2017, Wang, Ruining, Zhang, Wei, Momand, Jamo, Ronneberger, Ider, Boschker, Jos E., Mazzarello, Riccardo, Kooi, Bart J., Riechert, Henning, Wuttig, Matthias, Calarco, Raffaella

A highly unconventional growth scenario is reported upon deposition of GeTe films on the hydrogen passivated Si(111) surface. Initially, an amorphous film forms for growth parameters that should yield a crystalline material. The entire amorphous film then crystallizes once a critical thickness of four GeTe bilayers is reached, subsequently following the GeTe(111) 

2016, Bragaglia, Valeria, Arciprete, Fabrizio, Zhang, Wei, Mio, Antonio Massimiliano, Zallo, Eugenio, Perumal, Karthick, Giussani, Alessandro, Cecchi, Stefano, Boschker, Jos Emiel, Riechert, Henning, Privitera, Stefania, Rimini, Emanuele, Mazzarello, Riccardo, Calarco, Raffaella

Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows.

2015, Boschker, Jos E., Galves, Lauren A., Flissikowski, Timur, Lopes, Joao Marcelo J., Kiemer, Alexandra K., Riechert, Henning, Calarco, Raffaella

Van der Waals (vdW) epitaxy is an attractive method for the fabrication of vdW heterostructures. Here Sb2Te3 films grown on three different kind of graphene substrates (monolayer epitaxial graphene, quasi freestanding bilayer graphene and the SiC (6√3 × 6√3)R30° buffer layer) are used to study the vdW epitaxy between two 2-dimensionally (2D) bonded materials. It is shown that the Sb2Te3 /graphene interface is stable and that coincidence lattices are formed between the epilayers and substrate that depend on the size of the surface unit cell. This demonstrates that there is a significant, although relatively weak, interfacial interaction between the two materials. Lattice matching is thus relevant for vdW epitaxy with two 2D bonded materials and a fundamental design parameter for vdW heterostructures.