?ngstrom-Depth Resolution with Chemical Specificity at the Liquid-Vapor Interface

R Dupuy and J Filser and C Richter and T Buttersack and F Trinter and S Gholami and R Seidel and C Nicolas and J Bozek and D Egger and H Oberhofer and S Thürmer and U Hergenhahn and K Reuter and B Winter and H Bluhm, PHYSICAL REVIEW LETTERS, 130, 156901 (2023).

DOI: 10.1103/PhysRevLett.130.156901

The determination of depth profiles across interfaces is of primary importance in many scientific and technological areas. Photoemission spectroscopy is in principle well suited for this purpose, yet a quantitative implementation for investigations of liquid-vapor interfaces is hindered by the lack of understanding of electron- scattering processes in liquids. Previous studies have shown, however, that core-level photoelectron angular distributions (PADs) are altered by depth-dependent elastic electron scattering and can, thus, reveal information on the depth distribution of species across the interface. Here, we explore this concept further and show that the experimental anisotropy parameter characterizing the PAD scales linearly with the average distance of atoms along the surface normal obtained by molecular dynamics simulations. This behavior can be accounted for in the low- collision-number regime. We also show that results for different atomic species can be compared on the same length scale. We demonstrate that atoms separated by about 1 angstrom along the surface normal can be clearly distinguished with this method, achieving excellent depth resolution.

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