Publications

@article{Bone2021,

title = {Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic-Metal Interfaces},

author = {T. G. Boné and A. Windischbacher and M. S. Sättele and K. Greulich and L. Egger and T. Jauk and F. Lackner and H. F. Bettinger and H. Peisert and T. Chassé and M. G. Ramsey and M. Sterrer and G. Koller and P. Puschnig},

doi = {10.1021/acs.jpcc.1c01306},

year  = {2021},

date = {2021-01-01},

journal = {J. Phys. Chem. C},

volume = {125},

pages = {9129-9137},

abstract = {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.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Egger2020,

title = {Charge-promoted self-metalation of porphyrins on an oxide surface},

author = {L. Egger and M. Hollerer and C. S. Kern and H. Herrmann and P. Hurdax and A. Haags and X. Yang and A. Gottwald and M. Richter and S. Soubatch and F. S. Tautz and G. Koller and P. Puschnig and M. G. Ramsey and M. Sterrer},

doi = {10.1002/anie.202015187},

year  = {2021},

date = {2021-01-01},

journal = {Angew. Chem. Int. Ed.},

volume = {60},

pages = {5078-5082},

abstract = {Metalation and self-metalation reactions of porphyrins on oxide surfaces have recently gained interest. The mechanism of porphyrin self-metalation on oxides is, however, far from being understood. Herein, we show by a combination of results obtained with scanning tunneling microscopy, photoemission spectroscopy, and DFT computations, that the self-metalation of 2H-tetraphenylporphyrin on the surface of ultrathin MgO(001) films is promoted by charge transfer. By tuning the work function of the MgO(001)/Ag(001) substrate, we are able to control the charge and the metalation state of the porphyrin molecules on the surface.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Saettele2020,

title = {Going beyond Pentacene: Photoemission Tomography of a Heptacene Monolayer on Ag(110)},

author = {M. S. Sättele and A. Windischbacher and L. Egger and A. Haags and P. Hurdax and H. Kirschner and A. Gottwald and M. Richter and F. C. Bocquet and S. Soubatch and F. S. Tautz and H. F. Bettinger and H. Peisert and T. Chassé and M. G. Ramsey and P. Puschnig and G. Koller},

doi = {10.1021/acs.jpcc.0c09062},

year  = {2021},

date = {2021-01-01},

journal = {J. Phys. Chem. C},

volume = {125},

pages = {2918-2925},

abstract = {Longer acenes such as heptacene are promising candidates for optoelectronic applications but are unstable in their bulk structure as they tend to dimerize. This makes the growth of well-defined monolayers and films problematic. In this article, we report the successful preparation of a highly oriented monolayer of heptacene on Ag(110) by thermal cycloreversion of diheptacenes. In a combined effort of angle-resolved photoemission spectroscopy and density functional theory (DFT) calculations, we characterize the electronic and structural properties of the molecule on the surface in detail. Our investigations allow us to unambiguously confirm the successful fabrication of a highly oriented complete monolayer of heptacene and to describe its electronic structure. By comparing experimental momentum maps of photoemission from frontier orbitals of heptacene and pentacene, we shed light on differences between these two acenes regarding their molecular orientation and energy-level alignment on the metal surfaces.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Wallauer2020,

title = {Tracing orbital images on ultrafast time scales},

author = {R. Wallauer and M. Raths and K. Stallberg and L. Münster and D. Brandstetter and X. Yang and J. Güdde and P. Puschnig and S. Soubatch and C. Kumpf and F. C. Bocquet and F. S. Tautz and U. Höfer},

doi = {10.1126/science.abf3286},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Science},

volume = {371},

pages = {1056-1059},

abstract = {Frontier orbitals determine fundamental molecular properties such as chemical reactivities. Although electron distributions of occupied orbitals can be imaged in momentum space by photoemission tomography, it has so far been impossible to follow the momentum-space dynamics of a molecular orbital in time, for example, through an excitation or a chemical reaction. Here, we combined time-resolved photoemission using high laser harmonics and a momentum microscope to establish a tomographic, femtosecond pump-probe experiment of unoccupied molecular orbitals. We measured the full momentum-space distribution of transiently excited electrons, connecting their excited-state dynamics to real-space excitation pathways. Because in molecules this distribution is closely linked to orbital shapes, our experiment may, in the future, offer the possibility of observing ultrafast electron motion in time and space.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Brandstetter2020,

title = {kMap.py: A Python program for simulation and data analysis in photoemission tomography},

