Autocorrected Off-axis Holography of 2D Materials

TL;DR

This paper introduces an advanced electron holography technique for high-resolution, aberration-corrected imaging of 2D materials, enabling detailed electrostatic potential measurements at the monolayer level.

Contribution

It develops an electron holography method with automatic aberration correction, improving spatial resolution and electrostatic potential analysis of 2D materials like h-BN.

Findings

Measured electrostatic potential variation with layer number

Detected increased potential at zig-zag edges

Demonstrated high spatial resolution imaging

Abstract

The reduced dimensionality in two-dimensional materials leads a wealth of unusual properties, which are currently explored for both fundamental and applied sciences. In order to study the crystal structure, edge states, the formation of defects and grain boundaries, or the impact of adsorbates, high resolution microscopy techniques are indispensible. Here we report on the development of an electron holography (EH) transmission electron microscopy (TEM) technique, which facilitates high spatial resolution by an automatic correction of geometric aberrations. Distinguished features of EH beyond conventional TEM imaging are the gap-free spatial information signal transfer and higher dose efficiency for certain spatial frequency bands as well as direct access to the projected electrostatic potential of the 2D material. We demonstrate these features at the example of h-BN, at which we measure the electrostatic potential as a function of layer number down to the monolayer limit and obtain evidence for a systematic increase of the potential at the zig-zag edges.