Surface morphology’s role in water freezing onset: A study of graphene on ruthenium thin films produced with two different methods

Ice formation strongly impacts on human activities in large parts of the world. Fundamental understanding of the icing properties of surfaces, with the aim of designing coatings and structures with anti-icing properties, is therefore an important research field. Optically transparent anti-icing solutions are needed for applications such as windshields on cars, sensor windows for long-time monitoring and camera lenses. Graphene is particularly attractive in this context because it is nearly transparent and robust. However, up until now little work has been done on the anti-icing properties of graphene and functionalized graphene. Here we present a study of the anti-icing properties of a range of graphene samples deposited on ruthenium films of varying thickness grown on sapphire. Both physical vapor deposition (200 nm) and an alternative coating technique known as thermal laser epitaxy (15 nm) were used for fabricating the ruthenium films. We show that the freezing onset for one of the graphene coatings grown with the alternative method is superior to previously published results on the freezing onset of graphene and fluorinated graphene. We also show that one can achieve similar results on a very high-quality bare sapphire surface. Our results obtained on surfaces with pits with curvatures estimated in the nanometer range indicate an insensitivity to chemical differences. This is in agreement with existing theory which proposes that the freezing onset is similar for all types of surfaces, as long as they display pits within a given radius of curvature range, differing only when surfaces become very rough or very smooth relative to the critical radius for ice nucleation.