\AA ngstrom depth resolution with chemical specificity at the liquid-vapor interface

TL;DR

This paper demonstrates a method using photoelectron angular distributions to achieve angstrom-scale depth resolution with chemical specificity at liquid-vapor interfaces, overcoming previous limitations in liquid studies.

Contribution

It introduces a quantitative approach linking PAD anisotropy to atomic depth, enabling precise, chemically specific depth profiling at liquid interfaces.

Findings

Anisotropy parameter scales linearly with atomic depth

Different atomic species can be compared on the same length scale

Achieves about 1 Å depth resolution

Abstract

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 anisotropy parameter characterizing the PAD scales linearly with the average distance of atoms along the surface normal. 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~\AA~along the surface normal can be clearly distinguished with this method, achieving excellent depth resolution.