2025 |
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106. | S. Mearini, D. Brandstetter, Y. Y. Grisan Qiu, D. Baranowski, I. Cojocariu, M. Jugovac, P. Gargiani, M. Valvidares, L. Schio, L. Floreano, A. Windischbacher, P. Puschnig, V. Feyer, C. M. Schneider Substrate Stabilized Charge Transfer Scheme In Coverage Controlled 2D Metal Organic Frameworks Journal Article In: Small, vol. 2500507, 2025. Abstract | Links | BibTeX | Tags: Orbital Cinema @article{Mearini2025, Recently, 2D metal-organic frameworks (2D MOFs), characterized by complexcharge transfer mechanisms, have emerged as a promising class of networksin the development of advanced materials with tailored electronic andmagnetic properties. Following the successful synthesis of a 2D MOF formedby nickel (Ni) linkers and 7,7,8,8-tetracyanoquinodimethane (TCNQ) ligands,this work investigates how the Ni-to-ligand ratio influences the electroniccharge redistribution in an Ag(100)-supported 2D MOF. The interplaybetween linker-ligand and substrate-MOF charge transfer processes leads to astable equilibrium, resulting in a robust electronic structure that remainsindependent of stoichiometric ratios. This stability is primarily based on theelectron transfer from the metal substrate, which compensates for chargeimbalances introduced by the metal-organic coordination across differentMOF configurations. Despite minor changes observed in the magneticresponse of the Ni centers, these findings emphasize the robustness of theelectronic structure, which remains largely unaffected by structural variations,highlighting the potential of these 2D MOFs for advanced applications inelectronics and spintronics. |
105. | Y. Y. Grisan Qiu, D. Brandstetter, S. Mearini, D. Baranowski, I. Cojocariu, M. Jugovac, G. Zamborlini, P. Gargiani, M. Valvidares, A. Windischbacher, P. Puschnig, V. Feyer, C. M. Schneider Conformation-Driven Nickel Redox States and Magnetism in 2D Metal–organic Frameworks Journal Article In: Adv. Funct. Mater., vol. 2418186, 2025. Abstract | Links | BibTeX | Tags: Orbital Cinema @article{Qiu2025, 2D metal–organic frameworks (2D MOFs) attract considerable attention because of their versatile properties and as potential candidates for single-atom catalysis, high-density information storage media or molecular electronics and spintronics devices. Their unique characteristics arise from an intricate interplay between the metal center, the surrounding ligands and the underlying substrate. Here, the intrinsic magnetic and electronic properties of a single-layer MOF on graphene is investigated with a combination of spectroscopic techniques and theoretical modeling. Taking advantage of the weak interaction between the MOF and graphene substrate, it is specifically focused on the influence of the coordination environment on these properties. Notably, two distinct coordination configurations are observed for the transition metal centers within the 2D MOF, and clarify how axial distortions in the ligand field affect the hybridization between the Ni 3d states and the π-symmetric molecular orbitals of 7,7,8,8-tetracyanoquinodimethane ligands, leading to the coexistence of two Ni redox states with different spin configurations. Furthermore, the transition from a nearly free-standing MOF is examined to metal-supported frameworks, elucidating the impact of substrate interactions on the electronic and magnetic properties. The findings advance the understanding of MOFs and offer insights into developing functional materials with tailored magnetic and electronic properties. |
104. | A. Haags, D. Brandstetter, X. Yang, L. Egger, H. Kirschner, A. Gottwald, M. Richter, G. Koller, F. C. Bocquet, C. Wagner, M. G. Ramsey, S. Soubatch, P. Puschnig, F. S. Tautz Tomographic identification of all molecular orbitals in a wide binding energy range Journal Article Forthcoming In: ArXiv, Forthcoming. Abstract | Links | BibTeX | Tags: Orbital Cinema @article{Haags2025, In the past decade, photoemission orbital tomography (POT) has evolved into a powerful tool to investigate the electronic structure of organic molecules adsorbed on surfaces. Here we show that POT allows for the comprehensive experimental identification of all molecular orbitals in a substantial binding energy range, in the present case more than 10 eV. Making use of the angular distribution of photoelectrons as a function of binding energy, we exemplify this by extracting orbital-resolved partial densities of states (pDOS) for 15 π and 23 σ orbitals from the experimental photoemission intensities of the prototypical organic molecule bisanthene (C28H14) on a Cu(110) surface. In their entirety, these experimentally measured orbital-resolved pDOS for an essentially complete set of orbitals serve as a stringent benchmark for electronic structure methods, which we illustrate by performing density functional theory (DFT) calculations employing four frequently-used exchange-correlation functionals. By computing the respective molecular-orbital-projected densities of states of the bisanthene/Cu(110) interface, a one-to-one comparison with experimental data for an unprecedented number of 38 orbital energies becomes possible. The quantitative analysis of our data reveals that the range-separated hybrid functional HSE performs best for the investigated organic/metal interface. At a more fundamental level, the remarkable agreement between the experimental and the Kohn-Sham orbital energies over a binding energy range larger than 10,eV suggests that -- perhaps unexpectedly -- Kohn-Sham orbitals approximate Dyson orbitals, which would rigorously account for the electron extraction process in photoemission spectroscopy but are notoriously difficult to compute, in a much better way than previously thought. |
