Substrate-Selective Morphology of Caesium-Iodide Clusters on Graphene.

Formation and characterization of low-dimensional nanostructures is crucial for controlling the properties of two-dimensional (2D) materials such as graphene. Here, we study the structure of low-dimensional adsorbates of caesium-iodide (CsI) on free-standing graphene using aberration-corrected transmission electron microscopy (AC-TEM) at atomic resolution. CsI is deposited onto graphene as charged clusters by electrospray ion-beam deposition (ES-IBD). The interaction with the electron beam forms two-dimensional CsI crystals only on bi-layer graphene, while CsI clusters consisting of 4, 6, 7, and 8 ions are exclusively observed on single-layer graphene. Chemical characterisation by electron energy-loss spectroscopy (EELS) imaging and precise structural measurements evidence the possible influence of charge transfer on the structure formation of the CsI clusters and layers, leading to different distances of the Cs and I to the graphene. KEYWORDS: graphene, electrospray ion-beam deposition, transmission electron microscopy, mass spectrometry, alkali halide atomic clusters and two-dimensional crystals.