Nanostructured surfaces

The nanoindentation of Cu diffusion layers in LiNbO3 crystal
D.Yu. Sugak1,2, I.I. Syvorotka1,2, O.A. Buryy1, U.V. Yakhnevych1, N. Levintant-Zayonts3, H.V. Savytskyy4, O.Yu. Bonchyk4 
1Department of Semiconductor Electronics, Lviv Polytechnic National University, 12, Bandera Str.,79000 Lviv, Ukraine. 
E-mail: yakhnevych.u@gmail.com
2 Scientific Research Company “Electron-Carat”, 202, Stryiska Str., 79000 Lviv, Ukraine
3 Institute of Fundamental Technological Research Polish Academy of Science, ul. Pawinskiego 5B; 02-106 Warszawa, Poland
4 Pidstryhach Institute for Applied Problems of Mechanics and Mathematics, National Academy of Sciences of Ukraine, 3-b, Naukova Str., 79060 Lviv, Ukraine

The possibility of modifying of surface layers of LiNbO3 as well as other oxide crystals by the diffusion of ions with variable valence is a subject of particular attention since it can be used for manufacturing of integrated optics devices, photorefractive materials and materials with phototropic properties. In turn, the modification of LiNbO3 surface layers by the diffusion of hydrogen or metal ions, the implantation or the ion irradiation requires the knowledge about changing of the surface mechanical properties caused by a certain treatment [1]. The purpose of this work was to investigate the changes of the mechanical properties of diffusion layers of copper doped LiNbO3 by nanoindentation technique along the diffusion direction when the indenter acts perpendicular to it. The mechanical properties of modified diffusion layers in LiNbO3 were determined using a commercially available ultra-low load indentation system, the Nano Indenter (CSM Instruments SA, Switzerland). Scanning was carried out in X and Z crystallographic directions, at that the indenter presses on a plate in the crystal-physics direction Y (X + 90o). The resulting nanohardness value is minimal in the area close to the crystal surface. The thickness of this area is about 100 μm. Further its value increases with the sigmoid dependence and reaches the value inherent the virgin lithium niobate at a distance of more than 600 microns from the crystal edge. The changes of nanohardness in a diffusion-modified layer of LiNbO3 are related with incorporation of copper ions into the regular positions of the LiNbO3 lattice. The results of studies of depth dependencies of the mechanical properties in the diffusion-modified layer of LiNbO3 correlate well with the measurements of changes in absorption spectra in this layer, which are also caused by copper ions incorporation into the crystal. The formation mechanism of the layers modified by the copper diffusion was proposed.

1.	Sosunov A.V., Volyntsev A.B., Tsiberkin K.B., Yuriev V.A., Ponomarev R.S. Features of structure and mechanical properties LiNbO3 // Ferroelectrics.–2017.–506.–P. 24–31.