Investigation of Particle-in-Cell Acceleration Techniques for Plasma Simulations

COLISEUM is an application framework that integrates plasma propagation schemes and arbitrary 3D surface geometries. Using Particle-in-Cell (PIC) schemes to model the plasma propagation high fidelity modeling of the plasma and its interactions with the surfaces is possible. In order to improve the computational performance of the Particle-in-Cell scheme with Direct Simulation Monte Carlo collision modeling (PIC-DSMC) within COLISEUM, AQUILA, acceleration techniques have been developed that significantly decrease the amount of CPU time needed to obtain a steady-state solution. These techniques have been demonstrated to decrease the CPU time from 3 to 24 times with little appreciable differences in the global particle properties and number densities. This work investigates the differences in the local plasma properties that result from the application of the different acceleration techniques. Results show that the subcycling acceleration scheme does accurately capture the macroscopic flow properties (such as particle counts and species number densities) and the velocity distributions in the lower density regions of the flow field. However, the higher density regions of the flow field (such as in the main beam of the plasma source) show significant differences that are believed to be associated with the simplifying assumptions used in the original collision modeling scheme within the PIC-DSMC module AQUILA

Investigation of single, binary, and ternary metal oxides of iridium, rhodium, and palladium for neural interfacing applications

In this dissertation, thin film single, binary, and ternary metal oxides of iridium (Ir), ruthenium (Ru), rhodium (Rh), and palladium (Pd) were synthesized for use as electrode/microelectrode coatings for neural interfacing applications using DC reactive magnetron sputtering. Synthesis conditions which enhanced the electrochemical properties of films as measured by cyclic voltammetry and electrochemical impedance spectroscopy in a phosphate buffered saline solution of the single metal oxides were identified to be 30 mTorr working pressure, 20% oxygen partial pressure, and cathode power densities ≤ 4.9 W/cm2. These parameters were then used to develop the binary and ternary metal oxide films. The binary metal oxides studied included Ir(1-x)Mx where M = Pd, Rh, Ru, and the ternary metal oxides studied included Ir(1-x-z)MxMz’, where M,M´ = Pd, Rh, and Ru. The binary metal oxide concentrations which produce robust microstructures and exceptional electrochemical performance have been identified to be x ≥ 0.5 for Ir(1-x)RhxOy, x ≥ 0.34 for Ir(1-x)RuxOy, and x ≥ 0.14 for Ir(1-x)PdxOy. Similar compositional ranges have been identified for the ternary metal oxides and include x ≥ 0.16 and z ≥ 0.05 for Ir(1-x-z)PdxRuzOy, x ≥ 0.13 and z ≥ 0.04 for Ir(1-x-z)PdxRhzOy, and x ≥ 0.2 and z ≥ 0.14 for Ir(1-x-z)RuxRhzOy

Synthesis of silicon nanocrystal memories by sputter deposition

In Silizium-Nanokristall-Speichern werden im Gate-Oxid eines Feldeffekttransistors eingebettete Silizium Nanokristalle genutzt, um Elektronen lokal zu speichern. Die gespeicherte Ladung bestimmt dann den Zustand der Speicherzelle. Ein wichtiger Aspekt in der Technologie dieser Speicher ist die Erzeugung der Nanokristalle mit einerwohldefinierten Größenverteilung und einem bestimmten Konzentrationsprofil im Gate-Oxid. In der vorliegenden Arbeit wurde dazu ein sehr flexibler Ansatz untersucht: die thermische Ausheilung von SiO2/SiOx (x < 2) Stapelschichten. Es wurde ein Sputterverfahren entwickelt, das die Abscheidung von SiO2 und SiOx Schichten beliebiger Zusammensetzung erlaubt. Die Bildung der Nanokristalle wurde in Abhängigkeit vom Ausheilregime und der SiOx Zusammensetzung charakterisiert, wobei unter anderem Methoden wie Photolumineszenz, Infrarot-Absorption, spektroskopische Ellipsometrie und Elektronenmikroskopie eingesetzt wurden. Anhand von MOS-Kondensatoren wurden die elektrischen Eigenschaften derart hergestellter Speicherzellen untersucht. Die Funktionalität der durch Sputterverfahren hergestellten Nanokristall-Speicher wurde erfolgreich nachgewiesen.In silicon nanocrystal memories, electronic charge is discretely stored in isolated silicon nanocrystals embedded in the gate oxide of a field effect transistor. The stored charge determines the state of the memory cell. One important aspect in the technology of silicon nanocrystal memories is the formation of nanocrystals near the SiO2-Si interface, since both, the size distribution and the depth profile of the area density of nanocrystals must be controlled. This work has focussed on the formation of gate oxide stacks with embedded nanocrystals using a very flexible approach: the thermal annealing of SiO2/SiOx (x < 2) stacks. A sputter deposition method allowing to deposit SiO2 and SiOx films of arbitrary composition has been developed and optimized. The formation of Si NC during thermal annealing of SiOX has been investigated experimentally as a function of SiOx composition and annealing regime using techniques such as photoluminescence, infrared absorption, spectral ellipsometry, and electron microscopy. To proof the concept, silicon nanocrystal memory capacitors have been prepared and characterized. The functionality of silicon nanocrystal memory devices based on sputtered gate oxide stacks has been successfully demonstrated

