More Like this

1. Scalable Programming of LaAlO ₃ /SrTiO ₃ Interfaces via Ultra‐Low‐Voltage Electron‐Beam Lithography

   https://doi.org/10.1002/admi.202500442  

   Yang, Dengyu; Ramachandran, Ranjani; Yu, Muqing; Eom, Kitae; Lee, Kyoungjun; Irvin, Patrick; Eom, Chang‐Beom; Levy, Jeremy (November 2025, Advanced Materials Interfaces)

   Abstract Interface engineering at complex oxide heterostructures enables a wide range of electronic functionalities critical for next‐generation devices. Here it is demonstrated that ultra‐low‐voltage electron beam lithography (ULV‐EBL) creates high‐quality mesoscale structures at LaAlO₃/SrTiO₃(LAO/STO) interfaces with greater efficiency than conventional methods. Nanowires, tunnel barriers, and electron waveguides are successfully patterned that exhibit distinctive transport characteristics including 1D superconductivity, nonlinear current–voltage behavior, and ballistic electron flow. While conductive atomic force microscopy (c‐AFM) previously enabled similar interface modifications, ULV‐EBL provides significantly faster patterning speeds (10 mm s⁻¹vs 1 µm s⁻¹), wafer‐scale capability (>(10 cm)²vs <(90 µm)²), and maintenance of pattern quality under vacuum conditions. Additionally, an efficient oxygen plasma treatment method is developed for pattern erasure and surface cleaning, which reveals novel surface reaction dynamics at oxide interfaces. These capabilities establish ULV‐EBL as a versatile approach for scalable interface engineering in complex oxide heterostructures, with potential applications in reconfigurable electronics, sensors, and oxide‐based devices. 

   more » « less
2. Ultrafast Light‐Driven Electronic and Structural Changes in LaFeO ₃ Perovskites Probed by Femtosecond X‐Ray Absorption Spectroscopy

   https://doi.org/10.1002/adma.202502932  

   Lazemi, Masoud; Mohammad, Fabian J; Park, Sang Han; Katoch, Abhishek; Blankesteijn, Hans JFA; Botello‐Méndez, Andrés R; van_der_Minne, Emma; Birkhölzer, Yorick A; van_den_Bosch, Iris_C G; Kiens, Ellen M; et al (July 2025, Advanced Materials)

   Abstract Conducting real‐time, element‐specific studies of photo‐excited systems is a long‐standing challenge. The development of X‐ray free‐electron lasers (XFELs) has paved the way for the emergence of a promising technique: femtosecond X‐ray absorption spectroscopy (fs‐XAS). This powerful technique reveals electronic and geometric characteristics, providing unprecedented insight into their dynamic interactions under nonequilibrium conditions. Herein, the fs‐XAS technique is employed at PAL‐XFEL to unravel light‐driven ultrafast electronic and structural changes in epitaxial lanthanum iron oxide (LaFeO₃) thin films. Density functional theory (DFT) and multiplet calculations are utilized to expound on the experimental results. The analyses reveal that photoexcitation initially induces high‐ and intermediate‐spin Fe²⁺states through ligand‐to‐metal charge transfer (LMCT), followed by polaron formation. It is demonstrated that the reduced overlap between the oxygen 2pand iron 3dorbitals accounts for all experimental observations, including 1) the XAS shifts to lower energies, 2) the decrease in the crystal field splitting, and 3) the relatively larger shifts observed in the oxygen 1sXAS. 

   more » « less
3. Intrinsic exchange bias from interfacial reconstruction in an epitaxial Ni _x Co _y Fe _{3− x −y} O ₄ (111)/ $\alpha$ -Al ₂ O ₃ (0001) thin film family

   https://doi.org/10.1088/1361-648X/ad789d  

   Yang, Detian; Liu, Yaohua; Xu, Xiaoshan (September 2024, Journal of Physics: Condensed Matter)

