@phdthesis{Nuber2011,
  author    = {Nuber, Andreas},
  title     = {Intrinsische und extrinsische Einfl{\"u}sse auf zweidimensionale elektronische Zust{\"a}nde},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-66213},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2011},
  abstract  = {Im Rahmen dieser Arbeit wurden mit Hilfe von hochaufgel{\"o}ster ARPES die Auswirkungen verschiedener intrinsischer und extrinsischer Einfl{\"u}sse auf zweidimensionale elektronische Zust{\"a}nde untersucht: Eine {\"A}nderung der Morphologie aufgrund einer (2 × 1)-Rekonstruktion bewirkt beim OFZ von Au(110) im Vergleich zur nicht-rekonstruierten Oberfl{\"a}che eine Verschiebung der Bindungsenergie von ca. 700meV. Dieses Verhalten wurde in LDA-slab-layer-Rechungen reproduziert und durch gezielte Modifikation der Oberfl{\"a}chenstruktur sowie kontrollierte Beeinflussung des OFZ durch die Adsorbate Ag, Na und Au verstanden. Eine Linienbreitenanalyse der sehr scharfen Minorit{\"a}ts-QWS in d{\"u}nnen Fe- Filmen auf W(110) erm{\"o}glichte eine Absch{\"a}tzung der Elektron-Elektron- Wechselwirkung und eine Bestimmung der Elektron-Phonon-Kopplungskonstanten. Die starke Anisotropie der Dispersion der QWS ist des weiteren durch den Vergleich mit GGA-slab-layer-Rechnungen als intrinsische Eigenschaft dieser Zust{\"a}nde identifiziert worden. Mit Hilfe eines erweiterten PAM wurde zudem die k⊥-Dispersion des, den QWS zugrunde liegenden Volumenbandes, bestimmt. Die spinabh{\"a}ngigen Einflussfaktoren Spin-Orbit- und Austausch-Wechselwirkung sowie deren Kombination wurden am Beispiel des OFZ von d{\"u}nnen Au-Filmen auf Ni(111), sowie an QWS in d{\"u}nnen Ni-Filmen auf W(110) untersucht. Die in SPR-KKR-Photoemissionrechungen gefundene leichte Asymmetrie der spinaufgel{\"o}sten Dispersion wurde in den spinintegrierten ARPESMessungen nicht beobachtet. Ab 9ML Au-Bedeckung konnte die Rashba- Aufspaltung des OFZ aufgel{\"o}st werden. Eine durch das W(110)-Substrat induzierte Rashba-Aufspaltung wurde bei sp-artigen QWS in d{\"u}nnen Ni- Filmen beobachtet, welche jedoch mit weiteren Strukturen hybridisieren, was eine eindeutige Aussage {\"u}ber die tats{\"a}chliche Natur der Aufspaltung erschwert.},
  subject      = {Niederdimensionales System},
  language  = {de}
}
@phdthesis{Wiessner2013,
  author    = {Wießner, Michael},
  title     = {Isolierte Molek{\"u}le und delokalisierte Zust{\"a}nde: Einblick in die elektronische Struktur organischer Adsorbate mittels winkelaufgel{\"o}ster Photoemission},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-95265},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {Die vorliegende Arbeit demonstriert an Hand von verschiedenen Modellsystemen wie detailliert sich die grundlegenden Eigenschaften molekularer Adsorbate mit der winkelaufgel{\"o}sten Photoemission erkunden lassen. Die von Peter Puschnig et al. vorgestellte Verkn{\"u}pfung zwischen Photoemissionsintensit{\"a}t und den Molek{\"u}lorbitalen im Grundzustand mittels einer Fouriertransformation war dabei entscheidend, um die verschiedenen physikalischen Effekte einordnen und verstehen zu k{\"o}nnen. W{\"a}hrend f{\"u}r Coronen oder HBC die Orbitale im Grundzustand sehr gut zum Experiment passen, lassen sich f{\"u}r PTCDA und NTCDA einige Abweichungen von der DFT-Rechnung auf Basis der (semi-)lokalen GGA- oder LDA-Funktionale erkennen, die sich bei Messungen mit s-Polarisation hervorheben lassen. Diese k{\"o}nnen auf den Einfluss des Endzustandes in der Photoemission zur{\"u}ckgef{\"u}hrt werden. Im Rahmen der Dysonorbitale lassen sich die daf{\"u}r verantwortlichen Relaxationseffekte zwischen dem N-Elektronensystem des Molek{\"u}ls im Grundzustand und dem (N-1)-Elektronensystem des zur{\"u}ckbleibenden Kations explizit beschreiben. Die Berechnung des Photoemissionssignals mittels Fouriertransformation des Grundzustandes kann dar{\"u}ber hinaus weitere physikalische Effekte nicht korrekt ber{\"u}cksichtigen. Erste Anzeichen hierf{\"u}r konnten am PTCDA-HOMO bei einer Photonenenergie von 27 eV und s-Polarisation detektiert werden. Dar{\"u}ber hinaus kann die N{\"a}herung des Photoelektronenendzustands als ebene Welle den beobachteten zirkularen Dichroismus am HOMO und LUMO von PTCDA nicht erkl{\"a}ren. Erst in der Erweiterung durch eine Partialwellenzerlegung des Photoelektronenendzustands tritt ein dichroisches Signal in der theoretischen Beschreibung auf. F{\"u}r das delokalisierte pi-Elektronensystem von PTCDA ist aber selbst diese Verfeinerung noch nicht ausreichend, um das Experiment korrekt beschreiben und weitere Eigenschaften vorhersagen zu k{\"o}nnen. Qualitativ lassen sich die Ver{\"a}nderungen im CDAD bei der Transformation um 90° f{\"u}r HOMO und LUMO mit einem gruppentheoretischen Ansatz verstehen. Damit ist es m{\"o}glich, den molekularen Zust{\"a}nden ihre irreduzible Darstellung zuzuweisen, wor{\"u}ber sich f{\"u}r PTCDA die Verteilung der quantenmechanischen Phase rekonstruieren l{\"a}sst. Dies ist deshalb {\"a}ußerst bemerkenswert, da {\"u}blicherweise in physikalischen Experimenten nur die Intensit{\"a}t und keine Informationen {\"u}ber die Phase messbar sind. Damit k{\"o}nnen die Photoemissionsmessungen im k||-Raum vollst{\"a}ndig in den Realraum transformiert werden, wodurch die laterale Ortsinformation {\"u}ber die h{\"o}chsten besetzen Molek{\"u}lorbitale von PTCDA zug{\"a}nglich wird. Neben der Bestimmung der molekularen Orbitale, deren Struktur von der Anordnung der Atome im Molek{\"u}l dominiert wird, enth{\"a}lt die winkelaufgel{\"o}ste Photoemission Informationen {\"u}ber die Adsorbat-Substrat-Wechselwirkung. F{\"u}r hoch geordnete Monolagen ist es m{\"o}glich, die verschiedenen Verbreiterungsmechanismen zu trennen und zu analysieren. Bei den untersuchten Systemen sind die Verbreiterungen aufgrund von unterschiedlichen Adsorptionspl{\"a}tzen oder Probeninhomogenit{\"a}ten ebenso wie die experimentelle Aufl{\"o}sung der 2D-Analysatoren vernachl{\"a}ssigbar gegen{\"u}ber Lebensdauereffekten und evtl. Verbreiterung aufgrund von Dispersionseffekten. Bereits bei den {\"a}ußerst schwach wechselwirkenden Systemen Coronen auf Ag(111) und Au(111) unterscheiden sich die beiden Systeme in ihrer Lorentzverbreiterung beim HOMO. In erster N{\"a}herung l{\"a}sst sich dies auf eine Lebensdauer