Surface chemistry altering electronic behaviour of liquid metal-derived tin oxide nanosheets†

Possessing excellent electronic properties and high chemical stability, semiconducting n-type two-dimensional (2D) tin dioxide (SnO₂) nanosheets have been featured in sensing and electrocatalysis applications recently. Derived from non-layered crystal structures, 2D SnO₂ has abundant unsaturated dangling bonds existing at the surface, providing interfacial activity. How the surface chemistry alters the electronic properties of 2D SnO₂ nanomaterials remains unexplored. In this study, we synthesised ultra-thin 2D SnO₂ nanosheets using a liquid metal (LM) touch printing technique and investigated experimentally and theoretically how the interactions of organic solvents composed of alkyl and hydroxyl groups with the surface of LM-derived 2D SnO₂ modulate the electronic properties. It was found that alkane solvents can physically absorb onto the SnO₂ surface with no impact on the material conductivity. Alcohol-based solvents on the other hand interact with the SnO₂ surface via chemical absorptions primarily, in which oxygen atoms of hydroxyl groups in the alcohols form bonds with the surface atoms of SnO₂. The binding stability is determined by the length and configuration of the hydrocarbon chain in alcohols. As representative long-chain alcohols, 1-octanol and 1-pentanol attach onto the SnO₂ surface strongly, lowering the binding energy of Sn⁴⁺ and reducing the electron transfer ability of SnO₂ nanosheets. Consequently, the electronic properties, i.e. conductivity and electronic mobility of SnO₂ nanosheet-based electronic devices are decreased significantly.