Organic and Inorganic Contamination on Commercial AFM Cantilevers

Abstract

It has been found that a common shipping and packaging material for commercial AFM cantilever tips, poly(dimethylsiloxane) (PDMS), causes a thin layer of silicone oil contamination on AFM cantilever tips. Due to the similarity of elemental compositions between silicone oils and AFM cantilevers (both contain silicon and oxygen), it is difficult to detect such contaminants with the widely used surface characterization technique, X-ray photoelectron spectroscopy (XPS), since XPS provides mainly elemental and short-range chemical information. However, by using static time-of-flight secondary-ion mass spectrometry (TOF-SIMS), a technique that is extremely surface-sensitive, silicone oils on AFM cantilevers can easily be identified by their molecular fragments. A simple dip cleaning procedure using a mixture of concentrated sulfuric acid and hydrogen peroxide (piranha solution) was found to be an easy and effective way to remove organic contamination, including silicone oils, from AFM cantilever tips. It has also been shown, in both XPS and TOF-SIMS spectra, that a small amount of Au is present on the tip side of AFM cantilevers. This is most likely due to thermal diffusion of Au during the deposition of Au on the back side of the cantilevers, placed there to enhance laser reflectivity in the detection system of AFM instruments. No simple dipping approach was found to remove Au contamination on the tip side without also damaging the required Au coating on the back side of the cantilevers.