Rolling up two-dimensional sheets into nanoscrolls

Since discovery of graphene, various structures of two-dimensional (2D) sheets, such as nanoribbon, wrinkles, and folded layers, have been studied due to their unprecedented properties. Among them, a helical tube structure, which is called a nanoscroll, has been reported in naturally scrolled form of a graphene sheet. It has been expected that graphene nanoscrolls (GNSs) have exceptional properties, which are totally different from those of its constituent graphene sheet and multiwall carbon nanotubes (MWCNTs). Here we report a straightforward and controllable way to fabricate nanoscrolls of two dimensional sheets, such as graphene and molybdenum disulfide (MoS₂). We rolled up graphene sheets into nanoscrolls by sweeping them up with vigorously generated bubbles in a solution. It was verified that there is no formation of significant defects after scrolling process and the graphene layers in a nanoscroll are decoupled. GNSs behave like randomly stacked monolayers without any coupling between the adjacent layers and show p-type electrical conductance, which is distinct from graphene's electrical properties. In contrast, the stiffer MoS₂ was folded, not scrolled during scrolling process. Raman shift and photoluminescence (PL) of folded MoS₂ showed strong interlayer coupling between the stacked layers, which is opposite for the case of GNSs. To prevent this coupling effect, thin layer of lipids was deposited on the surface of MoS₂ before scrolling process. Inserted lipid layers between MoS₂ monolayers suppressed interlayer interactions, leading to enhanced PL intensity. Our work provides a novel way to fabricate various forms of 2D sheets, such as scrolled and folded structures, which are highly intriguing due to high possibility to seek for new physics in the scrolled structures of one-atom thick 2D sheets.