Kelvin probe force microscopy characterization of self-assembled monolayers on metals deposited with dip-pen nanolithography

The ability of self-assembled monolayers to modify the surface electronic states of metals and semiconductors is of interest for a variety of technological applications. When such changes occur at the nanoscale with precise control, an important contribution to nanotechnologies can be achieved. Here, Kelvin probe force microscopy is employed to accurately characterize the work function changes induced by nanopatterns of mercaptohexadecanoic acid deposited on gold by dip-pen nanolithography. Using this technique in conjunction with other AFM scanning modes reveals that, depending on the lithography conditions, the nanodeposits can assume three different structures: an ordered phase with upright molecules; an ordered phase with horizontal molecules; and finally, a disordered phase with molecules adopting different conformations. Thanks to this controlled tunability of the adsorbate structure, the metal work function is demonstrated to be finely tuned within an interval of 50 meV. © 2009 American Chemical Society.