Minimizing Tip-Sample Contact Force in Automated Atomic Force Microscope Based Force Spectroscopy

In atomic force microscope based force spectroscopy, it is often necessary to minimize the tip-sample contact force. While it is possible to control the contact force using force feedback, this method is susceptible to sensor drift and is often under-utilized due to the noise associated with the feedback process. Here we present a method to control the tip-sample contact force for repeated pulling cycles without relying on force feedback or tedious user-controlled z-stage step increments. The custom pulling program uses the data recorded during the previous retraction cycle to automatically reposition the sample surface to account for changes in topography and system drift. Using this method we were able to complete 250 automated pulling cycles, 76% of which had evidence of tip-sample contact. Of those pulling cycles with tip-sample contact, the average contact force was 83 pN, with the maximum contact force not exceeding 292 pN.