More Like this

1. Emergence of a metallic surface state for narrow bandgap Mott insulator Sr ₃ Ir ₂ O ₇ (001) thin films

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

   Komesu, Takashi; Zhang, Yuanyuan; Kumar, Shiv; Kumar, Amit; Miyai, Yudai; Shimada, Kenya; Adegbite, Peace_Ikeoluwa; Hong, Xia; Dowben, P_A (March 2025, Journal of Physics: Condensed Matter)

   Abstract We report evidence of a finite density of states at the Fermi level at the surface of epitaxial thin films of the narrow bandgap Mott insulator Sr₃Ir₂O₇(001). The Brillouin zone critical points for Sr₃Ir₂O₇(001) thin films have been determined by a comparison of the band mapping from angle-resolved photoemission spectroscopy and low energy electron diffraction. Angle-resolved x-ray photoemission studies reveal the surface termination of Sr₃Ir₂O₇(001) is Sr–O. The absence of dispersion with photon energy, or changing wave vector along the surface normal, indicates the two-dimensional character of the bands contributing to the density of states close to the Fermi level for Sr₃Ir₂O₇(001) thin films. Thus, the finite density of states at the Fermi level is attributed to surface states or surface resonances. The appearance of a finite density of states at the Fermi level is consistent with the increased conductivity with decreasing film thickness for ultrathin Sr₃Ir₂O₇(001) films. 

   more » « less
2. 2D photofragmentation LIF imaging of H ₂ O ₂ and HO ₂ in the effluent of an atmospheric-pressure plasma jet: effects of solid and liquid interfaces

   https://doi.org/10.1088/1361-6463/ae1300  

   Herrera_Quesada, María_J; Pfaff, Sebastian; Polito, Jordyn; Kushner, Mark_J; Frank, Jonathan_H; Stapelmann, Katharina (October 2025, Journal of Physics D: Applied Physics)

   Abstract Two-dimensional (2D) absolute measurements of hydrogen peroxide (H₂O₂) and approximations of the hydroperoxyl radical (HO₂) in the effluent of a COST Reference Microplasma Jet operated with a He/H₂O feed gas are presented. Gas-phase densities are mapped using photofragmentation laser-induced fluorescence (PF-LIF) under three boundary conditions: open effluent, a solid target, and a liquid target. A novel method is presented for separating PF-LIF signals from H₂O₂and HO₂using comparative measurements in oxygen-rich and oxygen-free environments to exploit the preferential formation of HO₂in the presence of molecular oxygen. This separation strategy is supported by results from a plug-flow plasma chemistry model. Measured densities agree closely with model predictions in both magnitude and trend, while the 2D experimental distributions provide additional insight into the spatial dependencies of these species. In particular, the results show distinct differences in species transport depending on the target type: solid surfaces induce lateral deflection and reduced centerline densities, whereas liquid interfaces promote axial accumulation and higher near-axis concentrations. 

   more » « less
3. Revealing the roles of the solid–electrolyte interphase in designing stable, fast-charging, low-temperature Li-ion batteries

   https://doi.org/10.1073/pnas.2420398122  

   Tao, Lei; Zhang, Hanrui; Shah, Sameep Rajubhai; Yang, Xixian; Lai, Jianwei; Guo, Yanjun; Russell, Joshua A; Xia, Dawei; Min, Jungki; Huang, Weibo; et al (April 2025, Proceedings of the National Academy of Sciences)

   Designing the solid–electrolyte interphase (SEI) is critical for stable, fast-charging, low-temperature Li-ion batteries. Fostering a “fluorinated interphase,” SEI enriched with LiF, has become a popular design strategy. Although LiF possesses low Li-ion conductivity, many studies have reported favorable battery performance with fluorinated SEIs. Such a contradiction suggests that optimizing SEI must extend beyond chemical composition design to consider spatial distributions of different chemical species. In this work, we demonstrate that the impact of a fluorinated SEI on battery performance should be evaluated on a case-by-case basis. Sufficiently passivating the anode surface without impeding Li-ion transport is key. We reveal that a fluorinated SEI containing excessive and dense LiF severely impedes Li-ion transport. In contrast, a fluorinated SEI with well-dispersed LiF (i.e., small LiF aggregates well mixed with other SEI components) is advantageous, presumably due to the enhanced Li-ion transport across heterointerfaces between LiF and other SEI components. An electrolyte, 1 M LiPF₆in 2-methyl tetrahydrofuran (2MeTHF), yields a fluorinated SEI with dispersed LiF. This electrolyte allows anodes of graphite, μSi/graphite composite, and pure Si to all deliver a stable Coulombic efficiency of 99.9% and excellent rate capability at low temperatures. Pouch cells containing layered cathodes also demonstrate impressive cycling stability over 1,000 cycles and exceptional rate capability down to −20 °C. Through experiments and theoretical modeling, we have identified a balanced SEI-based approach that achieves stable, fast-charging, low-temperature Li-ion batteries. 

   more » « less
4. Increasing contrast in water-embedded particles via time-gated mid-infrared photothermal microscopy

   https://doi.org/10.1364/OL.513742  

   Samolis, Panagis_D; Sander, Michelle_Y (March 2024, Optics Letters)

   The transient dynamics of photothermal signals provide interesting insights into material properties and heat diffusion. In a mid-infrared (mid-IR) photothermal microscope, the imaging contrast in a standard amplitude imaging can decrease due to thermal diffusion effects. It is shown that contrast varies for poly-methyl 2-methylpropenoate (PMMA) particles of different sizes when embedded in an absorbing medium of water (H₂O) based on levels of heat exchange under the water absorption resonance. Using time-resolved boxcar (BC) detection, analysis of the transient thermal dynamics at the bead–water interface is presented, and the time decay parameters for 500 nm and 100 nm beads are determined. Enhanced (negative) imaging contrast is observed for less heat exchange between the water and bead, as in the case for the 100 nm bead. For the 500 nm bead, boxcar imaging before heat exchange starts occurring, leads to an increase of the imaging contrast up to a factor of 1.6. 

   more » « less
5. Accelerating ion transport in polycrystalline conductors: On pores and grain boundaries

   https://doi.org/10.1126/sciadv.adt7795  

   Truong, Erica; Patel, Sawankumar V; Liu, Haoyu; Chen, Yudan; Lacivita, Valentina; Zhang, Chi; Oyekunle, Ifeoluwa P; Ojelade, Islamiyat; Jin, Yongkang; Jones, Brendon T; et al (May 2025, Science Advances)

   Polycrystalline ion conductors are widely used as solid electrolytes in energy storage technologies. However, they often exhibit poor ion transport across grain boundaries and pores. This work demonstrates that strategically tuning the mesoscale microstructures, including pore size, pore distribution, and chemical compositions of grain boundaries, can improve ion transport. Using LiTa₂PO₈as a case study, we have shown that the combination of LiF as a sintering agent with Hf⁴⁺implantation improves grain-grain contact, resulting in smaller, evenly distributed pores, reduced chemical contrast, and minimized nonconductive impurities. A suite of techniques has been used to decouple the effects of LiF and Hf⁴⁺. Specifically, LiF modifies particle shape and breaks large pores into smaller ones, while Hf⁴⁺addresses the chemical mismatches between grains and grain boundaries. Consequently, this approach achieves nearly two orders of magnitude improvement in ion conduction. Tuning mesoscale structures offers a cost-effective method for enhancing ion transport in polycrystalline systems and has notable implications for synthesizing high-performance ionic materials. 

   more » « less