author = {D. Brandstetter and X. Yang and D. Lüftner and F. S. Tautz and P. Puschnig},

doi = {10.1016/j.cpc.2021.107905},

year  = {2021},

date = {2021-01-01},

journal = {Comp. Phys. Commun.},

volume = {263},

pages = {107905},

abstract = {Ultra-violet photoemission spectroscopy is a widely-used experimental technique to investigate the valence electronic structure of surfaces and interfaces. When detecting the intensity of the emitted electrons not only as a function of their kinetic energy, but also depending on their emission angle, as is done in angle-resolved photoemission spectroscopy (ARPES), extremely rich information about the electronic structure of the investigated sample can be extracted. For organic molecules adsorbed as well-oriented ultra-thin films on metallic surfaces, ARPES has evolved into a technique called photoemission tomography (PT). By approximating the final state of the photoemitted electron as a free electron, PT uses the angular dependence of the photocurrent, a so-called momentum map or k-map, and interprets it as the Fourier transform of the initial state’s molecular orbital, thereby gaining insights into the geometric and electronic structure of organic/metal interfaces. In this contribution, we present kMap.py which is a Python program that enables the user, via a PyQt-based graphical user interface, to simulate photoemission momentum maps of molecular orbitals and to perform a one-to-one comparison between simulation and experiment. Based on the plane wave approximation for the final state, simulated momentum maps are computed numerically from a fast Fourier transform (FFT) of real space molecular orbital distributions, which are used as program input and taken from density functional calculations. The program allows the user to vary a number of simulation parameters, such as the final state kinetic energy, the molecular orientation or the polarization state of the incident light field. Moreover, also experimental photoemission data can be loaded into the program, enabling a direct visual comparison as well as an automatic optimization procedure to determine structural parameters of the molecules or weights of molecular orbitals contributions. With an increasing number of experimental groups employing photoemission tomography to study molecular adsorbate layers, we expect kMap.py to serve as a helpful analysis software to further extend the applicability of PT.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Knippertz2020,

title = {Vertical bonding distances and interfacial band structure of PTCDA on a Sn-Ag surface alloy},

author = {J. Knippertz and L. L. Kelly and M. Franke and C. Kumpf and M. Cinchett and M. Aeschlimann and B. Stadtmüller},

doi = {10.1103/PhysRevB.102.075447},

year  = {2020},

date = {2020-08-28},

journal = {Phys. Rev. B},

volume = {102},

pages = {075447},

abstract = {Molecular materials enable a vast variety of functionalities for novel electronic and spintronic devices. The unique possibility to alter organic molecules or metallic substrates offers the opportunity to optimize interfacial properties for almost any desired field of application. For this reason, we extend the successful approach to control metal-organic interfaces by surface alloying. We present a comprehensive characterization of the structural and electronic properties of the interface formed between the prototypical molecule PTCDA and a Sn-Ag surface alloy grown on an Ag(111) single crystal surface. We monitor the changes of adsorption height of the surface alloy atoms and electronic valence band structure upon adsorption of one layer of PTCDA using the normal incidence x-ray standing wave technique in combination with momentum-resolved photoelectron spectroscopy. We find that the vertical buckling and the surface band structure of the SnAg2 surface alloy is not altered by the adsorption of one layer of PTCDA, in contrast to our recent study of PTCDA on a PbAg2 surface alloy [B. Stadtmüller et al., Phys. Rev. Lett. 117, 096805 (2016)]. In addition, the vertical adsorption geometry of PTCDA and the interfacial energy level alignment indicate the absence of any chemical interaction between the molecule and the surface alloy. We attribute the different interactions at these PTCDA/surface alloy interfaces to the presence or absence of local σ-bonds between the PTCDA oxygen atoms and the surface atoms. Combining our findings with results from literature, we are able to propose an empiric rule for engineering the surface band structure of alloys by adsorption of organic molecules.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Metzger2020,

title = {Plane-wave final state for photoemission from nonplanar molecules at a metal-organic interface},

author = {C. Metzger and M. Graus and M. Grimm and G. Zamborlini and V. Feyer and M. Schwendt and D. Lüftner and P. Puschnig and A. Schöll and F. Reinert},

