3D Nanoprinting of All-Metal Nanoprobes for Electric AFM Modes

Abstract

3D nanoprinting via focused electron beam induced deposition (FEBID) is applied for fabrication of all-metal nanoprobes for atomic force microscopy (AFM)-based electrical operation modes. The 3D tip concept is based on a hollow-cone (HC) design, with all-metal material properties and apex radii in the sub-10 nm regime to allow for high-resolution imaging during morphological imaging, conductive AFM (CAFM) and electrostatic force microscopy (EFM). The study starts with design aspects to motivate the proposed HC architecture, followed by detailed fabrication characterization to identify and optimize FEBID process parameters. To arrive at desired material properties, e-beam assisted purification in low-pressure water atmospheres was applied at room temperature, which enabled the removal of carbon impurities from as-deposited structures. The microstructure of final HCs was analyzed via scanning transmission electron microscopy—high-angle annular dark field (STEM-HAADF), whereas electrical and mechanical properties were investigated in situ using micromanipulators. Finally, AFM/EFM/CAFM measurements were performed in comparison to non-functional, high-resolution tips and commercially available electric probes. In essence, we demonstrate that the proposed all-metal HCs provide the resolution capabilities of the former, with the electric conductivity of the latter onboard, combining both assets in one design.

Additive Manufacturing of Co3Fe Nano-Probes for Magnetic Force Microscopy

“…The demands for ideal MFM tips are listed in the introduction and require a novel design of the probe, as discussed in the following. In this special case, we aim on the fabrication on flat, tip-less self-sensing cantilever (SS-CL) platforms [ 32 , 33 , 34 ] ( Figure 1 a), which are equipped with specially designed electrodes (shaded yellow) to provide a general basis for a variety of AFM nano-probe concepts, ranging from magnetic over electric [ 24 ] towards thermal sensors [ 23 ]. The missing tip, however, leads to the requirement of a total tip height of at least to ensure that the nano-probe is the lowest point of the SS-CL, which is inclined by about 11° after mounting.…”

“…Recently, a FEBID-based, Pt hollow-cone concept was introduced for conductive-AFM (CAFM) tips on the same SS-CL platforms [ 24 ], which provides a few advantages: (1) sufficient contact area to the SS-CL to prevent detachment, (2) enhanced mechanical rigidity for AFM operation, (3) sharp tip apexes of or less for high-resolution imaging, and (4) the single material character to eliminate delamination aspects, as relevant here as well. Figure 1 c shows the feasibility of such hollow cones for the Co 3 Fe precursor, although vertical growth rates were much lower than for Pt-based materials (exact factors strongly depend on the exact deposition parameters [ 24 ]). This leads to longer processing times on the one hand, but it also entails morphological challenges due to shadowing effects [ 24 , 36 ].…”

“…Figure 1 c shows the feasibility of such hollow cones for the Co 3 Fe precursor, although vertical growth rates were much lower than for Pt-based materials (exact factors strongly depend on the exact deposition parameters [ 24 ]). This leads to longer processing times on the one hand, but it also entails morphological challenges due to shadowing effects [ 24 , 36 ]. As lateral forces during MFM are drastically lower compared to contact mode operation in CAFM, the large interface area is not absolutely needed, which would require complex patterning procedures for controlled growth.…”

“…By that, (3D) FEBID has successfully been applied for mask repair [ 14 ], sensing applications [ 15 , 16 ], plasmonics [ 17 ], nano-magnetics [ 18 , 19 ], and scanning probe applications [ 7 ]. Concerning the latter, FEBID is well suited due to several advantages: (1) structures can be precisely grown on almost any surface morphology, including pre-finished cantilevers or existing tips [ 20 , 21 ]; (2) flexible 3D designs [ 12 ] can be realized to either adapt nano-tips to individual requirements, as demonstrated by Jaafar et al for Co- and Fe-base nanoprobes [ 6 ], or even advanced nano-probe concepts can be realized, as demonstrated for magnetic resonance force microscopy [ 22 ], scanning thermal microscopy [ 23 ], or electrical modes [ 24 ]; and (3) FEBID allows for sharp apexes in the sub-10 nm regime [ 11 , 23 ] on a regular basis to enable high-resolution AFM imaging [ 23 , 24 ]. Concerning MFM tips in particular, FEBID has previously been used for pillar-shaped tips for MFM probes, mostly performed with single material precursors (Fe, Co) [ 6 , 25 , 26 , 27 , 28 ].…”

Selected Area Deposition of High Purity Gold for Functional 3D Architectures

“…While nanoscale 3D applications are limited due to the FEBID purity described above, several example applications have emerged. For instance, magnetic 3D structures [ 20 , 21 , 22 ], vibrating sensors [ 23 ], chiral [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ] and split ring resonators [ 32 , 33 ], and other [ 34 , 35 ] plasmonic devices, scanning probe tips [ 36 , 37 , 38 ], and some nanomechanical applications [ 39 , 40 ] have all been demonstrated.…”