arXiv subjects

Joana Valerio

Publications and source records attributed to Joana Valerio.

3 recordsLinked to original sources

arXiv2026

Train-Resolved Statistical Recovery of Weak SAXS Signals in Liquids at the European XFEL

We present a train-resolved SAXS methodology for recovering weak scattering signals from high-repetition-rate XFEL datasets and apply it to aqueous L-cysteine solutions measured at the European XFEL. Independent scale-plus-offset fitting was performed for matched cysteine and water train pairs, followed by subtraction of transmission-matched water--water controls. The 0.5 M dataset reveals a reproducible sign-changing residual SAXS signal that increases with incident XFEL transmission and remains after removal of detector-wide scaling, additive offsets, and matched water--water control residuals. Convergence and block-averaging analyses show that the residual emerges progressively as independent train pairs are accumulated and exhibits uncertainty scaling close to the expected inverse square-root dependence on N. These results establish a statistically robust transmission-dependent residual SAXS contribution whose microscopic origin remains unresolved, while demonstrating that train-resolved observables combined with matched controls can substantially improve sensitivity to weak scattering signals in high-repetition-rate XFEL experiments.

physics.optics↗

arXiv2026

Time Resolved Study of Laser Induced Ultrafast Alloying Processes in Au/Pd Core Shell Nanorods

Femtosecond laser-induced alloying presents a novel approach to modifying bimetallic systems. Visualizing ultrafast processes during laser-induced alloying is essential to uncover fundamental mechanisms associated with phase transformations, which enables precise control over material composition and structure at the atomic level. In this study, we investigated the ultrafast dynamics of laser-induced alloying of Au/Pd core-shell nanorods using a time-resolved X-ray diffraction technique at an X-ray free-electron laser facility, capturing the structural evolution from picoseconds to microsecond timescales. We found that a laser fluence threshold of ~ 48 mJ/cm2 with 800 nm excitation is sufficient for melting and subsequent alloy formation. Above this threshold, the formation of Au1.51Pd0.49 was observed, and we found that alloying is not a single-step phenomenon; instead, it is a dynamic process involving interdiffusion.

cond-mat.mtrl-sci↗

arXiv2023

3D-Printed Sheet Jet for Stable Megahertz Liquid Sample Delivery at X-ray Free Electron Lasers

X-ray Free Electron Lasers (XFELs) can probe chemical and biological reactions as they unfold with unprecedented spatial and temporal resolution. A principal challenge in this pursuit is the delivery of samples to the X-ray interaction point in a way that produces data of the highest possible quality and efficiency. This is hampered by constraints posed by the light source and operation within a beamline environment. For liquid samples, the solution typically involves a high-speed liquid jet, capable of keeping up with the rate of X-ray pulses. However, conventional jets are not ideal because of radiation-induced explosions of the jet, as well as their cylindrical geometry combined with the X-ray pointing instability of many beamlines causes the interaction volume to differ for every pulse. This complicates data analysis and contributes to measurement errors. An alternative geometry is a liquid sheet jet which, with its constant thickness over large areas, eliminates the X-ray pointing related problems. Since liquid sheets can be made very thin, the radiation-induced explosion is reduced, boosting their stability. They are especially attractive for experiments which benefit from small interaction volumes such as fluctuation X-ray scattering and several types of spectroscopy. Although they have seen increasing use for soft X-ray applications in recent years, there has not yet been wide-scale adoption at XFELs. Here, we demonstrate liquid sheet jet sample injection at the European XFEL. We evaluate several aspects of its performance relative to a conventional liquid jet including thickness profile, stability, and radiation-induced explosion dynamics at high repetition rates. The sheet jet exhibits superior performance across these critical experimental parameters. Its minute thickness also suggests ultrafast single-particle solution scattering is a possibility.

physics.ins-det↗