Doctoral Thesis
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Polyelektrolyt-Multischichten werden durch die sequentielle Adsorption von entgegengesetzt geladenen Polyelektrolyten auf einem festen Substrat hergestellt. Die Präparation layer-by-layer ermöglicht die Beschichtungen von Flächen im cm-Bereich mit Schichtdicken im µm-Bereich sowie einer Kontrolle der Molekülanordnung senkrecht zur Substratoberfläche im nm-Bereich. Aus diesen Eigenschaften ergeben sich zahlreiche Anwendungsmöglichkeiten. Ein Schwerpunkt dieser Arbeit ist die Analyse der Polyelektrolyt-Adsorption bei der Präparation von Multischichten bestehend aus dem Polykation Polyallylaminhydrochlorid (PAH) und dem Polyanion Polystyrolsulfonat (PSS) bzw. Polydiallyldimethylammonium (PDADMA) und PSS. Die Untersuchung der Multischichten unter in-situ Bedingungen erfolgt mittels Ellipsometrie. Zu diesem Zweck wird ein Formalismus der ellipsometrischen Datenauswertung entwickelt, um die Messgenauigkeit bei der Untersuchung dünner, transparenter Schichten zu optimieren. Im Fall von PDADMA/PSS-Multischichten verläuft das Schichtwachstum nicht-linear mit der Anzahl an adsorbierten Doppelschichten. Der nicht-lineare Verlauf wird mit der unterschiedlichen Linienladungsdichte zwischen einer PDADMA- und einer PSS-Kette in Verbindung gebracht. Die quantitative Analyse der ellipsometrischen in-situ-Messungen ergibt, dass alle untersuchten PDADMA/PSS-Multischichten (präpariert aus 0,1 mol/L NaCl-Lösung bei Raumtemperatur) mindestens zwei verschiedene Wachstumsregimes aufweisen: Erst wächst die Schichtdicke parabolisch mit der Anzahl an deponierten Polyanion/Polykation-Schichtpaaren, nach Nlin Schichtpaaren erfolgt ein Übergang in lineares Schichtwachstum, charakterisiert durch eine konstante Dicke pro Schichtpaar dBL. Das parabolische Wachstumsregime lässt sich mit einer Asymmetrie im Adsorptionsverhalten von PDADMA und PSS erklären: Während die adsorbierenden PSS-Moleküle die Oberflächenladung lediglich neutralisieren, führt ein PDADMA-Beschichtungsschritt zu einer Ladungsüberkompensation und hinterlässt eine effektiv positiv geladene Oberfläche. Die deponierte Stoffmenge nimmt mit jeder PDADMA/PSS-Doppelschicht zu, bis nach Nlin Doppelschichten die adsorbierenden PSS-Ketten nicht mehr imstande sind alle positiven Oberflächenladungen zu neutralisieren. Die beiden Wachstumsparameter Nlin und dBL hängen in einem linearen Zusammenhang voneinander ab, da beide einem gemeinsamen Mechanismus folgen: Je mehr Doppelschichten ein parabolisches Wachstumsverhalten zeigen (Nlin), desto höher ist die Oberflächenbelegungsdichte am Ende des parabolischen Wachstumsregimes und desto größer die Doppelschichtdicke dBL. Das Adsorptionsverhalten von PDADMA- und PSS-Ketten wird analysiert, indem das Molekulargewicht Mw beider Polyelektrolyte systematisch variiert wird (zwischen Mw(PDADMA) = 24 kDa ... 322 kDa sowie Mw(PSS) = 8,6 kDa ... 168 kDa). Die Flächenbelegungsdichte pro Doppelschicht wächst proportional zu Mw(PDADMA) an, bis ab dem Schwellwert Mw(PDADMA) = 80 kDa eine Sättigung eintritt und das Schichtwachstum unabhängig vom Wert des PDADMA-Molekulargewichts wird (Nlin = 15 Doppelschichten und dBL = (12,3 ± 1,3) nm). Die Daten legen nahe, dass unterhalb des PDADMA-Schwellwerts lediglich ein Teil einer PDADMA-Kette auf der PSS-terminierten Multischicht adsorbiert und der restliche Teil der adsorbierten Kette in Lösung ragt. Oberhalb des PDADMA-Schwellwertes adsorbiert mindestens noch ein zweiter Abschnitt der Kette und es ragt mindestens ein loop in Lösung. Dies führt zu einer konstanten Gleichgewichtsdicke der Monoschicht unabhängig vom Molekulargewicht. Unterschreitet das PSS-Molekulargewicht den Schwellwert Mw(PSS) = 25 kDa, so beobachtet man den gegenteiligen Effekt: beide Wachstumsparameter Nlin und dBL nehmen deutlich zu. Die größten gemessene Werte (unter Verwendung von 8,6 kDa PSS) lauten Nlin = 33 und dBL = 28,7 nm. Neutronenreflektionsmessungen zeigen, dass dieser Effekt mit der Diffusion der kurzen PSS-Ketten innerhalb der Multischicht einhergeht. Die Ausdehnung der Diffusionszone von 8,6 kDa PSS beträgt 80 nm und nimmt bis zum Erreichen des PSS-Schwellwertes monoton mit Mw(PSS) ab. Im Gegensatz dazu bilden PSS-Ketten mit einem Molekulargewicht oberhalb des Schwellwertes klar lokalisierte, lateral homogene Schichten (mit einer Grenzflächenunschärfe von 2 ... 4,6 nm). Entgegen der intuitiven Erwartung hat eine höhere Adsorptionszeit keinen Einfluss auf die Diffusionszone. Der limitierende Faktor ist die Diffusionszone selbst. In Übereinstimmung mit der theoretischen Erwartung führt die Diffusion von kurzen PSS-Ketten während der Multischicht-Präparation zu einem exponentiellen Wachstum der PDADMA/PSS-Multischichten, sobald Mw(PSS) < 25 kDa. In diesem Fall durchläuft das Schichtwachstum nacheinander erst ein exponentielles, dann ein parabolisches und schließlich ein lineares Regime.
