Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code

The present work investigates electron transport and heating mechanisms using an (r, z) particle-in-cell (PIC) simulation of a typical rf-driven axisymmetric magnetron discharge with a conducting target. It is shown that for the considered magnetic field topology the electron current flows through different channels in the (r, z) plane: a ``transverse'' one, which involves current flow through the electrons' magnetic confinement region (EMCR) above the racetrack, and two ''longitudinal'' ones. Electrons gain energy from the electric field along these channels following various mechanisms, which are rather distinct from those sustaining dc-powered magnetrons. The longitudinal power absorption involves mirror-effect heating (MEH), nonlinear electron resonance heating (NERH), magnetized bounce heating (MBH), and the heating by the ambipolar field at the sheath-presheath interface. The MEH and MBH represent two new mechanisms missing from the previous literature. The MEH is caused by a reversed electric field needed to overcome the mirror force generated in a nonuniform magnetic field to ensure sufficient flux of electrons to the powered electrode, and the MBH is related to a possibility for an electron to undergo multiple reflections from the expanding sheath in the longitudinal channels connected by the arc-like magnetic field. The electron heating in the transverse channel is caused mostly by the essentially collisionless Hall heating in the EMCR above the racetrack, generating a strong ExB azimuthal drift velocity. The latter mechanism results in an efficient electron energization, i.e., energy transfer from the electric field to electrons in the inelastic range. Since the main electron population energized by this mechanism remains confined within the discharge for a long time, its contribution to the ionization processes is dominant

Human resources for maternal health: multi-purpose or specialists?

A crucial question in the aim to attain MDG5 is whether it can be achieved faster with the scaling up of multi-purpose health workers operating in the community or with the scaling up of professional skilled birth attendants working in health facilities. Most advisers concerned with maternal mortality reduction concur to promote births in facilities with professional attendants as the ultimate strategy. The evidence, however, is scarce on what it takes to progress in this path, and on the 'interim solutions' for situations where the majority of women still deliver at home. These questions are particularly relevant as we have reached the twentieth anniversary of the safe motherhood initiative without much progress made

Die Schatzhäuser von Olympia

Die Thesauren auf der Schatzhausterrasse in Olympia bieten die Möglichkeit, Landschaftsstile der Stifterstädte in der Archaik zu vergleichen. Die lange Forschungsgeschichte hat dazu geführt, dass sich viele Forscher mit unterschiedlichsten Ansätzen der Architektur dieser Gebäude genähert haben. Es lässt sich aber durch die Zusammenstellung aller Daten und Fakten zeigen, dass nur sehr wenige Ergebnisse als gesichert betrachtet werden können, vor allem hinsichtlich der Zuordnung zu den Stifterpoleis. Die Nebeneinanderstellung der Befunde zeigt auf, dass diesbezüglich eher ein großes Durcheinander entstanden ist. Ziel dieser Publikation soll also der Versuch sein, Klarheit in die Unübersichtlichkeit des Forschungsstandes zu bringen. In einem für die Publikation neu geschriebenen Anhang werden die aktuellen Erkenntnisse zu den unteritalischen Dächern kritisch betrachtet

Charakterisierung und Regelung von Hochfrequenz-Plasmen zur Sputterabscheidung unter Berücksichtigung der Elektronendynamik und des Magnetischen Asymmetrieeffekts

Eine der Schlüsselaufgaben der heutigen Produktionstechnik ist die Bearbeitung von Oberflächen, z.B. durch reaktives Sputtern. Die Herstellung von Dünnschichten benötigt eine präzise Regelung dieser Prozesstechnik, die auf in-situ-Messgrößen basieren sollte. Die Multipolresonanzsonde (MRP) ist dafür geeignet. In dieser Arbeit ist die MRP systematisch hinsichtlich ihrer Einsatzfähigkeit in Prozessplasmen untersucht worden. Sie bietet eine zuverlässige Auswertung der Elektronendichte, einer der wesentlichsten Plasmaparameter. In reaktiven Sputterprozessen kommen zur Erhöhung der Plasmadichte Magnetfelder zum Einsatz, welche den Magnetischen Asymmetrieeffekt induzieren können, der in dieser Arbeit erstmalig systematisch experimentell untersucht wurde. Dies ermöglicht eine Kontrolle wesentlicher Größen wie der Self-Bias Spannung, der Teilchenflüsse bzw. -energien sowie der Elektronendynamik. Die Resultate werden zur Regelung eines reaktiven Sputterprozesses mit der MRP als Sensor genutzt

Experimental investigations of plasma dynamics in the hysteresis regime of reactive RF sputter processes

Reactive radio frequency (RF) sputter processes are highly relevant for thin film deposition, but there is no complete understanding of the fundamentals of their operation. While the Berg model describes the hysteresis regime considering the oxygen coverage of the boundary surfaces, a complete fundamental understanding of the plasma–surface interactions and their effects on the discharge is still missing. In this work, we provide such fundamental insights based on an extensive experimental analysis of the physics in the hysteresis regime of magnetized reactive sputter processes, where the same reactive gas admixture can lead to different discharge characteristics depending on the previous state of the plasma. A variety of plasma and surface diagnostics is used to reveal these insights. A low pressure capacitively coupled RF discharge (CCP, 13.56 MHz) with a magnetron-like magnetic field topology adjacent to the target is operated in argon gas with a variable admixture of O$_2$. The applied RF power, the gas flows/pumping speed, as well as the neutral gas pressure are changed systematically to understand the effects of these external control parameters on the hysteresis regime. The magnetic asymmetry effect is found to play an important role, since an axially non-uniform magnetic field is used to realize a local electron confinement at the target. Similar to process control in applications, the DC self-bias is measured to stabilize the surface composition using a feedback controller with the oxygen gas flow as the manipulated variable