Parallel Mode Differential Phase Contrast in Transmission Electron Microscopy, II: K2CuF4 Phase Transition

Gary W Paterson,Gavin M Macauley,Yoshihiko Togawa,Stephen Mcvitie

doi:10.1017/s1431927621012575

Gary W Paterson, Gavin M Macauley + Show 2 more

Open Access

https://doi.org/10.1017/s1431927621012575

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Abstract

AbstractIn Part I of this diptych, we outlined the theory and an analysis methodology for quantitative phase recovery from real-space distortions of Fresnel images acquired in the parallel mode of transmission electron microscopy (TEM). In that work, the properties of the method, termed TEM-differential phase contrast (TEM-DPC), were highlighted through the use of simulated data. In this work, we explore the use of the TEM-DPC technique with experimental cryo-TEM images of a thin lamella of a low-temperature two-dimensional (2D) ferromagnetic material, K2CuF4, to perform two tasks. First, using images recorded below the ordering temperature, we compare the TEM-DPC method with the transport of intensity one for phase recovery and discuss the relative advantages the former has for experimental data. Second, by tracking the induction of the sample as it is driven through a phase transition by heating, we extract estimates for the critical temperature and critical exponent of the order parameter. The value of the latter is consistent with the 2D XY class, raising the prospect that a Kosterlitz–Thoules transition may have occurred.

Highlights

In Part I of this two-part series (Paterson et al, 2021), we showed that the real-space distortions of Fresnel images taken in a transmission electron microscope of samples supporting electrostatic or magnetostatic fields may contain information sufficient for quantitative recovery of the electron-optical phase imparted on the imaging electrons
The technique, which we refer to as transmission electron microscopy (TEM)-differential phase contrast (TEM-DPC), has origins dating back decades (Fuller & Hale, 1960), but has gone largely unused since
Using the TEM-DPC technique for quantitative phase recovery from Fresnel images and the nonrigid image alignment tools reported in Part I of this work (Paterson et al, 2021), we have characterized the induction of a thin lamella of K2CuF4, a material of increasing interest for the quasi 2D ferromagnetism it supports

Summary

Introduction

In Part I of this two-part series (Paterson et al, 2021), we showed that the real-space distortions of Fresnel images taken in a transmission electron microscope of samples supporting electrostatic or magnetostatic fields may contain information sufficient for quantitative recovery of the electron-optical phase imparted on the imaging electrons. Using simulated data from different magnetic samples, we showed that the TEM-DPC technique has further potential benefits over the TIE one in some cases.

Results

Conclusion