Angle-Resolved Photoemission of Solvated Electrons in Sodium-Doped Clusters

Angle-resolved photoelectron spectroscopy of the unpaired electron in sodium-doped water, methanol, ammonia, and dimethyl ether clusters is presented. The experimental observations and the complementary calculations are consistent with surface electrons for the cluster size range studied. Evidence against internally solvated electrons is provided by the photoelectron angular distribution. The trends in the ionization energies seem mainly determined by the degree of hydrogen bonding in the solvent and the solvation of the ion core. The onset ionization energies of water and methanol clusters do not level off at small cluster sizes, but decrease slightly with increasing cluster size

Novel Ground-State Crystals with Controlled Vacancy Concentrations: From Kagom\'{e} to Honeycomb to Stripes

We introduce a one-parameter family, $0 \leq H \leq 1$, of pair potential functions with a single relative energy minimum that stabilize a range of vacancy-riddled crystals as ground states. The "quintic potential" is a short-ranged, nonnegative pair potential with a single local minimum of height $H$ at unit distance and vanishes cubically at a distance of \rt. We have developed this potential to produce ground states with the symmetry of the triangular lattice while favoring the presence of vacancies. After an exhaustive search using various optimization and simulation methods, we believe that we have determined the ground states for all pressures, densities, and $0 \leq H \leq 1$. For specific areas below 3\rt/2, the ground states of the "quintic potential" include high-density and low-density triangular lattices, kagom\'{e} and honeycomb crystals, and stripes. We find that these ground states are mechanically stable but are difficult to self-assemble in computer simulations without defects. For specific areas above 3\rt/2, these systems have a ground-state phase diagram that corresponds to hard disks with radius \rt. For the special case of H=0, a broad range of ground states is available. Analysis of this case suggests that among many ground states, a high-density triangular lattice, low-density triangular lattice, and striped phases have the highest entropy for certain densities. The simplicity of this potential makes it an attractive candidate for experimental realization with application to the development of novel colloidal crystals or photonic materials.Comment: 25 pages, 11 figure

Electromechanical optimization of high reluctance torque variable flux machines under structural mechanical constraints

A design approach for high speed variable flux machines with fiber reinforced polymer filled flux barriers is presented. To ensure high speed strength, the interfacial strength between the composite and electrical sheet is investigated, as it represents a strict boundary condition in the design process. A tool chain for a combination of electromagnetic and mechanical design is presented and its target values and boundary conditions are discussed. Measurements of the interfacial shear strength between electrical sheet and the composite are carried out and the results are investigated with respect to the design process. An optimization based on the measurement data is carried out and the results of machines with and without composite reinforcement are compared

