Excitons are fundamental electronic excitations in a semiconductor. They are bound states consisting of an electron in the conduction band and a positively charged hole in the valence band. They have hydrogen-like properties and are therefore referred to as the hydrogen analogues in solid states. In the semiconductor Cuprous Oxide, Cu2O, highly excited states of excitons can be observed with principal quantum numbers up to n = 25. These states are called Rydberg excitons in analogy to th...

In magnetic semiconductors the optical spectrum and, in particular, the absorption edge representing the band-gap are strongly affected by the onset of the magnetic order. This contribution to the band-gap energy has hitherto been described theoretically in terms of a Heisenberg Hamiltonian, in which a delocalized conduction carrier is coupled to the localized magnetic moments by the exchange interaction. Such models, however, do not take into account the strong correlations displayed in a wi...

In dieser Arbeit wurde das Adsorptionsverhalten verschiedener Substanzen aus der Gas- oder Flüssigphase an Modellmembranen untersucht. Lipidmembranen spielen in lebenden Organismen eine wesentliche Rolle. In Form von Doppelschichten organisieren sie die Abgrenzung der Zelle und der intrazellulären Kompartimente. In der Lunge reguliert eine komplexe Lipid-Protein Monolage, das sogenannte pulmonale Surfactant, den störungsfreien Gasaustausch. Heutzutage ist die menschliche Lunge vielen potenzie...

The successful implementation of nanoscale materials in next generation optoelectronic devices crucially depends on our ability to functionalize and design low dimensional materials according to the desired field of application. Recently, organic adsorbates have revealed an enormous potential to alter the occupied surface band structure of tunable materials by the formation of tailored molecule-surface bonds. Here, we extend this concept of adsorption-induced surface band structure engineerin...

Organic photovoltaic devices operate by absorbing light and generating current. These two processes are governed by the optical and transport properties of the organic semiconductor. Despite their common microscopic origin—the electronic structure—disclosing their dynamical interplay is far from trivial. Here we address this issue by time-resolved photoemission to directly investigate the correlation between the optical and transport response in organic materials. We reveal that optical gener...

The discovery and realization of graphene as an ideal two-dimensional (2D) material has triggered extensive efforts to create similar 2D materials with exciting spin-dependent properties. Here, we report on a novel Sn 2D superstructure on Au(111) that shows similarities and differences to the expected electronic features of ideal stanene. Using spin- and angle-resolved photoemission spectroscopy, we find that a particular Sn/Au superstructure reveals a linearly dispersing band centered at the ...

The quantification of the electronic transport energy gap of a molecular semiconductor is essential for pursuing any challenge in molecular optoelectronics. However, this remains largely elusive because of the difficulties in its determination by conventional spectroscopic methods. This communication presents an in-device molecular spectroscopy (i-MOS) technique, which permits measuring this gap seamlessly, in real device operative conditions, at room temperature and without any previous know...

Marcus’s theory of electron transfer, initially formulated six decades ago for redox reactionsin solution, is now of great importance for very diverse scientific communities. The molecularscale tunability of electronic properties renders organic semiconductor materials in principlean ideal platform to test this theory. However, the demonstration of charge transfer indifferent Marcus regions requires a precise control over the driving force acting on the chargecarriers. Here, we make use of a ...

We investigate the nonlinear optical response of a thin film of ion-implanted VO2 nanocrystals with open aperture z-scans involving femtosecond near-infrared pulses. Beyond the established nonlinearity related to the insulator-metal phase transition of VO2, the metallic state features a pronounced saturable absorption for 100 fs pulses from a modelocked Yb:fiber source at = 1036 nm. In contrast, we find a pronounced reverse saturable absorption for 90 fs pulses in the telecom window at...

Modern computer processors are nowadays approaching limits due to their quantum limitations. The basic principle of modern electronics is measuring a small electrical charge of electrons passing through electronic circuits. An alternative approach based on novel materials could be the solution, which instead relies on the fundamental quantum- mechanical property – spin. The fundamental requirements that apply to a device based on quantum spin qubits include the ability to scale a quantum syst...

Quantum computers have the potential to speed up certain problems that are hard for classical computers. Hybrid systems, such as the nitrogen vacancy (NV) center in diamond, are among the most promising systems to implement quantum computing, provided the control of the different types of qubits can be efficiently implemented. In the case of the NV center, the anisotropic hyperfine interaction allows one to control the nuclear spins indirectly, through gate operations targeting the elect...

The combination of magnetic resonance with laser spectroscopy provides some interesting options for increasing the sensitivity and information content of magnetic resonance. This review covers the basic physics behind the relevant processes, such as angular momentum conservation during absorption and emission. This can be used to enhance the polarization of the spin system by orders of magnitude compared to thermal polarisation as well as for detection with sensitivities down to the level of ...

Electron paramagnetic resonance (EPR) is a spectroscopic technique to study the interaction between free electrons and the local molecular environment. Over the past 60 years, EPR instrumentation and methodology has been developed to study, for example, the structure and dynamics of proteins, chemical reactions of organic-based radicals, transition-metal chemistry, catalytic reactions, electron transfer processes, and metalloenzymes. Because of these past developments, EPR has become a p...

Hybrid quantum registers, such as electron-nuclear spin systems, have emerged as promising hardware for implementing quantum information and computing protocols in scalable systems. Nevertheless, the coherent control of such systems still faces challenges. Particularly, the lower gyromagnetic ratios of the nuclear spins cause them to respond slowly to control fields, resulting in gate times that are generally longer than the coherence time of the electron. Here, we demonstrate a scheme for ci...

Initializing quantum registers with high fidelity is a fundamental precondition for many applications like quantum information processing and sensing. The electronic and nuclear spins of a Nitrogen-Vacancy (NV) center in diamond form an interesting hybrid quantum register that can be initialized by a combination of laser, microwave, and radio-frequency pulses. However, the laser illumination, which is necessary for achieving electron spin polarization, also has the unwanted sideeffect of depo...

This thesis aims to further the understanding of the two-photon interaction dynamic in bulk direct semiconductors in an electronically excited state. The central goal is to assess the practicability of controlling the two-photon transition strength using an ultrafast all-optical scheme and ultimately identify the key parameters and requirements necessary to observe degenerate two-photon gain in these media. Here, a transfer of stimulated two-photon emission to the semiconductor medium is very...

This work will focus on the characterization of different dielectric barrier discharges (DBD) that are used in analytical applications. These discharges are primarily used as ion sources that provide charged species for the subsequent detection with atmospheric mass spectrometers (MS) or ion mobility spectrometers (IMS). The main method of investigation for the DBDs will be based on optical methods such as temporally-, spatially-, and spectrally-resolved optical emission spectroscopy (TSSROES...

Die Messung flüchtiger toxischer Elemente in kleinen Konzentrationen ist von großer Bedeutung im Bereich der analytischen Chemie. Eine Methode dabei ist die optische Emissionsspektrometrie an dielektrisch behinderten Plasmen. Dabei wird der gasförmige Analyt in das Plasma eingeleitet, dissoziiert und anschließend angeregt. Die Intensität des ausgesendeten Lichts ist dann proportional zur Konzentration des Analyten im Plasma. Die Mechanismen bei der Interaktion zwischen dem Plasma und dem Anal...

Analyzing and characterizing mechanical properties of polymers is a vast field of research. In this thesis, linear and nonlinear rheological investigations have been used to study the relaxation behavior of various glass-forming liquids. In simple (non-associating and non-polymeric) liquids, the microscopic flow behavior is associated to the mass transport which is defined by the dynamics of the molecules and therefore the structural relaxation. This is usually discussed in the literatur...