2024 |
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103. | S. Mearini, D. Baranowski, D. Brandstetter, A. Windischbacher, I. Cojocariu, P. Gargiani, M. Valvidares, L. Schio, L. Floreano, P. Puschnig, V. Feyer, C. M. Schneider Band Structure Engineering in 2D Metal–Organic Frameworks Journal Article In: Advanced Science, vol. 11, iss. 38, no. 2404667, 2024. Abstract | Links | BibTeX | Tags: Orbital Cinema @article{Mearini2024, The design of 2D metal–organic frameworks (2D MOFs) takes advantage ofthe combination of the diverse electronic properties of simple organic ligandswith different transition metal (TM) centers. The strong directional nature ofthe coordinative bonds is the basis for the structural stability and the periodicarrangement of the TM cores in these architectures. Here, direct and clearevidence that 2D MOFs exhibit intriguing energy-dispersive electronic bandswith a hybrid character and distinct magnetic properties in the metal cores,resulting from the interactions between the TM electronic levels and theorganic ligand 𝝅-molecular orbitals, is reported. Importantly, a method toeffectively tune both the electronic structure of 2D MOFs and the magneticproperties of the metal cores by exploiting the electronic structure of distinctTMs is presented. Consequently, the ionization potential characteristic ofselected TMs, particularly the relative energy position and symmetry of the 3dstates, can be used to strategically engineer bands within specificmetal–organic frameworks. These findings not only provide a rationale forband structure engineering in 2D MOFs but also offer promisingopportunities for advanced material design. |
102. | A. Haags Advances in Photoemission Orbital Tomography PhD Thesis 2024, ISBN: 978-3-95806-766-0. @phdthesis{Haags2024, |
101. | W. Bennecke, A. Windischbacher, D. Schmitt, J. P. Bange, R. Hemm, C. S. Kern, G. D’Avino, X. Blase, D. Steil, S. Steil, M. Aeschlimann, B. Stadtmüller, M. Reutzel, P. Puschnig, G. S. M. Jansen, S. Mathias Disentangling the multiorbital contributions of excitons by photoemission exciton tomography Journal Article In: Nature Communications, vol. 15, no. 1804, pp. 10, 2024. Abstract | Links | BibTeX | Tags: Orbital Cinema @article{Bennecke2024, Excitons are realizations of a correlated many-particle wave function, specifi-cally consisting of electrons and holes in an entangled state. Excitons occurwidely in semiconductors and are dominant excitations in semiconductingorganic and low-dimensional quantum materials. To efficiently harness thestrong optical response and high tuneability of excitons in optoelectronics andin energy-transformation processes,access to the full wavefunction of theentangled state is critical, but has so far not been feasible. Here, we show howtime-resolved photoemission momentum microscopy can be used to gainaccess to the entangled wavefunction and to unravel the exciton’s multiorbitalelectron and hole contributions. For the prototypical organic semiconductorbuckminsterfullerene (C60), we exemplify the capabilities of exciton tomo-graphy and achieve unprecedented access to key properties of the entangledexciton state including localization, charge-transfer character, and ultrafastexciton formation and relaxation dynamics. |
2023 |
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100. | A. Adamkiewicz, M. Raths, M. Stettner, M. Theilen, L. Münster, S. Wenzel, M. Hutter, S. Soubatch, C. Kumpf, F. C.Bocquet, R. Wallauer, F. S. Tautz, U. Höfer Coherent and Incoherent Excitation Pathways in Time-Resolved Photoemission Orbital Tomography of CuPc/Cu(001)-2O Journal Article In: J.Phys. Chem. C, vol. 127, pp. 20411, 2023. Abstract | Links | BibTeX | Tags: Orbital Cinema @article{Adamkiewicz2023, Time-resolved photoemission orbital tomography (tr-POT) offers unique possibilities for tracing molecular electron dynamics. The recorded pump-induced changes of the angle-resolved photoemission intensities allow one to characterize unoccupied molecular states in momentum space and to deduce the incoherent temporal evolution of their population. Here, we show for the example of CuPc/Cu(001)-2O that the method also gives access to the coherent regime and that different excitation pathways can be disentangled by a careful analysis of the time-dependent change of the photoemission momentum pattern. In particular, we demonstrate by varying photon energy and polarization of the pump light how the incoherent temporal evolution of the LUMO distribution can be distinguished from coherent contributions of the projected HOMO. Moreover, we report the selective excitation of molecules with a specific orientation at normal incidence by aligning the electric field of the pump light along the molecular axis. |
99. | A. Windischbacher Investigating Ground and Excited State Properties of Complex Organic/Inorganic Interfaces With Ab-Initio Calculations PhD Thesis 2023. @phdthesis{nokey, |
98. | C. S. Kern Exploring the Frontiers of Photoemission Orbital Tomography PhD Thesis 2023. @phdthesis{Kern2023b, |
