Process control in low pressure capacitive radio frequency plasmas based on kinetic simulations

Diese kumulative Dissertation fasst 7 Publikationen der Autorin zusammen, die sich mit dem Thema der Prozesskontrolle in kapazitiv gekoppelten Niederdruck-Hochfrequenzplasmen (engl. CCPs) beschäftigen. Die Prozesskontrolle durch maßgeschneiderte Spannungsformen (engl. VWT), Elektrodenoberflächenanpassung und Magnetfelder werden anhand von Particle-In-Cell-Simulationen untersucht. Die Auswirkungen von VWT in geometrisch asymmetrischen Entladungen, die Elektronengeschwindigkeit und Winkelverteilungsfunktionen in Mehrfrequenz-CCPs, die Gültigkeit der klassischen Plasmaleitfähigkeit, magnetisierte CCPs bei hoher Frequenz (60 MHz) sowie die Steuerung der Plasmauniformität durch Elektrodenstrukturen und Anpassung des Oberflächenmaterials werden untersucht. Insgesamt wurden mehrere neue Konzepte für die Plasmakontrolle entdeckt, die ein hohes Potenzial für die wissensbasierte Verbesserung von Plasmaprozessen in der Halbleiterfertigung und anderen Bereichen haben

Effect of cooling rate on the microstructure and mechanical properties of a low-carbon low-alloyed steel

Heavy plate steels with bainitic microstructures are widely used in industry due to their good combination of strength and toughness. However, obtaining optimal mechanical properties is often challenging due to the complex bainitic microstructures and multiple phase constitutions caused by different cooling rates through the plate thickness. Here, both conventional and advanced microstructural characterization techniques which bridge the meso- and atomic-scales were applied to investigate how microstructure/mechanical property-relationships of a low-carbon low-alloyed steel are affected by phase transformations during continuous cooling. Mechanical tests show that the yield strength increases monotonically when cooling rates increase up to 90 K/s. The present study shows that this is associated with a decrease in the volume fraction of polygonal ferrite (PF) and a refinement of the substructure of degenerated upper bainite (DUB). The fine DUB substructures feature C-rich retained austenite/martensite-austenite (RA/M-A) constitutes which decorate the elongated micrograin boundaries in ferrite. A further increase in strength is observed when needle-shaped cementite precipitates form during water quenching within elongated micrograins. Pure martensite islands on the elongated micrograin boundaries lead to a decreased ductility. The implications for thick section plate processing are discussed based on the findings of the present work

Frequency coupling in low-pressure dual-frequency capacitively coupled plasmas revisited based on the Boltzmann term analysis

Electron power absorption dynamics is investigated in radio-frequency (RF) argon capacitively coupled plasmas (CCPs) at low pressure (4–70 Pa) excited by a dual-frequency waveform with frequencies of 27.12 MHz and 1.937 MHz. Based on the spatio-temporal dynamics of the ambipolar electric field a novel interpretation of the mechanism of frequency coupling is given, which is not based on the hard wall model, as in previous explanations. Within this framework, frequency coupling arises due to the decreased size of the ambipolar region outside the sheath when the low-frequency sheath is close to its full expansion, which leads to decreased ionization in this region. It is shown, under the circumstances considered here, ohmic power absorption is dominant. The spatio-temporally averaged ambipolar power absorption shows nonmonotonic behaviour as a function of pressure, first increasing, then, after reaching a local maximum, decreasing as the pressure is increased. It is shown, that the reason for this nonmonotonic behaviour is ultimately connected to the frequency coupling mechanism

Effect of aspect ratio on the deformation behavior of dislocation-free Ni3AlNi_{3}Al nanocubes

This study concentrates on several factors which govern the nanoscale plasticity of in situ compressed dislocation-free $Ni_{3}Al$ nanocubes: cube size, aspect ratio and the presence of grooves. The yield strength of dislocation-free $Ni_{3}Al$ nanocubes exhibits an apparent size dependence. The size dependence is strong when cubes are smaller than 300 nm. Compared with the strength of bulk $Ni_{3}Al$ single crystals, the strength of nanocubes is two orders of magnitude higher, which clearly demonstrates that there is a size effect. Nanocube plasticity strongly depends on the alignment and the shape of the cubes. Deformed aligned nanocubes either display only a few localized deformation events (slip lines) or were homogenously compressed into flats due to multiple slip dislocation-mediated plasticity. For an aligned cube, crack initiation at the intersection of a slip line with a groove in the cube surface was observed. In case of a double cube, crack initiation occurs at surface irregularities, while subsequent crack propagation occurs along one or more slip planes

The value of open-source clinical science in pandemic response: lessons from ISARIC

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