des entstandenen Photolochs zur{\"u}ckf{\"u}hren, welches je nach St{\"a}rke der Substratkopplung unterschiedlich schnell mit Substratelektronen aufgef{\"u}llt werden kann. Die Lorentzbreite als Indikator f{\"u}r die Wechselwirkung bzw. Hybridisierungsst{\"a}rke zeigt f{\"u}r die Systeme mit Ladungstransfer vom Substrat in das Molek{\"u}l eine sehr viel gr{\"o}ßere Verbreiterung. Zum Beispiel betr{\"a}gt die Lorentzbreite des LUMO f{\"u}r NTCDA/Ag(110) FWHM=427 meV, und somit eine mehr als f{\"u}nfmal so große Verbreiterung als f{\"u}r das HOMO von Coronen/Au(111). Diese starke Verbreiterung geht im Fall von NTCDA/Ag(110) wie auch bei den untersuchten Systemen NTCDA/Cu(100) und PTCDA/Ag(110) einher mit einem Ladungstransfer vom Substrat ins Molek{\"u}l, sowie mit der Ausbildung eines zus{\"a}tzlichen charakteristischen Signals in der Winkelverteilung des LUMO, dem Hybridisierungszustand bei kx,y=0{\AA}-1. Die Intensit{\"a}t dieses Zustands korreliert bei den Systemen NTCDA auf Cu(100) bzw. auf Ag(110) jeweils mit der Lorentzbreite des LUMO-Zustands. Die Hybridisierung zwischen Molek{\"u}l und Substrat hat noch weitere Auswirkungen auf die beobachtbaren physikalischen Eigenschaften. So f{\"u}hrt die starke Hybridisierung mit dem Substrat wiederum dazu, dass sich die intermolekulare Dispersion f{\"u}r die Elektronen im LUMO-Zustand deutlich verst{\"a}rkt. Der direkte {\"U}berlapp der Wellenfunktionen ist im System PTCDA/Ag(110) laut DFT-Rechnungen relativ klein und f{\"u}hrt lediglich zu einer Bandbreite von 60 meV. Durch die Hybridisierung mit den delokalisierten Substratb{\"a}ndern erh{\"o}ht sich der Grad der Delokalisierung im LUMO-Zustand, d.h. die Bandbreite steigt auf 230 meV, wie das Experiment best{\"a}tigt. Im Gegensatz zu fr{\"u}heren STM/STS-basierten Messungen [Temirov2006] kann mit der Kombination aus DFT-Rechnung und ARPES-Experiment eindeutig nachgewiesen werden, dass das Substrat im Fall von PTCDA/Ag(110) die Bandbreite verst{\"a}rken kann, sodass sich die effektive Masse der Lochladungstr{\"a}ger von meff=3,9me auf meff=1,1me reduziert. Im Blick auf die eingangs gestellte Frage, ob sich molekulare Adsorbate eher wie isolierte Molek{\"u}le oder als periodische Festk{\"o}rper beschreiben lassen, kommt diese Arbeit auf ein differenziertes Ergebnis. In den Impulsverteilungen, die sich aus der Form der molekularen Wellenfunktionen ableiten lassen, spiegelt sich eindeutig der isolierte molekulare Charakter wieder. Dagegen zeigt sich in der Energiedispersion E(k||) ein delokalisierter, blochartiger Charakter, und es konnte demonstriert werden, dass es zu einem Vermischen von Metall- und Molek{\"u}lwellenfunktionen kommt. Molekulare Adsorbate sind also beides, isolierte Molek{\"u}le und zweidimensionale Kristalle mit delokalisierten Zust{\"a}nden.},
  subject      = {Organisches Molek{\"u}l},
  language  = {de}
}
@article{DauthWiessnerFeyeretal.2014,
  author    = {Dauth, M. and Wiessner, M. and Feyer, V. and Sch{\"o}ll, A. and Puschnig, P. and Reinert, F. and Kuemmel, S.},
  title     = {Angle resolved photoemission from organic semiconductors: orbital imaging beyond the molecular orbital interpretation},
  series = {New Journal of Physics},
  volume    = {16},
  journal   = {New Journal of Physics},
  issn      = {1367-2630},
  doi       = {10.1088/1367-2630/16/10/103005},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-115180},
  pages     = {103005},
  year      = {2014},
  abstract  = {Fascinating pictures that can be interpreted as showing molecular orbitals have been obtained with various imaging techniques. Among these, angle resolved photoemission spectroscopy (ARPES) has emerged as a particularly powerful method. Orbital images have been used to underline the physical credibility of the molecular orbital concept. However, from the theory of the photoemission process it is evident that imaging experiments do not show molecular orbitals, but Dyson orbitals. The latter are not eigenstates of a single-particle Hamiltonian and thus do not fit into the usual simple interpretation of electronic structure in terms of molecular orbitals. In a combined theoretical and experimental study we thus check whether a Dyson-orbital and a molecular-orbital based interpretation of ARPES lead to differences that are relevant on the experimentally observable scale. We discuss a scheme that allows for approximately calculating Dyson orbitals with moderate computational effort. Electronic relaxation is taken into account explicitly. The comparison reveals that while molecular orbitals are frequently good approximations to Dyson orbitals, a detailed understanding of photoemission intensities may require one to go beyond the molecular orbital picture. In particular we clearly observe signatures of the Dyson-orbital character for an adsorbed semiconductor molecule in ARPES spectra when these are recorded over a larger momentum range than in earlier experiments.},
  language  = {en}
}
@phdthesis{Boariu2014,
  author    = {Boariu, Florin Loredan},
  title     = {The "Hidden-Order" Phase Transition of URu2Si2 : Investigated by Angle-Resolved Photoelectron Spectroscopy},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-98259},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {In 1985, an enigmatic second order phase transition was discovered in the actinide compound URu2Si2. Evading a microscopic description for nearly three decades in spite of numerous experimental and theoretical attempts, the name "hidden order Transition" was adopted for the effect. (...)},
  subject      = {Actinoide},
  language  = {en}
}
@phdthesis{Berner2015,
  author    = {Berner, G{\"o}tz},
  title     = {Funktionelle oxidische Heterostrukturen aus dem Blickwinkel der Spektroskopie},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-121721},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2015},