With the growing importance of advanced lighting technologies, customers expect additional functionality and higher comfort from fluorescent lamps. However, the ability to regulate light intensity (dimmed operation), in particular, exerts enormous stress on fluorescent lamps’ electrodes, leading to increased electrode erosion and significantly reduced lifetimes. During the operation of a fluorescent lamp, free barium (the main compound of the electrode emitter) is produced at the electrode responsible for lowering the work function in order to enable energy-efficient and durable electrodes with lifetimes of up to 20,000 hours. Despite their relatively long lifetimes, electrodes remain the lifetime-limiting factor of a fluorescent lamp. Therefore, for practical applications (e.g., maintaining quality control, adjusting operational parameters, and evaluating new electrode designs), electrode erosion is of special interest. The actual erosion-measurement methods determine a time-averaged erosion level over several hundred operation hours. Thus, a quasi-instantaneous measuring method (short measurement) is still necessary to determine erosion during operation. Such a method would allow us to compare erosion under different discharge conditions (currents, frequencies, or heating currents) from the same electrode in the same lamp. This work focuses on the determination of absolute electrode erosion during the stationary operation of commonly used fluorescent lamps. Commercial T8 lamps (fluorescent lamps with a diameter of 8/8 inch) are investigated at the operating mode of commonly used electronic ballasts with frequencies of several kHz. Operations under standard and dimmed conditions with an additional heating current to reduce electrode erosion are investigated. Electrode erosion is characterized by the erosion of barium, the main compound of the electrode. Therefore, laser-induced fluorescence (LIF), which is the most sensitive method for this application, is applied to determine the absolute densities of the eroded barium in the electrode region. These densities are affected by the plasma in the electrode region and do not directly represent the absolute barium erosion. To overcome this limitation, a new method based on a special measurement technique in combination with a barium-diffusion-model is developed to determine the absolute barium erosion based on the measured densities. It has been found that the barium densities in the electrode region are lower than the equilibrium pressures produced by the reduction of the barium oxide. This could be caused either by a reduced reaction rate, the reduced diffusion of the reactant (primarily barium oxide) or by reduced barium transport through the porous emitter. However, these results suggest that barium erosion depends on temperature and emitter structure, which vary over an electrode’s lifetime. For currents significantly higher than the nominal lamp current, a drastic increase in emitter evaporation is found. Such, an increase in the lamp current from 300 mA to 500 mA leads to an increase in emitter evaporation by a factor of five. Using the lamp for a long period of time under these conditions therefore reduces the lifetime by a factor of five. Notably, at this dramatically increased erosion level, the hot spot temperature only increases from 1120 K to 1170 K. Investigation of various frequencies from 50 Hz to 5 kHz revealed no significant dependence of emitter evaporation on frequency.
The main issue of this thesis was the investigation of dusty plasmas in magnetic fields. We made use of spherical paramagnetic as well as non-magnetic plastic particles in the micrometer range, so-called dust particles. The particles were then trapped in the sheath region of the driven lower electrode of an rf discharge. The plasma chamber was surrounded by coils to apply a horizontal magnetic field with field strengths of up to B=50mT at the particles’ position. In this configuration the sheath electric field and the external magnetic field were perpendicular to each other. Only the electrons could be magnetized but this leads to several forces acting on the dust particles. In some aspects the dust clusters with the magnetic particles show a behavior that is in complete contrast to those consisting of the standard non-magnetic plastic particles. Both types of particles have in common that the dust clusters were found to move either towards the positive or negative ExB-direction as a reaction to the magnetic field. Whether the positive or negative direction was preferred depended on the experimental conditions. The forces that lead to this transport are plasma-based forces induced by the magnetic field. These investigations were performed on two-dimensional horizontal particle systems. Vertically aligned dust particles due to the ion focus interaction have also been studied to determine the influence of horizontal magnetic fields on the stability of such dust pairs. Under certain conditions the vertical alignment can be broken up by the magnetic field. Some additional experiments on the interaction of non-magnetic dust particles in a plasma with UV irradiation were performed, but a significant decrease of dust charge due to a photoelectric effect was not detected. In summary, even relatively weak horizontal magnetic fields have a strong influence on dust particle systems.
