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We report the results of an ultrahigh vacuum scanning tunneling microscope (STM) study of n-alkanethiol [CH3 (CH2) n-iSH](C „) monolayers self-assembled on Au (lll) single-crystal surfaces. The STM images show that the saturation coverage self-assembled monolayer (SAM) unit cell measures 0.86 x 1.0 nm and contains four thiolate molecules. The observed unit cell is consistent with results from recent X-ray, electron, and helium diffraction studies. This unit cell corresponds to a c (4x2) superlattice of a basic (V3 x V3) R30 dense-packed monolayer. The domain size ranges from 5.0 to 15 nm with domains separated by molecular-width rotational boundaries, antiphase boundaries, and stacking faults. SAMs composed of longer chain thiols (Cs and Cio) were stable in vacuum for over 40 days.

Alkanethiols self-assemble on Au surfaces toform densely-packed, monomolecularfilms. Because of their ease-of …