  abstract  = {In oxidischen Heterostrukturen rufen Neuordnung von Ladung und Spin eine Vielzahl von unerwarteten physikalischen Eigenschaften hervor. Die M{\"o}glichkeit, Leitf{\"a}higkeit, Magnetismus oder auch Hochtemperatur-Supraleitung zu kontrollieren, machen diese k{\"u}nstlich hergestellten Materialien vor allem in Hinblick auf eine zuk{\"u}nftige Anwendung in der Mikroelektronik {\"a}ußerst interessant. Dies erfordert jedoch ein grunds{\"a}tzliches Verst{\"a}ndnis f{\"u}r die zugrunde liegenden Mechanismen. Die vorliegende Doktorarbeit befasst sich mit photonengest{\"u}tzter Spektroskopie, die einen direkten Zugang zur elektronischen Struktur dieser Heterostruktursysteme erm{\"o}glicht. Ein weiteres Ziel ist es, geeignete spektroskopische Methoden zur Charakterisierung der vergrabenen Schichten zu etablieren. Zwei prototypische oxidische Mehrschichtsysteme stehen im Zentrum der hier vorgestellten Untersuchungen. Das LaAlO3/SrTiO3-Heterostruktursystem weist ab einer kritischen LaAlO3-Filmdicke an der Grenzfl{\"a}che ein zweidimensionales Elektronensystem mit hochmobilen Ladungstr{\"a}gern auf. Als treibender Mechanismus wird die elektronische Rekonstruktion diskutiert. Im Rahmen dieser Arbeit wurde dieses zweidimensionale Elektronensystem mithilfe der Photoelektronenspektroskopie und der resonanten inelastischen R{\"o}ntgenstreuung charakterisiert. Die daraus bestimmten Ladungstr{\"a}gerdichten weisen im Vergleich mit Daten aus Transportmessungen auf eine Koexistenz von lokalisierten und mobilen Ladungstr{\"a}gern an der Grenzfl{\"a}che hin. Die Analyse von Rumpfniveau- und Valenzbandspektren zeigt, dass man zur Erkl{\"a}rung der experimentellen Resultate ein modifiziertes Bild der elektronischen Rekonstruktion ben{\"o}tigt, bei der Sauerstofffehlstellen an der LaAlO3-Oberfl{\"a}che als Ladungsreservoir dienen k{\"o}nnten. Mithilfe der resonanten Photoelektronenspektroskopie war es m{\"o}glich, die metallischen Zust{\"a}nde am chemischen Potential impulsaufgel{\"o}st zu spektroskopieren. So gelang es erstmals, die vergrabene Fermi-Fl{\"a}che einer oxidischen Heterostruktur zu vermessen. Außerdem konnten Titan-artige Zust{\"a}nde identifiziert werden, die h{\"o}chstwahrscheinlich durch Sauerstofffehlstellen im SrTiO3 lokalisiert sind. Diese werden als m{\"o}gliche Quelle f{\"u}r den Ferromagnetismus interpretiert, der mit der supraleitenden Phase in der LaAlO3/SrTiO3-Heterostruktur koexistiert. Bei dem anderen hier untersuchten Mehrschichtsystem handelt es sich um die LaNiO3-LaAlO3-{\"U}bergitterstruktur. Der Einbau des metallischen LaNiO3 in eine Heterostruktur ist aufgrund seiner N{\"a}he zu einer korrelationsinduzierten isolierenden Phase hinsichtlich einer kontrollierten Ausbildung von neuartigen Phasen besonders interessant. In der Tat beobachtet man unterhalb einer LaNiO3-Schichtdicke von vier Einheitszellen einen kontinuierlichen Metall-Isolator-{\"U}bergang, der sich in den Valenzbandspektren durch einen Verlust an Quasiteilchenkoh{\"a}renz {\"a}ußert. Auch wenn die impulsaufgel{\"o}sten Daten am Fermi-Niveau durch Photoelektronenbeugung beeinflusst sind, so l{\"a}sst sich dennoch eine Fermi-Fl{\"a}che identifizieren. Ihre Topologie bietet die M{\"o}glichkeit eines Fermi-Fl{\"a}chen-Nestings mit der Ausbildung einer Spindichtewelle. Die Resultate unterst{\"u}tzen die Hinweise auf eine magnetische Ordnung im zweidimensionalen Grundzustand.},
  subject      = {Heterostruktur},
  language  = {de}
}
@article{CharnukhaThirupathaiahZabolotnyyetal.2015,
  author    = {Charnukha, A. and Thirupathaiah, S. and Zabolotnyy, V. B. and B{\"u}chner, B. and Zhigadlo, N. D. and Batlogg, B. and Yaresko, A. N. and Borisenko, S. V.},
  title     = {Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor},
  series = {Scientific Reports},
  volume    = {5},
  journal   = {Scientific Reports},
  number    = {10392},
  doi       = {10.1038/srep10392},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-151987},
  year      = {2015},
  abstract  = {In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature T\(_{c}\)\(\approx\)55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe\(_{0.92}\)Co\(_{0.08}\)AsO, is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.},
  language  = {en}
}
@phdthesis{Seibel2016,
  author    = {Seibel, Christoph},
  title     = {Elektronische Struktur von Halbleiteroberfl{\"a}chen mit starker Spin-Bahn-Wechselwirkung: Topologie, Spinpolarisation und Robustheit},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-140418},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2016},
  abstract  = {Neue Erkenntnisse {\"u}ber elektronische Eigenschaften von Festk{\"o}rpern legen den Grundstein f{\"u}r innovative Anwendungen der Zukunft. Von zentraler Bedeutung sind insbesondere die Eigenschaften der Elektronenspins. Um diese besser zu verstehen, befasst sich die vorliegende Arbeit mit der experimentellen Analyse der elektronischen Struktur von topologischen Isolatoren (Sb\$_2\$Te\$_3\$ , Bi\$_2\$Se\$_x\$Te\$_{3-x}\$, Bi\$_{1.5}\$Sb\$_{0.5}\$Te\$_{1.8}\$Se\$_{1.2} und Bi\$_{1.4}\$Sb\$_{1.1}\$Te\$_{2.2}\$S\$_{0.3}\$) und Kristallen mit starker Spin-Bahn-Wechselwirkung (BiTeI) mittels Photoelektronenspektroskopie. Zu Beginn werden die zum Verst{\"a}ndnis dieser Arbeit ben{\"o}tigten Grundlagen erkl{\"a}rt sowie die unterschiedlichen zum Einsatz kommenden Techniken eingef{\"u}hrt. Der Hauptteil der Arbeit teilt sich in drei Forschungsschwerpunkte. Der erste Teil befasst sich mit den elektronischen Eigenschaften der Valenzbandstruktur von Sb2Te3 und den auftretenden Oberfl{\"a}chenzust{\"a}nden. Durch gezielte Variation der Energie der anregenden Strahlung wird der Charakter der Wellenfunktion des topologischen Oberfl{\"a}chenzustands und dessen Wechselwirkung mit Valenzzust{\"a}nden erforscht. Dabei spielt die Topologie der Volumenbandstruktur eine grundlegende Rolle. Der zus{\"a}tzliche Vergleich zu Photoemissionsrechnungen erm{\"o}glicht detaillierte Einblicke in die Wechselwirkung zwischen Oberfl{\"a}chen- und Volumenzust{\"a}nden und gibt Aufschluss dar{\"u}ber, wie diese vermittelt werden. Im zweiten Abschnitt wird durch die Analyse des gemessenen Photoelektronenspins das Zusammenspiel der Spintextur des Grundzustands und Endzust{\"a}nden in Bi2Te3 untersucht. Dabei treten, im Gegensatz zu Grundzustandsrechnungen, Radialkomponenten des Polarisationsvektors in nichtsymmetrischer Messgeometrie auf. Sowohl deren Energieabh{\"a}ngigkeit als auch deren Auftreten in Photoemissionsrechnungen (1-Schritt-Modell) deutet darauf hin, dass diese ihren Ursprung in {\"U}bergangsmatrixelementen des Photoemissionsprozesses haben. Dieses Ergebnis