2017, Bragaglia, Valeria, Mio, Antonio M., Calarco, Raffaella

A high degree of vacancy ordering is obtained by annealing amorphous GeTe-Sb2Te3 (GST) alloys deposited on a crystalline substrate, which acts as a template for the crystallization. Under annealing the material evolves from amorphous to disordered rocksalt, to ordered rocksalt with vacancies arranged into (111) oriented layers, and finally converts into the stable trigonal phase. The role of the interface in respect to the formation of an ordered crystalline phase is studied by comparing the transformation stages of crystalline GST with and without a capping layer. The capping layer offers another crystallization interface, which harms the overall crystalline quality.

2017, Zallo, Eugenio, Cecchi, Stefano, Boschker, Jos E., Mio, Antonio M., Arciprete, Fabrizio, Privitera, Stefania, Calarco, Raffaella

The present work displays a route to design strain gradients at the interface between substrate and van der Waals bonded materials. The latter are expected to grow decoupled from the substrates and fully relaxed and thus, by definition, incompatible with conventional strain engineering. By the usage of passivated vicinal surfaces we are able to insert strain at step edges of layered chalcogenides, as demonstrated by the tilt of the epilayer in the growth direction with respect of the substrate orientation. The interplay between classical and van der Waals epitaxy can be modulated with an accurate choice of the substrate miscut. High quality crystalline GexSb2Te3+x with almost Ge1Sb2Te4 composition and improved degree of ordering of the vacancy layers is thus obtained by epitaxial growth of layers on 3–4° stepped Si substrates. These results highlight that it is possible to build and control strain in van der Waals systems, therefore opening up new prospects for the functionalization of epilayers by directly employing vicinal substrates.

2018-3-19, Zallo, Eugenio, Cecchi, Stefano, Boschker, Jos E., Mio, Antonio M., Arciprete, Fabrizio, Privitera, Stefania, Calarco, Raffaella

[no abstract available]