97. | C. S. Kern, A. Windischbacher, P. Puschnig Photoemission orbital tomography for excitons in organic molecules Journal Article In: Phys. Rev. B, vol. 108, pp. 085132, 2023. Abstract | Links | BibTeX | Tags: Orbital Cinema @article{Kern2023, Driven by recent developments in time-resolved photoemission spectroscopy, we extend the successful method of photoemission orbital tomography (POT) to excitons. Our theory retains the intuitive orbital picture of POT, while respecting both the entangled character of the exciton wave function and the energy conservation in the photoemission process. Analyzing results from three organic molecules, we classify generic exciton structures and give a simple interpretation in terms of natural transition orbitals. We validate our findings by directly simulating pump-probe experiments with time-dependent density functional theory. |
2022 |
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96. | D. Brandstetter Photoemission Distributions from Time-Dependent Density Functional Theory Masters Thesis 2022. Abstract | Links | BibTeX | Tags: DACH @mastersthesis{Brandstetter2022, A recent study in photoemission orbital tomography [Science 371, 1056 (2021)] has demonstrated that transiently excited electrons can be traced in time. This has become possible through measuring their signature in the angle-resolved momentum distribution of photoelectrons released by a high-energy probe pulse. Further developing this exciting and powerful new technique, dubbed orbital cinematography, is a desirable track for future experimental development. In this work, we use time-dependent density functional theory to scout ahead and perform an ab-initio simulation of a sub-femtosecond pump-probe angle-resolved photoemission experiment. We investigate potential issues and possible remedies in the description of ARPES within the framework of TD-DFT and conclude with momentum maps of the frontier orbitals. |
95. | P. Hurdax Charge Transfer Across Ultrathin Dielectric Layers: A Controlled Study of the Phenomenon on MgO on Ag(100) PhD Thesis 2022. @phdthesis{Hurdax2022b, |
94. | F. Presel, C. S. Kern, T. G. Boné, F. Schwarz, P. Puschnig, M. G. Ramsey, M. Sterrer Charge and adsorption height dependence of the self-metalation of porphyrins on ultrathin MgO(001) films Journal Article In: Phys. Chem. Chem. Phys., vol. 24, pp. 28540-28547, 2022. Abstract | Links | BibTeX | Tags: DACH @article{Presel2022, We have experimentally determined the adsorption structure, charge state, and metalation state of porphin, the fundamental building block of porphyrins, on ultrathin Ag(001)-supported MgO(001) films by scanning tunneling microscopy and photoemission spectroscopy, supported by calculations based on density functional theory. By tuning the substrate work function to values below and above the critical work function for charging, we succeeded in the preparation of 2H-P monolayers which contain negatively charged and uncharged molecules. Significantly, it is shown that the porphin molecules self-metalate at room temperature, forming the corresponding Mg-porphin, irrespective of their charge state. This is in contrast to self-metalation of tetraphenyl porphyrin (TPP), which occurs on planar MgO(001) only if the molecules are negatively charged. The different reactivity is explained by the reduced molecule-substrate distance of the planar porphin molecule compared to the bulkier TPP. The results of this study shed light on the mechanism of porphyrin self-metalation on oxides and highlight the role of the adsorption geometry on the chemical reactivity. |
93. | P. Hurdax, C. S. Kern, T. G. Boné, A. Haags, M. Hollerer, L. Egger, X. Yang, H. Kirschner, A. Gottwald, M. Richter, F. C. Bocquet, S. Soubatch, G. Koller, F. S. Tautz, M. Sterrer, P. Puschnig, M. G. Ramsey Large Distortion of Fused Aromatics on Dielectric Interlayers Quantified by Photoemission Orbital Tomography Journal Article In: ACS Nano, vol. 16, pp. 17435-17443, 2022. Abstract | Links | BibTeX | Tags: DACH @article{Hurdax2022, Polycyclic aromatic compounds with fused benzene rings offer an extraordinary versatility as next-generation organic semiconducting materials for nanoelectronics and optoelectronics due to their tunable characteristics, including charge-carrier mobility and optical absorption. Nonplanarity can be an additional parameter to customize their electronic and optical properties without changing the aromatic core. In this work, we report a combined experimental and theoretical study in which we directly observe large, geometry-induced modifications in the frontier orbitals of a prototypical dye molecule when adsorbed on an atomically thin dielectric interlayer on a metallic substrate. Experimentally, we employ angle-resolved photoemission experiments, interpreted in the framework of the photoemission orbital tomography technique. We demonstrate its sensitivity to detect geometrical bends in adsorbed molecules and highlight the role of the photon energy used in experiment for detecting such geometrical distortions. Theoretically, we conduct density functional calculations to determine the geometric and electronic structure of the adsorbed molecule and simulate the photoemission angular distribution patterns. While we found an overall good agreement between experimental and theoretical data, our results also unveil limitations in current van der Waals corrected density functional approaches for such organic/dielectric interfaces. Hence, photoemission orbital tomography provides a vital experimental benchmark for such systems. By comparison with the state of the same molecule on a metallic substrate, we also offer an explanation why the adsorption on the dielectric induces such large bends in the molecule. |