wird mit Spinpolarisationsmessungen am Oberfl{\"a}chenzustand des nicht-topologischen Schichtsystems BiTeI verglichen. Im dritten Teil werden Auswirkungen unterschiedlicher Manipulationen der untersuchten Materialien auf deren elektronische Eigenschaften beschrieben. Die Adsorption von Bruchteilen einer monoatomaren Lage des Alkalimetalls Caesium auf die Oberfl{\"a}che des topologischen Isolators Sb2Te3 wird systematisch untersucht. Dadurch kann dessen intrinsische p-Dotierung teilweise abgebaut werden, wobei die Valenzbandstruktur trotz der Reaktivit{\"a}t des Adsorbats intakt bleibt. Des Weiteren werden Auswirkungen von {\"A}nderungen der Kristallst{\"o}chiometrie durch Volumendotierung vergleichend diskutiert. Ausblickend befasst sich das Kapitel mit dem Verhalten geringer Mengen ferromagnetischer Materialen (Fe, Ni) auf den Oberfl{\"a}chen der topologischen Isolatoren. F{\"u}r die verschiedenen Adsorbate werden Trends aufgezeigt, die von Temperatur und Zusammensetzung des Substratkristalls abh{\"a}ngen.},
  subject      = {Elektronenstruktur},
  language  = {de}
}
@phdthesis{Maass2017,
  author    = {Maaß, Henriette},
  title     = {Spin-dependence of angle-resolved photoemission from spin-orbit split surface states},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-151025},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Spin- and angle-resolved photoelectron spectroscopy is the prime method to investigate spin polarized electronic states at solid state surfaces. In how far the spin polarization of an emitted photoelectron reflects the intrinsic spin character of an electronic state is the main question in the work at hand. It turns out that the measured spin polarization is strongly influenced by experimental conditions, namely by the polarization of the incoming radiation and the excitation energy. The photoemission process thus plays a non-negligible role in a spin-sensitive measurement. This work is dedicated to unravel the relation between the result of a spin-resolved measurement and the spin character in the ground state and, therefore, to gain a deep understanding of the spin-dependent photoemission process. Materials that exhibit significant spin-splittings in their electronic structure, owing to a strong spin-orbit coupling, serve as model systems for the investigations in this work. Therefore, systems with large Rashba-type spin-splittings as BiTeI(0001) and the surface alloys BiAg2/Ag(111) and PbAg2/Ag(111) are investigated. Likewise, the surface electronic structure of the topological insulators Bi2Te2Se(0001) and Bi2Te3(0001) are analyzed. Light polarization dependent photoemission experiments serve as a probe of the orbital composition of electronic states. The knowledge of the orbital structure helps to disentangle the spin-orbital texture inherent to the different surface states, when in addition the spin-polarization is probed. It turns out that the topological surface state of Bi2Te2Se(0001) as well as the Rashba-type surface state of BiTeI(0001) exhibit chiral spin-textures associated with the p-like in-plane orbitals. In particular, opposite chiralities are coupled to either tangentially or radially aligned p-like orbitals, respectively. The results presented here are thus evidence that a coupling between spin- and orbital part of the wave function occurs under the influence of spin-orbit coupling, independent of the materials topology. Systematic photon energy dependent measurements of the out-of-plane spin polarization of the topological surface state of Bi2Te3(0001) reveal a strong dependence and even a reversal of the sign of the photoelectron spin polarization with photon energy. Similarly, the measured spin component perpendicular to the wave vector of the surface state of BiAg2/Ag(111) shows strong modulations and sign reversals when the photon energy is changed. In BiAg2/Ag(111) the variations in the photoelectron spin polarization are accompanied by significant changes and even a complete suppression of the photoemission intensity from the surface state, indicating that the variations of the spin polarization are strongly related to the photoemission cross section. This relation is finally analyzed in detail by employing a simple model, which is based on an evaluation of the transition matrix elements that describe the presented experiments. The model shows that the underlying cause for the observed photoelectron spin reversals can be found in the coupling of the spin structure to the spatial part of the initial state wave function, revealing the crucial role of spin-orbit interaction in the initial state wave function. The model is supported by ab initio photoemission calculations, which show strong agreement with the experimental results.},
  subject      = {Photoelektronenspektroskopie},
  language  = {en}
}
@phdthesis{Aulbach2018,
  author    = {Aulbach, Julian},
  title     = {Gold-Induced Atomic Wires on Terraced Silicon Surfaces: Formation and Interactions of Silicon Spin Chains},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-169347},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Atomic nanowires formed by self-assembled growth on semiconducting surfaces represent a feasible physical realization of quasi-1D electron systems and can be used to study fascinating 1D quantum phenomena. The system in the focus of this thesis, Si(553)-Au, is generated by Au adsorption onto a stepped silicon surface. It features two different chain types, interspersed with each other: A Au chain on the terrace, and a honeycomb chain of graphitic silicon located at the step edge. The silicon atoms at the exposed edges of the latter are predicted to be spin-polarized and charge-ordered [1], leading to an ordered array of local magnetic moments referred to as ``spin chains''. The present thesis puts this spin chain proposal to an experimental test. A detailed scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) scrutiny reveals a distinct unoccupied density of states (DOS) feature localized at every third Si step-edge atom, which aligns perfectly with the density functional theory (DFT) prediction. This finding provides strong evidence for the formation of spin chains at the Si(553)-Au step edges, and simultaneously rules out the