Influence of Film and Substrate Structure on Photoelectron Momentum Maps of Coronene Thin Films on Ag(111)

Udhardt, Christian; Otto, Félix; Kern, Christian S.; Lüftner, Daniel; Huempfner, Tobias; Kirchhuebel, Tino; Helgert, Christian; Meißner, Matthias; Schröter, Bernd; Forker, Roman; Puschnig, Peter; Fritz, Torsten

doi:10.1021/acs.jpcc.7b03500

Cited by 16 publications

(15 citation statements)

References 43 publications

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“…The orbitals appear similar to those presented by Lüder et al [30]. It should be noted that an experimental analysis of Coronene orbital imaging data is complicated by the degeneracy of HOMO and HOMO-1 and the rotational symmetry of the Coronene molecule, which means that multiple orientations of the molecular orbital can occur simultaneously [31]. This leads to a momentum map in which the rotated contributions of both states are overlapped [32], which breaks the direct Fourier transform relationship between measurement and orbital [33].…”

Section: Sparsity-based Orbital Reconstructionsupporting

confidence: 80%

Efficient orbital imaging based on ultrafast momentum microscopy and sparsity-driven phase retrieval

et al. 2020

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We present energy-resolved photoelectron momentum maps for orbital tomography that have been collected with a novel and efficient time-of-flight momentum microscopy setup. This setup is combined with a 0.5 MHz table-top femtosecond extremeultraviolet light source, which enables unprecedented speed in data collection and paves the way towards time-resolved orbital imaging experiments in the future. Moreover, we take a significant step forward in the data analysis procedure for orbital imaging, and present a sparsity-driven approach to the required phase retrieval problem, which uses only the number of non-zero pixels in the orbital. Here, no knowledge of the object support is required, and the sparsity number can easily be determined from the measured data. Used in the relaxed averaged alternating reflections algorithm, this sparsity constraint enables fast and reliable phase retrieval for our experimental as well as noise-free and noisy simulated photoelectron momentum map data.

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Section: Sparsity-based Orbital Reconstructionsupporting

confidence: 80%

Efficient orbital imaging based on ultrafast momentum microscopy and sparsity-driven phase retrieval

et al. 2020

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“…In this work, we demonstrate that monolayers of heptacene on Cu(110) behave markedly different compared to all previously studied oligoacene monolayers on coinage metal surfaces, and, to the best of our knowledge, are also dissimilar to any other polycyclic aromatic hydrocarbons adsorbed on metal substrates studied so far. 16 , 26 , 46 , 47 By using STM and combining PT with density functional theory (DFT) calculations, we show that not only the LUMO but also the LUMO + 1 receives charge when heptacene adsorbs face-on and orients along the Cu rows. Conversely, for heptacene still face-on but rotated by 90°, significantly less charge is transferred to the molecule, resulting in only the LUMO being filled and the molecular energy levels being shifted significantly toward the Fermi edge.…”

Section: Introductionmentioning

confidence: 99%

Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic–Metal Interfaces

et al. 2021

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Charge-transfer processes at molecule–metal interfaces play a key role in tuning the charge injection properties in organic-based devices and thus, ultimately, the device performance. Here, the metal’s work function and the adsorbate’s electron affinity are the key factors that govern the electron transfer at the organic/metal interface. In our combined experimental and theoretical work, we demonstrate that the adsorbate’s orientation may also be decisive for the charge transfer. By thermal cycloreversion of diheptacene isomers, we manage to produce highly oriented monolayers of the rodlike, electron-acceptor molecule heptacene on a Cu(110) surface with molecules oriented either along or perpendicular to the close-packed metal rows. This is confirmed by scanning tunneling microscopy (STM) images as well as by angle-resolved ultraviolet photoemission spectroscopy (ARUPS). By utilizing photoemission tomography momentum maps, we show that the lowest unoccupied molecular orbital (LUMO) is fully occupied and also, the LUMO + 1 gets significantly filled when heptacene is oriented along the Cu rows. Conversely, for perpendicularly aligned heptacene, the molecular energy levels are shifted significantly toward the Fermi energy, preventing charge transfer to the LUMO + 1. These findings are fully confirmed by our density functional calculations and demonstrate the possibility to tune the charge transfer and level alignment at organic–metal interfaces through the adjustable molecular alignment.

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“…It would be advantageous to substantiate this interpretation by simulations of momentum maps for benzene interacting with Pd(110) rather than benzene in the gas phase, that is, by using the wave functions of the benzene/Pd(110) interface as intitial states in the simulation of the photoemission intensity. We have demonstrated that this may indeed improve the agreement with measured momentum maps [60][61][62]. For molecule/metal interfaces with considerable interactions, however, in the present case such simulations are hampered by the fact that the DFT electronic structure has a severe shortcoming.…”

Section: Discussionmentioning

confidence: 61%

“…Moreover, the fact that the experimental MM of π 2 appears much sharper in the k [001] -direction than the simulated MM may aslo originate from molecule-substrate interaction. Not only does it lead to energetically broadened molecular resonances, but it also causes an enhanced intermolecular band dispersion which in turn results in substructures and sharper features in constant-binding energy momentum maps [60][61][62].…”

Section: Discussionmentioning

confidence: 99%

Can photoemission tomography be useful for small, strongly-interacting adsorbate systems?

et al. 2019

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Molecular orbital tomography, also termed photoemission tomography, which considers the final state as a simple plane wave, has been very successful in describing the photoemisson distribution of large adsorbates on noble metal surfaces. Here, following a suggestion by Bradshaw and Woodruff (2015 New J. Phys. 17 013033), we consider a small and strongly-interacting system, benzene adsorbed on palladium (110), to consider the extent of the problems that can arise with the final state simplification. Our angle-resolved photoemission experiments, supported by density functional theory calculations, substantiate and refine the previously determined adsorption geometry and reveal an energetic splitting of the frontier π-orbital due to a symmetry breaking which has remained unnoticed before. We find that, despite the small size of benzene and the comparably strong interaction with palladium, the overall appearance of the photoemission angular distributions can basically be understood within a plane wave final state approximation and yields a deeper understanding of the electronic structure of the interface. There are, however, noticeable deviations between measured and simulated angular patterns which we ascribe to molecule-substrate interactions and effects beyond a plane-wave final state description.

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Influence of Film and Substrate Structure on Photoelectron Momentum Maps of Coronene Thin Films on Ag(111)

Cited by 16 publications

References 43 publications

Efficient orbital imaging based on ultrafast momentum microscopy and sparsity-driven phase retrieval

Efficient orbital imaging based on ultrafast momentum microscopy and sparsity-driven phase retrieval

Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic–Metal Interfaces

Can photoemission tomography be useful for small, strongly-interacting adsorbate systems?

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