Cluster approach to scattering in MoS2 photoemission

Abstract

We examine the photoemission cross sections and Wigner time delays from MoS 2 core-level orbitals Mo4s, Mo4p, S3s. We employ a cluster approach and study the photoemission process for progressively larger model clusters, in order to assess the scattering effects by neighboring atoms. First we explore how the fully differential cross section (FDCS) from the localized orbitals evolves as we increase the cluster size. In order to establish the underlying scattering mechanics that are mapped into the FDCS and Wigner time delays, we jointly analyze them in terms of the polar emission angle and photoemission energy for fixed azimuthal angles. The Wigner-time-delay scale goes from a few tens up into the hundreds of attoseconds when increasingly large clusters are considered, indicating the presence of high order scattering processes and interference. We find that, for the largest clusters, some internal propagation pathways start taking shape, which in an infinite system would amount to band structure positive energy states. We conclude that second- or higher-order neighbors around the main emitter strongly affect the photoelectron propagation and yield, therefore supporting their importance for models that aim for quantitative descriptions.