Study of graphene-tin and graphene-tin oxide hybrid nanostructures by scanning probe methods

What is it about?

We prepare tin nanoparticles (NPs) by evaporating 7–8 nm Sn on highly oriented pyrolytic graphite (HOPG) substrates. Graphene/Sn nanostructures are obtained by transferring graphene on top of the tin NPs immediately after evaporation. We show by scanning tunnelling microscopy (STM) and spectroscopy (STS) that tin NPs reduce significantly the environmental p-type doping of graphene. Furthermore, we demonstrate by low-temperature STM and STS measurements that superconductivity is induced in graphene, either directly supported by Sn NPs or suspended between them. Additionally, we prepare semiconducting SnOx NPs by annealing the evaporated tin at 500 °C. STS measurements performed on hybrid graphene/SnOx nanostructures reveal the electronic band gap of SnOx NPs.

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Why is it important?

Graphene/nanoparticle hybrids can have many potential applications such as in energy harvesting and storage, transparent conducting films, chemical- and biosensors, or drug delivery. In particular, Sn-based nanoparticles (Sn, SnO, SnO2) attached to graphene has been proposed as a most promising anode for lithium ion batteries. Here, graphene acts as the matrix material, which is able to constrain the volume expansion of Sn upon the formation of lithium rich alloys. Enhanced electrochemical performance was also obtained by the synthesis of layer-by-layer (graphene/Sn/graphene) 3D nanocomposites or by using carbon coated Sn NPs embedded in graphene as anode material. Graphene decorated with tin or tin-oxide NPs are promising candidates also as field emitters or gas sensors. Furthermore, it was recently shown by charge transport measurements that tin decorated graphene became a superconductor at low temperatures, and the superconducting phase transition could be controlled electrostatically. In order to better understand the interaction between tin and graphene, we performed a detailed microscopic investigation and characterized graphene/Sn hybrids by scanning tunnelling microscopy (STM) and spectroscopy (STS), a study which was lacking until this point from the literature.

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