Im Rahmen dieser Dissertation wurden organische Dünnschichten und deren Grenzflächen an Metallen mittels Photoemissionsspektroskopie untersucht. Hierbei wurden, unter Einstrahlung von Photonen mit einer Energie von zumeist 20-50 eV Elektronen des Valenzbandes des zu untersuchenden Probensystems ausgelöst, und in Abhängigkeit der kinetischen Energie und des Austrittswinkels bzw. Impulses charakterisiert. Eine wesentliche Aufgabe dieser Arbeit war es, die technische Entwicklung experimenteller Apparaturen des letzten Jahrzehnts dazu zu verwenden, um mit möglichst großer energetischer Auflösung bereits etablierte aber dennoch vielversprechende Systeme erneut zu untersuchen. Im ersten Hauptabschnitt wurden hierzu Einzel- und Doppelschichten bestehend aus Pentacenmolekülen mittels Molekularstrahlepitaxie auf einer Ag(110)-Oberfläche abgeschieden. Eine anschließende Untersuchung der emittierten Photoelektronen mittels Impulsmikroskopie, wodurch man in der Lage ist, die Photoelektronen des gesamten oberen Halbraumes gleichzeitig zu detektieren, ergab eine Verkippung der Moleküle der ersten und zweiten Lage der Doppelschichten. Im Vergleich hierzu liegen die Moleküle der Einzelschicht flach auf dem Substrat auf. Der Übergang von der Einzel- zur Doppelschicht erwirkt demnach eine Verkippung der Moleküle der ersten Lage, welche aufgrund der direkten Wechselwirkung mit dem Substrat nicht zu erwarten war. Im weiteren Verlauf dieses Abschnittes konnten unter Verwendung eines hemisphärischen Analysators mit hoher Energieauflösung weitere Feinheiten des Valenzbandspektrums, wie z.B. ein ungewöhnlicher Kurvenverlauf des Intensitätsmaximums des zweiten besetzten Molekülorbitals der ersten (unteren) Pentacenlage ausgemacht werden. Im zweiten Hauptabschnitt wurde eine energetisch schmale Resonanz, welche in der Literatur mit dem Kondoeffekt in Verbindung gebracht wird, im Valenzbandspektrum zweier unterschiedlicher Metall-Phthalocyaninmoleküle (Nickel- und Kupfer-Phthalocyanin) auf den drei Oberflächen Ag(100), Ag(110) und Ag(111) adsorbiert und auf ihre Temperaturabhängigkeit im Bereich von 20-300 Kelvin untersucht. Hierbei ergab sich neben der Feststellung des Vorhandenseins des Maximums auf allen drei Silber-Oberflächen ein energetischer Versatz dieses Maximums durch Abkühlen der Probe im Falle der Substrate Ag(100) und Ag(110), welcher in der vorliegenden Größenordnung von bis zu 100 meV ungewöhnlich für bisherige bekannte Kondosysteme ist. Auf Ag(111) konnte kein signifikanter Versatz im Rahmen der Messungenauigkeit festgestellt werden. Im weiteren Verlauf wurden auch von diesen Probensystemen Messungen mittels Impulsmikroskopie durchgeführt, welche in den dadurch erhaltenen Impulskarten geringe Anomalien aufwiesen. Insgesamt kann das vorliegende Verhalten dieser Systeme bis zum Abschluss dieser Arbeit nicht endgültig erklärt werden. Die für organische Systeme höchst ungewöhnliche Theorie der Ausbildung eines Kondogitters, in welcher die Wechselwirkung einzelner Störstellen zur Ausbildung eines elektronenartigen Bandes führt, wäre jedoch zunächst in der Lage, ein derartiges Verhalten, wenn auch nicht in dem hier gezeigten Ausmaß, teilweise zu erklären. / In this dissertation organic thin films and their interfaces to metals are investigated by photoemission spectroscopy. Electrons of the valence band of the sample system to be investigated are excited under irradiation of photons with an energy in the order of 20-50 eV, and characterized as a function of the kinetic energy and the exit angle or momentum. An essential task of this work was to use the technical development of state-of-the-art experimental apparatuses of the last decade in