Abstract
The ability to analyze nanoparticles in the atom probe has often been limited by the complexity of the sample preparation. In this work, we present a method to lift–out single nanoparticles in the scanning electron microscope. First, nanoparticles are dispersed on a lacey carbon grid, then positioned on a sharp substrate tip and coated on all sides with a metallic matrix by physical vapor deposition. Compositional and structural insights are provided for spherical gold nanoparticles and a segregation of silver and copper in silver copper oxide nanorods is shown in 3D atom maps. Using the standard atom probe reconstruction algorithm, data quality is limited by typical standard reconstruction artifacts for heterogeneous specimens (trajectory aberrations) and the choice of suitable coatings for the particles. This approach can be applied to various unsupported free-standing nanoparticles, enables preselection of particles via correlative techniques, and reliably produces well-defined structured samples. The only prerequisite is that the nanoparticles must be large enough to be manipulated, which was done for sizes down to ~50 nm.
Highlights
Atom probe tomography (APT) has immense potential to enable new insights into the compositional and structural makeup of nanoparticles (NPs)
The ability to analyze nanoparticles in the atom probe has often been limited by the complexity of the sample preparation
We introduce our NP APT specimen preparation method with two NP systems: spherical gold nanoparticles (Au-NP) and Ag2Cu2O3 (SCO—Silver Copper Oxide) nanorods (SCO-rod)
Summary
Atom probe tomography (APT) has immense potential to enable new insights into the compositional and structural makeup of nanoparticles (NPs). APT with its single atom analysis principle allows for the analysis of all chemical elements at the nanometer and sub-nanometer scale (Gault et al, 2012; Larson et al, 2013; Miller & Forbes, 2014; Lefebvre-Ulrikson et al, 2016). APT works by successively removing atoms/molecules as ions from a nanoscale, needle-shaped specimen (field ion emitter) using a high electric field. After this field evaporation, the formed ions are accelerated and projected onto a time-resolved single-atom 2D detector. The 3D structural information is reconstructed using detector hit position and hit sequence while time-of-flight provides the mass-to-charge-state ratio for chemical identification (Gault et al, 2012; Larson et al, 2013; Miller & Forbes, 2014; Lefebvre-Ulrikson et al, 2016)
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