Probing the Local Electronic Structure of Chemical Species During Ultrafast Superconducting Film Growth with Fast In-Situ X-ray Absorption Spectroscopy

We propose an in-situ XANES study at the Cu K-edge to investigate the oxidation state evolution of Cu during the Transient Liquid Assisted Growth (TLAG) of superconducting REBCO films (YBCO, GdBCO, and ErBCO). Using the CLAESS beamline, we will employ a fast acquisition technique at a preselected single photon energy characteristic of the Cu+1 feature. Our study will span the entire TLAG process, including the rapid heating ramp (BaCO₃ + CuO + RE₂O₃ → BaCu₂O₂ + RE₂O₃ transformation), the pressure jump initiating ultrafast REBCO growth (100–2000 nm/s), and the cooling stage for oxygenation of the final superconducting film. The compatibility of our TLAG setup with CLAESS has been successfully demonstrated in prior beamtime (proposal: 2024028362). Post-growth characterization will include EXAFS measurements to analyze local atomic displacements at varying temperatures (850–950°C) and oxygen partial pressures (2–10 mbar), performed in fluorescence mode. The expected outcomes include insights into the oxidation state of the transient liquid at different PO₂ conditions, its impact on REBCO nucleation and growth, and correlations between EXAFS-determined c-axis changes and growth rates measured via in-situ electrical conductivity. Additionally, XANES and EXAFS data from CLAESS will be compared with XRD data from the NCD-SWEET beamline under identical growth conditions. This study will address critical knowledge gaps regarding transient liquid formation and oxidation state evolution in TLAG, ultimately refining the understanding of nucleation and growth mechanisms in ultrafast, non-equilibrium processes. The findings will contribute to optimizing high-performance superconducting films for coated conductor technology and fusion reactor applications.