Tilted fluctuation electron microscopy

Ellis Kennedy,Colin Ophus,Neal Reynolds,Frances Hellman,M C Scott,Luis Rangel Dacosta

doi:10.1063/5.0015532

Abstract

Fluctuation electron microscopy (FEM) is a scanning nanodiffraction-based method that offers a unique approach to characterizing nanometer-scale medium-range order (MRO) in disordered materials. In addition to determining the degree of MRO, careful analysis of scanning nanodiffraction data can also be used to determine strain in thin film amorphous samples. We applied FEM to characterize the strain and MRO of magnetron sputtered amorphous tantalum (a-Ta) thin films over a range of tilt angles from 0° to 45° in order to measure any deviations between the in-plane and out-of-plane strain and MRO. We validate our approach using electron diffraction simulations of FEM experiments for a-Ta. We measure anisotropic strain in the simulated a-Ta diffraction patterns and find that the experimental a-Ta is isotropically strained within the accuracy of our method. Our approach provides a workflow for acquiring tilted scanning nanodiffraction data, determining the relative strain and ordering as a function of in- and out-of-plane directions, and removing any artifacts induced in FEM data due to strain. We also describe some limitations of the tilted FEM method when applied to thin films with very low strains.

Highlights

E medium-range order (MRO) and its distribution on the scale of 1–4 nm are difficult to measure
We applied Fluctuation electron microscopy (FEM) to characterize the strain and MRO of magnetron sputtered amorphous tantalum (a-Ta) thin films over a range of tilt angles from 0 to 45 in order to measure any deviations between the in-plane and out-of-plane strain and MRO
We measure anisotropic strain in the simulated a-Ta diffraction patterns and find that the experimental a-Ta is isotropically strained within the accuracy of our method

Summary

Introduction

E MRO and its distribution on the scale of 1–4 nm are difficult to measure. X-ray and neutron diffraction and Raman spectroscopy are commonly used for strain characterization but cannot provide information on such small length scales.7,8 Fluctuation electron microscopy (FEM). Our approach provides a workflow for acquiring tilted scanning nanodiffraction data, determining the relative strain and ordering as a function of in- and out-of-plane directions, and removing any artifacts induced in FEM data due to strain.

Results

Conclusion