In this thesis, the first on-line mass measurements of the isotopes 52,53K have been performed. These measurements by multi-reflection time-of-flight mass spectrometry with the ISOLTRAP setup at ISOLDE/CERN are linked to previously measured masses of exotic Ca isotopes, which had shown an unexpected large neutron-shell gap at the neutron number N = 32 for the magic proton core Z = 20. The new measurements provide the first exploration of the N = 32 neutron-shell closure below the proton number Z = 20. With a measured empirical two-neutron shell gap of about 3MeV for 51K, the N = 32 gap is smaller as compared to that of 52Ca, which measures about 4MeV, but is still significantly present. This confirms that the nuclear shell effect measured for calcium isotopes is not a phenomenon purely raised by its closed-proton-shell configuration, but is also present in potassium isotopes that possess an open proton shell and an unpaired proton. The second main objective of this thesis was the development of new techniques for efficient mass separation in Penning traps and multi-reflection devices, because the success of nuclear mass measurements with high precision depends crucially on the purity of the ion ensemble. The two main difficulties that have been addressed are, first, when the masses of the ions of interest and the masses of contaminant ions are very similar, and second, when the contaminant ions are predominantly present in the beam from ISOLDE. For the removal of contaminant ions in a high-vacuum Penning trap with high resolving power, a new technique for mass separation has been developed. A simultaneous application of a dipolar radio-frequency field at the magnetron frequency of all ions (mass independent at leading order) and a quadrupolar radio-frequency field at the cyclotron frequency (highly mass dependent) of a chosen ion species provides a new way of ion purification. The result is that the magnetron radius of all ions is increased by the effect of the dipolar excitation, and, at the same time, the quadrupolar excitation leads to a conversion of the radial eigenmotions for the chosen species. The consequence of this simultaneous process is that the wanted ions move back to the trap axes while all other ions are radially ejected from the trap. The advantage of the new method is the simultaneous ejection of all unwanted species in a high vacuum, which otherwise have to be addressed by a dipolar excitation at different frequencies, or by use of complex waveforms if a broadband ejection is required. A comparable (general) broadband ejection as achieved by the new method was previously only achieved in buffer-gas filled Penning traps. Further technical developments were performed with ISOLTRAP’s multi-reflection time-of-flight mass separator. The goal was to improve on situations when dealing with highly contaminated beams from ISOLDE during on-line Penning-trap measurements. In such cases, the number of events obtained in a limited time can be very low for the reason that only a limited number of ions, which predominantly consist of contaminant ions, can be stored and separated in the multi-reflection device at a given time to avoid non-negligible Coulomb interactions between the ions. The situation at ISOLTRAP has been significantly improved by a more efficient use of the separation cycle of the multi-reflection device. The mass-separation cycle is by far shorter (on the order of 10 ms) than a Penning-trap mass measurement (on the order of seconds). Thus, the separation in the multi-reflection device has been decoupled from the Penning-trap mass measurement and is repeated rapidly, while the purified ions are accumulated, stored, and cooled in the preparation Penning trap of ISOLTRAP. The collected ions of interest can then be transferred to the precision-measurement trap. This method increases the possible ratio of the number of contaminant ions to ions of interest by up to two orders of magnitude, i.e. the ratio of the corresponding process durations. Additionally, space-charge problems in multi-reflection devices have been investigated by setting up an off-line apparatus at Greifswald. The dynamical effects of ions in multi-reflection devices under non-negligible Coulomb interactions have been investigated in order to search for possibilities for improvements on such situations. This resulted in a new method of manipulating the ion densities in the device. The ions move in a cloud with large spatial extend for the major part of the trapping time and can later be compressed to small bunches for high-resolution mass separation. Proof-of-principle measurement have been performed with a low number of stored ions, where successful isobar separation has been demonstrated.