order to investigate already established but nevertheless promising systems with the highest possible energetic resolution. In the first main section, single and double layers consisting of pentacene were deposited by molecular beam epitaxy on an Ag(110) surface. A subsequent examination of the emitted photoelectrons by momentum microscopy, which enables the simultaneous measurement of the entire upper half-space, revealed a tilting of the molecules of the first and second layers of the double layers. In comparison, the molecules of the single layer lie flat on the substrate. Therefore, the transition from the single to the double layer causes a tilting of the molecules of the first layer, which was not to be expected due to the direct interaction with the substrate. In the further course of this section, using a hemispherical analyzer with high energy resolution, further small energetic features of the valence band spectrum could be detected, e.g. an unusual shape of the intensity of the second occupied orbital of the first (bottom) pentacene layer. In the second main section, an energetically narrow resonance, which is associated with the Kondo effect in the literature, was investigated in the valence band spectrum of two different metal phthalocyanine molecules (nickel and copper) adsorbed on the three surfaces Ag(100), Ag(110) and Ag(111) for their temperature dependence in the range of 20-300 Kelvin. Besides the determination of the occurrence of the maximum on all three silver surfaces, an energetic shift of this maximum resulted from cooling the sample on the substrates Ag(100) and Ag(110), which in the present order of magnitude of approx. 100 meV is unusual for the previously known Kondo systems. On Ag(111) no significant shift could be found within the uncertainty of the measurement. In the further course, measurements of these sample systems were also carried out using a momentum microscope, which showed minor anomalies in the resulting momentum maps. Overall, the presented behaviour of these systems could not be explained within the frame of this dissertation. However, the theory of the formation of a Kondo lattice, in which the interaction of individual impurities leads to the formation of an electron-like band, which is highly unusual for organic systems, might be able to partially explain such a behaviour, even if not to the extent shown here.

Die große Vielfalt an organischen Komplexen, kombiniert mit der Möglichkeit, die chemische Reaktivität und den elektronischen Grundzustand unterschiedlicher Komplexe innerhalb derselben Molekülfamilie abzustimmen, machen solche Materialien für elektronische Anwendungen attraktiv. Auf Grund ihrer langen Spin-Lebensdauer sind Moleküle auch für Spintronik-Anwendungen sehr geeignet. In dieser Arbeit werden die Grenzflächen zwischen organischen Halbleitern und Metallen sowie zwei organischen Halbleitern durch spektroskopische Techniken untersucht. Das erste Kapitel beinhaltet eine allgemeine Einführung zu organischen Halbleitern und Eigenschaften von Grenzflächen. Im experimentellen Teil werden die untersuchten Moleküle und verwendeten Messmethoden detailliert vorgestellt. Der dritte Teil dieser Arbeit zeigt die Auswirkung verschiedener Substrate (Co und Ni) oder Molekülkombinationen (CoPc und FePc) auf die Wechselwirkungs- und Ladungsübertragungskanäle. In dem nachfolgenden Teil werden elektronische Zustände und Wechselwirkungen an Organik-Organik Grenzflächen am Beispiel von VOPc/F16CuPc und F16CoPc/rubren diskutiert. Der letzte Teil dieser Arbeit zeigt, wie die Eigenschaften der Substrate und die Modifikation der Moleküle die molekulare Orientierung beeinflussen können.

