Plasma-assisted surface nanostructuring of epitaxial Pb1−xSnxTe (0 ≤ x ≤ 1) films

Abstract

In this work, we report a novel approach to the surface nanostructuring of lead tin telluride films using inductively coupled argon plasma treatment with the average ion energy of 200 eV and the duration of 20–60 s. The nanostructuring was carried out on the plasma treated surface of epitaxial single-crystal Pb1−xSnxTe films grown on BaF2(111) substrates using molecular beam epitaxy. The plasma treatment of the surface of the Pb1−xSnxTe films with the low and medium Sn content (x = 0–0.6) resulted in the formation of the arrays of ‘capped’ conical nanostructures with the height up to 420 nm, depending on the Sn content and treatment duration, and the surface density of ∼109 cm−2. The plasma treatment of the surface of the films with the high Sn content (x = 0.8–1) yielded the formation of a second group of flat nanostructures without ‘caps’, which had necklace-like rings consisting of multiple nanodroplets around their rims. Using transmission electron microscopy, we show that the quasi-spherical droplet ‘caps’ of the nanostructures consist of Pb ‘wrapped’ in Sn. We explain the physical mechanism of the observed plasma-assisted nanostructure self-formation in the framework of the multi-stage model including physical sputtering, redeposition, vapour-liquid-solid mechanism and micromasking mechanism.