92. | X. Yang, M. Jugovac, G. Zamborlini, V. Feyer, G. Koller, P. Puschnig, S. Soubatch, M. G. Ramsey, F. S. Tautz Momentum-selective orbital hybridization Journal Article In: Nat. Commun., vol. 13, pp. 5148, 2022. Abstract | Links | BibTeX | Tags: DACH @article{Yang2022, When a molecule interacts chemically with a metal surface, the orbitals of the molecule hybridise with metal states to form the new eigenstates of the coupled system. Spatial overlap and energy matching are determining parameters of the hybridisation. However, since every molecular orbital does not only have a characteristic spatial shape, but also a specific momentum distribution, one may additionally expect a momentum matching condition; after all, each hybridising wave function of the metal has a defined wave vector, too. Here, we report photoemission orbital tomography measurements of hybrid orbitals that emerge from molecular orbitals at a molecule-on-metal interface. We find that in the hybrid orbitals only those partial waves of the original orbital survive which match the metal band structure. Moreover, we find that the conversion of the metal’s surface state into a hybrid interface state is also governed by momentum matching constraints. Our experiments demonstrate the possibility to measure hybridisation momentum-selectively, thereby enabling deep insights into the complicated interplay of bulk states, surface states, and molecular orbitals in the formation of the electronic interface structure at molecule-on-metal hybrid interfaces. |
91. | A. Haags, X. Yang, L. Egger, D. Brandstetter, H. Kirschner, F. C. Bocquet, G. Koller, A. Gottwald, M. Richter, J. M. Gottfried, M. G. Ramsey, P. Puschnig, S. Soubatch, F. S. Tautz Momentum-space imaging of σ-orbitals for chemical analysis Journal Article In: Sci. Adv., vol. 8, pp. eabn0819, 2022. Abstract | Links | BibTeX | Tags: DACH @article{Haags2021, Tracing the modifications of molecules in surface chemical reactions benefits from the possibility to image their orbitals. While delocalized frontier orbitals with π character are imaged routinely with photoemission orbital tomography, they are not always sensitive to local chemical modifications, particularly the making and breaking of bonds at the molecular periphery. For such bonds, σ orbitals would be far more revealing. Here, we show that these orbitals can indeed be imaged in a remarkably broad energy range and that the plane wave approximation, an important ingredient of photoemission orbital tomography, is also well fulfilled for these orbitals. This makes photoemission orbital tomography a unique tool for the detailed analysis of surface chemical reactions. We demonstrate this by identifying the reaction product of a dehalogenation and cyclodehydrogenation reaction. |
90. | M. S. Sättele, A. Windischbacher, K. Greulich, L. Egger, A. Haags, H. Kirschner, R. Ovsyannikov, E. Giangrisostomi, A. Gottwald, M. Richter, S. Soubatch, F. S. Tautz, M. G. Ramsey, P. Puschnig, G. Koller, H. F. Bettinger, T. Chassé, H. Peisert Hexacene on Cu(110) and Ag(110): Influence of the Substrate on Molecular Orientation and Interfacial Charge Transfer Journal Article In: J. Phys. Chem. C, vol. 126, pp. 5036-5045, 2022. Abstract | Links | BibTeX | Tags: DACH @article{Saettele2022, Hexacene, composed of six linearly fused benzene rings, is an organic semiconductor material with superior electronic properties. The fundamental understanding of the electronic and chemical properties is prerequisite to any possible application in devices. We investigate the orientation and interface properties of highly ordered hexacene monolayers on Ag(110) and Cu(110) with X-ray photoemission spectroscopy (XPS), photoemission orbital tomography (POT), X-ray absorption spectroscopy (XAS), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT). We find pronounced differences in the structural arrangement of the molecules and the electronic properties at the metal/organic interfaces for the two substrates. While on Cu(110) the molecules adsorb with their long molecular axis parallel to the high symmetry substrate direction, on Ag(110), hexacene adsorbs in an azimuthally slightly rotated geometry with respect to the metal rows of the substrate. In both cases, molecular planes are oriented parallel to the substrate. A pronounced charge transfer from both substrates to different molecular states affects the effective charge of different C atoms of the molecule. Through analysis of experimental and theoretical data, we found out that on Ag(110) the LUMO of the molecule is occupied through charge transfer from the metal, whereas on Cu(110) even the LUMO+1 receives a charge. Interface dipoles are determined to a large extent by the push-back effect, which are also found to differ significantly between 6A/Ag(110) and 6A/Cu(110). |
89. | A. Thomas, T. Leoni, O. Siri, C. Becker, M. Unzog, C. S. Kern, P. Puschnig, P. Zeppenfeld A One-Dimensional High-Order Commensurate Phase of Tilted Molecules Journal Article In: Phys. Chem. Chem. Phys., vol. 24, pp. 9118-9122, 2022. Abstract | Links | BibTeX | Tags: DACH @article{Thomas2022, We report on the formation of a high-order commensurate (HOC) structure of 5,14-dihydro-5,7,12,14-tetraazapentacene (DHTAP) molecules on the highly corrugated Cu(110)–(2 × 1)O surface. Scanning tunnelling microscopy shows that the DHTAP molecules form a periodic uniaxial arrangement in which groups of seven molecules are distributed over exactly nine substrate lattice spacings along the [10] direction. DFT-calculations reveal that this peculiar arrangement is associated with different tilting of the seven DHTAP molecules within the quasi one-dimensional HOC unit cell. The orientational degree of freedom thus adds a new parameter, which can efficiently stabilize complex molecular structures on corrugated surfaces. |