doi = {10.1103/PhysRevB.101.165421},

year  = {2020},

date = {2020-04-01},

journal = {Phys. Rev. B},

volume = {101},

issue = {16},

pages = {165421},

publisher = {American Physical Society},

abstract = {In recent years, the method of orbital tomography has been a useful tool for the analysis of a variety of molecular systems. However, the underlying plane-wave final state has been largely expected to be applicable to planar molecules only. Here, we demonstrate on photoemission data from the molecule C60 adsorbed on Ag(110) that it can indeed be a valid approximation for truly three-dimensional molecules at a metal-organic interface. A comparison of the experimental data supported by density functional theory (DFT) calculations of the full interface and simulations of the photoemission process with a more exact final state enables the determination of the adsorption geometry and orientation of the C60 molecules in a monolayer on the Ag(110) surface. Additionally, charge transfer into the molecules is used to confirm the lifting in degeneracy of the t1u molecular orbitals as predicted by DFT calculations.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Haag2020,

title = {Signatures of an atomic crystal in the band structure of a C60 thin film},

author = {N. Haag and D. Lüftner and F. Haag and J. Seidel and L. L. Kelly and G. Zamborlini and M. Jugovac and V. Feyer and M. Aeschlimann and P. Puschnig and M. Cinchetti and B. Stadtmüller},

doi = {10.1103/PhysRevB.101.165422},

year  = {2020},

date = {2020-04-01},

journal = {Phys. Rev. B},

volume = {101},

issue = {16},

pages = {165422},

publisher = {American Physical Society},

abstract = {Transport phenomena in molecular materials are intrinsically linked to the orbital character and the degree of localization of the valence states. Here we combine angle-resolved photoemission with photoemission tomography to determine the spatial distribution of all molecular states of the valence band structure of a C60 thin film. While the two most frontier valence states exhibit a strong band dispersion, the states at larger binding energies are characterized by distinct emission patterns in energy and momentum space. Our findings demonstrate the formation of an atomic crystal-like band structure in a molecular solid with delocalized π-like valence states and strongly localized σ states at larger binding energies.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Hurdax2020,

title = {Controlling the Charge Transfer across Thin Dielectric Interlayers},

author = {P. Hurdax and M. Hollerer and P. Puschnig and D. Lüftner and L. Egger and M. G. Ramsey and M. Sterrer},

doi = {10.1002/admi.202000592},

year  = {2020},

date = {2020-01-01},

journal = {Adv. Mater. Interfaces},

volume = {7},

pages = {2000592},

abstract = {Whether intentional or unintentional, thin dielectric interlayers can be found in technologies ranging from catalysis to organic electronics. While originally considered as passive decoupling layers, recently it has been shown that they can actively promote charge transfer from the underlying metal to adsorbates. This charging can have profound effects on the surface chemistry of atoms, atomic clusters, and molecules, their magnetic moments, and charge injection at the contacts of organic devices. Yet, controlled studies required to understand the charge transfer process in depth are still lacking. Here, a comprehensive analysis of the phenomenon of charge transfer using the atomically controlled system of pentacene on ultrathin MgO(100) films on Ag(100) is presented. It is shown that the charge transfer process is governed by the charged and uncharged molecular species with distinct energy levels in the first monolayer. The experimental approach applied in this work allows to observe and control their ratio through direct tuning of either the work function or the thickness of the dielectric interlayer.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Sturmeit2020,

title = {Molecular anchoring stabilizes low valence Ni(I)TPP on copper against thermally induced chemical changes},

author = {H. M. Sturmeit and I. Cojocariu and M. Jugovac and A. Cossaro and A. Verdini and L. Floreano and A. Sala and G. Comelli and S. Moro and M. Stredansky and M. Corva and E. Vesselli and P. Puschnig and C. M. Schneider and V. Feyer and G. Zamborlini and M. Cinchetti},

doi = {10.1039/D0TC00946F},

year  = {2020},

date = {2020-01-01},

journal = {J. Mater. Chem. C},

volume = {8},

pages = {8876-8886},

abstract = {Many applications of molecular layers deposited on metal surfaces, ranging from single-atom catalysis to on-surface magnetochemistry and biosensing, rely on the use of thermal cycles to regenerate the pristine properties of the system. Thus, understanding the microscopic origin behind the thermal stability of organic/metal interfaces is fundamental for engineering reliable organic-based devices. Here, we study nickel porphyrin molecules on a copper surface as an archetypal system containing a metal center whose oxidation state can be controlled through the interaction with the metal substrate. We demonstrate that the strong molecule–surface interaction, followed by charge transfer at the interface, plays a fundamental role in the thermal stability of the layer by rigidly anchoring the porphyrin to the substrate. Upon thermal treatment, the molecules undergo an irreversible transition at 420 K, which is associated with an increase of the charge transfer from the substrate, mostly localized on the phenyl substituents, and a downward tilting of the latters without any chemical modification.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Haags2020,