interpretation of previous studies which attributed the x3 step-edge superstructure to a Peierls instability. To study the formation of spin chains in further detail, an additional member of the so-called Si(hhk)-Au family -- Si(775)-Au -- is analyzed. Based on DFT modeling (performed by S.C. Erwin, Naval Research Laboratory, USA) and detailed STM and STS experiments, a new structure model for this surface is developed, and the absence of spin chains at the Si(775)-Au step edges is demonstrated. The different step-edge charge distributions of all known Si(hhk)-Au surfaces are traced back to an electron transfer between the terrace and the step edge. Accordingly, an unintentional structure defect should create a localized spin at the Si(775)-Au step edge. This prediction is verified experimentally, and suggest that surface chemistry can be used to create and destroy Si spin chains. Having clarified why spin chains form on some Si(hhk)-Au surfaces but not on others, various interaction effects of the Si(553)-Au spin chains are inspected. A collaborative analysis by SPA-LEED (M. Horn-von Hoegen group, University of Duisburg-Essen, Germany), DFT (S.C. Erwin), and STM reveals strong lateral coupling between adjacent spin chains, bearing interesting implications for their magnetic ordering. The centered geometry uncovered leads to magnetic frustration, and may stabilize a 2D quantum spin liquid. Moreover, a complex interplay between neighboring Au and Si chains is detected. Specifically, the interaction is found effectively ``one-way'', i.e., the Si step edges respond to the Au chains but not vice versa. This unidirectional effect breaks the parity of the Si chains, and creates two different configurations of step edges with opposite directionality. In addition to the static properties of the Si(553)-Au surface mentioned above, the occurrence of solitons in both wire types is witnessed in real space by means of high-resolution STM imaging. The solitons are found to interact with one another such that both move in a coupled fashion along the chains. Likewise, STM experiments as a function of the tunneling current suggest an excitation of solitons along the step edge by the STM tunneling tip. Solitons are also found to play an essential role in the temperature-dependent behavior of the Si(553)-Au step edges. It is an accepted fact that the distinct x3 superstructure of the Si(553)-Au step edges vanishes upon heating to room temperature. As a first step in exploring this transition in detail over a large temperature range, a previously undetected, occupied electronic state associated with the localized step-edge spins is identified by means of angle-resolved photoemission spectroscopy (ARPES). A tracking of this state as a function of temperature reveals an order-disorder-type transition. Complementary STM experiments attribute the origin of this transition to local, thermally activated spin site hops, which correspond to soliton-anitsoliton pairs. Finally, a manipulation of the Si(553)-Au atomic wire array is achieved by the stepwise adsorption of potassium atoms. This does not only increase the filling of the Au-induced surface bands culminating in a metal-insulator transition (MIT), but also modifies the Si step-edge charge distribution, as indicated by STM and ARPES experiments. [1] S. C. Erwin and F. Himpsel, Intrinsic magnetism at silicon surfaces, Nat. Commun. 1, 58 (2010).},
  subject      = {Rastertunnelmikroskopie},
  language  = {en}
}
@phdthesis{Graus2018,
  author    = {Graus, Martin},
  title     = {Anwendung und Weiterentwicklung der Orbitaltomographie},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-163194},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Als Orbitaltomographie wird eine junge Methode innerhalb der Photoelektronenspektrokopie bezeichnet, welche es erm{\"o}glicht, Molek{\"u}lorbitale mit hoher Ortsaufl{\"o}sung abzubilden. Hierf{\"u}r werden die zu untersuchenden Molek{\"u}le durch elektromagnetische Strahlung angeregt und die mittels Photoeffekt emittierten Elektronen hinsichtlich ihres Impulses und ihrer kinetischen Energie charakterisiert. Moderne Photoemissionsexperimente erlauben die simultane Vermessung des gesamten Impulshalbraumes oberhalb der Probe. Die detektierte Intensit{\"a}tsverteilung stellt dann unter bestimmten Bedingungen das Betragsquadrat eines hemisph{\"a}rischen Schnittes durch den Fourierraum des spektroskopierten Orbitals dar, wobei der Radius der Hemisph{\"a}re von der Energie der anregenden Strahlung abh{\"a}ngt. Bei den in dieser Arbeit untersuchten Systemen handelt es sich um adsorbierte Molek{\"u}le, die hochgeordnete Schichten auf kristallinen Edelmetalloberfl{\"a}chen bilden. Im Fall eindom{\"a}nigen Wachstums liefern die parallel orientierten Molek{\"u}le identische Photoemissionssignale. Kommt es hingegen zur Ausbildung von Rotations- und Spiegeldom{\"a}nen, stellt die gemessene Impulsverteilung eine Superposition der unterschiedlichen Einzelbeitr{\"a}ge dar. Somit lassen sich R{\"u}ckschl{\"u}sse auf die Orientierungen der Molek{\"u}le auf den Substraten ziehen. Diese Charakterisierung molekularer Adsorptionsgeometrien wird anhand verschiedener Modellsysteme vorgestellt. Variiert man die Energie der anregenden Strahlung und somit den Radius der hemisph{\"a}rischen Schnitte durch den Impulsraum, ist es m{\"o}glich den Fourierraum des untersuchten Molek{\"u}lorbitals dreidimensional abzubilden. Kombiniert man die gemessenen Intensit{\"a}ten mit Informationen {\"u}ber die Phase der Wellenfunktion im Impulsraum, die durch zus{\"a}tzliche Experimente oder rechnerisch gewonnen werden k{\"o}nnen, l{\"a}sst sich durch eine Fouriertransformation ein dreidimensionales Bild des Orbitals generieren, wie Schritt f{\"u}r Schritt gezeigt wird. Im Zuge eines Photoemissionsprozesses kann das Molek{\"u}l in einen angeregten vibronischen Zustand {\"u}bergehen. Mittels Photoemissionsexperimenten mit hoher Energieaufl{\"o}sung lassen sich Unterschiede zwischen den Impulsverteilungen der schwingenden Molek{\"u}le und denen im vibronischen Grundzustand feststellen. Ein Vergleich der Messdaten mit Simulationen kann die Identifikation der angeregten Schwingungsmode erm{\"o}glichen, was eine neue Methode darstellt, Erkenntnisse {\"u}ber die Elektron-Phonon-Kopplung in molekularen Materialien zu gewinnen.},
