AVS 71 Session AC+MI-ThA: Early Career and Rising Stars

Thursday, September 25, 2025 2:15 PM in Room 207 A W

Thursday Afternoon

Start	Invited?	Item
2:15 PM	Invited	AC+MI-ThA-1 Beyond the Braggs: Studying Disorder and Dynamics in Actinide and Rare Earth Compounds with Synchrotron Light Daniel Chaney, Luigi Paolasini, Alexei Bosak (ESRF) Be it for our fundamental understanding of the various complex phenomena present in actinide and rare earth containing materials, or for their many possible applications, understanding the vibrational behaviour of atoms within a material, the so-called lattice dynamics, is of great importance. Furthermore, it is has become ever more apparent over the last decade that there exists a strong link between a material's functional properties with the presence of atomic scale disorder and the short-range correlations that exist within. To explore these two regimes as well as the coupling between them we operate two synergistic instruments at the ID28 beamline, an inelastic x-ray scattering spectrometer to probe lattice dynamics and a diffuse x-ray scattering diffractometer to study correlated disorder. This presentation will detail the state of the art for diffuse and inelastic x-ray scattering as implemented on the ID28 beamline and the application to actinide and rare earth containing materials using a series of recent case studies.
2:45 PM		AC+MI-ThA-3 Applications of Scanning Tunneling Microscopy in Heavy Element Studies Benjamin Heiner, Miles Beaux (Los Alamos National Laboratory) Scanning Tunneling Microscopy and Spectroscopy (STM/S) are powerful techniques for investigating atomic, molecular, and surface properties. At Los Alamos National Laboratory, a specialized instrument designed to contain and probe samples containing heavy elements (i.e. actinides) allows us to study of the most uncharacterized elements on the periodic table. This capability has facilitated new insights into the electronic structure of plutonium oxides, intermetallics, and complexes. Using temperature-resolved STS, we can directly and continuously measure the total density of states of these materials across the Fermi energy, addressing a critical gap in experimental plutonium data. These advancements provide valuable information for understanding the electronic behavior of plutonium, with implications for fundamental science and nuclear materials research. Additionally, our ongoing efforts aim to apply these techniques to molecular complexes containing a single actinide atom, enabling both STM imaging and localized STS probing of individual actinide atoms.LA-UR-25-22710
3:00 PM		AC+MI-ThA-4 Electronic Structure of Uranium-Based Ferromagnet UPS Sabin Regmi (Idaho National Laboratory); Alexei Fedorov (Lawrence Berkeley National Laboratory); Dariusz Kaczorowski (Polish Academy of Sciences); Peter Oppeneer (Uppsala University); Krzysztof Gofryk (Idaho National Laboratory) Strongly correlated f-electron systems often exhibit intriguing properties such as unconventional superconductivity and heavy fermion behaviors. Particularly in 5f-electron systems, the understanding of the relation between f electrons and observed physical properties has been a challenge due to their duality. Here, we present an angle-resolved photoemissions spectroscopy (ARPES) study of uranium-based ferromagnet UPS, supported by density-functional theory calculations. Measurements carried out at on and off-resonant photon energies suggest strong contribution from U 5f in the vicinity of the Fermi level and c-f hybridization. The results reveal the Fermi surface, underlying electronic structure in this system, and the nature of the 5f electrons in this ferromagnetic material. This work provides a valuable platform to advance the fundamental understanding of the 5f electronic structure in uranium-based and actinide materials in general. **This work is supported by Idaho National Laboratory’s laboratory directed research and development (LDRD) program and the US Department of energy (DOE) Basic Energy Sciences, Materials Sciences and Engineering Division.
