Electron Beam-Induced Deposition for Atom Probe Tomography Specimen Capping Layers

Abstract

Six precursors were evaluated for use as in situ electron beam-induced deposition capping layers in the preparation of atom probe tomography specimens with a focus on near-surface features where some of the deposition is retained at the specimen apex. Specimens were prepared by deposition of each precursor onto silicon posts and shaped into sub-70-nm radii needles using a focused ion beam. The utility of the depositions was assessed using several criteria including composition and uniformity, evaporation behavior and evaporation fields, and depth of Ga+ ion penetration. Atom probe analyses through depositions of methyl cyclopentadienyl platinum trimethyl, palladium hexafluoroacetylacetonate, and dimethyl-gold-acetylacetonate [Me2Au(acac)] were all found to result in tip fracture at voltages exceeding 3 kV. Examination of the deposition using Me2Au(acac) plus flowing O2 was inconclusive due to evaporation of surface silicon from below the deposition under all analysis conditions. Dicobalt octacarbonyl [Co2(CO)8] and diiron nonacarbonyl [Fe2(CO)9] depositions were found to be effective as in situ capping materials for the silicon specimens. Their very different evaporation fields [36 V/nm for Co2(CO)8 and 21 V/nm for Fe2(CO)9] provide options for achieving reasonably close matching of the evaporation field between the capping material and many materials of interest.

Atom Probe Microscopy of Strengthening Effects in Alloy 718

“…Most contemporary APM data calibration approaches rely on the presence of crystallographic features, or some knowledge of the tip geometry obtained via high-resolution scanning or TEM (Arslan et al, 2008; Gault et al, 2012 b ; Diercks et al, 2017). Alternatively, the precipitate morphology-based calibration has been successfully demonstrated for large plate-shaped precipitates in an Al–Mg–Li alloy in the case where known precipitate/matrix crystallographic orientation relationships are available (Gault et al, 2012 b ).…”

Atom probe analysis of electrode materials for Li-ion batteries: challenges and ways forward

“…Going back to the discussion point above of a possible change in the very surface composition via adsorption, and that the shielding can be achieved extrinsically also for NMC811, we would need to find a way to perform metal deposition reachable through UHV-transport or directly inside the FIB. The chemical-vapour deposition from the gas-injection-system inside the FIB may also be an option for coating specimens 69 , yet the field evaporation behaviour of the deposited precursor rarely enables satisfactory analysis conditions 70 . In addition, FIB-based deposition under cryogenic conditions requires much fine-tuning to be achieved properly 71,72 , and may need to be followed by an appropriate level of in-situ curing via illumination by the electron and/or ion beam 73 .…”

Modern Focused-Ion-Beam-Based Site-Specific Specimen Preparation for Atom Probe Tomography

“…Likewise, simultaneous FIB milling with high current and energy SEM imaging during precursor flow, as described above by Felfer et al (2015), may encourage deposits to minimize the presence of voids. FIB-based deposits have the added advantage that, after NP deposition, all of the remaining specimen processing steps can be done in the FIB, and multiple deposition types are available (Diercks et al, in submission). ALD is also an option that should be space filling; however, it is known that NP deposits of the type described here can produce high-variability ALD growth.…”