In der vorliegenden Arbeit wurden die Wechselwirkungen zwischen den reaktiven Sauerstoffspezies (ROS) und den Lipiden, die das Grundgerüst der Zellmembran bilden, sowie die daraus resultierenden chemischen und physikalischen Veränderungen der Membran untersucht. Außerdem wurde der Schutz einer Modellmembran durch Adsorption eines Polymers untersucht. Da natürliche Zellmembrane hoch komplexe Systeme sind, in und an denen chemische und strukturelle Prozesse häufig gleichzeitig ablaufen, wurden Lipidmonoschichten und Liposomen als Modellmembranen für die Untersuchungen gewählt. Die Radikale wurden mithilfe der Fenton-Reaktion erzeugt. Um ein vollständiges Bild des Radikalangriffs auf Modellmembrane zu erhalten, war es notwendig verschiedene Untersuchungsmethoden zu verwenden. Die Lipidmonoschichten und deren Phasenumwandlungen wurden vor und nach dem Radikalangriff mithilfe des Langmuir-Troges und den damit aufgenommenen Isothermen untersucht. Die Fluoreszenz- und die Brewsterwinkel-Mikroskopie wurde genutzt, um die Veränderungen des Phasenübergangs und somit die Veränderungen der Form und des Wachstums von Lipid-Domänen (flüssig-kondensierten Phase) durch den Radikalangriff zu beobachten. Die laterale periodische Struktur und das vertikale Elektronendichteprofil der Lipidmonoschicht wurden mit der Röntgendiffraktion und Röntgenreflexion vor und nach dem Radikalangriff untersucht. Mit der Infrarot-Reflexion-Absorption Spektroskopie (IRRAS) können Aussagen über die chemische Veränderungen der Lipide nach dem Radikalangriff getroffen werden. Die Liposomen wurden mit Differenzkalorimetrie untersucht, um die Verschiebung der Phasenübergangstemperatur durch den Radikalangriff zu beobachten. Der Radikalangriff auf Liposomen wurde mit Fluorenzmikroskopie verfolgt. Im ersten Teil der Arbeit wurde die Wechselwirkung von ROS mit zwitterionisch geladenen Lipiden untersucht. Die Modellmembranen bestanden aus Phosphatidylcholinen. Fasst man alle Ergebnisse der Untersuchungen zusammen, führt dies zum folgenden Resultat: Die Radikale reagieren bevorzugt mit der Kopfgruppe der zwitterionischen Phosphatidylcholinen. Es entstehen negativ geladene Phospholipide mit einer kleineren Kopfgruppe. Die Alkylketten bleiben nach dem Radikalangriff unverändert. Wie die Isothermen und die Brewsterwinkel-Mikroskopie bei Monoschichten sowie die Thermogramme bei Liposomen zeigen, hat die Reaktion keinen erkennbaren Einfluss auf das thermodynamische Verhalten. Erst durch Zugabe bzw. bei Vorhandensein von „freien“ Eisen-Ionen wird die Veränderung der Phosphocholine durch die Radikale beobachtbar. Die „freien“ Eisen-Ionen binden an die negativ geladenen Phospholipde. Dies führt im Fall von DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) Monoschichten zu einer irreversiblen Verfestigung. Weiterhin kommt es zur Abnahme der molekularen Fläche in der flüssig-kondensierten Phase. Im Fall von DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) Liposomen führt der Radikalangriff, bei Vorhandensein von „freien“ Eisen-Ionen, ebenfalls zu einer Verfestigung. Am Ende des Radikalangriffs sind die Liposomen zerstört. Im zweiten Teil der Arbeit wurde die Wechselwirkung von ROS mit negativ geladenen Phospholipiden untersucht. Dabei wurde herausgefunden, dass die negative Ladung der Phospholipide nach dem Radikalangriff erhalten bleibt. Die Alkylkettenlänge bleibt konstant. Die durchgeführten IRRAS Messungen zeigen ebenfalls keine Veränderungen der Alkylketten. Aufgrund der Beobachtung, dass Eisen-Ionen negativ geladene Modellmembranen verfestigen, sollte im dritten Teil dieser Arbeit die Eisenanbindung an negativ geladene Monoschichten am Beispiel des Cardiolipin TMCL quantifiziert werden. Bei einem physiologischen pH-Wert führt eine Eisen-Ionen Konzentration im mikromolaren Bereich zu einer irreversiblen Verfestigung der Monoschicht. Der pH-Wert ist ein entscheidender Parameter. Eine irreversible Verfestigung der Monoschicht kann durch einen pH-Wert von 1,3 oder niedriger verhindert werden, wenn die Eisenkonzentration kleiner als 1000 µM ist. Bei höheren Eisenkonzentrationen tritt auch bei diesem pH-Wert eine Verfestigung ein. Im vierten Teil dieser Arbeit wurde die Wechselwirkung von ROS mit einer negativ geladenen Lipid-Monoschicht (DMPG) mit adsorbierten Polykationen (Polyethylenimin (PEI)) untersucht. Die adsorbierte Polymerschicht dient zum Schutz der Lipidmonoschicht. Der Radikalangriff wurde mit verschiedenen Fenton-Konzentrationen durchgeführt. Es war eine signifikant höhere Fenton-Konzentration als bei dem Radikalangriff auf eine DPPC Monoschicht notwendig, um Veränderungen zu induzieren.
