He⁺ FIBID-fabricated 3D AFM tip architectures: an exploratory study of hollow pillars, helices, and spirals

Atomic force microscopy (AFM) relies strongly on tip geometry and mechanical integrity for stable and reproducible surface measurements. Here, we present an exploratory study of tungsten-carbon (W-C) AFM tips with complex three-dimensional (3D) architectures fabricated by helium ion beam-induced deposition (He⁺ FIBID) directly onto commercial AFM cantilevers bearing a pre-existing tip. Hollow nanopillars, nanohelices, and nanospirals were tested on a calibrated reference sample with a nominal step height of 20 nm using two AFM instruments under comparable operating conditions. Under the conditions explored here, selected 3D-printed tips reproduced the nominal step height of the calibration structure, yielding values consistent with those obtained using commercial probes on the same sample. To relate probe operation to structural outcome, each tip was examined by electron microscopy before and after AFM use. The main degradation modes were geometric deformation of the apex or shaft and mechanical fracture, most frequently at the tip-cantilever interface. While a few structures remained operational through repeated measurement cycles, others failed during the initial approach or early scanning stages, highlighting current limitations in robustness and reproducibility. These results show that complex He⁺ FIBID-grown nanoarchitectures can operate as AFM probes under basic test conditions, while also making clear that substantial optimization is still required.