TY  - JOUR
A1  - Kern, Christian S.
A1  - Haags, Anja
A1  - Egger, Larissa
A1  - Yang, Xiaosheng
A1  - Kirschner, Hans
A1  - Wolff, Susanne
A1  - Seyller, Thomas
A1  - Gottwald, Alexander
A1  - Richter, Mathias
A1  - de Giovannini, Umberto
A1  - Rubio, Angel
A1  - Ramsey, Michael G.
A1  - Bocquet, François C.
A1  - Soubatch, Serguei
A1  - Tautz, F. Stefan
A1  - Puschnig, Peter
A1  - Moser, Simon
T1  - Simple extension of the plane-wave final state in photoemission: bringing understanding to the photon-energy dependence of two-dimensional materials
JF  - Physical Review Research
N2  - 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.
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-350330
VL  - 5
IS  - 3
ER  - 
TY  - JOUR
A1  - Lüftner, Daniel
A1  - Milko, Matus
A1  - Huppmann, Sophia
A1  - Scholz, Markus
A1  - Ngyuen, Nam
A1  - Wießner, Michael
A1  - Schöll, Achim
A1  - Reinert, Friedrich
A1  - Puschnig, Peter
T1  - CuPc/Au(1 1 0): Determination of the azimuthal alignment by a combination of angle-resolved photoemission and density functional theory
JF  - Journal of Electron Spectroscopy and Related Phenomena
N2  - 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.
KW  - density functional theory
KW  - angle-resolved photoemission spectroscopy
KW  - organic molecule
KW  - organic–metal interface
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-120986
SN  - 0368-2048
VL  - 195
ER  -