This thesis delves into some very important scientific challenges for the stellarator concept as a whole and W7-X in particular, namely, how one effectively interfaces the hot plasma with the material walls of the experiment, in special how the plasma heat and particle fluxes are controlled. The fundamental concept that will be used in W7-X for particle and heat exhaust is the island divertor. A number of theoretical and numerical studies have been performed to guide the design of the divertor components. The actual divertor components are in series production at this time, and are largely compatible with the expected heat loads. However, with the sophisticated codes now available, it has become clear that there are some, otherwise very attractive, operational scenarios that could lead to overloading of the W7-X divertors. At least one mitigation strategy was proposed but was until now not analyzed in sufficient detail. In this thesis, state-of-the-art codes are used to analyze this previously proposed mitigation strategy; they are also used to develop several alternative mitigation schemes, which may in the end be advantageous. The work performed here shows not only that it is conceivable to solve this already identified problem in new and arguably better ways but also that the W7-X coil set has enough degrees of freedom that many important long-pulse plasma effects can be effectively mimicked in short-pulse operation. This opens up a rich research program in the early phases of operation and may therefore lead to a significant acceleration of the scientific program to control and optimize the divertor operation in W7-X. The main scientific challenge for the island divertor operation in W7-X is that, since the divertor geometry is now fixed, the magnetic field structure must be adjusted to the divertor geometry, or additional plasma-facing components must be manufactured and installed. Well before this thesis work was done, such additional plasma-facing components were proposed. These are called scraper elements (SEs). As a part of this work, computer simu- lations were performed in order to obtain a better knowledge base regarding the SEs. To analyze the effect of the SE, edge plasma physics simulation code EMC3-Eirene, was used, in combination with state-of-the-art magneto hydrodynamic (MHD) equilibrium codes. This combination was computationally non-trivial and new, and it has led to important insights. One main result of this study is that the SEs significantly reduce the particle exhaust capabilities in steady state operation; this is a concern for W7-X. To test and further quantify this deleterious effect, physics experiments with a prototype SE should be performed as soon as possible, ideally in the first operation campaigns before the approximately two-year break needed to complete W7-X for steady-state operation. In 3 this first operation phase, however, the necessary combination of plasma parameters, heating power, and achievable pulse length is not accessible. This means, on the one hand, that the problem described will not be present in the first operation phase; on the other hand, the physics implications of installing an SE would appear not to be experimentally testable in that phase. One major finding of this thesis is that the coil system of W7-X is flexible enough to allow such an early experimental test. Different stages of high performance long-pulse discharge can be effectively mimicked in the experiment by a targeted use of the available coil sets. Thus, even in the early phases of the W7-X program one can assess both the protection capabilities of the SEs and their effects on particle exhaust and plasma performance in general. These mimic scenarios also have the potential to test other possibilities for divertor pro- tection besides the SE. Such strategies are addressed in this thesis. The two most promising strategies identified here can be classified as plasma shift and iota control. Both adjust the edge magnetic field to better fit the divertor geometry. This is done slowly but dynamically — i.e. during a long plasma discharge.
The current work is focused on the study of two surface modification plasma processes, (i) the active screen plasma nitriding (ASPN) and nitrocarburizing (ASPNC) for the hardening of ferrous surfaces and (ii) the microwave plasma assisted chemical vapor deposition (MW-PACVD) for the synthesis of single crystal and doped diamond. Conventional and active screen plasma nitriding processes have been investigated in a cylindrical, industrial scale ASPN reactor with a volume of about 1 m3, using low-pressure pulsed dc H2-N2 plasmas with admixtures of CH4 or CO2. The experiments were carried out (i) with the plasma at an internal model probe, (ii) with the plasma at the active screen (floated model probe) and (iii) with the plasma at the active screen and an additional plasma at the biased model probe. For deeper insights in ASPN and ASPNC processes, a laboratory scale plasma nitriding monitoring reactor, PLANIMOR, has been constructed. The main feature of this reactor is the linear configuration of the electrode setup combined with a tubular glass vessel, overcoming the experimental disadvantages of cylindrical laboratory scale ASPN reactors. With the help of infrared laser absorption spectroscopy (IRLAS) the rotational temperature of the stable molecules in the gas phase and the concentrations of the precursor, CH4, and the reaction products (NH3, HCN, C2H2, C2H4, CO, CH3) could be determined in both reactors, depending on the plasma power, the gas mixture, the plasma at the model probe and the admixture of CH4. Furthermore, the admixture of CO2 as the carbon containing precursor has been studied in the ASPN reactor leading to an additional reaction product H2O. The concentration of the molecular species has been found being in a range of 1012 to 1016 molecules cm-3. Also optical emission spectroscopy (OES) has been applied during the studies for analyzing the emission of the plasmas in the nitriding and nitrocarburizing processes. A similar behavior of the plasma chemistry in PLANIMOR comparing to that in the ASPN reactor has been found. Beside the plasma chemical investigations, both reactors have been used