In the present work, charge transfer in organic semiconductors is investigated by means of photoemission spectroscopy. Organic charge transfer systems consist of electron donors and acceptors and in some cases exhibit new electronic properties that are not observed in the individual constituents. Examples are metallic conductivity and changed optical or transport gaps. The main focus were interfaces between donor and acceptor molecules that were prepared as thin films by thermal evaporation in ultra-high vacuum. In particular, the strong electron acceptor F6TCNNQ was combined with several scientifically relevant donors, with the aim of achieving a large charge transfer. As reference systems, potassium doped F6TCNNQ and the interface between F6TCNNQ and gold were studied. In both systems, a large electron transfer to F6TCNNQ with similar spectroscopic signatures was observed. The investigated organic interfaces all showed charge transfer that manifested itself in form of changes in the core levels of F6TCNNQ that were similar for each system. Also, new occupied states in the former gaps of the molecules were found. For every investigated interface the Fermi energy was pinned above the respective highest occupied molecular orbitals which entails semiconducting behaviour and no metal-like delocalised charge carriers. For the combination of F6TCNNQ and dibenzopentacene, a blended film was prepared by co-deposition and compared with the corresponding interface. It was found that the electronic properties of the blend are initially determined by electrostatic interactions, whereas annealing leads to a large charge transfer due to a temperature induced change of molecular orientation. Moreover, the acceptors F2TCNQ and F16CoPc were used in order to compare systems with the same donor and different acceptors. Differences in the degree of charge transfer and interface morphology were observed. The last part of this work addresses the electronic properties of an organic rectifier that was fabricated by collaboration partners. It is built up of an organic heterojunction of two phtalocyanines (CuPc and F16CoPc) between two gold contacts. The energy level alignment across the device and the charge transfer reactions at the different interfaces are discussed with regard to the functionality of the device.

While in conventional superconductors coupling between electrons and phonons is known to be responsible for the electron pairing, for the high temperature superconductors the pairing media remains under debates. Since the interactions of electrons with other degrees of freedom (phonons, magnetic excitations, etc) manifest themselves by an additional renormalization in the electronic dispersion, they can be investigated by means of Angle Resolved Photoelectron Spectroscopy. In the work renormalization in two families of high Tc cuprates have been studied. Along the diagonal of the two-dimensional BZ, the renormalization effects are represented by an unusual band dispersion that develops a so-called ‘‘kink’’. In the vicinity of the (pi, 0) point of the BZ, where the order parameter reaches its maximum, the renormalization is noticeably stronger and makes itself evident even in the shape of a single spectral line measured for a fixed momentum. It was shown that for the Bi-2212 samples substitution of Cu atoms in Cu-O plane changes renormalization features in ARPES spectra both in nodal and antinodal parts of the Brillouin zone. The smearing of the dip in the in the spectral line shape measured at (pi; 0) point can be well explained by coupling of electrons to the magnetic resonance mode. The effect of Zn and Ni substitution on the antinodal ARPES spectra was shown to be in good agreement with the influence of these impurities on magnetic resonance mode seen in inelastic neutron scattering experiments. This, in addition to the previous ARPES studies of temperature and doping dependence of peak-dip-hump structure, mass renormalization near antinodal region and a kink in the nodal part of Brillouin zone, provides further evidence that the coupling to magnetic excitations, rather than to phonons, is responsible for the observed unusual renormalization. Unlike the well studied Bi-2212 family of cuprates, photoemission on YBCO-123 turns out to be much more complicated. The observed spectra have a strong contribution from a heavily overdoped surface component with the hole doping level of about x~0.30, which is weakly dependent on the sample stochiometry. Absence of any signs of superconductivity in the spectra of the overdoped component was argued to result from the unusually high doping level. This conclusion is supported by the fact that the overdoped bands give rise to the Fermi surface and band structure consistent with the predictions of the LDA calculations, as well as, by the dependence of the photoemission matrix element on the excitation energy, which closely follows that of the superconducting bulk component. Specific experimental geometry was used to enhance the signal coming from the superconducting component. In particular, experiments with circularly polarized light bundled with simple theoretical considerations enabled better separation of the surface and the bulk components. This type of experiments also suggests that the overdoped component is mainly localized in the topmost CuO2 bilayer, while the next bilayers in the YBCO-123 structure already represent bulk properties and retain superconductivity. Using partially Ca substituted samples it was possible to obtain spectra with a suppressed overdoped component. The likely reason for the suppression is a shift of the most probable cleavage plane from the Ba–O interface to the Y layer. Spectra from the Ca substituted sample clearly reveal a sizable superconducting gap, and strong renormalization effects in the vicinity of the antinodal point. The fact that the renormalization vanishes above Tc and has strong momentum dependence, diminishing away from the (pi; 0)/(0; pi) point, strongly suggests that the reason for this renormalization in YBCO-123 is coupling of the electronic subsystem to spin resonance, similar to the case of Bi-2212.

