In scanning tunneling microscopy, moiré fringes appear if surface atomic layers have a different crystal structure than the bulk crystal. This can for example be due to surface reconstruction of the crystal, or when a thin layer of a second crystal is on the surface, e.g. single-layer,[16][17] double-layer graphene,[18] or Van der Waals heterostructure of graphene and hBN,[19][20] or bismuth and antimony nanostructures.[21]