Probing the limits of the rigid-intensity-shift model in differential phase contrast scanning transmission electron microscopy

TL;DR

This paper investigates the limitations of the rigid-intensity-shift model in DPC-STEM, analyzing when it holds and proposing strategies to improve phase reconstruction accuracy.

Contribution

It provides a detailed analysis of the breakdown of the rigid-shift model and offers guidelines and probe-shaping strategies for better quantitative phase imaging.

Findings

Rigid-shift model breaks down at high phase gradients.

Feature size relative to probe affects model validity.

Proposed probe-shaping improves phase reconstruction accuracy.

Abstract

The rigid-intensity-shift model of differential phase contrast scanning transmission electron microscopy (DPC-STEM) imaging assumes that the phase gradient imposed on the probe by the sample causes the diffraction pattern intensity to shift rigidly by an amount proportional to that phase gradient. This behaviour is seldom realised exactly in practice. Through a combination of experimental results, analytical modelling and numerical calculations, we explore the breakdown of the rigid-intensity-shift behaviour and how this depends on the magnitude of the phase gradient and the relative scale of features in the phase profile and the probe size. We present guidelines as to when the rigid-intensity-shift model can be applied for quantitative phase reconstruction using segmented detectors, and propose probe-shaping strategies to further improve the accuracy.