Bibliografische Beschreibung, Referat und Schlagwörter M.S. Chem. Ing. Sung Gook Park Thema: Organic Modified GaAs Schottky Contacts Einreichungsdatum: 28. September 2001 Im Rahmen dieser Arbeit wurden organische Halbleitermaterialien verwendet, um damit die Transporteigenschaften von Metal/GaAs(100) Schottky-Kontakten zu kontrollieren. Ziel ist es, Strom-Spannungs- (J-V) und Kapazitäts-Spannungs-Kennenlien (C-V) zu verstehen. Zur chemischen und elektronischen Charakterisierung der GaAs(100)-Oberflächen, organische Molekül/GaAs(100)-Grenzflächen und der Metall/organische Molekül-Grenzflächen wurden die Photoelektronenspektroskopie (PES) und Nahkantenröntgenabsorptionsspektroskopie (NEXAFS) eingesetzt. Verschiedene GaAs(100)-Oberflächen, wie die reine GaAs(100)-c(4x4)-, die Wasserstoff-Plasma behandelte GaAs(100)- und die chalkogenpassivierte GaAs-Oberflächen, wurden als Substrate für die organische Molekularstrahldeposition (OMBD) verwendet. In der Arbeit wird der Einfluss der chemischen und elektronischen Eigenschaften dieser Substratoberflächen auf das Wachstum von organischen Molekülen auf deren Oberflächen untersucht. 3,4,9,10-Perylentetracarboxylic Dianhydrid (PTCDA) und Dimethyl-3,4,9,10-Perylentetracarboxyl Diimid wurden zur organischen Modifizierung von Metall/GaAs(100)-Schottky-Kontakten verwendet. Die organischen Moleküle werden anfänglich an Defekten der GaAs(100)-Oberflächen adsorbiert. Die Adsorption an Defekten führt zu einer Reduktion der inhomogenen Bandverbiegung der GaAs(100)-Oberfläche. Aus den PES-Spektren wurden Energiebanddiagramme für organische Schicht/GaAs(100)-Grenzflächen und Metall/organische Grenzflächen abgeleitet. Entsprechend der relativen energetischen Lagen des Leitungsbandminimums von GaAs(100)-Oberflächen und des niedrigsten unbesetzten Molekülorbitals der organischen Schichten werden Interfacedipole ausgebildet. Die Verwendung von anorganischen Substraten mit systematisch variierender Elektronenaffinität (EA) stellt eine neue Methode zur Bestimmung des Transportniveaus von Elektronen in der organischen Schicht dar. Bei Einfügung von dünnen PTCDA-Schichten zwischen Ag-Elektrode und GaAs(100)-Oberfläche, wurde beobachtet, dass die J-V-Kennlinien in Abhängigkeit von der Dicke der organischen Schicht und der Behandlung der GaAs-Oberflächen systematisch variierte. Dieses Verhalten kann unter Verwendung des Energieniveaudiagramms, das mittels PES bestimmt wurde, und durch eine Barrierenerniedrigung infolge von Bildkräften gut erklärt werden. Durch die Kombination von Oberflächenbehandlung und Einfügen einer dünnen definierten organischen Schicht kann die effektive Barrierenhöhe in einem breiten Bereich verändert, d. h. letztendlich definiert eingestellt und kontrolliert werden. Daraus ergibt sich die Möglichkeit, die Leistungsaufnahme von GaAs-Schottky-Kontakten zu reduzieren. <Schlagwörter> Organische Moleküle, Organische Molekularstrahldeposition (OMBD), GaAs(100), Metall/Hableiter- Schottky-Kontakt, Photoemissionspektroskopie (PES), Nahkantenröntgenabsorptionsspektroskopie (NEXAFS), Elektrische Messungen

Perovskite-based photovoltaic is one of the most promising classes of emerging solar cell technologies. This material class combines several advantageous properties, including low exciton binding energy, high charge carrier diffusion length and high optical absorption. Despite these excellent attributes, some challenges remain in perovskite research. Most notably the device stabilities and lifetimes need to be significantly improved in order to push this technology towards commercialization. Defect physics in perovskite photovoltaics has been shown to be a main factor in understanding long-term device instabilities. However, the number of measurement techniques that can track changes in the ionic landscape during device degradation is very limited, as the perovskite layer is buried under charge extraction layers and metallic contacts. In this thesis argon gas-cluster ion beam etching is combined with x-ray and ultraviolet photoelectron spectroscopy to achieve high resolution energetic and compositional depth profiles. In contrast to most layer-to-layer techniques this method can be applied after any operation time of the photovoltaic and therefore nicely investigate potential changes