Anisotropic friction and nano-welding in 2D ferroelectric SnSe monolayer nanoplates

2D ferroelectric materials have been developed rapidly in the recent years because of its huge potential for creating the artificial multiferroics and novel non-volatile devices. Therefore, understanding the coupling between the thin film and graphene substrate is essential. Here, we report the anisotropic friction in SnSe monolayers first discovered by scanning tunneling microscope due to the strong commensuration between the monolayer and graphene substrate, while the SnSe bilayers show more isotropic manner on epitaxial graphene substrate. By controllably moving SnSe nanoplates, the nanoplates can merge without creating any grain boundary by in-situ annealing. These results show potential for controllably manipulation and construction of nanostructures among 2D materials.