Growth and scanning tunneling spectroscopy of self-assembled pi-conjugatedoligomers

A novel technique for the fabrication of pi-conjugated oligomers bonded to a substrate is presented. On a gold substrate, monolayers of small monomeri c organic units are alternately deposited by self-assembly. In each deposit ion step, polymerization takes place at the interface between two monolayer s through a condensation reaction. Chain growth is verified and analyzed by ellipsometry, gas chromatography, mass-spectrometry and X-ray photoelectro n spectroscopy. The layers are also imaged by scanning tunneling microscopy (STM), and current-voltage spectra have been recorded by STM in interrupte d feedback. The salient features for the oligomers, as compared to the bare gold substrate, can be explained by the presence of a thin (similar to 1 n m) layer of semiconductor with similar to 2 eV energy barrier for tunneling electrons. (C) 1999 Elsevier Science S.A. All rights reserved.