The interplay between drift and electrical measurement in conduction atomic force microscopy

In Conduction Atomic Force Microscopy (CAFM), it is sometimes required to monitor electrical data at a single location over an extended period of time. However, thermal drift of the microscope will cause the tip to move with respect to the sample and thus limit the collection of data. We investigate a method to prolong the time a tip dwells at a location by choosing the AFM cantilever to have small spring constants in the lateral directions. The basis of the approach is that the tip can only move (or slip) once the lateral forces caused by drift overcome the friction force pinning the tip to the surface. We demonstrate the effect experimentally using platinum wire tips and diamond coated tips on SiO2 and HfO2 dielectric films. Simultaneous measurement of the current flow and lateral force signals show that the onset of tip slipping correlates with the beginning of a decrease in the measured current flow, and the onset of slip is prolonged for blunt tips or cantilevers having soft lateral spring constants. The approach not only provides a way to improve the CAFM method for time dependent measurements but also assists in interpreting CAFM data in the presence of drift.