TY  - JOUR
A1  - Wiessner, M.
A1  - Rodriguez Lastra, N. S.
A1  - Ziroff, J.
A1  - Forster, F.
A1  - Puschnig, P.
A1  - Dössel, L.
A1  - Müllen, K.
A1  - Schöll, A.
A1  - Reinert, F.
T1  - Different views on the electronic structure of nanoscale graphene: aromatic molecule versus quantum dot
JF  - New Journal of Physics
N2  - Graphene's peculiar electronic band structure makes it of interest for new electronic and spintronic approaches. However, potential applications suffer from quantization effects when the spatial extension reaches the nanoscale. We show by photoelectron spectroscopy on nanoscaled model systems (disc-shaped, planar polyacenes) that the two-dimensional band structure is transformed into discrete states which follow the momentum dependence of the graphene Bloch states. Based on a simple model of quantum wells, we show how the band structure of graphene emerges from localized states, and we compare this result with ab initio calculations which describe the orbital structure.
KW  - well
KW  - confinement
KW  - states
KW  - Ag(111)
KW  - photoemission
KW  - vicinal surfaces
KW  - coronene
KW  - energy
KW  - films
KW  - nanographenes
Y1  - 2012
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-130184
VL  - 14
IS  - 113008
ER  - 
TY  - JOUR
A1  - Sessi, Paolo
A1  - Silkin, Vyacheslav M.
A1  - Nechaev, Ilya A.
A1  - Bathon, Thomas
A1  - El-Kareh, Lydia
A1  - Chulkov, Evgueni V.
A1  - Echenique, Pedro M.
A1  - Bode, Matthias
T1  - Direct observation of many-body charge density oscillations in a two-dimensional electron gas
JF  - Nature Communications
N2  - Quantum interference is a striking manifestation of one of the basic concepts of quantum mechanics: the particle-wave duality. A spectacular visualization of this effect is the standing wave pattern produced by elastic scattering of surface electrons around defects, which corresponds to a modulation of the electronic local density of states and can be imaged using a scanning tunnelling microscope. To date, quantum-interference measurements were mainly interpreted in terms of interfering electrons or holes of the underlying band-structure description. Here, by imaging energy-dependent standing-wave patterns at noble metal surfaces, we reveal, in addition to the conventional surface-state band, the existence of an 'anomalous' energy band with a well-defined dispersion. Its origin is explained by the presence of a satellite in the structure of the many-body spectral function, which is related to the acoustic surface plasmon. Visualizing the corresponding charge oscillations provides thus direct access to many-body interactions at the atomic scale.
KW  - scanning tunneling spectroscopy
KW  - acoustic surface plasmon
KW  - metal surfaces
KW  - Cu(111)
KW  - excitations
KW  - microscopy
KW  - local density
KW  - standing wave formation
KW  - states
KW  - steps
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-145246
VL  - 6
IS  - 8691
ER  - 
TY  - JOUR
A1  - Sauer, C
A1  - Wießner, M
A1  - Schöll, A
A1  - Reinert, F
T1  - Observation of a molecule-metal interface charge transfer related feature by resonant photoelectron spectroscopy
JF  - New Journal of Physics
N2  - We report the discovery of a charge transfer (CT) related low binding energy feature at a molecule-metal interface by the application of resonant photoelectron spectroscopy (RPES). This interface feature is neither present for molecular bulk samples nor for the clean substrate. A detailed analysis of the spectroscopic signature of the low binding energy feature shows characteristics of electronic interaction not found in other electron spectroscopic techniques. Within a cluster model description this feature is assigned to a particular eigenstate of the photoionized system that is invisible in direct photoelectron spectroscopy but revealed in RPES through a relative resonant enhancement. Interpretations based on considering only the predominant character of the eigenstates explain the low binding energy feature by an occupied lowest unoccupied molecular orbital, which is either realized through CT in the ground or in the intermediate state. This reveals that molecule-metal CT is responsible for this feature. Consequently, our study demonstrates the sensitivity of RPES to electronic interactions and constitutes a new way to investigate CT at molecule-metal interfaces.
KW  - transfer dynamics
KW  - photoemission
KW  - states
KW  - interface
KW  - charge transfer
KW  - organic thin films
KW  - resonant photoelectron spectroscopy
KW  - energy
KW  - model calculation
KW  - NEXAFS spectroscopy
KW  - ce compounds
KW  - absorption
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148672
VL  - 17
IS  - 043016
ER  -