Effect of low-temperature oxidation and heat treatment under vacuum on the Al-Be interdiffusion process.

The oxidation of the Be/Al and Al/Be bilayer thin film systems deposited by magnetron sputtering have been studied by photoelectron spectroscopy and transmission electron microscopy. Both systems are oxidized according to the Cabrera-Mott model in the air. A Be/BeO/Al/Al2O3 structure is formed, with aluminium represented as localized nanocrystals. The thickness of the beryllium in the Al/Be system and the formed beryllium oxide is not enough to prevent the diffusion of aluminium ions under the influence of the Mott potential, and as a result, the surface layer is a mixture of beryllium and aluminium oxides. The effect of oxidation processes on the intermixing of non-interacting metals in a bilayer nanostructure has been shown for the first time. Annealing of the Be/Al bilayer leads to beryllium diffusion to the surface and the reduction of aluminium oxide, which leads to the destruction of the bilayer structure. In the Al/Be system in the range up to 200 °C, additional beryllium oxide is formed with increasing temperature, and the rest of the metallic beryllium diffuses into the aluminium layer. Based on studies, we conclude that multilayer Al/Be nanostructures have potentially low thermal stability, which requires the use of barrier layer techniques to limit interdiffusion.

Effect of annealing on the interface formation in Mo/Be multilayer structures without/with a barrier layer.

In the present paper, the formation of an interface region in the multilayer periodic Mo/Be structure with/without a B4C or Si barrier layer depending on the annealing conditions was studied using X-ray photoelectron spectroscopy. The formation of different beryllides at the interfaces Be-on-Mo and Mo-on-Be was explained by the impact of the deposition-induced exchange caused by ballistic collisions and surface free energy. The influence of the high temperatures on the thermal stability of Mo/Be multilayer systems without/with a barrier layer was studied. Since the appropriately selected barrier layers prevent the formation of the interlayer region of mirrors at room temperature, it was concluded that it would also lead to a weakening of interlayer diffusion in multilayer mirrors at higher temperatures. The effect of barrier layer insertion on the thermal stability of Mo/Be structures was analyzed in detail. It was established that regardless of the material, the introduction of a barrier layer: (i) limits the formation of beryllides with an increase in the annealing temperature at the Be-on-Mo interface; (ii) prevents the formation of MoBe2, while forming MoBe12 beryllide at the Mo-on-Be interface; and (iii) does not limit the beryllium oxidation process at the Mo-on-Be interface.

Inhibition of chemical interaction of molybdenum and silicon in a Mo/Si multilayer structure by the formation of intermediate compounds.

In the present study, the formation of intermediate compounds in the Mo/Si multilayer was realized by the introduction of barrier layers at the interfaces. Their impact on the interdiffusion of Mo and Si was analyzed via X-ray photoelectron spectroscopy. It was established that the insertion of a thin Be barrier layer led to the formation of beryllide MoBe12 at the interface Si-on-Mo, which prevented the formation of molybdenum disilicide and improved the interface. The insertion of the B4C barrier layer led to its complete decomposition with the formation of borides and carbides of molybdenum and silicon (MoBx, SiBx, MoxC and SiCx) at the Si-on-Mo interface. The formation of only MoBx and SiCx was detected at the Mo-on-Si interface. It was important that the insertion of a thin B4C barrier layer did not fully prevent the formation of MoSi2 at both (Si-on-Mo and Mo-on-Si) the interfaces. These facts allowed us to assume that the diffusion barrier function of the B4C interlayer could be caused by the stability of the formed compounds, rather than the stability of the B4C layer itself.

Angle resolved photoelectron spectroscopy as applied to X-ray mirrors: an in depth study of Mo/Si multilayer systems.

We present an approach adapted to study the interface (composition and extension) of X-ray multilayer mirrors using angle resolved photoelectron spectroscopy (ARXPS). In the approach we rely on the concept of the average effective attenuation length (EAL) of the photoelectron and not on the inelastic mean free path (IMPF), which allows us to take into account the contribution of elastically scattered electrons and to increase the accuracy of the determined thickness of the layers. We apply the developed approach to study the formation of interfaces in a multilayer periodic Mo/Si mirror. The chemical composition and significance of the interfaces depending on the number of periods were investigated by means of the ARXPS spectra decomposition technique. Formation of a molybdenum silicide MoSi2 at the interfaces was revealed. It was shown that molybdenum silicide with different thicknesses is formed at the interfaces depending on the film order. In addition, it was established that increasing the period number of the [Mo/Si] system leads to a decrease of the interface extension.