APT Analysis of Nano-Objects: Simulation-informed Field Emitter Design and Fabrication Methods

Atom Probe Tomography (APT) has not yet established itself as a prominent nano-objects (NOs) characterization method. This contradicts with APT’s potential in providing experimental data for the structure-property-relationship analysis of NOs with near-atomic resolution and chemical sensitivity in the parts per million (ppm) range. This work addresses the challenging specimen design and fabrication. APT specimen (field emitter tip) design concepts are derived based on full-scale APT simulation of single NOs on substrate tips. Free-standing NOs of different dimensions, encapsulated NOs, and various offset NO positions relative to the field emitter’s axis were investigated. The quantifiable data describes the loss of NO data and data quality with an increasing offset of the NO. By encapsulating NOs, the APT output can be optimized by setting the relative field evaporation property of coating and NO material. Two NO specimen fabrication methods are introduced following the simulation findings. Both encapsulate NOs on pre-sharpened field emitter tips and omit focused-ion beam (FIB) milling. i) The pick and coat method combines an in-situ SEM pick and place NO transfer using micromanipulation with ex-situ electron beam physical vapor deposition (EB-PVD) encapsulation. The NO positioning reproducibly works for various types of NOs. Probing damage can be reduced with the exposure, but the dynamic nature of NOs needs to be considered for APT experiments. ii) The application of co-electrodeposition on pre-sharpened field emitter tips produced APT data of NOs. By omitting FIB lift-outs, co-electrodeposition offers upscaling potential for specimen fabrication. Well-positioned NOs can be produced using high specimen outputs.