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Das Stickstoff-Fehlstellen-Zentrum (NV-Zentrum) in Diamant ist eines der vielver- sprechendsten Spinsysteme für Anwendungen im Bereich Quanten-Computing, -Information und -Sensorik. Die Abhängigkeit der Fluoreszenzintensität vom Spinzu- stand ermöglicht dabei das rein optische Auslesen des Spinzustandes. Für alle Anwendungen, die auf aktive Spinmanipulation angewiesen sind, ist Mikrowellen- strahlung unverzichtbar. Die Fähigkeit, den Spinzustand von NV-Zentren vollständig zu kontrollieren, wird durch die Richtung, Intensität und Polarisation der Mikrow- ellenstrahlung definiert. Es gibt verschiedene Ansätze, um geeignete Mikrowellen- strahlung zu erzeugen, aber oft ist die Feldintensität zu gering oder es gibt andere Einschränkungen, z.B. eine geringe Frequenzbandbreite. Im ersten Teil meiner Arbeit untersuche ich transparente Leiter auf Basis von Indium- Zinn-Oxid (ITO), um die Mikrowellenansteuerung von NV-Zentren zu optimieren. Dabei wird eine detaillierte Analyse von ITO auf Diamant bezüglich einzelner NV-Zentren vorgestellt. Ein mathematisches Modell wurde entwickelt, um die Feldverteilung vorherzusagen. Zusätzlich wird eine Methode zur Kontrolle der Mikrowellenpolarisation mit einer transparenten ITO-Struktur vorgestellt, die zu einer vollständigen Kontrolle des Spinzustands des NV-Zentrums führt. Weiterhin werden Simulationen in Kombination mit einem analytischen Modell verwendet, um optimale Mikrowellenparameter für die Spinkontrolle vorherzusagen. Für eine kommerzielle Anwendung von NV-Zentren als Magnetfeldsensor sind Pro- duktionskosten und Bauteilkomplexität wichtige Faktoren, die in der Forschung oft vernachlässigt werden. Der zweite Teil meiner Arbeit konzentriert sich da- her auf einen mikrowellenfreien Ansatz zur Magnetometrie mit NV-Zentren. Der Einfluss der Laseranregung auf den magnetischen Kontrast wird an einzelnen NV- Zentren, Ensembles von NV-Zentren und Nano-Diamantpulver mit einer hohen NV- Zentrenkonzentration dargestellt und nachfolgend zur Demonstration von isotropen Magnetfeldmessung verwendet. Abschließend wird die Anwendbarkeit durch die Konstruktion eines Magnetfeldsensors aus Komponenten der Automobilbranche gezeigt. The nitrogen vacancy center (NV center) in diamond is one of the most promising spin systems for applications in quantum computing, information and sensing. The dependency of the fluorescence intensity on the spin state allows a purely optical readout of the spin state. A green laser can be used to pump the NV center in the spin ground state while microwave radiation can manipulate the spin state of the NV center. For all applications depending on active spin manipulation, microwave radiation is indispensable. The ability to fully control the spin state of NV centers is defined by direction, strength and polarization of the microwave radiation. Different approaches exist to deliver the microwave radiation, but they often lack in strength or have other restrictions, e.g. a small frequency band width. In the first part of my thesis, I investigate transparent conductors based on indium tin oxide (ITO) to optimize microwave delivery. In this process a detailed analysis of ITO on diamond concerning confocal microscopy through this transparent film is presented. A mathematical model was developed and tested to predict the field distribution in possible applications. Additionally a method to control microwave polarization with a transparent ITO structure is shown which results in full spin state control of the NV center. Furthermore simulations combined with a analytical model are used to predict optimal microwave parameters for spin control. For a commercial application of NV centers as a magnetic field sensor, important factors are production cost and device complexity which are often neglected in research. The second part of my thesis therefore focuses on a microwave free approach of NV center magnetometry for industry applications. The influence of laser excitation on magnetic contrast was studied on single NV centers, ensembles of NV centers and nano diamond powder with a high NV center concentration. The findings were used to demonstrate isotropic magnetic field sensing. Finally, the applicability was shown by constructing a magnetic field sensor from automotive grade components.

To date, only a few studies have investigated the potential of coal fly ash particles to trigger heterogeneous ice nucleation in cloud droplets. The presented measurements aim at expanding the sparse dataset and improving process understanding of how physicochemical particle properties can influence the freezing behavior of coal fly ash particles immersed in water. Firstly, immersion freezing measurements were performed with two single particle techniques, i.e., the Leipzig Aerosol Cloud Interaction Simulator (LACIS) and the SPectrometer for Ice Nuclei (SPIN). The effect of suspension time on the efficiency of the coal fly ash particles when immersed in a cloud droplet is analyzed based on the different residence times of the two instruments and employing both dry and wet particle generation. Secondly, two cold-stage setups, one using microliter sized droplets (Leipzig Ice Nucleation Array) and one using nanoliter sized droplets (WeIzmann Supercooled Droplets Observation on Microarray setup) were applied. We found that coal fly ash particles are comparable to mineral dust in their immersion freezing behavior when being dry generated. However, a significant decrease in immersion freezing efficiency was observed during experiments with wet-generated particles in LACIS and SPIN. The efficiency of wet-generated particles is in agreement with the cold-stage measurements. In order to understand the reason behind the deactivation, a series of chemical composition, morphology, and crystallography analyses (single particle mass spectrometry, scanning electron microscopy coupled with energy dispersive X-ray microanalysis, X-ray diffraction analysis) were performed with dry- and wet-generated particles. From these investigations, we conclude that anhydrous CaSO4 and CaO – which, if investigated in pure form, show the same qualitative immersion freezing behavior as observed for dry-generated coal fly ash particles – contribute to triggering heterogeneous ice nucleation at the particle–water interface. The observed deactivation in contact with water is related to changes in the particle surface properties which are potentially caused by hydration of CaSO4 and CaO. The contribution of coal fly ash to the ambient population of ice-nucleating particles therefore depends on whether and for how long particles are immersed in cloud droplets.

Image charge detection is a non-perturbative pre-detection approach for deterministic ion implantation. Using low energy ion bunches as a model system for highly charged single ions, we experimentally studied the error and detection rates of an image charge detector setup. The probability density functions of the signal amplitudes in the Fourier spectrum can be modelled with a generalised gamma distribution to predict error and detection rates. It is shown that the false positive error rate can be minimised at the cost of detection rate, but this does not impair the fidelity of a deterministic implantation process. Independent of the ion species, at a signal to-noise ratio of 2, a false positive error rate of 0.1% is achieved, while the detection rate is about 22%