for the treatment of C15 steel samples. These samples have been analyzed with the help of GDOES resulting in the elements profile of the treated surfaces. It has been found that samples treated in PLANIMOR reach comparable nitriding results as samples treated in the ASPN reactor. Another focus of interest during the investigations about plasma nitrocarburizing has been the application of a carbon containing screen electrode as carbon source. For this purpose the carbon containing precursor and the steel screen have been substituted by a meshed carbon electrode, acting as the active screen. This change of the setup leads to a decrease of the NH3 production by a factor of 2.5 and an increase of the concentrations of HCN by a factor of 30 and of C2H2 by a factor of 70. The investigations of MW-PACVD processes used for diamond layer deposition have been carried out in a jacketed stainless steel reactor (JR), dedicated to the deposition of single crystalline diamond under high pressure and plasma power conditions. Using H2-plasmas with admixtures of CH4 and B2H6, the experiments were carried out in order to analyze the dependence of the plasma chemistry on several parameters, such as plasma power, pressure and gas mixture, in a wide pressure (p = 25…270 mbar) and power range (P = 0.6…4 kW). Using IRLAS the concentrations of six molecular species (B2H6, CH4, C2H2, C2H4, C2H6, CH3) have been monitored. With the help of OES the concentration of atomic boron could be determined. The concentrations of the detected molecular and atomic species were found to be in a range of 1010 to 1017 cm-3. With the help of the line-ratio-method the rotational temperature of the stable molecules has been determined. The temperature increased with pressure and power from 340 to 425 K. Using the Doppler broadening of the absorption line of CH3 at ν = 612,413 cm-1, the gas temperature has found to be Tg = (2000 ± 200) K under lower pressure and power conditions. For the H2-CH4 gas mixture, the experimental obtained molecular densities have been compared to those of a 1D-radial thermochemical model. The calculated radial densities have been integrated axially. For the same range the chemical processes in JR have been compared with those in a bell-jar (BJ) reactor. The hydrocarbon chemistry in JR has found to be similar to that in a BJ reactor.
The aim of this thesis is to concentrate on the investigation of these ROS&RNS composition distribution and their production pathways in the gas phase produced by a plasma jet. By understanding the physical mechanisms behind the generation of the ROS&RNS a precise tuning and design of the composition distribution in the gas phase can be achieved. One crucial physical parameter is the dissipated power inside the plasma. Only if this parameter is known a meaningful comparison of different feed gas settings is possible. Therefore, a concept for measuring the dissipated power inside the plasma for the modified micro-scaled atmospheric pressure plasma jet( µAPPJ) is designed. Additionally, due to achievements within this thesis it is now possible to ignite a homogeneous discharge in argon and helium within the geometry of the µAPPJ. The used feed gas is a determining factor concerning the electron energy distribution function and consequently influencing the production mechanism of the ROS&RNS. First of all, the electrical characterisation of the modified µAPPJ was performed including the alpha-to-gamma transition. It is shown that the alpha-to-gamma transition power is increasing with increasing frequency. For the first time it is now feasible to investigate the influence of the dissipated power on the neutral gas temperature, the metastable atom densities and the ROS&RNS production for the modified µAPPJ with argon and helium as feed gas. Due to the possibility of changing the feed gas and controlling the dissipated power a fundamental insight into the production mechanism of the ROS&RNS generated by the plasma jet is achieved. With rising dissipated power the temperature and the metastable densities as well as the ozone and nitrogen dioxide concentrations are increasing. By adding molecular oxygen and nitrogen to the feed gas of a plasma jet the ROS&RNS composition can be tuned. However, also the dissipated power is changed by the small amount of admixtures. Due to the developed dissipated power measurements within this thesis it was possible to disentangle the influence of the admixture on the power and on the ROS&RNS production. If the dissipated power is fixed for the µAPPJ with argon and helium feed gas, respectively, the highest amount of ozone was measured with oxygen admixture in an argon discharge, the highest amount of dinitrogen pentoxide with nitrogen admixture in an argon discharge and the highest amount of nitrogen dioxide with nitrogen admixture in a helium discharge. Beyond the influence of the dissipated power and the molecular admixture on the ROS&RNS production the feed gas temperature is a crucial parameter for the corresponding chemical reactions. By changing this parameter the distribution of ozone and nitrogen dioxide can be tuned precisely in such a way that with increasing temperature the ozone density goes down and the nitrogen dioxide density rises. Another determinant for the ROS&RNS composition produced by an atmospheric pressure plasma jet is the influence of ambient air. If the ambient air is changing from pure nitrogen to pure oxygen atmosphere the ozone density produced by the plasma jet is increasing. For the same conditions the nitrogen dioxide has a maximum at an oxygen-to-nitrogen ratio of 1:1. To avoid the influence of the ambient air on the reactive species production the afterglow of the µAPPJ was prolonged with a glass tube. By increasing the amount of molecular admixtures to the feed gas with each in equal quantities a totally different ROS&RNS composition can be obtained compared without the glass tube. It figures out that for small molecular admixtures the reactive species composition is nitrogen dominated and for higher admixtures it is oxygen dominated. Consequently, by shielding the ambient air from the active effluent and by admixing molecular oxygen and nitrogen the ROS&RNS composition can be designed.
