@article{KernHaagsEggeretal.2023,
  author    = {Kern, Christian S. and Haags, Anja and Egger, Larissa and Yang, Xiaosheng and Kirschner, Hans and Wolff, Susanne and Seyller, Thomas and Gottwald, Alexander and Richter, Mathias and de Giovannini, Umberto and Rubio, Angel and Ramsey, Michael G. and Bocquet, Fran{\c{c}}ois C. and Soubatch, Serguei and Tautz, F. Stefan and Puschnig, Peter and Moser, Simon},
  title     = {Simple extension of the plane-wave final state in photoemission: bringing understanding to the photon-energy dependence of two-dimensional materials},
  series = {Physical Review Research},
  volume    = {5},
  journal   = {Physical Review Research},
  number    = {3},
  doi       = {10.1103/PhysRevResearch.5.033075},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-350330},
  year      = {2023},
  abstract  = {Angle-resolved photoemission spectroscopy (ARPES) is a method that measures orbital and band structure contrast through the momentum distribution of photoelectrons. Its simplest interpretation is obtained in the plane-wave approximation, according to which photoelectrons propagate freely to the detector. The photoelectron momentum distribution is then essentially given by the Fourier transform of the real-space orbital. While the plane-wave approximation is remarkably successful in describing the momentum distributions of aromatic compounds, it generally fails to capture kinetic-energy-dependent final-state interference and dichroism effects. Focusing our present study on quasi-freestanding monolayer graphene as the archetypical two-dimensional (2D) material, we observe an exemplary E\(_{kin}\)-dependent modulation of, and a redistribution of spectral weight within, its characteristic horseshoe signature around the \(\bar {K}\) and \(\bar {K´}\) points: both effects indeed cannot be rationalized by the plane-wave final state. Our data are, however, in remarkable agreement with ab initio time-dependent density functional simulations of a freestanding graphene layer and can be explained by a simple extension of the plane-wave final state, permitting the two dipole-allowed partial waves emitted from the C 2p\(_z\) orbitals to scatter in the potential of their immediate surroundings. Exploiting the absolute photon flux calibration of the Metrology Light Source, this scattered-wave approximation allows us to extract E\(_{kin}\)-dependent amplitudes and phases of both partial waves directly from photoemission data. The scattered-wave approximation thus represents a powerful yet intuitive refinement of the plane-wave final state in photoemission of 2D materials and beyond.},
  language  = {en}
}
@article{LueftnerMilkoHuppmannetal.2014,
  author    = {L{\"u}ftner, Daniel and Milko, Matus and Huppmann, Sophia and Scholz, Markus and Ngyuen, Nam and Wießner, Michael and Sch{\"o}ll, Achim and Reinert, Friedrich and Puschnig, Peter},
  title     = {CuPc/Au(1 1 0): Determination of the azimuthal alignment by a combination of angle-resolved photoemission and density functional theory},
  series = {Journal of Electron Spectroscopy and Related Phenomena},
  volume    = {195},
  journal   = {Journal of Electron Spectroscopy and Related Phenomena},
  issn      = {0368-2048},
  doi       = {10.1016/j.elspec.2014.06.002},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-120986},
  pages     = {293-300},
  year      = {2014},
  abstract  = {Here we report on a combined experimental and theoretical study on the structural and electronic properties of a monolayer of Copper-Phthalocyanine (CuPc) on the Au(1 1 0) surface. Low-energy electron diffraction reveals a commensurate overlayer unit cell containing one adsorbate species. The azimuthal alignment of the CuPc molecule is revealed by comparing experimental constant binding energy (kxky)-maps using angle-resolved photoelectron spectroscopy with theoretical momentum maps of the free molecule's highest occupied molecular orbital (HOMO). This structural information is confirmed by total energy calculations within the framework of van-der-Waals corrected density functional theory. The electronic structure is further analyzed by computing the molecule-projected density of states, using both a semi-local and a hybrid exchange-correlation functional. In agreement with experiment, the HOMO is located about 1.2 eV below the Fermi-level, while there is no significant charge transfer into the molecule and the CuPc LUMO remains unoccupied on the Au(1 1 0) surface.},
  language  = {en}
}