Abstract
By structural and analytical TEM and scanning electron microscopy experiments we show that atomically-resolved structural characterization of oxidation-sensitive two-dimensional 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 and transition metal dichalcogenides. 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 characterization of the pristine structures is now possible.
Highlights
Nowadays, the number of two-dimensional (2D) materials is fast-growing and transition metal phosphorous trisulfides (TMPTs) are one of the new-born stars due to their magnetic and electric properties [1,2,3], allocating them as promising candidates for future heterostructure devices [4,5,6], for instance, combined with members of the material class of transition metal dichalcogenides (TMDs) [7]
We start by testing the effect of the KOH solution on the surface morphology and chemistry of KOHtreated and untreated bulk MnPS3 flakes using scanning electron microscopy (SEM)
Polymer-assisted TEM sample preparation method, which was based on the conventional scotchtape method
Summary
The number of two-dimensional (2D) materials is fast-growing and transition metal phosphorous trisulfides (TMPTs) are one of the new-born stars due to their magnetic and electric properties [1,2,3], allocating them as promising candidates for future heterostructure devices [4,5,6], for instance, combined with members of the material class of transition metal dichalcogenides (TMDs) [7]. Many different sample preparation methods were applied for 2D materials: standard transfer with polymer [13], direct transfer for the case of graphene [14], polyimide-assisted transfer for the case of h-BN [15], liquid exfoliation [16], and scotch tape method with potassium hydroxide (KOH). As the KOH method is conducted in an ambient atmosphere and involves a highly reactive chemical, in this preparation process chemical reactions take place and structural decomposition occurs [18, 19]. TEM imaging of the atomic structure of oxidation-sensitive TMPTs and TMDs, when prepared with the KOH method, is very difficult. To prevent the materials from oxidation during TEM preparation, a stamping method conducted in an oxygen-free
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