Rare-earth nitride thin films: growth study and characterization

PhD Candidate: Ana Meléndez

Date: Friday, 27 November 2026
Time: 10.00 AM
Venue: Sala d'Actes Carles Miravitlles & ONLINE (Register here)

Abstract

Rare-earth mononitrides (RENs) are a family of materials that combine semiconducting and magnetic properties, making them promising candidates for spintronic and magneto-electronic applications. However, their propensity to form nitrogen vacancies, which act as electron donors, together with their extreme air sensitivity, has complicated their experimental investigation and led to contradictory reports of their intrinsic properties. Although modern ultra-high-vacuum thin film growth techniques have significantly improved the quality of available samples, comprehensive studies relating growth conditions to the structural, electronic, magnetic, and optical properties of RENs remain limited.

This thesis presents a systematic investigation of the growth and characterization of epitaxial HoN, SmN, and YbN thin films grown by molecular beam epitaxy under moderate growth conditions. Film quality and physical properties were studied using a combination of in situ X-ray photoelectron spectroscopy (XPS), reflection high-energy electron diffraction (RHEED), and electrical transport measurements, complemented by ex situ X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). In-situ XPS was used to monitor the electronic structure, confirming the semiconducting character of all investigated materials. The influence of nitrogen vacancies on the electronic structure of SmN was investigated using X-ray absorption spectroscopy (XAS) and XPS. Magnetization measurements on optimized and mildly nitrogen deficient HoN films revealed a saturation moment substantially lower than the value predicted by Hund's rules, attributed to intrinsic effects. Small concentrations of nitrogen vacancies produced only minor changes in the magnetic properties. The optical properties of SmN, HoN, and YbN were investigated by ex situ SE, which allowed to determine band-gap energies, resistivities, and free carrier concentrations depending on nitrogen deficiency.

Overall, this work demonstrates that the structural, electronic, magnetic, and optical properties of rare earth mononitrides are highly sensitive to growth conditions and stoichiometry. The methodologies developed provide a robust framework for the controlled synthesis and characterization of high quality REN thin films, thereby contributing to a deeper understanding of the relationship between defects, electronic structure, and the functional properties of this class of materials.

Supervisors

•  Isabel Alonso, ICMAB-CSIC
• Simone Altendorf, MPI-CPFS

PhD committee

•  President: Jordi Fraxedas, ICN2, Spain
• Secretary: Mariona Coll, ICMAB-CSIC, Spain
• Vocal: Frank Güell, UB, Spain

University: Universitat Autònoma de Barcelona (UAB)

PhD Programme: Materials Science