The formation of a novel surface reconstruction upon Co deposition on freshly cleaved Ge(111)-(2 x 1) surfaces was studied by means of scanning tunnelling microscopy at 4.5K. It had previously been demonstrated that, at this low substrate temperature, the deposited Co atoms remained immobile after they became embedded underneath the Ge(111)-(2 x 1) surface. It was now demonstrated that, at higher substrate temperatures, the embedded Co atoms were able to diffuse below the surface in a direction parallel to the upper π-bonded chain rows. This one-dimensional temperature-induced mobility resulted in sub-surface accumulation of Co atoms at atomic steps, at domain boundaries and on atomically flat Ge terraces at, e.g., vacancies or adatoms, where reconstructed Co/Ge intermixing layers were formed. Voltage dependent scanning tunnelling microscopic images revealed that the Co related surface reconstruction locally exhibited an ordered atomic structure with the same inter-atomic distance as that of the initial 2 x 1 reconstructed pure Ge(111) surface. On the other hand, the presence of the Co resulted in a doubling of the periodicity along the [2¯1¯1] direction in the scanning tunnelling microscopic images, which could be related to the modified electronic properties of the π-bonded chains.

Formation of Co/Ge Intermixing Layers after Co Deposition on Ge(111)2 x 1 Surfaces. D.A.Muzychenko, K.Schouteden, V.I.Panov, C.Van Haesendonck: Nanotechnology, 2012, 23[43], 435605