Molecule-dependent topography determined by noncontact atomic force microscopy: carboxylates on TiO2(1 1 0)

The feasibility of noncontact atomic force microscopy (NC-AFM) in single-molecule analysis is experimentally demonstrated. Carboxylates (RCOO−) with different R’s were identified molecule-by-molecule on the TiO2(1 1 0) substrate. The constant frequency-shift topography exhibited a good correlation with the physical topography of the carboxylates with RH, CH3, C(CH3)3 and CCH. The molecule-dependent topography was interpreted with the van der Waals force pulling the tip into the adsorbates. The constant frequency-shift topography of a series of fluorine-containing acetates (RCH3, CHF2, and CF3) revealed that the intramolecular electric polarization perturbs the tip–molecule force through electrostatic couplings.