COUNTING THE LAYER NUMBER OF FREE-STANDING MONTMORILLONITE NANOSHEETS USING ANNULAR DARK FIELD SCANNING TRANSMISSION ELECTRON MICROSCOPY

Abstract

In this report, we demonstrate the direct determination of the layer number of free-standing montmorillonite (MMT) nanosheets using annular dark field (ADF) scanning transmission electron microscopy (STEM). The layer number of the free-standing MMT nanosheets deposited on a holey carbon-coated grid was successfully counted to range from monolayer to four layers by the difference in the ADF contrast. Meanwhile, counting of the layer numbers was difficult using conventional TEM and bright field STEM due to the low contrast. Therefore, ADF–STEM can potentially be applied to further investigate the clay nanosheets and their molecular complexes by the atomic scale imaging for a deeper understanding of clay-nanosheet-based chemistry.