RBS investigations of ion beam mixed hard coatings on tool steel

Silicon nitride hard coatings on tool steel produced by ion beam mixing following sputter or vapour deposition were investigated by RBS and Vickers microhardness measurements. Atomic mixing in the coating/steel interface region resulting in an improved adhesion and in a significant increase of the microhardness of the surface layers was found. Ion beam mixing with gas ions and high fluences leads to blistering of the implanted atoms in the silicon nitride layer.     

Kinetics of Hydrogenation and Variations in Resistance of Vanadium Thin Films Treated in Atomic Hydrogen Flow

Methods of nuclear reactions, x-ray diffraction analysis, transmission electron and nuclear microscopy were used to investigate the mechanism of hydrogenation of thin vanadium films in their treatment in a flow consisting of a mixture of molecular and atomic hydrogen. It has been shown that the main component penetrating into the metal from the gas phase is atomic hydrogen. At a gas pressure of 10^–2 Pa and room temperature, the dissolution of particles which, in the gas phase, are in molecular form, occurs at a much lower rate. It has been established that the (initially high) rate of variation of the hydrogen concentration in the film decreases during hydrogenation and gradually approaches zero. As this takes place, the hydrogen concentration in vanadium reaches its limiting value equal to about 42.5 at. %. A mathematical model of the hydrogenation of a vanadium film is proposed which describes experimental results based on the relaxation dependence of the hydrogen concentration on hydrogenation time. Comparative analysis of the variations in hydrogen concentration in a film and in film resistance is performed. It has been established that the dependence of the resistance on hydrogen concentration for a thin film hydrogenated in a flow of atomic hydrogen differs from the similar dependence for a bulk material hydrogenated in the atmosphere of molecular hydrogen under the conditions of thermodynamic equilibrium. The features of the behavior of the resistance of a thin film on hydrogenation time revealed experimentally are caused, as in the case of a bulk material, by the formation of the phase of vanadium hydride in the film. The possibility of using vanadium thin films for measuring absolute values of the atomic hydrogen flow density is discussed.     

Characterization of the Edge Plasma of the CASTOR-Tokamak

The edge plasma of the CASTOR-tokamak was investigated by Langmuir and collector probes. T_e – values derived from both methods agree satisfactorily and are in the range from 15 eV to 45 eV, depending on the minor radius and the magnitude of the discharge current. However, the collector probe measurements indicate an anisotropic plasma and impurity flow in the edge plasma.     

Crystalline to amorphous transformations in ion implanted GaP

Abstract

The amorphization process of GaP by ion implantation is studied. The samples of 〈111〉 oriented GaP were implanted at 130 K with various doses 5 × 10¹³-2 × 10¹⁶ cm^?2 of 150 keV N⁺ ions and with the doses of 6 × 10¹²-1.5 × 10¹⁵ cm^?2 of 150 keV Cd⁺ ions. Room temperature implantations were also performed to see the influence of temperature on defect production. Rutherford backscattering and channelling techniques were used to determine damage in crystals. The damage distributions calculated from the RBS spectra have been compared with the results of Monte-Carlo simulation of the defect creation.

The estimated threshold damage density appeared to be independent on ion mass and is equal 6.5 × 10²⁰ keV/cm³. It is suggested that amorphization of GaP is well explained on the basis of a homogenous model.     

Radioactivity distribution at MAFF

A detailed account on the distribution of radioactive nuclei in the vacuum system of the planned Munich Accelerator for Fission Fragments (MAFF) located at the FRM-II research reactor is presented. Tools used for the simulation of spacial and temporal distribution of radionuclides are explained. The latter allows for a detailed activity budget as well as estimates for the mass-separated ion yields at MAFF. Additionally, a concept to reduce the activity release from the MAFF slit system due to surface sputtering is presented. It is shown, that the use of low-density carbon foam, as a surface coating, reduces sputtering by orders of magnitude.