title = {Kekulene: On-Surface Synthesis, Orbital Structure, and Aromatic Stabilization},

author = {A. Haags and A. Reichmann and Q. Fan and L. Egger and H. Kirschner and T. Naumann and S. Werner and T. Vollgraff and J. Sundermeyer and L. Eschmann and X. Yang and D. Brandstetter and F. C. Bocquet and G. Koller and A. Gottwald and M. Richter and M. G. Ramsey and M. Rohlfing and P. Puschnig and J. M. Gottfried and S. Soubatch and F. S. Tautz},

doi = {10.1021/acsnano.0c06798},

year  = {2020},

date = {2020-01-01},

journal = {ACS Nano},

volume = {14},

pages = {15766-15775},

abstract = {We revisit the question of kekulene’s aromaticity by focusing on the electronic structure of its frontier orbitals as determined by angle-resolved photoemission spectroscopy. To this end, we have developed a specially designed precursor, 1,4,7(2,7)-triphenanthrenacyclononaphane-2,5,8-triene, which allows us to prepare sufficient quantities of kekulene of high purity directly on a Cu(111) surface, as confirmed by scanning tunneling microscopy. Supported by density functional calculations, we determine the orbital structure of kekulene’s highest occupied molecular orbital by photoemission tomography. In agreement with a recent aromaticity assessment of kekulene based solely on C–C bond lengths, we conclude that the π-conjugation of kekulene is better described by the Clar model rather than a superaromatic model. Thus, by exploiting the capabilities of photoemission tomography, we shed light on the question which consequences aromaticity holds for the frontier electronic structure of a π-conjugated molecule.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Hurdax2020a,

title = {Controlling the electronic and physical coupling on dielectric thin films},

author = {P. Hurdax and M. Hollerer and L. Egger and G. Koller and X. Yang and A. Haags and S. Soubatch and F. S. Tautz and M. Richter and A. Gottwald and P. Puschnig and M. Sterrer and M. G. Ramsey},

doi = {10.3762/bjnano.11.132},

year  = {2020},

date = {2020-01-01},

journal = {Beilstein J. Nanotechnol.},

volume = {11},

pages = {1492-1503},

abstract = {Ultrathin dielectric/insulating films on metals are often used as decoupling layers to allow for the study of the electronic properties of adsorbed molecules without electronic interference from the underlying metal substrate. However, the presence of such decoupling layers may effectively change the electron donating properties of the substrate, for example, by lowering its work function and thus enhancing the charging of the molecular adsorbate layer through electron tunneling. Here, an experimental study of the charging of para-sexiphenyl (6P) on ultrathin MgO(100) films supported on Ag(100) is reported. By deliberately changing the work function of the MgO(100)/Ag(100) system, it is shown that the charge transfer (electronic coupling) into the 6P molecules can be controlled, and 6P monolayers with uncharged molecules (Schottky–Mott regime) and charged and uncharged molecules (Fermi level pinning regime) can be obtained. Furthermore, it was found that charge transfer and temperature strongly influence the orientation, conformation, and wetting behavior (physical coupling) of the 6P layers on the MgO(100) thin films.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Felter2019,

title = {Momentum microscopy on the micrometer scale: photoemission micro-tomography applied to single molecular domains},

author = {J. Felter and J. Wolters and F. C. Bocquet and F. S. Tautz and C. Kumpf},

doi = {10.1088/1361-648X/aafc45},

year  = {2019},

date = {2019-01-25},

journal = {J. Phys.: Condens. Matter},

volume = {31},

pages = {114003},

abstract = {Photoemission tomography (PT) is a newly developed method for analyzing angularresolved photoemission data. In combination with momentum microscopy it allows fora comprehensive investigation of the electronic structure of (in particular) metal-organicinterfaces as they occur in organic electronic devices. The most interesting aspect in thiscontext is the band alignment, the control of which is indispensable for designing devices.Since PT is based on characteristic photoemission patterns that are used as fingerprints,the method works well as long as these patterns are uniquely representing the specificmolecular orbital they are originating from. But this limiting factor is often not fulfilledfor systems exhibiting many differently oriented molecules, as they may occur on highlysymmetric substrate surfaces. Here we show that this limitation can be lifted by recording thephotoemission data in a momentum microscope and limiting the probed surface area to onlya few micrometers squared, since this corresponds to a typical domain size for many systems.We demonstrate this by recording data from a single domain of the archetypal adsorbatesystem 1,4,5,8-naphthalenetetracarboxylic dianhydride on Cu(0 0 1). This proof of principleexperiment paves the way for establishing the photoemission μ-tomography method as anideal tool for investigating the electronic structure of metal-organic interfaces with so farunraveled clarity and unambiguity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hollerer2019,