  subject      = {ARPES},
  language  = {de}
}
@phdthesis{Metzger2021,
  author    = {Metzger, Christian Thomas Peter},
  title     = {Development of photoemission spectroscopy techniques for the determination of the electronic and geometric structure of organic adsorbates},
  doi       = {10.25972/OPUS-22952},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-229525},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {The projects presented in this thesis cover the examination of the electronic and structural properties of organic thin films at noble metal-organic interfaces. Angle-resolved photoemission spectroscopy is used as the primary investigative tool due to the connection of the emitted photoelectrons to the electronic structure of the sample. The surveyed materials are of relevance for fundamental research and practical applications on their own, but also serve as archetypes for the photoemission techniques presented throughout the four main chapters of this thesis. The techniques are therefore outlined with their adaptation to other systems in mind and a special focus on the proper description of the final state. The most basic description of the final state that is still adequate for the evaluation of photoemission data is a plane wave. Its simplicity enables a relatively intuitive interpretation of photoemission data, since the initial and final state are related to one another by a Fourier transform and a geometric factor in this approximation. Moreover, the initial states of some systems can be reconstructed in three dimensions by combining photoemission measurements at various excitation energies. This reconstruction can even be carried out solely based on experimental data by using suitable iterative algorithms. Since the approximation of the final state in the photoemission process by a plane wave is not valid in all instances, knowledge on the limitations of its applicability is indispensable. This can be gained by a comparison to experimental data as well as calculations with a more detailed description of the photoemission final state. One possible appraoch is based on independently emitting atoms where the coherent superposition of partial, atomic final states produces the total final state. This approach can also be used for more intricate studies on organic thin films. To this end, experimental data can be related to theoretical calculations to gain extensive insights into the structural and electronic properties of molecules in organic thin films.},
  subject      = {ARPES},
  language  = {en}
}
@phdthesis{Adler2021,
  author    = {Adler, Florian Rudolf},
  title     = {Electronic Correlations in Two-dimensional Triangular Adatom Lattices},
  doi       = {10.25972/OPUS-24175},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-241758},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {Two-dimensional triangular lattices of group IV adatoms on semiconductor substrates provide a rich playground for the investigation of Mott-Hubbard physics. The possibility to combine various types of adatoms and substrates makes members of this material class versatile model systems to study the influence of correlation strength, band filling and spin-orbit coupling on the electronic structure - both experimentally and with dedicated many-body calculation techniques. The latter predict exotic ground states such as chiral superconductivity or spin liquid behavior for these frustrated lattices, however, experimental confirmation is still lacking. In this work, three different systems, namely the \(\alpha\)-phases of Sn/SiC(0001), Pb/Si(111), and potassium-doped Sn/Si(111) are investigated with scanning tunneling microscopy and photoemission spectroscopy in this regard. The results are potentially relevant for spintronic applications or quantum computing. For the novel group IV triangular lattice Sn/SiC(0001), a combined experimental and theoretical study reveals that the system features surprisingly strong electronic correlations because they are boosted by the substrate through its partly ionic character and weak screening capabilities. Interestingly, the spectral function, measured for the first time via angle-resolved photoemission, does not show any additional superstructure beyond the intrinsic \(\sqrt{3} \times \sqrt{3} R30^{\circ}\) reconstruction, thereby raising curiosity regarding the ground-state spin pattern. For Pb/Si(111), preceding studies have noted a phase transition of the surface reconstruction from \(\sqrt{3} \times \sqrt{3} R30^{\circ}\) to \(3 \times 3\) at 86 K. In this thesis, investigations of the low-temperature phase with high-resolution scanning tunneling microscopy and spectroscopy unveil the formation of a charge-ordered ground state. It is disentangled from a concomitant structural rearrangement which is found to be 2-up/1-down, in contrast to previous predictions. Applying an extended variational cluster approach, a phase diagram of local and nonlocal Coulomb interactions is mapped out. Based on a comparison of theoretical spectral functions with scattering vectors found via quasiparticle interference, Pb/Si(111) is placed in said phase diagram and electronic correlations are found to be the driving force of the charge-ordered state. In order to realize a doped Mott insulator in a frustrated geometry, potassium was evaporated onto the well-known correlated Sn/Si(111) system. Instead of the expected insulator-to-metal transition, scanning tunneling spectroscopy data indicates that the electronic structure of Sn/Si(111) is only affected locally around potassium atoms while a metallization is suppressed. The potassium atoms were found to be adsorbed on empty \(T_4\) sites of the substrate which eventually leads to the formation of two types of K-Sn alloys with a relative potassium content of 1/3 and 1/2, respectively. Complementary measurements of the spectral function via angle-resolved photoemission reveal that the lower Hubbard band of Sn/Si(111) gradually changes its shape upon potassium deposition. Once the tin and potassium portion on the surface are equal, this evolution is complete and the system can be described as a band insulator without the need to include Coulomb interactions.},