   Abstract Intrinsic exchange bias is known as the unidirectional exchange anisotropy that emerges in a nominally single-component ferro-(ferri-)magnetic system. In this work, with magnetic and structural characterizations, we demonstrate that intrinsic exchange bias is a general phenomenon in (Ni, Co, Fe)-based spinel oxide films deposited on $\alpha$-Al₂O₃(0001) substrates, due to the emergence of a rock-salt interfacial layer consisting of antiferromagnetic CoO from interfacial reconstruction. We show that in Ni_xCo_yFe_3−x−yO₄(111)/ $\alpha$-Al₂O₃(0001) films, intrinsic exchange bias and interfacial reconstruction have consistent dependences on Co concentrationy, while the Ni and Fe concentration appears to be less important. This work establishes a family of intrinsic exchange bias materials with great tunability by stoichiometry and highlights the strategy of interface engineering in controlling material functionalities. 

   more » « less
4. Elucidating the Role of B-Site Cations toward CO ₂ Reduction in Perovskite-Based Solid Oxide Electrolysis Cells

   https://doi.org/10.1149/1945-7111/ac5e9b  

   Tezel, Elif; Guo, Dezhou; Whitten, Ariel; Yarema, Genevieve; Freire, Maikon; Denecke, Reinhard; McEwen, Jean-Sabin; Nikolla, Eranda (March 2022, Journal of The Electrochemical Society)

   Solid oxide electrolysis cells (SOECs) are promising for the selective electrochemical conversion of CO 2 , or mixed streams of CO 2 and H 2 O, into high energy products such as CO and H 2 . However, these systems are limited by the poor redox stability of the state-of-the-art Ni-based cathode electrocatalysts. Due to their favorable redox properties, mixed ionic-electronic conducting (MIEC) oxides have been considered as promising alternatives. However, improvement of the electrochemical performance of MIEC-based SOEC electrocatalysts is needed and requires an understanding of the factors that govern their activity. Herein, we investigate the effect of B-site 3 d metal cations (Cr, Fe, Co, Ni) of LaBO 3 perovskites on their CO 2 electrochemical reduction activity in SOECs. We find that their electrochemical performance is highly dependent on the nature of the B-site cation and trends as LaFeO 3 > LaCoO 3 > LaNiO 3 > LaCrO 3 . Among these perovskites, LaNiO 3 is the least stable and decomposes under electrochemical conditions. In situ characterization and ab initio theoretical calculations suggest that both the nature of the B-site cation and the presence of oxygen surface vacancies impact the energetics of CO 2 adsorption and reduction. These studies provide fundamental insights critical toward devising ways to improve the performance of MIEC-based SOEC cathodes for CO 2 electroreduction. 

   more » « less
5. Engineering the Coherent Phonon Transport in Polar Ferromagnetic Oxide Superlattices

   https://doi.org/10.1002/advs.202407382  

   Choi, In Hyeok; Jeong, Seung Gyo; Jeong, Do‐Gyeom; Seo, Ambrose; Choi, Woo Seok; Lee, Jong Seok (November 2024, Advanced Science)

   Abstract Artificial superlattices composed of perovskite oxides serves as an essential platform for engineering coherent phonon transport by redefining the lattice periodicity, which strongly influences the lattice‐coupled phase transitions in charge and spin degrees of freedom. However, previous methods of manipulating phonons have been limited to controlling the periodicity of superlattice, rather than utilizing complex mutual interactions that are prominent in transition metal oxides. In this study on oxide superlattices composed of ferromagnetic metallic SrRuO₃and quantum paraelectric SrTiO₃, phonon modulation by controlling the geometry of superlattice in atomic‐scale precision is realized, demonstrating the coherent phonon engineering using structural and magnetic phase transitions. By modulating the interface density, coherent‐incoherent crossover of the phonon transport at room temperature is observed, which is coupled with a change in interfacial structural continuity. Upon cooling, the close relation between phonon transport and multiple phase transitions is identified. In particular, the enhancement of the polar state in SrTiO₃layer at ≈200 K leads to the weakening of phonon coherence and a further reduction of thermal conductivity in superlattices compared to the bulk limit. These findings provide a guide to developing future thermoelectric nanodevices by engineering the coherence of phonons via the design of complex oxide heterostructures. 

   more » « less