3D Hollow Cone Nanoprobes for Electric AFM Applications

Since its introduction decades ago, Atomic Force Microscopy (AFM) evolved into a central characterization technologyin many scientific areas. As Abbe’s limit of diffraction is omitted by the use of a very sharp probe which is scannedacross a sample, Scanning Probe Microscopy techniques paved the way towards new insights and innovativeapplications in research and development. Moreover, AFM is not restricted to probe the topography of a sample only,but enables simultaneous mapping of a variety of surface properties, such as mechanical, electrical, chemical,magnetic of thermal, in a laterally resolved manner with nanometer resolution. Those advanced operation modes,however, require functionalized probes, which are often based on standard Si tips and further coated with relevantmaterials to induce intended functionalities. Aside of larger apex radii, reducing resolution capabilities, such coatingsare often prone to delamination effects due to mechanical stress during AFM operation, which reduce or eveneliminate the targeted sensitivity. Consequently, functional nanoprobes without any coatings would be desired, whilerevealing tip apexes in the sub-10 nm regime. A perfectly suited fabrication technique able to tackle those challengesis focused electron beam induced deposition (FEBID) [1]. It offers an unrivaled flexibility in terms of geometricalcomplexity and structural delicacy and poses little requirements to substrate material and surface morphology. Inaddition, post-growth treatments allow accurate tailoring of material’s properties towards the intended application[2]. Thus, FEBID is perfectly applicable for the fabrication or modification of AFM probes on pre-structured cantileversor pre-existing tips, respectively [3]. With this motivation in mind, we here present a Pt-based 3D hollow-cone conceptfor application in electrical AFM modes (CAFM, EFM, KFM). We start with fabrication on pre-structured AFMcantilevers (Fig.1a) and the chemical transfer into pure Pt structures (Fig.1b). That includes design optimization tomaximize mechan- ical rigidity, indispensably required for AFM operation, while apexes in the sub-10 nm regime areachieved on a regular basis (inset in Fig.1b). We then present the performance and advantages compare tocommercially available standard probes, as representatively shown by resolution comparison in Fig.1c and 1d. Finally,we present selected CAFM and EFM results, which further underline the advantages of such FEBID-based nanoprobes.Together with the fact, that those concepts are meanwhile patented together with our industrial partners, thiscontribution clearly shows the relevance of 3D-FEBID in the area of Atomic Force Microscopy.