Comparative Apex Electrostatics of Atom Probe Tomography Specimens

Published

April 28, 2021

Author(s)

Qihua Zhang, B. Klein, Norman A. Sanford, Ann Chiaramonti Debay

Abstract

Laser-assisted atom probe tomography (APT) is the only known analytical method that can simultaneously provide sub-nm 3D spatial resolution and quantitative sensitivity approaching 1 ppm. APT has been applied with great success to the analysis of metals, semiconductors, dielectrics, and even biological materials [1]; the method is particularly suited to 3D analyses of composite and multilayered nanostructures. In APT, a nano-needle shaped specimen is electrically biased just below the threshold for field evaporation of ions. Field evaporation is then triggered by weak thermal transients imparted by a low-powered pulsed laser. The character of the field-evaporation process is strongly dependent upon the electrostatic environment across the specimen's apex. The electrostatics can be complicated by a 3D or multilayered sample where different constituent materials and interfaces are progressively revealed as ions are field-emitted away and the tip recedes in length. Therefore, rigorous electrostatic analysis is required to help understand the fundamental processes of APT and aid in guiding data analysis. Traditionally, and regardless of the specimen composition, the apex electric field E has been approximated by the asymptotic relation, E = V / (kr), which was originally derived for sharp, metallic conductors [2]. Here, V is the applied voltage, r is the radius of curvature of the apex, and k is a dimensionless fitting parameter with 1.5 < k < 8.5. We have developed a simulation tool that self-consistently solves the nonlinear electrostatic Poisson equation along with the mobile charge carrier concentrations, and provides a detailed picture of the electrostatic environment of APT specimen tips. We consider cases of metals, semiconductors, and dielectrics and compare our Poisson solver to the closed- form, asymptotic solution given above. The solutions compare well, as expected, for metal tips. Surprisingly, the two methods also agree well for semiconductor tips—regardles

Citation

Journal of Electronic Materials

Pub Type

Journals

Download Paper

https://doi.org/10.1007/s11664-021-08932-6

Local Download

Keywords

atom probe tomography, field emission, field evaporation, field ion microscopy, electrostatics

Citation

Zhang, Q. , Klein, B. , Sanford, N. and Chiaramonti Debay, A. (2021), Comparative Apex Electrostatics of Atom Probe Tomography Specimens, Journal of Electronic Materials, [online], https://doi.org/10.1007/s11664-021-08932-6, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=931034 (Accessed December 23, 2024)