Optimization of CuW alloy electrodeposition towards high-tungsten content

With the help of the factorial design of experiments, optimization of the deposition of the CuW alloy was successfully done. The important deposition parameters were identified as pH, current density, and—the most important one—copper ion concentration. All of them were examined in their wide ranges. Under optimal conditions, in a citrate bath, with copper ion concentration of 1.0 mM, at current density of −100 mA cm⁻² and at pH ca. 8.3, the alloy layer had the highest tungsten content (circa 30 wt.%), satisfactory adhesion and a smooth and crackless morphology. The structure of the electrodeposited alloy can be described as an amorphous solid solution of Cu in W with built-in Cu nanocrystals.

     

Insulated wall potential stabilization modes in gas discharges

Arguments for demonstrating the contribution of the ion current in the process of wall potential stabilization at a positive value and the results of some experiments supporting this viewpoint, are presented. It is also shown that the variation in gas pressure leads to a change in the number of possible stabilization modes. It is argued that the values of the stable wall potentials are determined by the secondary emission properties of the wall surface, the tube configuration and the values of the charged particle fluxes to the wall. The wall-cathode and wall-anode capacitances may influence only the direction in which the wall potential will drift during the stabilization process, in the case when two stable values of the wall potential exist.     

Production of Negative Ion-Rich Plasma by Electron Attachment in Low Pressure Gases

The scope of this research is to investigate experimentally electron (ne), negative ion (n-) and positive ion (n+) densities characterizing laboratory negative ion-rich plasmas, produced by electron attachment in N2O3, O2 and I2, and to find out the factors limiting the achievement of very low ? (relative electron density ? = ne/n+). These plasmas may be of great interest for the production of negative ion beams. It is shown experimentally that it is possible to produce plasmas with a high proportion of negative ions (n-/n+ ? 90 %) and a low proportion of electrons, at densities n+ up to 1011 cm-3. The comparison of mass spectrometric data with kinetic calculations leads to the conclusion that the loss of negative ions by diffusion limits the lowest ? achieved at low ion density (n+ < 109 cm-3). At higher ion density, mutual neutralization seems to control the ? values. A general limitation seems to exist for the lowest ? attainable in small plasmas produced by electron attachment : the confinement of negative ions in a plasma is due to the presence of electrons and therefore this confinement becomes inefficient when ? drops to values as low as 10-3.     

Hydrogen superpermeation resistant to ion sputtering

A nonmetallic monolayer on the surface of a metallic membrane gives rise to the superpermeation of suprathermal hydrogen. This means that virtually the whole implanted flux passes through the membrane, depending neither on membrane temperature nor on its thickness. The fact that superpermeation is degrading at a sufficiently high energy of the incident hydrogen particles was considered to be a ‘natural’ result of sputtering of the monolayer. This view was equally applied to Nb, one of the best metals for superpermeation. It is shown in this article that Nb containing O impurity will be normally superpermeable to suprathermal hydrogen at any incident energy, the earlier observed sensitivity to sputtering being conditioned by the NbC layer originally present at the ‘real’ Nb surface. The dynamic exchange between the surface and bulk O impurity is proven to be responsible for the superpermeability of Nb resistant to sputtering. When the NbC layer is present, it hinders such an exchange. PACS 34.50.Dy; 66.30.-h; 82.65.+r     

Review of oxide formation in a plasma

The physical processes occurring at the surface and in the bulk of an oxide during plasma oxidation or anodization are discussed. It is shown that (i) the majority of oxygen ions used in the growth are formed by electron-assisted surface processes, (ii) the nature of the oxide surface and especially the presence of electrode contamination can have a determinant role in the oxygen exchange between the plasma and the oxide, and (iii) ion space charge can control the anodization kinetics. Two applications (formation of the insulating barrier of Josephson junctions, and GaAs MOSFET devices) are presented.     

Catalytic Activity of Anisotropic Gold Nanoplates towards Oxygen Reduction

Glassy carbon electrode (GCE) coated with anisotropic gold nanoplates (aAuNPs) was used for the study of oxygen reduction reaction (ORR) in 0.5 M sulfuric acid instead of bulk gold electrodes. The electrode cleaning/activation procedure lead to the removal of any charged and uncharged residues on the gold nanoplates, leaving the nanostructured surface highly active towards oxygen reduction. The advantages: much lower overpotential and larger current densities of oxygen reduction are ascribed to the unique nanostructures present on the carbon electrode surface‐the gold nanoplates. They are rich in edges providing a large population of Au (100) sites with unsaturated coordination exposed to the solution, and catalytically active. Measurements performed using a rotating disc electrode, modified with the gold nanoplates, confirmed that ORR proceeds via two separate steps: oxygen is reduced to hydrogen peroxide, and the peroxide is further reduced in a two‐electron reduction to water.     

The Cichoń diagram for degrees of relative constructibility

Following a line of research initiated in [4], we describe a general framework for turning reduction concepts of relative computability into diagrams forming an analogy with the Cichoń diagram for cardinal characteristics of the continuum. We show that working from relatively modest assumptions about a notion of reduction, one can construct a robust version of such a diagram. As an application, we define and investigate the Cichoń diagram for degrees of constructibility relative to a fixed inner model W. Many analogies hold with the classical theory as well as some surprising differences. Along the way, we introduce a new axiom stating, roughly, that the constructibility diagram is as complex as possible.     

Physics and applications of charged particle beam sources

The authors review the physics and a few applications of charged particle beam sources, most of which originate from, propagate through, or use as a target, a partially ionized plasma. The authors present the plasma phenomena and plasma conditions which are general to most of the charged particle sources, but also other approaches and the current status of the research. The authors describe the applications of charged particle beam sources using partially ionized plasmas in accelerators and ion implantation. The applications covered are those of accelerator sources and ion implantation