Extracting Quantitative Information from High Resolution Electron Microscopy

Abstract

Despite the development of high-resolution electron microscopy (HREM) that allows imaging of most materials, the extraction of quantitative information at atomic scale still requires considerable additional efforts. This review presents the recent developments on techniques that can be used to determine the local strain, chemical composition or atomic structure retrieval in HREM. The source of noise in images and effective methods for improving the signal-to-noise ratio in direct or Fourier space are discussed. The artefacts of filtering are commented. In all the methods, the sample thickness has to be determined. A detailed analysis of the thin foil relaxation effect on the measured distortion fields is presented as well as the possibilities of using finite element calculations for its modelling. The local composition measurement based on the chemically sensitive reflections; pattern recognition and the measurement of lattice parameters are described. Examples from semiconductor heterostructures are discussed. The current state of the strategies used for the retrieval of the atomic configuration of defects from HRTEM images is briefly presented. The limits of detection and the accuracy of the methods are summarised; and it is pointed out that electron holography, focal series reconstruction and the coming Cs corrected microscopes will help to obtain this information with better accuracy. Content

Impact of Thin LT-GaN Cap Layers on the Structural and Compositional Quality of MOVPE Grown InGaN Quantum Wells Investigated by TEM

“…Thin foil relaxation is taken into account with the help of field electron microscopy (FEM) calculations. This image processing technique is based on the principles described in [3].…”

High-Resolution Electron Microscopy of Semiconductor Heterostructures and Nanostructures

“…All these techniques were based on superimposing a two-dimensional reference lattice extrapolated from a non-distorted region of the material to the experimental one, built up from the set of intensity maxima in the HRTEM image, and calculating the local discrete displacement field at each node [30]. Subsequently, the strain field is calculated as the derivative of the displacement field.…”

“…The understanding of the wires growth can be completed following two approaches: (1) Measuring the strain field by applying peak-finding methods [19,30] (see Sect. 2.3) to HRTEM images of stacked nano-objects.…”

HRTEM techniques applied to nanocrystal modeling: towards an “atom-by-atom” description

“…Geometric Phase Analysis (GPA) [30] is a methodology for measuring and mapping structural displacement fields on HRTEM images using a reference lattice. Its application to HRTEM image analysis allows the local lattice distortion evaluation, which can be directly related to the local strain state.…”