Visualized Multiprobe Electrical Impedance Measurements with STM Tips Using Shear Force Feedback Control

Here we devise a multiprobe electrical measurement system based on quartz tuning forks (QTFs) and metallic tips capable of having full 3D control over the position of the probes. The system is based on the use of bent tungsten tips that are placed in mechanical contact (glue-free solution) with a QTF sensor. Shear forces acting in the probe are measured to control the tip-sample distance in the Z direction. Moreover, the tilting of the tip allows the visualization of the experiment under the optical microscope, allowing the coordination of the probes in X and Y directions. Meanwhile, the metallic tips are connected to a current-voltage amplifier circuit to measure the currents and thus the impedance of the studied samples. We discuss here the different aspects that must be addressed when conducting these multiprobe experiments, such as the amplitude of oscillation, shear force distance control, and wire tilting. Different results obtained in the measurement of calibration samples and microparticles are presented. They demonstrate the feasibility of the system to measure the impedance of the samples with a full 3D control on the position of the nanotips.