in the defect landscape. In the first part of this thesis, the impact of argon gas-cluster etching on the perovskite structure is investigated in order to identify potential damage that prevents this technique from being viable for perovskite materials. It is found that metallic lead is gradually created and a small preferential etching effect of the organic cations takes place during the depth profiling, but it is demonstrated that the major part of the crystal structure stays intact and that the energetics of the sample remains very stable. Moreover, it is demonstrated that fitting of the obtained ultraviolet photoelectron spectroscopy spectra leads to high resolution energetic and compositional depth profiles, which are suitable to identify potential loss mechanisms in full photovoltaic devices. In the second part, we investigate the increase in device performance of a perovskite photovoltaic during the first subsequent measurements under full illumination, which is a common example of a short-term instability. Ultraviolet photoelectron spectroscopy depth profiles reveal a strong band bending effect appearing after biasing the device which consequently leads to an increase in device open-circuit voltage. Density functional theory simulations link this band bending effect to the accumulation of iodine interstitials at the interface between the perovskite and the electron transport layer. In the final part, long-term degradation of perovskite photovoltaics is studied by investigating the impact of ionic additives on the perovskite active layer, which increases the lifetime of these devices significantly. It is found that most properties of the perovskite layer remain unaffected by the ionic additive, e.g. microstructure, energetic disorder and photoluminescence. Photoelectron spectroscopy depth profiling revealed an accumulation of iodine at the interface towards the electron transport layer, which is significantly reduced in additive-containing samples. Deep-level transient spectroscopy revealed a new mobile defect species in the ionic additive samples and at the same time a reduction of iodine diffusivity.

Photochrome Schalter (Photoschalter), wie Diarylethene (DAEs), Dihydropyrole (DHPs), Azobenzole und Spiropyrane sind für die Entwicklung von photoschaltbaren multifunktionalen Geräten interessant. Daher beschäftigt sich ein Großteil dieser Dissertation mit der Untersuchung der grundlegenden elektronischen Eigenschaften von Photoschaltern, u.a. Dipolmoment und Grenzniveaus. Ein besonderer Fokus liegt auf der dynamischen Anpassung der Energienieveaus zwischen den (in)organischen Halbleitern und den Photoschaltern mit externen Stimuli (z. B. Licht, Wärmeenergie). Zuerst werden die elektronischen Änderungen von DAE-Photoschaltern bei Lichtbeleuchtung durch direkt und inverse Photoemissionsspektroskopie und Dichtefunktionaltheorie nachgewiesen. Beispielsweise zeigt das höchste besetzte Molekülorbital (HOMO) von DAE-Dünnfilmen eine Differenz von 800 meV zwischen ihren beiden isomeren Zuständen. Mit diesen lichtgesteuerten Eigenschaften werden dann DAE-Moleküle verwendet, um die elektronische Struktur an Grenzflächen mit organischen und anorganischen Komponenten (z. B. P3HT, N2200, ZnO, ITO) zu modifizieren. Es wird gezeigt, dass DAE-Moleküle bei Lichtbeleuchtung die Energieniveauanordnung an der Grenzfläche um Hunderte von meV dynamisch und reversibel ändern können. Um Erkenntnisse über mehrere stimulationsinduzierte Schaltungen, z. B. Licht und Wärme, zu erhalten, wird hierfür ein Photoschalter Pyridyl-DHP (Py-DHP) vom T-Typ synthetisiert, da Py-DHP mit Licht in eine Richtung geschaltet und mit Wärmebehandlung zurückgeschaltet werden kann. Es hat sich herausgestellt, dass die schaltinduzierten elektronischen Änderungen durch ein Fermi-Level-Pinning aufgrund der Anwesenheit von molekularen Dipolen beeinflusst werden. Diese Studien bieten eine solide Grundlage für die Verwendung von Photoschaltern zur dynamischen Änderung der Energielevelanordnung und werden die Entwicklung verbesserter photoschaltbarer (opto-)elektronischer Geräte unterstützen. / Photochromic switches (photoswitches) such as diarylethenes (DAEs), dihydropyrenes (DHPs), azobenzenes and spiropyrans have attracted increasing interest for the development of