Im ersten Teil der Arbeit wird der erfolgreiche Aufbau einer Diagnostik zur quantitativen Bestimmung von Oberflächenladungsdichten beschrieben. Das Messprinzip bedient sich des elektro-optischen Pockelseffekts eines BSO-Kristalls, der in der Entladungszelle als Dielektrikum eingesetzt ist. Diese Methode arbeitet zeitlich und lateral aufgelöst, was die Untersuchung der Dynamik von Oberflächenladungen auf drei verschiedenen Zeitskalen ermöglicht. Die erste Zeitskala liegt in der Größenordnung von einigen 100 ns. Damit kann erstmals die Deposition von elektrischer Ladung auf einer dielektrischen Oberfläche während eines Entladungsdurchbruchs beobachtet werden. Die Deposition beginnt im Zentrum eines zuvor deponierten Ladungsspots. Die Polarität der neudeponierten Ladung ist der des ursprünglichen Ladungsspots entgegengesetzt. Die Folge ist, dass die absolute Ladungsdichte im Zentrum im Verlauf einiger hundert Nanosekunden kleiner wird als in den Randbereichen. Der Umladungsprozess wird so lange fortgesetzt, bis das elektrische Feld der neu deponierten Ladungen dem äußeren Feld so stark entgegenwirkt, dass die Spannung zur Aufrechterhaltung der Entladung unterschritten wird und die Entladung erlischt. Die zweite untersuchte Zeitskala liegt in der Größenordnung der Periodendauer der externen Spannung. Im Nulldurchgang der Spannung liegen zeitlich stationäre Ladungsdichteverteilungen auf dem Dielektrikum vor. Die Geometrie eines mittleren Ladungsspots wird in Abhängigkeit der anliegenden Spannungen und des Gasdrucks untersucht. Einerseits ist der Spotradius abhängig von den Ionisationsprozessen im Volumen, weil die Dichte der Raumladungen die Stärke des Elektronenfokus in das Innere der Entladung steuert. Andererseits wird die Spotbildung durch eine laterale Drift von Ladungsträgern kurz vor der Oberfläche aufgrund des elektrischen Feldes deponierter Ladungsträger beeinflusst. Die dritte untersuchte Zeitskala liegt in einer Größenordnung von Sekunden. Im Fall einer initial homogenen Oberflächenladungsverteilung nimmt die mittlere Ladungsdichte in einer Größenordnung von Sekunden monoton ab. Dieser Prozess stellt einen Ladungsabbau dar, dessen zeitliches Verhalten durch zwei überlagerte Exponentialfunktionen beschreiben ließ. Dadurch werden zwei Ladungsträgerpopulationen im BSO angenommen, die verschieden abgebaut werden. Im Fall einer initial inhomogenen Ladungsdichteverteilung wird ein Transport elektrischer Ladung auf der BSO-Oberfläche in einer Größenordnung von Sekunden beobachtet. Es wird weiterhin erstmals die durch einen Atmosphärendruck-Plasmajet deponierten Ladungen auf BSO zeitaufgelöst gemessen. Die zeitliche Entwicklung der Oberflächenladungen kann mit der Messung des elektrischen Stroms an einer der Ringelektroden des Jets korreliert werden. Dadurch wird geschlossen, dass der Ladungsaustauch nicht direkt durch einen Bullet verursacht wird. Er erzeugt stattdessen einen elektrisch leitfähigen Kanal zwischen der Düse des Jets zur BSO-Oberfläche. Infolgedessen kann Ladung, die sich auf der Innenseite der Jetkapillare befindet, auf den BSO-Kristall transportiert werden. Im zweiten Teil der Arbeit werden Kenngrößen entwickelt, die den Ordnungszustand einer aus Einzelobjekten zusammengesetzten Entladungsstruktur quantitativ beschreiben. Die Kenngrößen werten dabei die laterale Leuchtdichteverteilung der Entladungsemisssion, u.a. auf Basis der Tripel-Korrelationsfunktion. Dabei werden zwei separate Bifurkationsspannungen zwischen einer hexagonalen und einer ungeordneten Anordnung beobachtet: Bei der Verringerung der Spannung wird zunächst der Bifurkationspunkt der azimutalen Ordnung durchlaufen und anschließend der Bifurkationspunkt der radialen Ordnung. Die Systeme gehen jeweils in einen Zustand geringerer Ordnung über. Die Ursache des Ordnungsverlusts ist das zunehmende Fehlen von Entladungsspots, was im Mittel zu einer geringeren Wechselwirkung der Spots untereinander führt und das System an Freiheitsgraden gewinnt. Im dritten Teil dieser Arbeit wird erstmals ein Ansatz verfolgt, der die Steuerung lateral strukturierter Entladungen ermöglicht. Dafür wurde ein Aufbau konstruiert, bei dem ein gekühlter Halbleiter als Dielektrikum in der Entladungszelle dient. Dessen externe Beleuchtung führt bei einer anliegenden Spannung zu einer Änderung des Spannungsteilerverhältnisses der kapazitiven Elemente und schließlich zu einer lokalen Erhöhung der Spannung über dem Entladungsraum. Die Größe und Leuchtintensität der durch die Beleuchtung gezündeten Entladung ist stark abhängig von der beleuchteten Fläche, der Leistungsdichte der Beleuchtung und der anliegenden Spannung.
