Commonality of structural transformations in LiF and MgF2 ionic crystals with Co and Ni impurities and metal crystals with metal impurities during heat treatment

Abstract

The processes of formation of nickel and cobalt containing films on the surface of LiF:Co, LiF:Ni and MgF2:Co, MgF2:Ni single crystals due to high-temperature thermal annealing have been studied for the first time. The purpose of research was finding out the possibility of obtaining nanoscale metal containing films by intracrystalline diffusion of metal impurity from inside the ionic crystal to the surface. Methods of formation and properties of Ni and Co containing films on the ionic crystals is important due to the possibility of their application in optoelectronic devices, spintronics, for recording information with used of film as optical and magnetic media and in other fields. Thermal etching at 750–900 °C was carried out in vacuum and in air. The analysis of the surface of samples was carried out using an electron-ion scanning microscope. Elemental analysis of samples surface was carried out by mapping surface elements and at individual points. It was determined that impurities come out of dislocations in crystals and form metal containing film on the surface. The films contain predominantly Ni, Co, and O elements, as well as elements of the film interaction with air atmosphere. The value of the film thickness is estimated as lying in the range from 0.5 to 5.0 μm. After release of impurity from crystal dislocations, thermal etching pits of various shapes remain. An analogy is drawn between the processes of thermal etching of ionic crystals studied by us and metallic crystalline materials analyzed from scientific literature. General regularities are revealed and differences between two types of crystalline matrices due to high-temperature thermal annealing are noted.