Articolo in rivista, 2020, ENG, 10.1007/s12274-020-2657-4

ALD growth of ultra-thin Co layers on the topological insulator Sb2Te3

Emanuele Longo 1, Roberto Mantovan 1, Raimondo Cecchini 1, Michael D. Overbeek 3, Massimo Longo 1, Giovanna Trevisi 4, Laura Lazzarini 4, Graziella Tallarida 1, Marco Fanciulli 2 , Charles H. Winter 3, Claudia Wiemer 1

1 CNR- IMM, Unit of Agrate Brianza, Via C. Olivetti 2, Agrate Brianza (MB) 20864, Italy 2 Università degli Studi di Milano-Bicocca, Dipartimento di Scienza dei Materiali, Via R. Cozzi 55, Milano 20125, Italy 3 Department of chemistry, Wayne State University, Detroit, Michigan, 48202, USA 4 CNR-IMEM, Parco Area delle Scienze 37/A, Parma 43124, Italy

Taking the full advantage of the conformal growth characterizing atomic layer deposition (ALD), the possibility to grow Co thin films, with thickness from several tens down to few nanometers on top of a granular topological insulator (TI) Sb2Te3 film, exhibiting a quite high surface roughness (2-5 nm), was demonstrated. To study the Co growth on the Sb2Te3 substrate, we performed simultaneous Co depositions also on sputtered Pt substrates for comparison. We conducted a thorough chemical-structural characterization of the Co/Sb2Te3 and Co/Pt heterostructures, confirming for both cases, not only an excellent conformality, but also the structural continuity of the Co layers. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) analyses evidenced that Co on Sb2Te3 grows preferentially oriented along the [00? ] direction, following the underlying rhombohedric substrate. Differently, Co crystallizes in a cubic phase oriented along the [111] direction when deposited on Pt. This work shows that, in case of deposition of crystalline materials, the ALD surface selectivity and conformality can be extended to the definition of local epitaxy, where in-plane ordering of the crystal structure and mosaicity of the developed crystallized grains are dictated by the underlying substrate. Moreover, a highly sharp and chemically-pure Co/Sb2Te3 interface was evidenced, which is promising for the application of this growth process for spintronics

Nano research (Online)

Keywords

atomic layer deposition, X-ray diffraction, Co-fcc, Co-hcp, antimony telluride, metal organic chemical vapor deposition, spintronics

CNR authors

Fanciulli Marco, Longo Emanuele Maria, Lazzarini Laura, Mantovan Roberto, Trevisi Giovanna, Cecchini Raimondo, Tallarida Graziella, Longo Massimo, Wiemer Claudia

CNR institutes