ZnCo2O4 as (Photo-) Electrocatalyst for the Oxygen Evolution Reaction

Im Zuge dieser Masterarbeit werden die elektro- und photoelektrokatalytischen Eigenschaften von ZnCo2O4 zur Sauerstofferzeugung untersucht. Dazu wird p-Typ ZnCo2O4 gewachsen auf ein Titan-Netz Substrat gewachsen und in einer gewöhnlichen H-Zelle mit Kaliumhydroxid wässriger Lösung verwendet. Um die Katalyse bei Beleuchtung mit Sonnenlicht (Solarsimulator, 100 mW/cm2) in einer Flow-Zelle zu studieren, wird ZnCo2O4 auf einer transparenten und leitfähigen 2%Al:ZnO Schicht gewachsen. In diesem Fall dient c-Saphir als Substrat. Die Strukturen werden in einer Ultrahochvakuum Kammer durch reaktives Magnetronsputtern und/oder durch gepulste Laserdeposition hergestellt. Die Kristallstruktur der gewachsenen Proben wird durch Röntgenbeugung charakterisiert, die chemische Zusammensetzung durch Röntgenphotoelektronenspektroskopie und Augerelektronenspektroskopie untersucht. Die Experimente zeigen, dass ZnCo2O4 ein effizienter Katalysator für die Sauerstofferzeugung ist. ZnCo2O4 weist Überpotentiale im Bereich von 390470 mV und Tafel Steigungen von 56103 mV/dec in Kaliumhydroxid auf. Langzeit-Stabilitätstests demonstrieren die Funktion über mehrere hundert Stunden. Außerdem werden erste photoelektrochemische Experimente in einer Flow-Zelle durchgeführt. Jedoch beeinträchtigt die Instabilität von 2%Al:ZnO in Kaliumhydroxid wässriger Lösung die Stabilität des Systems enorm, auch wenn die Proben mit einer Schutzschicht aus Gold bedeckt werden.In this thesis, the electro- and photoelectrocatalytical properties for the oxygen evolution reaction of ZnCo2O4 have been investigated. p-type ZnCo2O4, grown on a Titanium mesh substrate, is used for electrochemistry measurements in a conventional H-cell with potassium hydroxide aqueous solution. In order to study the catalysis under illumination with sun light (solar simulator, 100 mW/cm2) in a flow cell, the ZnCo2O4 is grown on a transparent and conducting 2%Al:ZnO layer. In this case, a c-sapphire substrate is used. The structures are fabricated in an ultra high vacuum chamber by reactive magnetron sputtering and/or pulsed laser deposition. The crystal structure of the grown samples is characterized by x-ray diffraction and the chemical composition is analyzed by x-ray photoelectron spectroscopy and Auger electron spectroscopy. The electrochemical experiments show that ZnCo2O4 is an efficient catalyst for the oxygen evolution reaction, exhibiting overpotentials in the range of 390470 mV and Tafel slopes of 56103 mV/dec in potassium hydroxide. Long-term stability tests demonstrate performance over several hundreds of hours. Furthermore, first photoelectrochemical measurements with the solar simulator in a working flow cell have been done. However, 2%Al:ZnO is unstable in potassium hydroxide aqueous solution, strongly affecting the stability of the system, even when the samples are capped with gold layers.submitted by David DoppelbauerUniversität Linz, Masterarbeit, 2020(VLID)490443

Characterization of Siliconcarbonitride bonding layer for plasma activated direct fusion bonding

The financial support by the Austrian Federal Ministry of Labour and Economy, the National Foundation for Research, Technology and Development and the Christian Doppler Research Association is gratefully acknowledged

P-type cobaltite oxide spinels enable efficient electrocatalytic oxygen evolution reaction

Currently, energy-efficient electrocatalytic oxygen evolution from water involves the use of noble metal oxides. Here, we show that highly p-conducting zinc cobaltite spinel Zn1.2Co1.8O3.5 offers an enhanced electrocatalytic activity for oxygen evolution. We refer to previous studies on sputtered Zn-Co spinels with optimized conductivity for implementation as (p-type) transparent conducting oxides. Based on that, we manufacture off-stoichiometric conducting p-spinel catalytic anodes on tetragonal Ti, Au-Ti and hexagonal Al-doped ZnO carriers and report the evolution of O-2 at Tafel slopes between 40.5 and 48 mV dec(-1) and at overpotentials between 0.35 and 0.43 V (at 10 mA cm(-2)). The anodic stability, i.e., 50 h of continuous O-2 electrolysis in 1 M KOH, suggests that increasing the conductivity is advantageous for electrolysis, particularly for reducing the ohmic losses and ensuring activity across the entire surface. We conclude by pointing out the merits of improving p-doping in Zn-Co spinels by optimized growth on a tetragonal Ti-carrier and their application as dimension-stable 3d-metal anodes.</p

P-type cobaltite oxide spinels enable efficient electrocatalytic oxygen evolution reaction

Zinc cobaltite spinels show enhanced electrocatalytic activity for oxygen evolution. The spinels evolve O2 at Tafel slopes between 40.5 and 48 mV dec−1 and at overpotentials between 0.35 and 0.43 V at 10 mA cm−2. Their stability underlines their utility as 3d-metal anodes.</jats:p