INTERACTION OF SURFACE FREE ENERGY AND HUMIDITY ON AFM TIP-SAMPLE ADHESION MEASURED BY CHEMICAL FORCE MICROSCOPY

摘要

The synergistic effects of RH and sample surface energy on the image contrast and tip-sample adhesion obtained by AFM have been investigated. The main conclusions are: 1. Humidity plays a vital role on both the tip-sample adhesion force and image contrast when an AFM hydrophilic tip is used, but RH has little effect on image contrast and the adhesion force when scanned with a hydrophobic tip. 2. Image contrast enhancement at elevated RH levels is due to the presence of capillary forces. 3. At low humidity, sample surface chemistry has little effect on both the adhesion force and image contrast, regardless of the type of tips used; however, when hydrophilic tips are used and at elevated RHs, surface chemistry has a strong effect on these properties. 4. For hydrophilic tips and hydrophilic surfaces, the adhesion force increases with an increase in RH > 20% and the adhesion/RH curves go through a maximum. 5. A combination of RH and hydrophilic tip makes phase imaging AFM a powerful technique to detect and map chemical heterogeneity of surfaces at the nanoscale resolution.