Characterizing and understanding nanoscale wear of carbon-based atomic force microscope tips

Nanoscale wear is a key limitation of conventional atomic force microscope (AFM) probes that are used in high resolution imaging, measurement, and nanomanufacturing applications. Systematic characterization to understand the wear behavior of AFM tips is key to predicting and improving the lifetime of nanoscale probes. In this thesis work, a systematic wear test protocol that combines transmission electron microscopy, pull-off force measurements, inverse imaging and blind reconstruction has been developed to characterize tip evolution during sliding. Relationships between interface adhesion and pull-off force for non-parabolic tip geometries were developed to facilitate analysis of experimental data.;AFM tips made of monolithic ultrananocrystalline diamond (UNCD) were developed and characterized. Their nanoscale wear resistance under contact-mode scanning conditions is compared with conventional SiNx probes at two different relative humidity levels (∼15% and ∼70%). While SiN x probes exhibit significant wear that further increases with humidity, UNCD probes show little measurable wear. Systematic wear characterization of diamond-like carbon (DLC)-coated tips as a function of external load was also performed. Contact stresses for the evolving tip geometry during sliding were calculated. The quantitative relationship between contact stresses and wear volume loss rate demonstrate a nearly linear relationship. The results were also compared to an atomistic attrition model using Arrhenius kinetics. Finally, an iterative finite element (FE)-based wear simulation algorithm for a nanoscale single asperity tip was constructed where a local material removal model was used in conjunction with the FE stress state predictions simulates single asperity wear. The preliminary modeling results successfully demonstrate the evolution of a parabolic tip to a power-law shaped tip.