Chemical force microscopy of -CH3 and -COOH terminal groups in mixed self-assembled monolayers by pulsed-force-mode atomic force microscopy

Pulsed-force-mode atomic force microscopy (PFM-AFM), with functionalized pr obe tips, was applied to discrimination of chemical functionalities of a bi nary system of mixed self-assembled monolayers (SAMs) consisting of CH3- an d COOH-terminating alkane thiols. PFM-AFM enabled simultaneous imaging surf ace topography and distribution of adhesive forces between the tip and samp le surfaces. Since the adhesive forces were directly related to interaction between the chemical functional groups on the tip and sample surfaces, we combined the adhesive force mapping by PFM-AFM with the chemically modified tips to accomplish imaging the sample surface with the chemical sensitivit y. The adhesive force mapping by PFM-AFM with the CH3-modified tips in pure water clearly discriminated the hydrophobic CH3-terminating domains embedd ed in the COOH-terminating SAM matrix. (C) 2000 Elsevier Science B.V. All r ights reserved.