Polymer-assisted TEM specimen preparation method for oxidation-sensitive 2D materials.

By structural and analytical TEM and SEM experiments we show that atomically-resolved structural characterization of oxidation-sensitive two-dimensional (2D) material is strongly hindered when the final step of the preparation process, the transfer to the TEM grid, is performed with a wet etching method involving bases or acids, interacting with the highly reactive sample surface. Here we present an alternative polymer-assisted and mechanical-exfoliation-based sample preparation method and demonstrate it on selected oxidation-sensitive transition metal phosphorus trisulfides (TMPT) and transition metal dichalcogenides (TMD). The analysis, obtained from the samples prepared with both of the methods clearly show that oxidation is the origin of discrepancy, the oxidation during the final preparation step is strongly reduced only when the new method is applied, and atomically-resolved structural characterisation of the pristine structures is now possible.