88. | M. Stredansky, S. Moro, M. Corva, H. M. Sturmeit, V. Mischke, D. Janas, I. Cojocariu, M. Jugovac, A. Cossaro, A. Verdini, L. Floreano, Z. Feng, A. Sala, G. Comelli, A. Windischbacher, P. Puschnig, C. Hohner, M. Kettner, J. Libuda, M. Cinchetti, C. M. Schneider, V. Feyer, E. Vesselli, G. Zamborlini Disproportionation of Nitric Oxide at a Surface-Bound Nickel Porphyrinoid Journal Article In: Angew. Chem. Int. Ed., vol. 61, pp. e202201916, 2022. Abstract | Links | BibTeX | Tags: DACH @article{Stredansky2022, Uncommon metal oxidation states in porphyrinoid cofactors are responsible for the activity of many enzymes. The F430 and P450nor co-factors, with their reduced NiI- and FeIII-containing tetrapyrrolic cores, are prototypical examples of biological systems involved in methane formation and in the reduction of nitric oxide, respectively. Herein, using a comprehensive range of experimental and theoretical methods, we raise evidence that nickel tetraphenyl porphyrins deposited in vacuo on a copper surface are reactive towards nitric oxide disproportionation at room temperature. The interpretation of the measurements is far from being straightforward due to the high reactivity of the different nitrogen oxides species (eventually present in the residual gas background) and of the possible reaction intermediates. The picture is detailed in order to disentangle the challenging complexity of the system, where even a small fraction of contamination can change the scenario. |
2021 |
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87. | E. Parth Angle-resolved Photoemission of Molecules and Two-dimensional Materials from a Tight-binding Perspective Masters Thesis 2021. Abstract | Links | BibTeX | Tags: @mastersthesis{Parth2021, Angle-resolved photoemission spectroscopy (ARPES) offers the most direct access to investigate the electronic bandstructure of surfaces and solids. Nevertheless, the interpretation of ARPES data is often a complex task and simulations of bandstructures and ARPES intensity distributions are desirable. With the knowledge of the electronic eigenstates of a given system, it is possible to make predictions of the corresponding intensity distribution of an ARPES experiment. This can be achieved within the so called one-step model of photoemission which describes the photoexcitation from an initial state to a final, unbound state as a single coherent process. Thus, the photoemission matrix element not only depends on the initial and final state, but additionally on the polarization of the incident light beam. In this work, we focus on the differences in the angular distribution of the photoemission intensity arising from excitation with right and left handed circularly polarized light, respectively. This effect is referred to as circular dichroism in the angular distribution (CDAD). A common way of evaluating the photoemission matrix element appearing in the one-step model, if the final state is approximated as a plane wave, is the so called velocity gauge, which can be interpreted as Fourier transform of the initial state. Within this formalism the CDAD vanishes. Another way of evaluating the photoemission matrix element is the so called length-gauge. Here, the interaction Hamiltonian in the matrix element contains the position operator in place of the momentum operator in the velocity gauge. By specializing on planar hydrocarbons a general analytic expression of the photoemission matrix element and its polarization dependence is found. To this end, a tight-binding (TB) model, based on density functional theory (DFT) results, is constructed in order to calculate the electronic eigenstates of any planar hydrocarbon systems. This way a method to calculate the ARPES intensity distribution for arbitrary planar hydrocarbon molecules is derived. Using this model, the photoemission matrix element in length-gauge predicts a non-vanishing CDAD. As an alternative and potentially more accurate approach to simulate ARPES inten sity maps, also time-dependent density functional theory (TDDFT) calculations are performed. We utilize the so-called surface flux method, which produces ARPES intensities without the need to approximate the final state, and which serves as an ideal reference for benchmarking the TB-model. When comparing ARPES simulations of the TDDFT and the TB-model for graphene, significant differences in the CDAD intensity distributions are observed. Finally, we also compare experimental photoemission momentum maps for the organic molecule tetracene with the momentum maps obtained by the TB-model and observe reasonable agreement. Whether the evaluation of the matrix element in the length-gauge shows the correct CDAD effect for molecular systems in general, however is not evaluated and further testing is needed. |
86. | P. Schnabl Photoemission Tomography of Heptacene on Metallic Surfaces Bachelor Thesis 2021. Abstract | Links | BibTeX | Tags: @bachelorthesis{Schnabl2021, Photoemission tomography has been developed in the last decade and has proven to be a valuable method for analysing materials in the field of surface science. Combining data of angle-resolved photoelectron spectroscopy with ab-initio calculations based on density functional theory, photoemission tomography is used for the evaluation of photoemission spectra. The program ”kMap.py” utilizes this method and is used in this thesis to investigate experimental data of heptacene on the metallic surfaces Ag(110) and Cu(110)–(2 x 1)O. With the knowledge obtained from analysing the underlying fitting procedure, orientations of the heptacene molecules on both metallic surfaces were determined. Furthermore, a so-called orbital deconvolution was performed for each set of experimental data. Thereby the photoemission intensity of the emitted electrons is assigned to contributions of different molecular orbitals, which can be interpreted as an orbital projected density of states. |