The realistic description of the physical processes in quantum optical systems requires careful investigation of the interplay between quantum dissipation and entanglement generation. In this thesis, we have considered from a microscopical perspective the entanglement generation in semiconductor microcavities at short times, the dissipative evolution of the quantum harmonic oscillator towards a stationary state, and the nonclassical properties of the asymptotic states of different photonic systems. In our description of two-dimensional semiconductor microcavities we showed that two different pump configurations can be used to stimulate parametric scattering processes between polaritons that lead to the generation of internal polariton entanglement. A moving polariton induces an ultrafast electric polarisation as a source of light that serves as a probe of the internal entanglement properties. The identification of the nonclassical correlations of the emitted photons is based on entanglement witnesses that can also be used for the quantification of entanglement, e.g., in terms of the Schmidt number. The simultaneous creation of multiple branch entangled photon pairs renders it possible to generate an arbitrary number of entangled qubit states. By adjusting the number of pump beams and their spectral properties, one can optimize the Bell-type correlations within one ore more of those entangled qubits. Quantum dissipation can be studied in a microscopic setting with the well known model of a central oscillator coupled linearly to a bath of harmonic oscillators. We showed that equilibration of the central oscillator is the generic behaviour, which is prevented only in situations in which the classical oscillator equation of motion possesses undamped oscillatory solutions. Because of its localised spectral function, the infinite linear harmonic chain is an example for this behaviour. Thermalisation of the central oscillator depends on additional conditions. Equipartition of kinetic and potential energies requires the weak damping limit but is independent on the initial condition. The initial bath preparation enters the asymptotic temperature. Essential for the thermalisation of several oscillators is, that the asymptotic temperature is independent of the central oscillator frequency, which is fulfilled if the initial bath energy distribution matches that of a thermal state. Nevertheless, because this condition involves the sum of kinetic and potential energy, full thermalisation is possible in environments with nonthermal individual energy distributions, even in those far from thermal equilibrium. We showed, that even in the absence of full thermalisation the fluctuations of the central oscillator follow a generalised fluctuation dissipation theorem that reduces to the well known thermal result whenever the central oscillator thermalises in the strict sense. Photonic systems such as two-level emitters in a cavity or semiconductor microcavities are employed in quantum optics applications. The realistic theoretical description of the physical processes requires the use of methods from quantum optics as well as fromthe field of quantum dissipation. Our focus was on the correct theoretical description of the emission from systems with strong coupling. The analysis of the light generated by emitters in a cavity reveals a non-trivial dependence of the photon statistics on the light-matter coupling and temperature. Clearly identifiable parameters regimes with sub- and super-Poissonian photon statistics appear at strong and ultrastrong coupling, and lie immediately next to each other. We provided an approximate rule to relate the emission characteristics for a single emitter to those obtained for few emitters under an appropriate scaling of the emitter-cavity coupling. In accordance with this rule, the generation of noncassical light is easier with more emitters. The outright failure of the quantum optical master equation at predicting any of the features observed in the emission statistics shows that using the correct master equation is essential in all situations. Including internal dissipation channels we showed that a continuously driven semiconductor microcavity generates entangled light even at infinitely large times. The entanglement generation is thus robust against decoherence under realistic experimental conditions. Because the pair correlations between polaritons can sustain over long times and distances in these solid-state devices, a microcavity is a highly efficient source of entangled light and therefore well suited for quantum optics applications.