photoswitchable multifunctional devices. The present work of this thesis is to investigate the fundamental electronic properties of photoswitches, i.e., dipole moment, and frontier levels. Particular focus is on dynamically tuning the frontier level alignment between the (in)organic semiconductors and photoswitches with external stimuli (e.g., light, heat). First, the electronic changes of DAE photoswitches upon light illumination are evidenced by direct and inverse photoemission spectroscopy together with density functional theory calculations, for example, the highest occupied molecular orbital (HOMO) of DAE thin films exhibits an 800 meV difference between their two isomeric states. With these light-controlled properties, DAE molecules are then employed to modify the electronic structure at interfaces with organic and inorganic components (e.g., P3HT, N2200, ZnO, ITO). It is proved that upon light illumination DAE molecules can indeed dynamically and reversibly switch the interface frontier level alignment by hundreds of meV. To obtain knowledge on multiple stimuli-induced switchings, e.g., light and heat, a T-type photoswitch pyridyl-DHP (Py-DHP) is synthesized for this purpose, since Py-DHP can be switched with light in one direction and switched back with heat treatment. It is found that, the switching-induced electronic changes are impacted by a Fermi level pinning due to the presence of molecular dipoles. These studies provide a solid basis for the use of photoswitches for dynamically manipulating energy level alignment, and will aid the development of improved photoswitchable (opto-)electronic devices.

Bibliografische Beschreibung, Referat und Schlagwörter M.S. Chem. Ing. Sung Gook Park Thema: Organic Modified GaAs Schottky Contacts Einreichungsdatum: 28. September 2001 Im Rahmen dieser Arbeit wurden organische Halbleitermaterialien verwendet, um damit die Transporteigenschaften von Metal/GaAs(100) Schottky-Kontakten zu kontrollieren. Ziel ist es, Strom-Spannungs- (J-V) und Kapazitäts-Spannungs-Kennenlien (C-V) zu verstehen. Zur chemischen und elektronischen Charakterisierung der GaAs(100)-Oberflächen, organische Molekül/GaAs(100)-Grenzflächen und der Metall/organische Molekül-Grenzflächen wurden die Photoelektronenspektroskopie (PES) und Nahkantenröntgenabsorptionsspektroskopie (NEXAFS) eingesetzt. Verschiedene GaAs(100)-Oberflächen, wie die reine GaAs(100)-c(4x4)-, die Wasserstoff-Plasma behandelte GaAs(100)- und die chalkogenpassivierte GaAs-Oberflächen, wurden als Substrate für die organische Molekularstrahldeposition (OMBD) verwendet. In der Arbeit wird der Einfluss der chemischen und elektronischen Eigenschaften dieser Substratoberflächen auf das Wachstum von organischen Molekülen auf deren Oberflächen untersucht. 3,4,9,10-Perylentetracarboxylic Dianhydrid (PTCDA) und Dimethyl-3,4,9,10-Perylentetracarboxyl Diimid wurden zur organischen Modifizierung von Metall/GaAs(100)-Schottky-Kontakten verwendet. Die organischen Moleküle werden anfänglich an Defekten der GaAs(100)-Oberflächen adsorbiert. Die Adsorption an Defekten führt zu einer Reduktion der inhomogenen Bandverbiegung der GaAs(100)-Oberfläche. Aus den PES-Spektren wurden Energiebanddiagramme für organische Schicht/GaAs(100)-Grenzflächen und Metall/organische Grenzflächen abgeleitet. Entsprechend der relativen energetischen Lagen des Leitungsbandminimums von GaAs(100)-Oberflächen und des niedrigsten unbesetzten Molekülorbitals der organischen Schichten werden Interfacedipole ausgebildet. Die Verwendung von anorganischen Substraten mit systematisch variierender Elektronenaffinität (EA) stellt eine neue Methode zur Bestimmung des Transportniveaus von Elektronen in der organischen Schicht dar. Bei Einfügung von dünnen PTCDA-Schichten zwischen Ag-Elektrode und GaAs(100)-Oberfläche, wurde beobachtet, dass die J-V-Kennlinien in Abhängigkeit von der Dicke der organischen Schicht und der Behandlung der GaAs-Oberflächen systematisch variierte. Dieses Verhalten kann unter Verwendung des Energieniveaudiagramms, das mittels PES bestimmt wurde, und durch eine Barrierenerniedrigung infolge von Bildkräften gut erklärt werden. Durch die Kombination von Oberflächenbehandlung und Einfügen einer dünnen definierten organischen Schicht kann die effektive Barrierenhöhe in einem breiten Bereich verändert, d. h. letztendlich definiert eingestellt und kontrolliert werden. Daraus ergibt sich die Möglichkeit, die Leistungsaufnahme von GaAs-Schottky-Kontakten zu reduzieren. <Schlagwörter> Organische Moleküle, Organische Molekularstrahldeposition (OMBD), GaAs(100), Metall/Hableiter- Schottky-Kontakt, Photoemissionspektroskopie (PES), Nahkantenröntgenabsorptionsspektroskopie (NEXAFS), Elektrische Messungen

