Density-functional-theory simulations of the water and ice adhesion on silicene quantum dots

The absorption of water and ice on silicon is important to understand for many applications and safety concerns for electronic devices as most of them are fabricated using silicon. Meanwhile, recently silicene nanostructures have attracted much attention due to their potential applications in electronic devices such as gas or humidity sensors. However, for the moment, the theoretical study of the interaction between water molecules and silicene nanostructures is still rare although there is already theoretical work on the effect of water molecules on the silicene periodic structure. The specific conditions such as the finite size effect, the edge saturation of the silicene nanostructure, and the distance between the water/ice and the silicene at the initial onset of the contact have not been carefully considered before. Here we have modelled the absorption of a water molecule and a square ice on the silicene nanodot by using hybrid-exchange density-functional theory, complemented by the Van der Waals forces correction. Three different sizes of silicene nanodots have been chosen for simulations, namely 3 x 3, 4 x 4, and 5 x 5, with and without the hydrogen saturation on the edge. Our calculations suggest that the silicene nanodots chosen here are both hydrophilic and ice-philic. The water molecule and the square ice have tilted angles towards the silicene nanodot plane at similar to 70 degrees and similar to 45 degrees, respectively, which could be owing to the zig-zag structure on silicene. The absorption energies are size dependent for unsaturated silicene nanodots, whereas almost size independent for the hydrogen saturated cases. Our work on the single water molecule absorption energy on silicene nanodots is qualitatively in agreement with the previous theoretical and experimental work. However, the ice structure on silicene is yet to be validated by the relevant experiments. Our calculation results not only further complement the current paucity of water-to-silicene-nanostructure contact mechanisms, but also lead to the first study of square-ice contact mechanisms for silicene. Our findings presented here could be useful for the future design of semiconducting devices based on silicene nanostructures, especially in the humid and low-temperature environments.