconductor with an indirect bandgap. It has attracted attention for its thermoelectric properties, use as seed layers, and for alloys for piezoelectric application. ScN or other transition metal nitride semiconductors used for their interesting electrical properties are sensitive to contaminants, such as oxygen or fluorine. In this present article, the influence of depositions conditions on the amount of oxygen contaminants incorporated in ScN films were investigated and their effects on the electrical properties (electrical resistivity and Seebeck coefficient) were studied. The epitaxial-like films of thickness 125 +-5 nm to 155 +-5 nm were deposited by D.C.-magnetron sputtering on c-plane Al2O3, MgO(111) and r-plane Al2O3 at a substrate temperature ranging from 700 to 950 degree C. The amount of oxygen contaminants presents in the film, dissolved into ScN or as an oxide, was related to the adatom mobility during growth, which is affected by the deposition temperature and the presence of twin domain growth. The lowest values of electrical resistivity of 50 micro-ohm cm were obtained on ScN(111)/MgO(111) and on ScN(001)/r-plane Al2O3 grown at 950 degree C with no twin domains and the lowest amount of oxygen contaminant. At the best, the films exhibited an electrical resistivity of 50 micro-ohm cm with Seebeck coefficient values maintained at -40 microV K-1, thus a power factor estimated at 3.2 10-3 W m-1 K-2 (at room temperature).

physics.app-ph↗