While in conventional superconductors coupling between electrons and phonons is known to be responsible for the electron pairing, for the high temperature superconductors the pairing media remains under debates. Since the interactions of electrons with other degrees of freedom (phonons, magnetic excitations, etc) manifest themselves by an additional renormalization in the electronic dispersion, they can be investigated by means of Angle Resolved Photoelectron Spectroscopy. In the work renormalization in two families of high Tc cuprates have been studied. Along the diagonal of the two-dimensional BZ, the renormalization effects are represented by an unusual band dispersion that develops a so-called ‘‘kink’’. In the vicinity of the (pi, 0) point of the BZ, where the order parameter reaches its maximum, the renormalization is noticeably stronger and makes itself evident even in the shape of a single spectral line measured for a fixed momentum. It was shown that for the Bi-2212 samples substitution of Cu atoms in Cu-O plane changes renormalization features in ARPES spectra both in nodal and antinodal parts of the Brillouin zone. The smearing of the dip in the in the spectral line shape measured at (pi; 0) point can be well explained by coupling of electrons to the magnetic resonance mode. The effect of Zn and Ni substitution on the antinodal ARPES spectra was shown to be in good agreement with the influence of these impurities on magnetic resonance mode seen in inelastic neutron scattering experiments. This, in addition to the previous ARPES studies of temperature and doping dependence of peak-dip-hump structure, mass renormalization near antinodal region and a kink in the nodal part of Brillouin zone, provides further evidence that the coupling to magnetic excitations, rather than to phonons, is responsible for the observed unusual renormalization. Unlike the well studied Bi-2212 family of cuprates, photoemission on YBCO-123 turns out to be much more complicated. The observed spectra have a strong contribution from a heavily overdoped surface component with the hole doping level of about x~0.30, which is weakly dependent on the sample stochiometry. Absence of any signs of superconductivity in the spectra of the overdoped component was argued to result from the unusually high doping level. This conclusion is supported by the fact that the overdoped bands give rise to the Fermi surface and band structure consistent with the predictions of the LDA calculations, as well as, by the dependence of the photoemission matrix element on the excitation energy, which closely follows that of the superconducting bulk component. Specific experimental geometry was used to enhance the signal coming from the superconducting component. In particular, experiments with circularly polarized light bundled with simple theoretical considerations enabled better separation of the surface and the bulk components. This type of experiments also suggests that the overdoped component is mainly localized in the topmost CuO2 bilayer, while the next bilayers in the YBCO-123 structure already represent bulk properties and retain superconductivity. Using partially Ca substituted samples it was possible to obtain spectra with a suppressed overdoped component. The likely reason for the suppression is a shift of the most probable cleavage plane from the Ba–O interface to the Y layer. Spectra from the Ca substituted sample clearly reveal a sizable superconducting gap, and strong renormalization effects in the vicinity of the antinodal point. The fact that the renormalization vanishes above Tc and has strong momentum dependence, diminishing away from the (pi; 0)/(0; pi) point, strongly suggests that the reason for this renormalization in YBCO-123 is coupling of the electronic subsystem to spin resonance, similar to the case of Bi-2212.

