Folded Nanosheets: A New Mechanism for Nanodisk Formation

Two-dimensional (2D) nanostructures have generated significant interest in the scientific community as a result of their high surface area and remarkable optoelectronic properties. In this work, we present a simple colloidal synthesis for ultrathin nanosheets of both In2S3 and CuInS2. Contradictory phase designations exist for In2S3 at the nanoscale as a result of overlapping reflections from multiple phases in X-ray diffraction. We use high-resolution transmission electron microscopy to demonstrate definitively that hexagonal γ-In2S3 is formed. Continued heating of these nanostructures results in the formation of nanodisks twice the thickness of the original structure via folding and tearing of the intermediate sheet. Treatment of the In2S3 nanosheet with Cu + accelerates this process of tearing of the nanosheet of In2S3 and results in the formation of one-dimensional nanoribbons of CuInS2. High-resolution transmission electron microscopy images and mediumangle X-ray scattering measurements indicate that these nanoribbons consist of face-to-face stacked nanodisks.