Reversible short-range electrostatic imaging in frequency modulation atomic force microscopy on metallic surfaces

摘要

The mechanism of atomic-scale image formation in non-contact AFM on metallic surfaces is analysed using total-energy pseudopotential calculations. Depending on the tip-apex configuration, we find two different imaging modes. Both clean and metal contaminated Si tips provide atomic resolution arising from the very strong covalent tip-sample interaction, in striking similarity with the imaging mechanism found on semiconductor surfaces. A completely new mechanism, reversible short-range electrostatic imaging, due to subtle charge-transfer interactions is identified for oxidized Si tips. Contrary to the strong covalent-bond imaging, this new mechanism causes only negligible surface perturbation and can account for recent experimental results.