Chemically-sensitive interfacial force microscopy: Contact potential measurements of self-assembling monolayer films

We report contact potential difference (CPD) measurements of n- alkanethiol self-assembling monolayers (SAMs) adsorbed to Au substrates using an organomercaptan-modified Au probe. Our results demonstrate for the first time the feasibility and importance of controlling the chemical properties of force microscope probe surfaces. Moreover, control over the chemical characteristics of the probe provides a basis for distinguishing between chemically distinct surface features with nanometer resolution in force microscopy. We show that CPD values obtained using Au probes modified with methyl-terminated SAMs are stable and reproducible, whereas identical unmodified probes yield highly variable data. Our experimentally determined CPD values are in qualitative agreement with calculated CPDs for several Omega-terminated SAMs.