Physico-Chemical nanomaterials science
Nanophase separation in Ge-S-Ag glasses
I.M. Lishchynskyy1, I.G.Kaban2, P.M.Lytvyn3, A.V.Stronski3, T Wagner4

1 1V.Stephanyk Precarpathian national university Ivano-Frankivsk, Ukraine
E-mail: igor.lishchynskyy@gmail.com
2 Leibniz Institute for Solid State and Materials Research Dresden, Germany
3 V.Lashkaryov Institute of semiconductor physics NAS Ukraine, Kyiv, Ukraine
4 University of Pardubice, Pardubice, Czech Republic

Perspective technologies memory elements fabrication which are based on the phase change (Phase Change Memory --PCM), or creation of conductive bridges in high-ohmic medium (conductive-bridge memories -- CBM) are at present actively studied. As active media in such memory elements glasses from composition cross-sections As-S, Ge-Se and Ge-S doped by metals are used. Ge-S-Ag glasses are perspective, in particular due to high Tg values and thus they have higher termal stability. Besides that in Ge-S-Ag glasses such toxic agents as As and Se are absent.
In order to create effective memory cells it is necessary to know homogeneity areas of particular active media, thus in this work we studied phase separation in Ge-S-Ag glasses of different compositions.
At first stage we carried out SEM measurements for (GeS3)100-xAgx (x=0, 5, 10, 15, 20, 25 at.%) glasses. Also EDX analysis of separate clusters on surface of mentioned above glasses was carried out.
Glasses of GeS3, (GeS3)75Ag25 composition are homogeneous, for other compositions phase separation is observed. It was established that big areas enriched by silver are included in Ag-depleted phases of different sizes. For glass compositions with higher silver content (x = 15 at.%) situation is changing and enriched by Ag phase become dominant.
At second stage glasses (GeS2)100-xAgx were investigated. SEM images for (GeS2) and (GeS2)80Ag20 glasses correspond to the single phase homogeneous vitreous state. Glasses with 10 and 15 at.% silver content are non-homogeneous and consist from enriched and depleted by silver phases. 
Similar investigations were carried out for (Ge42S58)100-xAgx (x=0, 5, 10, 15, 20, 25 at.%) glass compositions. SEM images for all investigated compositions did not show phase separation for the given scan regimes. But we made suggestion that Ge42S58-Ag line of phase diagram intersect boundary between single phase and binary phase systems. Thus at the next stage AFM investigations of surfaces of (Ge42S58)100-xAgx glasses were carried out. It was found that in samples with 15 ат % silver content nanophase separation is observed.
Thus areas of phase separation for (GeS3)100-xAgx, (GeS2)100-xAgx, (Ge42S58)100-xAgx.chalcogenide glasses are established.