  subject      = {Rastertunnelmikroskopie},
  language  = {en}
}
@phdthesis{Uenzelmann2022,
  author    = {{\"U}nzelmann, Maximilian},
  title     = {Interplay of Inversion Symmetry Breaking and Spin-Orbit Coupling - From the Rashba Effect to Weyl Semimetals},
  doi       = {10.25972/OPUS-28310},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-283104},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Breaking inversion symmetry in crystalline solids enables the formation of spin-polarized electronic states by spin-orbit coupling without the need for magnetism. A variety of interesting physical phenomena related to this effect have been intensively investigated in recent years, including the Rashba effect, topological insulators and Weyl semimetals. In this work, the interplay of inversion symmetry breaking and spin-orbit coupling and, in particular their general influence on the character of electronic states, i.e., on the spin and orbital degrees of freedom, is investigated experimentally. Two different types of suitable model systems are studied: two-dimensional surface states for which the Rashba effect arises from the inherently broken inversion symmetry at the surface, and a Weyl semimetal, for which inversion symmetry is broken in the three-dimensional crystal structure. Angle-resolved photoelectron spectroscopy provides momentum-resolved access to the spin polarization and the orbital composition of electronic states by means of photoelectron spin detection and dichroism with polarized light. The experimental results shown in this work are also complemented and supported by ab-initio density functional theory calculations and simple model considerations. Altogether, it is shown that the breaking of inversion symmetry has a decisive influence on the Bloch wave function, namely, the formation of an orbital angular momentum. This mechanism is, in turn, of fundamental importance both for the physics of the surface Rashba effect and the topology of the Weyl semimetal TaAs.},
  subject      = {Rashba-Effekt},
  language  = {en}
}
@phdthesis{Bauernfeind2023,
  author    = {Bauernfeind, Maximilian Josef Xaver},
  title     = {Epitaxy and Spectroscopy of Two-Dimensional Adatom Systems: the Elemental Topological Insulator Indenene on SiC},
  doi       = {10.25972/OPUS-31166},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-311662},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {Two-dimensional (2D) topological insulators are a new class of materials with properties that are promising for potential future applications in quantum computers. For example, stanene represents a possible candidate for a topological insulator made of Sn atoms arranged in a hexagonal lattice. However, it has a relatively fragile low-energy spectrum and sensitive topology. Therefore, to experimentally realize stanene in the topologically non-trivial phase, a suitable substrate that accommodates stanene without compromising these topological properties must be found. A heterostructure consisting of a SiC substrate with a buffer layer of adsorbed group-III elements constitutes a possible solution for this problem. In this work, 2D adatom systems of Al and In were grown epitaxially on SiC(0001) and then investigated structurally and spectroscopically by scanning tunneling microscopy (STM) and photoelectron spectroscopy. Al films in the high coverage regime \( (\Theta_{ML}\approx2\) ML\( ) \) exhibit unusually large, triangular- and rectangular-shaped surface unit cells. Here, the low-energy electron diffraction (LEED) pattern is brought into accordance with the surface topography derived from STM. Another Al reconstruction, the quasi-one-dimensional (1D) Al phase, exhibits a striped surface corrugation, which could be the result of the strain imprinted by the overlayer-substrate lattice mismatch. It is suggested that Al atoms in different surface areas can occupy hexagonal close-packed and face-centered cubic lattice sites, respectively, which in turn lead to close-packed transition regions forming the stripe-like corrugations. On the basis of the well-known herringbone reconstruction from Au(111), a first structural model is proposed, which fits well to the structural data from STM. Ultimately, however, thermal treatments of the sample could not generate lower coverage phases, i.e. in particular, a buffer layer structure. Strong metallic signatures are found for In high coverage films \( (\Theta_{ML}\approx3\) to \(2\) ML\() \) by scanning tunneling spectroscopy (STS) and angle-resolved photoelectron spectroscopy (ARPES), which form a \( (7\times7) \), \( (6\times4\sqrt{3}) \), and \( (4\sqrt{3}\times4\sqrt{3}) \) surface reconstruction. In all these In phases electrons follow the nearly-free electron model. Similar to the Al films, thermal treatments could not obtain the buffer layer system. Surprisingly, in the course of this investigation a triangular In lattice featuring a \( (1\times1) \) periodicity is observed to host massive Dirac-like bands at \( K/K^{\prime} \) in ARPES. Based on this strong electronic similarity with graphene at the Brillouin zone boundary, this new structure is referred to as \textit{indenene}. An extensive theoretical analysis uncovers the emergence of an electronic honeycomb network based on triangularly arranged In \textit{p} orbitals. Due to strong atomic spin-orbit coupling and a comparably small substrate-induced in-plane inversion symmetry breaking this material system is rendered topologically non-trivial. In indenene, the topology is intimately linked to a bulk observable, i.e., the energy-dependent charge accumulation sequence within the surface unit cell, which is experimentally exploited in STS to confirm the non-trivial topological character. The band gap at \( K/K^{\prime} \), a signature of massive Dirac fermions, is estimated by ARPES to approximately 125 meV. Further investigations by X-ray standing wave, STM, and LEED confirm the structural properties of indenene. Thus, this thesis presents the growth and characterization of the novel quantum spin Hall insulator material indenene.},
  subject      = {Dreiecksgitter},
  language  = {en}
}
@phdthesis{CrespoVidal2023,
  author    = {Crespo Vidal, Can Raphael},
