## 4 Discussion  
The use of PtC tips for applications based on the quantum mechanical tunneling effect depends on the distribution, size, and the number of Pt grains in the nanostructure. These Pt grains are embedded in a DLC matrix. The intrinsic conduction mechanism is based on electron tunneling between the individual Pt grains [17]. The more densely the Pt grains are distributed, the lower the resistivity of the material [33]. For tunneling between two PtC tips through a vacuum gap, the same conditions apply except for the additional distance through the vacuum gap. Thus, if the Pt grains are not directly placed at the edge of the tip but are surrounded by the high resistivity DLC, the tunneling mechanism does not appear at all shown in Figure 9a. The tunneling mechanism is supported by increasing the tunneling bias voltage. However, attractive forces play a crucial role when using a moving tip over a fixed tip, as shown by [PERSON] et al. [15]. Since this depends particularly on the tunneling voltage, only small tunneling voltages can be used for this application. In addition, electron tunneling can only be realized with small grain spacings across the vacuum gap. The HRTEM analysis shows a difference in the PtC nanostructure depending on the FEBID and FIBID as well as used currents (Figure 5). Produced tips by the FEBID show a homogeneous distribution of Pt grains, but an increased amount of DLC. This leads to an increased occurrence of DLC regions in the edge region, which prevents electron tunneling (Figure 7a). The FIBID tips show a difference in nanostructure depending on the ion current used. The 9 pA tips have larger Pt grains and thus lower density in the distribution, resulting in larger inter-grain spacing (Figure 7b). The 260 pA tips have much smaller grains, greater density, and smaller spacing between Pt grains (Figure 7c). When binarizing the HRTEM images, it is noticeable that there is a more homogeneous occurrence of Pt grains in the edge region for the 260 pA tips compared to the 9 pA tips. The measurement of individual crystallites shows on average 1.5 nm longer lengths for the FIBID tips compared to the FEBID tips. However, there is only a  
Figure 9: Measurements of tunneling application in a MEMS with integrated tunneling tips with (**a**) the measurement of the 9 pA and (**b**) of the 260 pA FIB tip. The excitation (green) is shown by the waveform of each actuator voltage range, differing from each other due to the initial distances of the tips. Ut = tunneling bias voltage.  
small difference between the FIBID tips. Therefore, the results of [PERSON] et al. [23] on the independence of the crystallite size from electron or ion beam cannot be confirmed. When the tips are approached in the MEMS application with small tunneling bias voltages, the measurements show a non-contact behavior for the FEBID tips, a drop in the current course for the 9 pA FIBID tip, and an exponentially increasing current course corresponding to the expected quantum tunneling current for the 260 pA tip. From the fabrication of TEM lamellae, it is known that the structuring by high ion currents causes splitting and amorphization of the nanostructure. For this reason, TEM lamellae are cleaned in the final step by an ion current as low as possible. The same mechanism can be assumed for the production of FIB structures by deposition. However, in the case of FIBID tips, this supports the suitability for applying tunneling electrodes since the splitting by an increased ion current leads to denser distribution of smaller Pt grains. In summary, it can be seen that the combination of a sufficient amount of Pt, small grains, and dense distribution of the grains in the nanostructure is necessary to perform tunneling applications with FIBID/FEBID metal-organic tips.