Evaluation of intermittent contact mode AFM probes by HREM and using atomically sharp CeO2 ridges as tip characterizer

The imaging process of the atomic force microscope (AFM) in contact, noncon tact, and intermittent contact mode is still debated after more than a deca de of widespread use, in particular when imaged features are approaching at omic dimensions. Several models for the interaction between the tip and the surface have been suggested, but, generally they all need an exact descrip tion of the geometry of either the tip, the surface, or both. We present he re a tip characterizer with close to reproducible geometry, exactly known a ngles of all surfaces, and sharp features with close to atomic dimension. I t has been tested on three commercial AFM probes and a laboratory-made elec tron-beam-deposited tip, sharpened by oxygen plasma etching. High-resolutio n transmission electron microscopy has been used to unambiguously verify th e tip shapes down to atomic dimensions, both before and after imaging in in termittent contact mode. The effect on the recorded AFM images is shown of tip shape, tip wear, spallation, and accumulation on the tip of amorphous a nd crystalline debris. The imaging is shown to be a dynamic event, with a c ontinuously changing tip and occasional catastrophic events that give abrup t changes in imaging conditions. The tips are severely worn down already af ter scanning a few centimeters, but accumulated amorphous material may stil l give it imaging capabilities in the nanometer range, even with having a t ip radius exceeding 130 nm. Accumulated amorphous material seems to be more important than previously believed. Procedures for tip in situ characteriz ation and reliable imaging are suggested.