85. | M. Niederreiter Integer charge transfer in organic adsorbates on metallic substrates Masters Thesis 2021. @mastersthesis{Niederreiter2021, In this work charge transfer into molecular monolayers on metal substrates is studied. The first goal was to find clear experimental evidence for the coexistence of charged and uncharged copper-phthalocyanine CuPc molecules in monolayers (ML) on silver surfaces. The first findings were made using scanning tunneling microscopy STM, where images of CuPc monolayers on Ag(111) showed two distinct molecular species, which could be identified as charged and neutral from the appearance of their orbital structure. This is further supported by Konod resonance observations with scanning tunneling spectroscopy STS. On Ag(100) larger scale images also indicated two distinct species with different contrast. These findings are complemented by the results obtained with angle resolved ultraviolet photoemission spectroscopy ARUPS. Studying the sub-monolayer growth of CuPc on Ag(100) strongly suggests the coexistence of a charged and an uncharged CuPc species within the first ML. Estimates of the fraction of charged molecules could be made from the intensities of orbital features in ARUPS and from the measured work function behaviour. STM and ARUPS both suggest the coexistence of integer charge and neutral molecules on the metal substrate. Even beyond that, three different methods of determining the ratio of charged CuPc molecules have been used, which ultimately yield similar results and therefore support each other. These findings are in contradiction to the conventional wisdom that equilibration will lead to all molecules experiencing similar charge transfer. Furthermore, displacement studies with pentacene 5A and CuPc performed with ARUPS allow a deeper understanding of the process of charge transfer and the role the electron affinity (EA) plays in it. It could clearly be shown that CuPc displaces 5A both on the metallic Ag(100) and on the dielectric MgO(100) surface. This is remarkable since the binding mechanisms on these two surfaces would generally be considered very different from each other, with hybridization on the metal and charge transfer on the dielectric being the dominant processes. This strongly suggests that indeed the EA and therefore charge transfer play a central role in the binding process of the adsorbates. This work furthers the understanding of charge transfer on metals and paves the way for understanding displacement reactions and suggests a means of controlling and predicting molecular heterostructures. |
84. | L. Reicht Ab-initio Investigations of the Electronic Structure of Armchair Graphene Nanoribbons on the Au(111) Surface Masters Thesis 2021. Abstract | BibTeX | Tags: DACH @mastersthesis{Reicht2021, Armchair graphene nanoribbons (AGNR) have gained increased attention in the recent years, because it became possible to produce them atomically precise via a bottom-up approach. Due to their tunable band gap, AGNRs have the potential to be used in opto-electronic devices and therefore could replace silicon in specific applications. Given these prospects, it is not surprising, that a fair amount of research has gone into understanding their electronic structure. However there is still a lack in understanding how surfaces affect their electronic structure. This work tries to fill this gap by investigating the effect of a Au(111) surface on the electronic structure of 7-, 9- and 13-AGNR, which are the AGNRs that are probably the most relevant for technical applications. Special focus is placed on the simulation of angle-resolved photoemission spectroscopy (ARPES) experiments. The ever increasing resolution of ARPES allows the direct measurement of the electronic band structure. In order to understand the results of ARPES experiments, simulations of it are essential. Additionally to the ARPES simulations, various other aspects of the AGNRs were investigated with ab-initio simulations. These include the electronic band structure, density of states (DOS), band gap, adsorption position on Au(111), adsorption height and charge density. To perform these ab-initio investigations, density functional theory (DFT) is employed in this work. Using the Kohn-Sham orbitals from the DFT simulation, the photoemission intensities of ARPES experiments were calculated. Simulated ARPES band and momentum maps of 7-AGNR/Au(111) are compared to multiple experiments. They consistently show good agreement, thereby confirming the validity of the used methods. |
