Scanning Probe Microscopic Characterization of Electronic Properties of Self-Assembled Organic Monolayers on Au Surface

The surface ordering and electronic properties of $\sigma $-bonded 1-dodecanethiol molecules and a series of $\pi $-bonded molecules of comparable length self-assembled on Au-on-mica surface have been studied by atomic force and scanning tunneling microscopic measurements. The molecular-level surface-probe microscopic images show a higher degree of ordering in the monolayers of $\sigma $-bonded molecule compared to that of the conjugated $\pi $ molecules. This is explained in terms of a larger molecular volume and intermolecular repulsion in the later than the former. Electronic measurements reveal, as expected, a higher tunnel current in the $\pi $-bonded molecules compared to $\sigma $-bonded molecules.