arXiv subjects

Baptiste Julien

Publications and source records attributed to Baptiste Julien.

5 recordsLinked to original sources

arXiv2026

Composition-dependent Thin-film Synthesis of Layered Ternary Iron Nitrides FeMN2 (M = W, Mo)

Ternary transition-metal nitrides with layered crystal structures host anisotropic bonding and reduced dimensionality that may enable unconventional electronic and magnetic behavior. Yet, synthesis of such nitride thin films remains challenging because reactive sputtering often favors metastable rocksalt-derived structures. We report the composition-dependent synthesis, structure, and properties of layered FeMN2 (M = W, Mo) thin films with triangular Fe sublattices, prepared by reactive sputtering and post-deposition NH3 annealing. Using synchrotron grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray absorption spectroscopy (XAS), we investigate the evolution of phase formation, crystallographic texture, and local Fe coordination across composition. Both layered phase form over broad composition ranges. FeWN2 maintains high phase purity across compositions, consistent with cation substitution, whereas FeMoN2 only exhibits good phase purity at Fe-poor compositions. Azimuthal GIWAXS analysis shows that Fe-rich films in both systems exhibit out-of-plane fiber texture, which progressively evolves toward predominantly in-plane orientation near stoichiometry in FeWN2, while FeMoN2 develops a more randomly oriented polycrystalline microstructure. Electrical measurements reveal relatively low and composition-insensitive resistivity in FeWN2 (~1 m{\Omega}.cm), whereas FeMoN2 exhibits a pronounced resistivity maximum near nominal stoichiometry. Preliminary room-temperature magnetization measurements on FeWN2 further reveal weak ferromagnetic-like behavior in Fe-poor films, while stoichiometric compositions remain predominantly paramagnetic. These results demonstrate fundamentally different structural accommodation mechanisms in FeWN2 and FeMoN2, and highlight the strong coupling between composition, microstructure, and electronic/magnetic properties in layered nitride thin films.

cond-mat.mtrl-sci↗

arXiv2026

Thin film synthesis of SrZn2P2 with SrI2 post-annealing for enhanced crystallinity and optoelectronic quality

Ternary Zintl phosphides are promising light-absorbing semiconductors for thin-film optoelectronic applications, but strategies for controlling their microstructure and optoelectronic quality remain underexplored. Here, we report the synthesis of phase-pure SrZn2P2 thin films using radio-frequency co-sputtering in a PH3 + Ar atmosphere and investigate the impact of post-growth processing on their structural and optical properties. Grazing-incidence X-ray scattering and Raman spectroscopy confirm the formation of crystalline SrZn2P2 films over a finite compositional window. Optical measurements reveal strong absorption near the direct-band-gap energy (~1.8 eV) and near-band-edge photoluminescence. Further, we have studied the effects of chemically compatible halide-assisted annealing. It is found that SrI2 treatments lead to pronounced grain growth and reduced diffraction peak broadening while preserving phase purity, in contrast to rapid thermal or forming-gas annealing. Notably, annealing with SrI2 at 450 {\deg}C significantly enhances both the intensity and spatial uniformity of the photoluminescence, thus connecting the observed microstructural consolidation with improved radiative recombination. Our study demonstrates that halide-assisted annealing provides an effective pathway for microstructural control in SrZn2P2 thin films and highlights a generalizable processing strategy for advancing Zintl phosphide semiconductors toward optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Thin-Film Stabilization and Magnetism of {\eta}-Carbide Type Iron Nitrides

