CHEMICALLY-SENSITIVE INTERFACIAL FORCE MICROSCOPY - CONTACT POTENTIALMEASUREMENTS OF SELF-ASSEMBLING MONOLAYER FILMS

We report contact potential difference (CPD) measurements of n-alkanet hiol self-assembling monolayers (SAMs) adsorbed to Au substrates using an organomercaptan-modified Au probe. We perform experiments by apply ing a triangular-sweep voltage between the sample and probe while meas uring the resulting electrostatic force. The interfacial force microsc ope permits us to keep the probe/sample distance rigidly fixed, which allows us to directly measure the electrostatic force at a constant in terfacial separation. The CPD is determined by measuring the applied p otential necessary to null the electric field and eliminate the interf acial force between the two surfaces. We show that CPD values obtained using Au probes modified with methyl-terminated SAMs are stable and r eproducible, whereas identical unmodified probes yield highly variable data. Our experimentally determined CPD values are in qualitative agr eement with calculated CPDs for several different omega-terminated SAM s.