  title     = {Spectroscopic investigation of the three-dimensional topological insulators (MnBi\(_2\)Te\(_4\))(Bi\(_2\)Te\(_3\))\(_n\) and HgTe: band structure, orbital symmetries, and influence of the cation \(d\)-states},
  doi       = {10.25972/OPUS-31293},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312931},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {This thesis examines the electronic properties of two materials that promise the realization and observation of novel exotic quantum phenomena. For this purpose, angle-resolved photoemission forms the experimental basis for the investigation of the electronic properties. Furthermore, the magnetic order is investigated utilizing X-ray dichroism measurements. First, the bulk and surface electronic structure of epitaxially grown HgTe in its three-dimensional topological insulator phase is investigated. In this study, synchrotron radiation is used to address the three-dimensional band structure and orbital composition of the bulk states by employing photon-energy-dependent and polarization-dependent measurements, respectively. In addition, the topological surface state is examined on in situ grown samples using a laboratory photon source. The resulting data provide a means to experimentally localize the bulk band inversion in momentum space and to evidence the momentum-dependent change in the orbital character of the inverted bulk states. Furthermore, a rather new series of van der Waals compounds, (MnBi\(_2\)Te\(_4\))(Bi\(_2\)Te\(_3\))\(_n\), is investigated. First, the magnetic properties of the first two members of the series, MnBi\(_2\)Te\(_4\) and MnBi\(_4\)Te\(_7\), are studied via X-ray absorption-based techniques. The topological surface state on the two terminations of MnBi\(_4\)Te\(_7\) is analyzed using circular dichroic, photon-energy-dependent, and spin-resolved photoemission. The topological state on the (MnBi\(_2\)Te\(_4\))-layer termination shows a free-standing Dirac cone with its Dirac point located in the bulk band gap. In contrast, on the (Bi\(_2\)Te\(_3\))-layer termination the surface state hybridizes with the bulk valences states, forming a spectral weight gap, and exhibits a Dirac point that is buried within the bulk continuum. Lastly, the lack of unambiguous evidence in the literature showing a temperature-dependent mass gap opening in these magnetic topological insulators is discussed through MnBi\(_2\)Te\(_4\).},
  subject      = {ARPES},
  language  = {en}
}
@phdthesis{Baumgaertner2023,
  author    = {Baumg{\"a}rtner, Kiana Jasmin},
  title     = {Spectroscopic Investigation of the Transient Interplay at Hybrid Molecule-Substrate Interfaces after Photoexcitation: Ultrafast Electronic and Atomic Rearrangements},
  doi       = {10.25972/OPUS-33053},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-330531},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {This thesis is aimed at establishing modalities of time-resolved photoelectron spectroscopy (tr-PES) conducted at a free-electron laser (FEL) source and at a high harmonic generation (HHG) source for imaging the motion of atoms, charge and energy at photoexcited hybrid organic/inorganic interfaces. Transfer of charge and energy across interfaces lies at the heart of surface science and device physics and involves a complex interplay between the motion of electrons and atoms. At hybrid organic/inorganic interfaces involving planar molecules, such as pentacene and copper(II)-phthalocyanine (CuPc), atomic motions in out-of-plane direction are particularly apparent. Such hybrid interfaces are of importance to, e.g., next-generation functional devices, smart catalytic surfaces and molecular machines. In this work, two hybrid interfaces - pentacene atop Ag(110) and copper(II)-phthalocyanine (CuPc) atop titanium disulfide (1T-TiSe2) - are characterized by means of modalities of tr-PES. The experiments were conducted at a HHG source and at the FEL source FLASH at Deutsches Elektronen-Synchrotron DESY (Hamburg, Germany). Both sources provide photon pulses with temporal widths of ∼ 100 fs and thus allow for resolving the non-equilibrium dynamics at hybrid interfaces involving both electronic and atomic motion on their intrinsic time scales. While the photon energy at this HHG source is limited to the UV-range, photon energies can be tuned from the UV-range to the soft x-ray-range at FLASH. With this increased energy range, not only macroscopic electronic information can be accessed from the sample's valence and conduction states, but also site-specific structural and chemical information encoded in the core-level signatures becomes accessible. Here, the combined information from the valence band and core-level dynamics is obtained by performing time- and angle-resolved photoelectron spectroscopy (tr-ARPES) in the UV-range and subsequently performing time-resolved x-ray photoelectron spectroscopy (tr-XPS) and time-resolved photoelectron diffraction (tr-XPD) in the soft x-ray regime in the same experimental setup. The sample's bandstructure in energy-momentum space and time is captured by a time-of-flight momentum microscope with femtosecond temporal and sub-{\AA}ngstr{\"o}m spatial resolutions. In the investigated systems, out-of-equilibrium dynamics are traced that are connected to the transfer of charge and energy across the hybrid interfaces. While energetic shifts and complementary population dynamics are observed for molecular and substrate states, the shapes of involved molecular orbitals change in energy-momentum space on a subpicosecond time scale. In combination with theory support, these changes are attributed to iiiatomic reorganizations at the interface and transient molecular structures are reconstructed with sub-{\AA}ngstr{\"o}m precision. Unique to the material combination of CuPc/TiSe2, a structural rearrangement on the macroscopic scale is traced simultaneously: ∼ 60 \% of the molecules undergo a concerted, unidirectional in-plane rotation. This surprising observation and its origin are detailed in this thesis and connected to a particularly efficient charge transfer across the CuPc/TiSe2 interface, resulting in a charging of ∼ 45 \% of CuPc molecules.},
  subject      = {ARPES},
  language  = {en}
}