3:15 PM		AC+MI-ThA-5 The Plutonium Auto-reduction Reaction, Predicting Kinetics, and Assessing Impacts to Surface Science Measurements Timothy Gorey, Daniel Rodriguez, Sarah Hernandez (Los Alamos National Laboratory) Plutonium is a fascinating and difficult material to measure in vacuum systems due to its auto-catalytic reduction of higher oxides into plutonium sesquioxide (Pu₂O₃). This “auto-reduction” reaction complicates surface science measurements aiming to understand higher oxides, because these layers, when exposed to vacuum as is required for many surface-sensitive techniques (e.g. X-ray Photoelectron and Auger Electron spectroscopies (XPS and AES), and Secondary Ion Mass Spectrometry (SIMS)) spontaneously converts into sesquioxide. This presentation will discuss an XPS-focused study into the nuances of high oxide (PuO₂) surface analysis and propose likely mechanistic origins for the auto-reduction reaction as well as methods to predict the chemical progression of the surface.
3:30 PM		AC+MI-ThA-6 Magnetic Properties of UP₂ Probed by High-Magnetic Field Volodymyr Buturllim, Sabin Regmi (Idaho National Laboratory); Rubi KM (High Magnetic Field Laboratory, Los Alamos National Laboratory); Dariusz Kaczorowski (Polish Academy of Sciences); Neil Harrison (Los Alamos National Laboratory); Krzysztof Gofryk (Idaho National Laboratory) Due to its complex tetragonal crystal structure, with three distinct uranium sites, UP₂ stands out among other uranium dipnictides such as UAs₂, USb₂, and UBi₂. UP2 exhibits antiferromagnetic ordering at ambient pressure with T_N = 204 K and an effective moment of μ_eff = 2.29 μ_B/U. The neutron scattering experiment indicates that the ordered moment is parallel to the [0 0 1] direction and equals 2.0 μ_B/U. There is, however, a lack of information regarding the magnetic properties of UP₂ in high magnetic fields, particularly concerning its magnetic phase diagram. Here we present detailed experimental and theoretical studies of the magnetic properties of oriented high-quality single crystals of UP₂. The measurements were performed at the High Magnetic Field Laboratory, Los Alamos National Laboratory, using pulsed magnetic fields up to 60 T. We will discuss details of the obtained phase diagram and its relationships to the localization/delocalization of 5f-electrons in this material.
3:45 PM		AC+MI-ThA-7 Properties of Carbon-Related Point Defects in Plutonium Oxides Andrew Rowberg, Kyoung Eun Kweon, Scott Donald (Lawrence Livermore National Laboratory) Carbon is a ubiquitous impurity; therefore, investigating how it incorporates in materials is vital for understanding their properties, stability, and performance. Here, we evaluate the formation of carbon impurities in the most common stoichiometric plutonium oxides, PuO₂ and Pu₂O₃, which has not been systematically studied to date. We use hybrid density functional theory calculations to compute formation energies and other relevant properties of carbon species in various configurations. We find the stability of carbon defects to be strongly dependent on charge state and oxygen coordination environments. Accordingly, these properties can influence the phase evolution between PuO₂ and Pu₂O₃. We also evaluate the interactions between carbon and other defects present in these oxides.
4:00 PM		AC+MI-ThA-8 Vacancy-mediated Conduction Tunability in Epitaxial SmN Kevin Vallejo, Volodymyr Buturlim, Zachery Cresswell, Brelon May, Brooke Campbell (Idaho National Laboratory); Bobby Duersch (University of Utah); Krzysztof Gofryk (Idaho National Laboratory) We establish the relationship between native N vacancies, introduced through varying growth parameters, and electronic properties of SmN thin films grown via molecular beam epitaxy grown on MgO(001). We show substrate temperature having a larger impact on V$_N$ formation during growth than the ratio of Sm to N atoms. We observe a transition from insulating to conducting behavior of the film over a range of two orders of magnitude, from highly resistive to highly conductive. X-ray photoelectron spectroscopy and room temperature electrical transport results confirm the rapid degradation of the film despite the presence of capping layers. A ferromagnetic feature in the film is shown through low-temperature resistivity measurements to be the onset of ferromagnetic behavior. These promising results indicate a path forward in the epitaxy of versatile materials able to provide monolithic integration of different electronic behaviors without the associated strain brought about by heteroepitaxial integration of dissimilar materials. The integration between SmN and several transition metal nitride compounds has the potential to unlock new electronic and spintronic device architectures with low strain barriers.