Development of a dynamic atom probe

Abstract

Near atomic scale characterization can be achieved using probe tomography (APT) and cross-correlative transmission electron microscopy (TEM). However, pre-APT information about the specimen geometry and structure is necessary to produce accurate 3-D reconstructions and single atom identification. To solve these issues, a combined scanning TEM and APT system is being engineered and constructed, and this instrument has been termed a Dynamic Atom Probe (DyAP). The main goal of the development program is to demonstrate an electron imaging and diffraction system with sub-nanosecond temporal resolution, combined with atom probe tomography analysis with atomic scale resolution and chemical sensitivity in ppm. Three goals were identified to meet the objectives of the program: 1. Develop new methodology for analysis of oxides in the atom probe. 2. Attain a fundamental understanding of thermal transport in APT specimens under laser pulsed irradiation. 3. Develop and implement hardware for the DyAP, and carry out validation of dynamic experiments. Investigation of the behavior of oxides was performed by analyzing CeO2, (Pb,Zr)TiO3, and ZnMgO:Ga film on c-oriented [alpha]-Al2O3. A study of the impact of laser pulse energy and specimen base temperature on mass resolution, measurement of stoichiometry, multiple detector hits, and evaporation mechanisms were investigated. It was determined that laser pulse energy has effects on inhomogeneous heating of the specimen, formation of neutrals acompanied by loss of detection, and preferential evaporation of ionic species. A dynamic atom probe experiment was demonstrated using the ZnMgO:Ga on [alpha]-Al2O3. Laser pulsing in the atom probe was used to induce a phase transformation, given by the formation of spinel at the interface. APT results were correlated with TEM selected area diffraction patterns to confirm the transformation followed by APT analysis. The development program is funded by the National Science Foundation (NSF) through the Major Research Instrumentation program (MRI) award Number 1040456.