Robust fabrication of large-area in- and out-of-plane cross-section samples of layered materials with ultramicrotomy

TL;DR

This paper presents a robust ultramicrotomy-based method for preparing large-area layered material samples with controlled in- and out-of-plane cross-sections, enabling improved structural analysis via TEM.

Contribution

The authors develop a general ultramicrotomy technique for large-scale, damage-free preparation of layered material cross-sections, enhancing TEM sample quality and control.

Findings

Reproducible large-area cross-section samples achieved

Samples verified by high-resolution TEM and Raman spectroscopy

Method applicable to various layered materials

Abstract

Layered materials (LMs) such as graphene or MoS$_2$ have recently attracted a great deal of interest. These materials offer unique functionalities due to their structural anisotropy characterized by weak van der Waals bonds along the out-of-plane axis and covalent bonds in the in-plane direction. A central requirement to access the structural information of complex nanostructures built upon LMs is to control the relative orientation of each sample prior to their inspection e.g. with Transmission Electron Microscopy (TEM). However, developing sample preparation methods that result in large inspection areas and ensure full control over the sample orientation while avoiding damage during the transfer to the TEM grid is challenging. Here we demonstrate the feasibility of deploying ultramicrotomy for the preparation of LM samples in TEM analyses. We show how ultramicrotomy leads to the reproducible large-scale production of both in-plane and out-of-plane cross-sections, with bulk vertically-oriented MoS$_2$ and WS$_2$ nanosheets as proof of concept. The robustness of the prepared samples is subsequently verified by their characterization by means of both high-resolution TEM and Raman spectroscopy measurements. Our approach is fully general and should find applications for a wide range of materials as well as of techniques beyond TEM, thus paving the way to the systematic large-area mass-production of cross-sectional specimens for structural and compositional studies.