83. | A. Reichmann Electronic and Aromatic Structure of Kekulene Studied by Density Functional Theory Masters Thesis 2021. Abstract | Links | BibTeX | Tags: DACH @mastersthesis{Reichmann2021, In this work the geometric, aromatic and electronic structure of the polycyclic hydrocarbon kekulene (C48 H24 ) is studied using density functional theory (DFT), the harmonic oscillation model of aromaticity (HOMA), the simple Hückel molecular orbital theory and the probe particle model. Experimental results of kekulene adsorbed on the two copper substrates, Cu(111) and Cu(110) are compared to DFT optimized calculations regarding the same metal-organic interfaces as well as theoretical calculations of gas phase kekulene. Firstly, the energetically most favorable adsorption position of kekulene on the copper surfaces is obtained. With the optimized configuration the aromatic structure is investigated via the HOMA. In order to further analyze the aromaticity of kekulene, various theoretical models of kekulene are constructed by fixing the geometric structure of kekulene and by fixing electronic structure via the Hückel molecular orbital model. These models, the DFT optimized structures of free kekulene as well as the kekulene/Cu interface are examined in terms of their photoemission intensity, in order to gain insights into their electronic structure. The photoemission momentum maps are compared with photoemission momentum maps gained from angle resolved photoemission spectroscopy measurements. Furthermore, the density of states is investigated for the DFT optimized calculations and the charge density distribution and real space distribution of the frontier orbital nodal structure are investigated of all theoretical configurations. Finally the probe particle model is used in order to simulate non-contact atomic force microscopy and inelastic tunneling spectroscopy measurements. From the theoretical, as well as the experimental results, it is concluded that the aromatic Clar’s sextet model is a good predictor of kekulene’s aromatic structure. |
82. | C. Dösinger Simulation of Angle-Resolved Photoemission Intensity Maps for Two-Dimensional Materials Masters Thesis 2021. Abstract | Links | BibTeX | Tags: DACH @mastersthesis{Doesinger2021, Angle-resolved photoemission spectroscopy (ARPES) is the most direct experimental technique to investigate the electronic band structure of surfaces and layered materials. ARPES maps are routinely compared to results from ab-initio band structure calculations. However, simulations of photoemission cross-sections including transition matrix element effects which provide additional insights are rare, especially simulations that include spin-orbit coupling in the band structure calculation. In this thesis, the electronic ground state is calculated using density functional theory (DFT). Based on the ground state wave function, angle-resolved photoemission intensity maps are simulated within the one-step model of photoemission, by modelling the final state of the photoelectron as a plane wave. This plane wave final state (PWFS) approach has proven to work surprisingly well for monolayers of organic molecules on metal surfaces. For this work, the approach is extended to include spin-orbit coupling (SOC). The results of the simulations are compared to experiments and calculations using a tight binding approach. The method is applied to three classes of materials. First, the transition metal dichalcogenides (TMD) tungsten disulphide (WS2 ) and tungsten diselenide (WSe2 ), second, a monolayer of silver-tellurium on a silver-(111) surface (AgTe/Ag(111)), and, third, mono-layer and bilayer graphene. The simulations for the TMDs are able the correctly describe the ARPES intensities and the spin-splitting of the bands. However, results for AgTe/Ag(111) show discrepancies to the experiments. It is shown that it is possible to include SOC in the PWFS approach, which can yield reliable results. However, further tests are needed. |
81. | C. Stockinger Photoemission Tomography: Implementation and Testing of a Phase Retrieval Algorithm Bachelor Thesis 2021. Abstract | Links | BibTeX | Tags: @bachelorthesis{Stockinger2021, Photoemission tomography is a combined experimental and theoretical approach to understand angle resolved photoelectron spectroscopy (ARPES) distributions. By approximating the final state wave function as a plane wave, it has been shown that ARPES intensity distributions are proportional to the squared modulus of the Fourier transformation of the initial state wave function. The phase information of the wave function, however, is lost during the measurement process, which means that real space orbitals cannot simply be calculated by an inverse Fourier transformation. Nevertheless, the lost phase information can be retrieved using iterative methods. The main aim of this work is the implementation and testing of such a phase retrieval algorithm. |
80. | L. Egger, M. Hollerer, C. S. Kern, H. Herrmann, P. Hurdax, A. Haags, X. Yang, A. Gottwald, M. Richter, S. Soubatch, F. S. Tautz, G. Koller, P. Puschnig, M. G. Ramsey, M. Sterrer Charge-promoted self-metalation of porphyrins on an oxide surface Journal Article In: Angew. Chem. Int. Ed., vol. 60, pp. 5078-5082, 2021. Abstract | Links | BibTeX | Tags: DACH @article{Egger2020, 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. |
79. | I. Cojocariu, F. Feyersinger, P. Puschnig, L. Schio, L. Floreano, V. Feyer, C. M. Schneider Insight into intramolecular chemical structure modifications by on-surface reaction using photoemission tomography Journal Article In: Chem. Commun., vol. 57, pp. 3050-3053, 2021. Abstract | Links | BibTeX | Tags: DACH @article{Cojocariu2021, The sensitivity of photoemission tomography (PT) to directly probe single molecule on-surface intramolecular reactions will be shown here. PT application in the study of molecules possessing peripheral ligands and structural flexibility is tested on the temperature-induced dehydrogenation intramolecular reaction on Ag(100), leading from CoOEP to the final product CoTBP. Along with the ring-closure reaction, the electronic occupancy and energy level alignment of the frontier orbitals, as well as the oxidation state of the metal ion, are elucidated for both the CoOEP and CoTBP systems. |
