%P 5339 - 5351
%D 2014
%A DZ Gao
%A J Grenz
%A MB Watkins
%A FF Canova
%A A Schwarz
%A R Wiesendanger
%A AL Shluger
%V 8
%T Using Metallic Noncontact Atomic Force Microscope Tips for Imaging Insulators and Polar Molecules: Tip Characterization and Imaging Mechanisms
%N 5
%X We demonstrate that using metallic tips for noncontact atomic force microscopy (NC-AFM) imaging at relatively large (>0.5 nm) tip–surface separations provides a reliable method for studying molecules on insulating surfaces with chemical resolution and greatly reduces the complexity of interpreting experimental data. The experimental NC-AFM imaging and theoretical simulations were carried out for the NiO(001) surface as well as adsorbed CO and Co-Salen molecules using Cr-coated Si tips. The experimental results and density functional theory calculations confirm that metallic tips possess a permanent electric dipole moment with its positive end oriented toward the sample. By analyzing the experimental data, we could directly determine the dipole moment of the Cr-coated tip. A model representing the metallic tip as a point dipole is described and shown to produce NC-AFM images of individual CO molecules adsorbed onto NiO(001) in good quantitative agreement with experimental results. Finally, we discuss methods for characterizing the structure of metal-coated tips and the application of these tips to imaging dipoles of large adsorbed molecules.
%O © 2014 American Chemical Society. Terms of Use CC-BY. 

PubMed ID: 24787716
%L discovery1433814
%K NC-AFM, insulator, imaging mechanism, metallic tip, virtual AFM
%J ACS NANO