title = {Scanning Tunneling Microscopy of the Ordered Water Monolayer on MgO(001)/Ag(001) Ultrathin Films},

author = {M. Hollerer and D. Prochinig and P. Puschnig and E. Carrasco and H. -J. Freund and M. Sterrer},

doi = {10.1021/acs.jpcc.8b12256},

year  = {2019},

date = {2019-01-01},

journal = {J. Phys. Chem. C},

volume = {123},

pages = {3711-3718},

abstract = {Two-dimensionally ordered monolayers of water on MgO(001) have been extensively studied in the past using diffraction and spectroscopic and computational methods, but direct microscopic imaging has not been reported so far. Here, we present a scanning tunneling microscopy (STM) study, supported by infrared and X-ray photoelectron spectroscopy, of the c(4 × 2)-10H2O and p(3 × 2)-6H2O structures prepared on ultrathin MgO(001)/Ag(001) films. For the applied tunneling conditions, the contrast in the STM images originates from the hydroxyl groups, which result from water dissociation within the monolayer. The observed periodicities match the structures for the energetically most favorable c(4 × 2) and p(3 × 2) monolayer phases obtained from density functional calculations. Although the molecular water species within the monolayers, which are essential for the stabilization of the hydroxyl groups, could not be resolved, the STM results presented in this study provide further confirmation of the predicted structural models of the c(4 × 2)-10H2O and p(3 × 2)-6H2O monolayers.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Egger2018,

title = {Can photoemission tomography be useful for small, strongly-interacting adsorbate systems?},

author = {L. Egger and B. Kollmann and P. Hurdax and D. Lüftner and X. Yang and S. Weiß and A. Gottwald and M. Richter and G. Koller and S. Soubatch and F. S. Tautz and P. Puschnig and M. G. Ramsey},

doi = {10.1088/1367-2630/ab0781},

year  = {2019},

date = {2019-01-01},

journal = {New J. Phys.},

volume = {21},

pages = {043003},

abstract = {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.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Yang2019,

title = {Identifying surface reaction intermediates with photoemission tomography},

author = {X. Yang and L. Egger and P. Hurdax and H. Kaser and D. Lüftner and F. C. Bocquet and G. Koller and A. Gottwald and P. Tegeder and M. Richter and M. G. Ramsey and P. Puschnig and S. Soubatch and F. S. Tautz},

doi = {10.1038/s41467-019-11133-9},

year  = {2019},

date = {2019-01-01},

journal = {Nat. Commun.},

volume = {10},

pages = {3189},

abstract = {The determination of reaction pathways and the identification of reaction intermediates are key issues in chemistry. Surface reactions are particularly challenging, since many methods of analytical chemistry are inapplicable at surfaces. Recently, atomic force microscopy has been employed to identify surface reaction intermediates. While providing an excellent insight into the molecular backbone structure, atomic force microscopy is less conclusive about the molecular periphery, where adsorbates tend to react with the substrate. Here we show that photoemission tomography is extremely sensitive to the character of the frontier orbitals. Specifically, hydrogen abstraction at the molecular periphery is easily detected, and the precise nature of the reaction intermediates can be determined. This is illustrated with the thermally induced reaction of dibromo-bianthracene to graphene which is shown to proceed via a fully hydrogenated bisanthene intermediate. We anticipate that photoemission tomography will become a powerful companion to other techniques in the study of surface reaction pathways.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Yang2019a,

title = {Coexisting Charge States in a Unary Organic Monolayer Film on a Metal},

author = {X. Yang and L. Egger and J. Fuchsberger and M. Unzog and D. Lüftner and F. Hajek and P. Hurdax and M. Jugovac and G. Zamborlini and V. Feyer and G. Koller and P. Puschnig and F. S. Tautz and M. G. Ramsey and S. Soubatch},

