Kelvin probe force microscopy on surfaces: Investigation of the surface potential of self-assembled monolayers on gold

The local contact potential difference (CPD) between different linear alkan ethiols self-assembled as monolayers on Au substrates was investigated with Kelvin probe force microscopy (KPFM). Our results demonstrate that KPFM si multaneously provides information on the sample topography and its contact potential down to a lateral resolution of 100 nm. The reported CPD measurem ents allow the distinction between regions in the monolayer comprising thio l molecules with chemically different terminal head groups down to a resolu tion of 3 meV. Further more, the CPD values measured in monolayers having o ne type of functionality vary with the chain length of the molecules in the film, which is consistent with a dipole-layer model. Variations in the len gth of the alkyl chain reveal a linear dependence as a function of the (-CH 2-) units in the chain, with an increase in the CPD potential of 14.1 +/- 3 .1 mV per (-CH2-) unit.