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Nagoya University


IMAGE: High-resolution STM image of stanene prepared on a Ag2Sn surface alloy. The honeycomb stanene structure model is superimposed. view more 

Credit: Junji Yuhara

Nagoya University-led researchers produce 2D sheets of tin atoms predicted to have exotic uses in electronics.

Nagoya, Japan - Sometimes it pays to be two-dimensional. The merits of graphene, a 2D sheet of carbon atoms, are well established. In its wake have followed a host of "post-graphene materials" - structural analogues of graphene made of other elements like silicon or germanium.

Now, an international research team led by Nagoya University (Japan) involving Aix-Marseille University (France), the Max Planck Institute in Hamburg (Germany) and the University of the Basque country (Spain) has unveiled the first truly planar sample of stanene: single sheets of tin (Sn) atoms. Planar stanene is hotly tipped as an extraordinary electrical conductor for high technology.

Just as graphene differs from ordinary graphite, so does stanene behave very differently to humble tin in bulk form. Because of relatively strong spin-orbit interactions for electrons in heavy elements, single-layer tin is predicted to be a "topological insulator," also known as a quantum spin Hall (QSH) insulator. Materials in this remarkable class are electrically insulating in their interiors, but have highly conductive surfaces/edges. This, in theory, makes a single-layered topological insulator an ideal wiring material for nanoelectronics. Moreover, the highly conductive channels at the edge of these materials can carry special chiral currents with spins locked with transport directions, which makes them also very appealing for spintronics applications.

In previous studies, where stanene was grown on substrates of bismuth telluride or antimony, the tin layers turned out to be highly buckled and relatively inhomogeneous. The Nagoya team instead chose silver (Ag) as their host - specifically, the Ag(111) crystal facet, whose lattice constant is slightly larger than that of the freestanding stanene, leading to the formation of flattened tin monolayer in a large area, one step closer to the scalable industrial applications.


The alloy guaranteed the flatness of the tin layer, as confirmed by density-functional theory calculations. Junji Yuhara, lead author of an article by the team published in 2D Materials, explains: "Stanene follows the crystalline periodicity of the Ag2Sn surface alloy. Therefore, instead of buckling as it would in isolation, the stanene layer flattens out - at the cost of a slight strain - to maximize contact with the alloy beneath." This mutual stabilization between stanene and host not only keeps the stanene layers impeccably flat, but lets them grow to impressive sizes of around 5,000 square nanometers.



The article, "Large area planar stanene epitaxially grown on Ag(111)," was published in 2D Materials at DOI:10.1088/2053-1583/aa9ea0.