Diagnostics of ion generation and fluxes from cathodic arc spots for a better understanding of energetic deposition of thin films

This thesis is devoted to the investigation of ion generation and fluxes from cathodic arc spots for a better understanding of energetic deposition of thin film. The ion generation is related to the arc spot properties, and ion fluxes influence the film deposition. Significantly, the cathodic arc has the explosion characteristic for the ignition process, which is the generation process of ions. Thus, it is not easy to observe the spot characteristics, and some fundamental questions related to cathodic arc spot motion are still open. The multiply charged ions produced from the arc spot ignition process have a higher ion potential energy than ions of other deposition techniques; therefore, consideration of the effect of ion potential energy on film growth is required for the cathodic arc technique. The first part of this thesis deals with fundamental arc spot characteristics, especially the trend of spot motion in a magnetically steered arc source placed in vacuum or in a reactive gas atmosphere. This is investigated with a streak camera having high spatial and temporal resolutions. To answer the fundamental question of whether the spots have characteristic times, such as a 'periodic spot lifetime' or a 'the periodic characteristic time between spot ignitions”, the streak images were analyzed by fast Fourier transformation (FFT). It was found that the power spectrum of the arc spot fluctuations does not show any specific frequencies, which means the arc spot ignition process can be described by a fractal model, and the spectral slope in the log-log power-frequency diagram has a tendency to be reduced in the presence of a compound (for example oxide or nitride) layer on the cathode surface. Through the fractal analysis and measurements of optical emission spectroscopy, the fundamental limitation of the temporal resolution for the optical emission method is determined and considered. The second part of this thesis considers cathodic arc’s application aspects: the energetic deposition of thin films and coatings. Most studies related to energetic deposition have previously investigated the effects of ion kinetic energy on film deposition; however, this thesis focuses on the effects of ion potential energy on film growth. To investigate the effect of ion potential energy on film growth, plasma diagnostic by energy-resolved mass spectrometry and deposited film characterization by XRD, XRR, AFM, profilometry and SEM were carried out. The ion potential energy influences the preferential direction of film growth or a polycrystalline growth in the case of aluminum deposition. This result could be a starting point for further research into the effect of ion potential energy on film deposition

Synthesis of silicon nanocrystal memories by sputter deposition

In Silizium-Nanokristall-Speichern werden im Gate-Oxid eines Feldeffekttransistors eingebettete Silizium Nanokristalle genutzt, um Elektronen lokal zu speichern. Die gespeicherte Ladung bestimmt dann den Zustand der Speicherzelle. Ein wichtiger Aspekt in der Technologie dieser Speicher ist die Erzeugung der Nanokristalle mit einerwohldefinierten Größenverteilung und einem bestimmten Konzentrationsprofil im Gate-Oxid. In der vorliegenden Arbeit wurde dazu ein sehr flexibler Ansatz untersucht: die thermische Ausheilung von SiO2/SiOx (x < 2) Stapelschichten. Es wurde ein Sputterverfahren entwickelt, das die Abscheidung von SiO2 und SiOx Schichten beliebiger Zusammensetzung erlaubt. Die Bildung der Nanokristalle wurde in Abhängigkeit vom Ausheilregime und der SiOx Zusammensetzung charakterisiert, wobei unter anderem Methoden wie Photolumineszenz, Infrarot-Absorption, spektroskopische Ellipsometrie und Elektronenmikroskopie eingesetzt wurden. Anhand von MOS-Kondensatoren wurden die elektrischen Eigenschaften derart hergestellter Speicherzellen untersucht. Die Funktionalität der durch Sputterverfahren hergestellten Nanokristall-Speicher wurde erfolgreich nachgewiesen.In silicon nanocrystal memories, electronic charge is discretely stored in isolated silicon nanocrystals embedded in the gate oxide of a field effect transistor. The stored charge determines the state of the memory cell. One important aspect in the technology of silicon nanocrystal memories is the formation of nanocrystals near the SiO2-Si interface, since both, the size distribution and the depth profile of the area density of nanocrystals must be controlled. This work has focussed on the formation of gate oxide stacks with embedded nanocrystals using a very flexible approach: the thermal annealing of SiO2/SiOx (x < 2) stacks. A sputter deposition method allowing to deposit SiO2 and SiOx films of arbitrary composition has been developed and optimized. The formation of Si NC during thermal annealing of SiOX has been investigated experimentally as a function of SiOx composition and annealing regime using techniques such as photoluminescence, infrared absorption, spectral ellipsometry, and electron microscopy. To proof the concept, silicon nanocrystal memory capacitors have been prepared and characterized. The functionality of silicon nanocrystal memory devices based on sputtered gate oxide stacks has been successfully demonstrated