Generation and Characterization of Surface-Attached Ultrathin Liquid Sheets for Grazing-Incidence X-ray Scattering

Capturing the ultrafast structural dynamics that occur at the solid-liquid interface is key to understanding adsorption, desorption, diffusion, and aggregation processes in catalysis and interfacial chemical reactions. Hard-X-ray scattering in grazing-incidence geometry can, in principle, access interfacial structural changes with angstrom-scale structural sensitivity and ultrafast temporal resolution. However, the long optical paths of the optical pump and hard-X-ray pulses inside the liquid sample pose significant challenges to the temporal resolution, signal-to-noise ratio, and overall stability of such an experimental scheme. Here, we report a method for creating and characterizing ultrathin surface-attached free-flowing liquid sheets, whose submicrometer thickness enables ultrafast temporal resolution and reduces the bulk-liquid scattering contribution. The impinging-jet geometry produces stable micrometer-scale sheets whose morphology depends systematically on incidence angle, jet velocity, and capillary diameter. Gas-assisted shaping using a second capillary further narrows and thins the sheet, producing an extended ultrathin region and reducing the measured minimum thickness below 500~nm for acetonitrile. The resulting platform provides a reproducible, continuously flowing, surface-attached liquid geometry for grazing-incidence scattering experiments.