doi = {10.1021/acs.jpclett.9b02231},

year  = {2019},

date = {2019-01-01},

journal = {J. Phys. Chem. Lett.},

volume = {10},

pages = {6438-6445},

abstract = {The electronic and geometric structures of tetracene films on Ag(110) and Cu(110) have been studied with photoemission tomography and compared to that of pentacene. Despite similar energy level alignment of the two oligoacenes on these surfaces revealed by conventional ultraviolet photoelectron spectroscopy, the momentum-space resolved photoemission tomography reveals a significant difference in both structural and electronic properties of tetracene and pentacene films. Particularly, the saturated monolayer of tetracene on Ag(110) is found to consist of two molecular species that, despite having the same orientation, are electronically very different—while one molecule remains neutral, another is charged because of electron donation from the substrate.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Graus2017,

title = {Degeneracy Lifting of Adsorbate Orbitals Imaged by High-Resolution Momentum Microscopy},

author = {M. Graus and C. Metzger and M. Grimm and V. Feyer and P. Puschnig and A. Schöll and F. Reinert},

doi = {10.7566/JPSJ.87.061009},

year  = {2018},

date = {2018-01-01},

journal = {J. Phys. Soc. Jpn},

volume = {87},

pages = {061009},

abstract = {On the topical example of the symmetry splitting of degenerate orbitals due to adsorption we drive the technique of orbital imaging by momentum microscopy (k-PEEM) ahead, demonstrating the potential of the method when performed with high accuracy in terms of experimental quality, energy resolution and data evaluation. Upon adsorption on the twofold symmetric substrate Ag(110), the symmetry of Iron-phthalocyanine reduces from fourfold two twofold, leading to distinct binding energies of the two e1g orbitals which constitute the twofold degenerate lowest unoccupied molecular orbital of the gas-phase molecule. In this combined experimental and theoretical study, we show that by k-PEEM with high energy resolution the individual orbitals can be identified and distinguished by mapping in momentum space.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yang2018,

title = {On the decoupling of molecules at metal surfaces},

author = {X. Yang and I. Krieger and D. Lüftner and S. Weiß and T. Heepenstrick and M. Hollerer and P. Hurdax and G. Koller and M. Sokolowski and P. Puschnig and M. G. Ramsey and F. S. Tautz and S. Soubatch},

doi = {10.1039/C8CC03334J},

year  = {2018},

date = {2018-01-01},

urldate = {2018-01-01},

journal = {Chem. Commun.},

volume = {54},

pages = {9039-9042},

abstract = {We report a method to achieve physical and electronic decoupling of organic molecules from a metal surface. Oxygen adsorbed on the Cu(100) surface immobilizes the surface electrons in the Cu–O covalent bonds. This results in electronic surface hardening and prevents charge transfer from the metal into perylene-tetracarboxylic dianhydride molecules subsequently deposited on this surface.},

keywords = {DACH},

pubstate = {published},

tppubtype = {article}

}

@article{Kollmann2018,

title = {Synthesis and combined experimental and theoretical characterization of dihydro-tetraaza-acenes},

author = {B. Kollmann and Z. Chen and D. Lüftner and O. Siri and P. Puschnig},

doi = {10.1021/acs.jpcc.8b00985},

year  = {2018},

date = {2018-01-01},

journal = {J. Phys. Chem. C},

volume = {122},

pages = {6475-6482},

abstract = {We present a combined experimental and theoretical study of electronic and optical properties of dihydro-tetraaza-acenes (DHTAn). Using solvent-free condensation, we are able to synthesize not only DHTA5 but also the longer DHTA6 and DHTA7 molecules. We then investigate their gas-phase electronic structures by means of ab initio density functional calculations employing an optimally tuned range-separated hybrid functional. By comparing with the parent linear oligoacenes (nA) and based on computed ionization potentials and electron affinities, we predict DHTAn molecules to be more stable than acenes of the same length, where we expect DHTAn molecules to be persistent at least up to n = 7 rings. We further exploit the analogy with nA by analyzing the entire intramolecular π-band structure of the DHTAn molecules. This clearly reveals that the additional two electrons donated by the dihydropyrazine group are delocalized over the entire molecule and contribute to its π-electron system. As a consequence, the symmetry of the frontier orbitals of DHTAn differs from that of the parent nA molecule. This also affects the UV–vis absorption spectra which have been measured for DHTA5, 6, and 7 dissolved in dimethyl sulfoxide and analyzed by means of excited state calculations within a time-dependent density functional theory framework.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}