arXiv subjects

A. Le Febvrier

Publications and source records attributed to A. Le Febvrier.

4 recordsLinked to original sources

arXiv2026

Epitaxial MgSnN2 on 4H-SiC (0001): An Earth-Abundant Nitride for Green Optoelectronics and Photovoltaics

Group II-IV nitrides have recently emerged as a novel class of semiconductors composed of earth-abundant elements. Owing to their tunable bandgaps, comparable to those of III-nitrides, these materials are attractive candidates for replacing expensive Ga-based alloys in photovoltaics and green-gap optoelectronics. In this work, epitaxial growth of MgSnN2 layers on 4H-SiC(0001) substrates by direct current magnetron sputtering is demonstrated. Mg and Sn metal targets have been co-sputtered in nitrogen-containing atmosphere at growth temperatures up to 500 °C. X-ray diffraction and cross-sectional transmission electron microscopy confirm the MgSnN2 layers grow epitaxially in a wurtzite crystal structure, exhibiting the epitaxial relationships with the substrate: MgSnN2 [0001]//4H-SiC [0001] and MgSnN2 [10-10]//4H-SiC[10-10]. Improved crystalline quality is observed for higher deposition temperatures and near-stoichiometric composition, as evidenced by the narrowing of rocking curve linewidths. Optical characterization reveals high absorption coefficients (1e5 cm-1) in the visible spectrum, comparable to that of GaAs, highlighting the suitability of MgSnN2 for photovoltaic applications. A photoluminescence emission band at ~2.4 eV is detected, highly desirable for optoelectronic devices operating in the challenging green spectral region. These results establish MgSnN2 as an earth-abundant, environmentally friendly material, structurally compatible with III-nitrides, with potential for cost-efficient components in sustainable optoelectronics and photovoltaics.

cond-mat.mtrl-sci↗

arXiv2024

Eliminating the spin-down critical angle in polarizing neutron optics for expanding the polarization bandwidth

Polarized neutron scattering is a very important analysis technique for studies of magnetism, spintronics, and high-sensitivity measurements, among others, offering invaluable information. Yet, the efficiency of such experiments rely on the performance of the polarizing neutron optics to provide high reflectivity and polarization. Presently, state-of-the-art polarizers like Fe/Si supermirrors are not able to polarize neutrons at low scattering angles in a monochromatic beam or able to polarize neutrons with a variety of wavelengths as for a non-monochromatic beam. To overcome this limitation, it is suggested to use Co/Ti multilayers on Ti substrates owing to their favorable scattering length density characteristics. It is shown that this approach enables a wavelength bandwidth several times larger than achievable with state-of-the-art materials on Si or glass substrates. Consequently, enabling the possibility of polarizing neutrons across an extended wavelength range, including those with very high wavelengths.

cond-mat.mtrl-sci↗

arXiv2023

Reflective, polarizing, and magnetically soft amorphous Fe/Si multilayer neutron optics with isotope-enriched 11B4C inducing atomically flat interfaces

The utilization of polarized neutrons is of great importance in scientific disciplines spanning materials science, physics, biology, and chemistry. Polarization analysis offers insights into otherwise unattainable sample information such as magnetic domains and structures, protein crystallography, composition, orientation, ion-diffusion mechanisms, and relative location of molecules in multicomponent biological systems. State-of-the-art multilayer polarizing neutron optics have limitations, particularly low specular reflectivity and polarization at higher scattering vectors/angles, and the requirement of high external magnetic fields to saturate the polarizer magnetization. Here, we show that by incorporating 11B4C into Fe/Si multilayers, amorphization and smooth interfaces can be achieved, yielding higher neutron reflectivity, less diffuse scattering and higher polarization. Magnetic coercivity is eliminated, and magnetic saturation can be reached at low external fields (>2 mT). This approach offers prospects for significant improvement in polarizing neutron optics, enabling; nonintrusive positioning of the polarizer, enhanced flux, increased data accuracy, and further polarizing/analyzing methods at neutron scattering facilities.

cond-mat.mtrl-sci↗

arXiv2022

Influence of generated defects by Ar-implantation on the thermoelectric properties of ScN

Nowadays, making thermoelectric materials more efficient in energy conversion is still a challenge. In this work, to reduce the thermal conductivity and thus improve the overall thermoelectric performances, point and extended defects were generated in epitaxial 111-ScN thin films by implantation using argon ions. The films were investigated by structural, optical, electrical, and thermoelectric characterization methods. The results demonstrated that argon implantation leads to the formation of stable defects (up to 750 K operating temperature) were identified as interstitial type defect clusters and so-called argon-vacancy complexes. The insertion of those specific defects induces acceptor-type deep levels in the bandgap yielding to a reduce of the free carrier mobility. With a reduce electrical conductivity, the irradiated sample exhibited higher Seebeck coefficient maintaining the power factor of the film. The thermal conductivity is strongly reduced from 12 to 3 W.m-1.K-1 at 300 K, showing the effect of defects in increasing phonon scattering. Subsequent high temperature annealing, at 1573 K, leads to the progressive evolution of defects: the initial clusters of interstitial evolved to the benefit of smaller clusters and the formation of bubble. Thus, the number of free carriers, the resistivity and the Seebeck coefficient are almost restored but the mobility of the carriers remains low and a 30% drop in thermal conductivity is still effective (8.5 W.m-1.K-1). This study shows that the control defect engineering with defects introduced by irradiation using noble gases in a thermoelectric coating can be an attractive method to enhance the figure of merit of thermoelectric materials.

cond-mat.mtrl-sci↗