In this work systematic studies of the organic semiconductor CuPc have been presented. In general the investigation can be devided in three parts. In the first one we have studied the electronic structure of clean CuPc thin film. The next two parts are devoted to organic-organic and metal–organic interface formation, where one of the interface components is CuPc thin film. The main results of this thesis are: - The electronic structure of the pristine organic semiconductor CuPc (valence band and empty states) has been obtained by a combination of conventional and resonant photoemission, near-edge X-ray absorption, as well as by theoretical ab initio quantum-chemical calculations. A qualitative assignment of different VB structures has been given, or in other words the contributions of different atomic species as well as sites of the CuPc molecule to the electronic DOS has been established. In particular, it was shown, that the HOMO is mainly comprised of the spectral weights from the orbitals of carbon pyrolle atoms. Additional contributions to the HOMO stems from the benzene atoms. A combined experimental and theoretical study of the unoccupied electronic density of states of CuPc was presented. Our study allows identifying the contributions from different parts of the molecule to the unoccupied DOS and the measured spectra, which lays grounds for future studies of the evolution of the CuPc electronic states upon e.g. functionalization or doping. Application of similar studies to other organic semiconductors will also provide significant insight into their unoccupied electronic states. - The electronic properties of the organic heterointerfaces between fullerite and pristine copper phthalocyanine were studied. Both interfaces, CuPc/C60 and C60/CuPc, were found to be non-reactive with pronounced shifts of the vacuum level pointing to the formation of an interfacial dipole mainly at the CuPc side of the heterojunctions. The dipole values are close to the difference of the work functions of the two materials. Important interface parameters and hole-injection barriers were obtained. The sequence of deposition does not influence the electronic properties of the interfaces. - CuPc doped with potassium was studied by means of photoemission and photoabsorption spectroscopy. A detailed analysis of the core-level PE spectra allows one to propose possible lattice sites, which harbor the potassium ions. Contrasting to a few results reported in the literature, the films prepared in this thesis showed no finite electronic density of states at the Fermi level. - Two stages of the In/CuPc interface formation have been distinguished. The low-coverage stage is characterized by a strong diffusion of the In atoms into the organic film. Metal ions occupy sites close to the pyrolle nitrogen and strongly interact with molecules transferring negative charge to CuPc. Indium diffusion into the organic films saturates at a stoichiometry of In2CuPc. Subsequently, in the second stage the formation of a metallic indium film occurs on the top of the In2CuPc film. - Upon deposition on CuPc film Sn and Ag atoms do not diffuse into the organic film forming metallic clusters and/or thin metallic overlayer. Sharp metal-organic film interface is formed, in contrast to indium and potassium deposition. Presented experimental results also give evidence for absence of noticeable chemical reaction of Sn and Ag with CuPc thin film. - The systematic investigation of interface formation between CuPc thin film and various metals gives us the possibility to summarize all results with demonstrating similarities and differences for all systems studied.