Acta Physica Academiae Scientiarum Hungaricae 20. (1966)
1966 / 1-2. szám - P. Sviszt - P. Kovács - M. Farkas-Jahnke: Effect of Surface Damage on the Tendency for Darkening of ZnS Single Crystals
EFFECT OF SURFACE DAMAGE ON THE TENDENCY FOR DARKENING OF ZnS SINGLE CRYSTALS By P. Sviszt, P. Kovács and M. Farkas-Jahnke RESEARCH INSTITUTE FOR TECHNICAL PHYSICS OF THE HUNGARIAN ACADEMY OF SCIENCES, BUDAPEST (Presented by G. Szigeti — Received 13. X. 1964.) The tendency for darkening of the mechanically abraded and polished, etched and cleaved surfaces of hexagonal ZnS single crystals has been examined simultaneously with electron diffraction studies. The obtained results showed that there is a strong connection between the quality of the crystal surface and the tendency for darkening. 1. Introduction According to pictures published previously [1] the Zn precipitates produced during the photochemical decomposition of ZnS do not cover homogeneously the surface of the crystal. In the case of most of the crystals the Zn precipitates follow the stacking faults [2] perpendicular to the c-axis, as it was observed microscopically. In the case of a few other crystals not showing any oriented disorder and the surface of which seemed smooth before darkening, the orientation of the precipitated Zn could not be observed. The question arises whether the orientation of the Zn remains if a layer is removed from such a crystal and the surface so obtained is irradiated. To decide this question a layer has been removed from the surface of crystals with mechanical abrading and polishing, and then they were irradiated in humid air. The study of the darkening of these crystals, however, gave surprising results: even after a 5 hours’ irradiation no darkening observable with the naked eye could be seen on the abraded and polished surfaces, whereas if the surface was removed only by etching (without abrading and polishing) the darkening appeared in the same form as on the original crystals. 2 2. Experimental procedure The single crystals used for our experiments have been grown from vapour phase in our laboratory [3]. They were prisms of a hexagonal structure. The length of the prisms was 5 — 6 mm, their diameter 3 mm. The crystals emitted the blue band characteristic for self-activated ZnS-s excited with 365 mm mercury line. Acta Phys. Hung. Тот. XX. 1966