Variations in composition and structure occurring in multicomponent alloy targets during their service term

Abstract. Main part of the magnetron sputtering (MS) technology is a target that serves as a source for film/coating material. The target properties directly influence the properties of a film/coating deposited by MS. The target composition and microstructure may change during its exploitation, especially if the target has complex composition, e.g., multicomponent alloy. However, only a small part of the target in the MS serves as a source of film-forming particles. This is an erosion zone, an annular groove, which forms over time under the ion bombardment (IB) of the target. Usually, the groove area is about 25% of the target square while the rest square remains unchanged. As the groove develops, the composition and angle of expansion of the film-forming particles change, that affects the composition and thickness uniformity of the film. Therefore, the information of the composition and microstructure of the groove at the end of the target's service term allows predicting the possible changes in the properties of the film. In view of the told above, we used SEM and microanalysis to study the structure and composition of the grooves of CoCrCuFeNi, CoCrCuFeMnNi, AlCoCrCuFeNiV high entropy alloy targets at the beginning and at the end of their service. Initial microstructure of the surface of all targets was smooth and flat and composed of matrix and inclusions homogenously distributed in the matrix. The microrelief of the bottom and side walls of the grooves was different and depended on the intensity of the IB. In the area of strong IB the microrelief acquired features of a melted surface. In the area of moderate IB the microrelief was crossed in various directions by micro-trenches of various length and width. It was revealed that the shapes and distribution of these micro-trenches coincided with those of the inclusions observed on the original targets surfaces. It was also revealed that at the end of the service term the composition of the grooves became depleted with elements with maximal enthalpy of formation. Analysis of the obtained results led us to the following conclusions: (i) the signs of melting on the targets surfaces indicate that its temperature is close to the melting temperatures of the alloys; (ii) a new type of the effect of preferential sputtering has been established. The main condition for its existence is the presence in the target composition of the second phase in the form of microinclusions, which sputtering yield is noticeably higher than of the components of the first phase; (iii) the formation of specific microrelief on the targets surfaces upon IB with ions with energy typical for DC MS is a result of the combined action of two factors: high temperature and sputtering. Key words: DC MS, target, high entropy alloys, composition, structur

Polarized Luminescence of Bismuth Active Centers in Phosphosilicate Glasses

The polarization properties of bismuth active centers (BACs) are important for many applications of bismuth-doped fibers, but they are still lacking in study. In this paper, we present the measurements of polarized luminescence (PL) of the BACs formed in a Bi-doped phosphosilicate glass matrix. This research was performed on phosphosilicate fiber preforms used for the drawing of active bismuth-doped fibers for efficient optical amplifiers and lasers. The degree of polarization (DOP) of luminescence of the BACs associated with phosphorus and silica (BAC-P and BAC-Si) is provided and discussed. The DOP of luminescence at the 1320 nm wavelength appeared to be around 19%, 0% and 7.5% for pumps at 1240 nm, 762 nm and 425 nm, respectively. The DOP of PL caused by resonant excitation may be described in terms of a model of a partially anisotropic oscillator with the parameters represented by the principal axes of an ellipsoid. For the resonant excitation at 1240 nm, the ratio of the major principal axis to the minor one turned out to be 5.1 and 3.0 for BAC-P and BAC-Si, respectively