78. | M. S. Sättele, A. Windischbacher, L. Egger, A. Haags, P. Hurdax, H. Kirschner, A. Gottwald, M. Richter, F. C. Bocquet, S. Soubatch, F. S. Tautz, H. F. Bettinger, H. Peisert, T. Chassé, M. G. Ramsey, P. Puschnig, G. Koller Going beyond Pentacene: Photoemission Tomography of a Heptacene Monolayer on Ag(110) Journal Article In: J. Phys. Chem. C, vol. 125, pp. 2918-2925, 2021. Abstract | Links | BibTeX | Tags: DACH @article{Saettele2020, 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. |
77. | R. Wallauer, M. Raths, K. Stallberg, L. Münster, D. Brandstetter, X. Yang, J. Güdde, P. Puschnig, S. Soubatch, C. Kumpf, F. C. Bocquet, F. S. Tautz, U. Höfer Tracing orbital images on ultrafast time scales Journal Article In: Science, vol. 371, pp. 1056-1059, 2021. Abstract | Links | BibTeX | Tags: DACH @article{Wallauer2020, 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. |
2025 |
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106. | Substrate Stabilized Charge Transfer Scheme In Coverage Controlled 2D Metal Organic Frameworks Journal Article In: Small, vol. 2500507, 2025. |
105. | Conformation-Driven Nickel Redox States and Magnetism in 2D Metal–organic Frameworks Journal Article In: Adv. Funct. Mater., vol. 2418186, 2025. |
104. | Tomographic identification of all molecular orbitals in a wide binding energy range Journal Article Forthcoming In: ArXiv, Forthcoming. |
2024 |
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103. | Band Structure Engineering in 2D Metal–Organic Frameworks Journal Article In: Advanced Science, vol. 11, iss. 38, no. 2404667, 2024. |
102. | Advances in Photoemission Orbital Tomography PhD Thesis 2024, ISBN: 978-3-95806-766-0. |
101. | Disentangling the multiorbital contributions of excitons by photoemission exciton tomography Journal Article In: Nature Communications, vol. 15, no. 1804, pp. 10, 2024. |
2023 |
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100. | Coherent and Incoherent Excitation Pathways in Time-Resolved Photoemission Orbital Tomography of CuPc/Cu(001)-2O Journal Article In: J.Phys. Chem. C, vol. 127, pp. 20411, 2023. |
99. | Investigating Ground and Excited State Properties of Complex Organic/Inorganic Interfaces With Ab-Initio Calculations PhD Thesis 2023. |
98. | Exploring the Frontiers of Photoemission Orbital Tomography PhD Thesis 2023. |
97. | Photoemission orbital tomography for excitons in organic molecules Journal Article In: Phys. Rev. B, vol. 108, pp. 085132, 2023. |
2022 |
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96. | Photoemission Distributions from Time-Dependent Density Functional Theory Masters Thesis 2022. |
95. | Charge Transfer Across Ultrathin Dielectric Layers: A Controlled Study of the Phenomenon on MgO on Ag(100) PhD Thesis 2022. |
94. | Charge and adsorption height dependence of the self-metalation of porphyrins on ultrathin MgO(001) films Journal Article In: Phys. Chem. Chem. Phys., vol. 24, pp. 28540-28547, 2022. |
93. | Large Distortion of Fused Aromatics on Dielectric Interlayers Quantified by Photoemission Orbital Tomography Journal Article In: ACS Nano, vol. 16, pp. 17435-17443, 2022. |
92. | Momentum-selective orbital hybridization Journal Article In: Nat. Commun., vol. 13, pp. 5148, 2022. |
91. | Momentum-space imaging of σ-orbitals for chemical analysis Journal Article In: Sci. Adv., vol. 8, pp. eabn0819, 2022. |
90. | Hexacene on Cu(110) and Ag(110): Influence of the Substrate on Molecular Orientation and Interfacial Charge Transfer Journal Article In: J. Phys. Chem. C, vol. 126, pp. 5036-5045, 2022. |
89. | A One-Dimensional High-Order Commensurate Phase of Tilted Molecules Journal Article In: Phys. Chem. Chem. Phys., vol. 24, pp. 9118-9122, 2022. |
88. | Disproportionation of Nitric Oxide at a Surface-Bound Nickel Porphyrinoid Journal Article In: Angew. Chem. Int. Ed., vol. 61, pp. e202201916, 2022. |
2021 |
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87. | Angle-resolved Photoemission of Molecules and Two-dimensional Materials from a Tight-binding Perspective Masters Thesis 2021. |
86. | Photoemission Tomography of Heptacene on Metallic Surfaces Bachelor Thesis 2021. |
85. | Integer charge transfer in organic adsorbates on metallic substrates Masters Thesis 2021. |
84. | Ab-initio Investigations of the Electronic Structure of Armchair Graphene Nanoribbons on the Au(111) Surface Masters Thesis 2021. |
83. | Electronic and Aromatic Structure of Kekulene Studied by Density Functional Theory Masters Thesis 2021. |
82. | Simulation of Angle-Resolved Photoemission Intensity Maps for Two-Dimensional Materials Masters Thesis 2021. |
81. | Photoemission Tomography: Implementation and Testing of a Phase Retrieval Algorithm Bachelor Thesis 2021. |
80. | Charge-promoted self-metalation of porphyrins on an oxide surface Journal Article In: Angew. Chem. Int. Ed., vol. 60, pp. 5078-5082, 2021. |
79. | Insight into intramolecular chemical structure modifications by on-surface reaction using photoemission tomography Journal Article In: Chem. Commun., vol. 57, pp. 3050-3053, 2021. |
78. | Going beyond Pentacene: Photoemission Tomography of a Heptacene Monolayer on Ag(110) Journal Article In: J. Phys. Chem. C, vol. 125, pp. 2918-2925, 2021. |
77. | Tracing orbital images on ultrafast time scales Journal Article In: Science, vol. 371, pp. 1056-1059, 2021. |