Growth of multilayer ice films and the formation of cubic ice imaged with STM

Ice films as many as 30 molecular layers thick can be imaged with scanning tunneling microscopy (STM) when negative sample biases $<-6(\pm 1)\text{V}$ and subpicoamp tunneling currents are used. We observe that water deposited onto Pt(111) below 120 K forms amorphous films, whereas metastable cubic ice appears between 120 and 150 K. To determine the mechanisms of ice growth, we investigate the thickness-dependent film morphology. Cubic ice emerges from screw dislocations in the crystalline ice film that are caused by the mismatch in the atomic Pt- step height and the ice-bilayer separation.