Informatics for Quantitative Analysis of Atom Probe Tomography Images
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Informatics for Quantitative Analysis of Atom Probe Tomography Images Santosh K. Suram and Krishna Rajan Department of Materials Science and Engineering, Iowa State University Ames, IA 50011, U.S.A ABSTRACT An informatics based approach to extract refinements on the crystallographic information embedded in the Spatial Distribution Maps (SDMs) is developed. The complex SDM data is deconvoluted into meaningful spectra using Singular Value Decomposition (SVD). The interpretation of structural information from these spectra and generation of refined SDMs is discussed in detail. Our approach results in a method to generate SDMs that can map threedimensional crystallographic information as opposed to existing methods that map structural information on only one atomic plane at a time. The broader implications of this work on enhancing the interpretation and resolution of structural information in atom probe tomography studies are also discussed. INTRODUCTION Atom Probe Tomography (APT) is the highest spatial resolution analytical characterization technique there exists [11]. However, determining crystallographic structure using the atom probe has been a challenge since there is uncertainty attached to the atomic positions due to factors such as trajectory aberrations, preferential evaporation and inaccurate reconstruction parameters [1, 2]. Fourier Transform based methods have been used in the past to study structure of materials from APT data [3, 4, 5]. Their success has been limited due to the weak signal generated since these methods work in the reciprocal space. Recently, Geiser et al. [6] have proposed a real-space based approach – Spatial Distribution Maps (SDMs) to extract the crystallographic information obtained from the atom probe. This method has been further extended to identify lattice structure along various crystallographic orientations within a single reconstruction by Moody et al. [7]. Both these studies have used only the offset distribution of the peaks to study the crystallographic information within the SDMs. In this approach, we develop a SVD based approach to study the structural information embedded within the SDMs. Spectra generated using SVD of SDMs have been compared with the z- and xy-SDMs to analyze the structural information they provide. This approach has been further extended to enhance the image resolution in the xy-SDMs at peaks in the z-SDMs. METHODOLOGY Atom probe data was generated from a pure Tungsten specimen prepared via a standard electro-polishing procedure [8] using an LEAP-3000XSi equipment. The main purpose of this paper is to study the information within the SDMs and also to enhance the signal to noise ratio in the SDMs. Thus, a small dataset of size 150,000 atoms generated after the tip shape had stabilized over the first 600,000 atoms was reconstructed with zone axis at the center of the reconstructed volume. The region of interest within the atom probe data is shown in figure 1.
Spatial Distribution Maps SDMs are generated using the standard approach illustra
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