Transition-metal nitrides in {\eta}-carbide type structures exhibit unusual bonding motifs and proximity to magnetic instabilities. Yet they remain unexplored in thin-film form due to the difficulty of stabilizing nitrogen-poor ternaries among competing phases. Here, we report the thin-film synthesis and phase-stability mapping of the {\eta}-nitride systems Fe-W-N and Fe-Mo-N. Amorphous Fe-M-N (M = W, Mo) combinatorial libraries deposited by reactive co-sputtering crystallize upon rapid thermal annealing, enabling systematic identification of synthesis windows as a function of composition and annealing temperature. Using laboratory powder X-ray diffraction and synchrotron grazing incidence wide angle X-ray scattering, we establish that Fe3Mo3N-based {\eta}-carbide phases form over a substantially broader compositional and thermal range than W-based compositions, where {\eta} structures are stabilized only when the films are Fe-rich. These trends are rationalized using mixed chemical-potential vs. composition phase diagrams that capture the narrow nitrogen chemical-potential stability of {\eta}-nitrides. Magnetic measurements reveal that ferromagnetism is induced in Fe-rich Fe3.54Mo2.46N with a small exchange-bias-like response that is absent in Fe3W3N-based compositions, highlighting the sensitivity of magnetic behavior to modest deviations from stoichiometry. This work establishes practical thin-film synthesis routes for {\eta}-nitride materials and demonstrates how composition can be tuned to access emergent magnetic phenomena in these complex nitrides.

cond-mat.mtrl-sci↗

arXiv2025

Structural stability, elemental ordering, and transport properties of layered ScTaN2

Some ternary TM nitrides are predicted to adopt layered structures that make them interesting for thermoelectric conversion and quantum materials applications. Synthesis of TM ternary nitride films by physical vapor deposition often favors disordered 3D structures rather than the predicted 2D-like layered structure. In this study, we investigate the structural interplay in the Sc-Ta-N material system, focusing on ScTaN2. We use a two-step combinatorial approach to deposit Sc-Ta-N films by RF co-sputtering and then process the resulting 3D-structured precursor with RTA. Synchrotron GIWAXS on films annealed at 1200 {\deg}C for 20 min reveals the nucleation of the layered structure (P63/mmc) within a composition window of x = Sc/(Sc+Ta) = 0.2-0.5. We estimate the long-range order parameter in stoichiometric ScTaN2 films to be 0.86, corresponding to a fraction of antisites of 7%. Interestingly, we find that the structure can accommodate large off-stoichiometry in the Ta-rich region (x < 0.5), facilitated by making an alloy with the nearly isostructural Ta5N6 compound that exists on a composition tie-line. Transport measurements on ScTaN2 reveal a nearly temperature-independent high carrier density (1021 cm-3), suggesting a heavily doped semiconductor or semimetallic character. The carrier mobility is relatively small (9.5 cm2V-1s-1 at 2 K) and the residual-resistivity ratio is small, suggesting that electrical conduction is dominated by defects or disorder. Measured magnetoresistance is indicative of weak antilocalization at low temperatures. We highlight the interplay between ScTaN2 and Ta5N6 in stabilizing layered structures, emphasizes the importance of cation order/disorder for potential tunable alloys, and suggests that ScTaN2 is promising platform for exploring electronic properties in a tie line of stoichiometry.

cond-mat.mtrl-sci↗

arXiv2024

GdWN$_3$ is a Nitride Perovskite

Nitride perovskites $AB$N$_3$ are an emerging and highly under-explored class of materials that are of interest due to their intriguing calculated ferroelectric, optoelectronic, and other functional properties. Incorporating novel $A$-site cations is one strategy to tune and expand such properties; for example, Gd$^{3+}$ is compelling due to its large magnetic moment, potentially leading to multiferroic behavior. However, the theoretically predicted ground state of GdWN$_3$ is a non-perovskite monoclinic structure. Here, we experimentally show that GdWN$_3$ crystallizes in a perovskite structure. High-throughput combinatorial sputtering with activated nitrogen is employed to synthesize thin films of Gd$_{1-x}$W$_{x}$N$_{3-y}$ with low oxygen content within the bulk of the films. Ex-situ annealing crystallizes a polycrystalline perovskite phase in a narrow composition window near $x=1$. LeBail fits of synchrotron grazing incidence wide angle X-ray scattering data are consistent with a perovskite ground-state structure. New density functional theory calculations that included antiferromagnetic configurations confirm that the ground-state structure of GdWN$_3$ is a distorted $Pnma$ perovskite with antiferromagnetic ordering, in contrast to prior predictions. Initial property measurements find that GdWN$_3$ is paramagnetic down to $T=2$ K with antiferromagnetic correlations and that the absorption onset depends on cation stoichiometry. This work provides an important stepping stone towards the rapid expansion of the emerging family of nitride perovskites and towards our understanding of their potential multiferroic properties.

cond-mat.mtrl-sci↗