Imaging Top and Bottom

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Science  16 Oct 2009:
Vol. 326, Issue 5951, pp. 341
DOI: 10.1126/science.326_341c
CREDIT: HAN ET AL., ACS NANO 3, 10.1021/NN901030X (2009)

Scanning tunneling microscopy of adsorbed molecules on surfaces usually interrogates the topography of the topmost layer of atoms. For small molecules, this information is often sufficient to answer many structural questions, but for long-chain molecules, the bonding of the molecule to the surface can be obscured, especially at high surface coverages. Han et al. imaged both the topmost layer and the bonding interface of alkane thiols containing up to 10 carbon atoms adsorbed on gold. The application of an ac modulation of the tunneling gap allowed the buried methyl groups at the gold/sulfur interface to be imaged in a derivative mode. In the high coverage regime, the coexisting domains of different packing arrangements varied in their gold/sulfur bonding motifs in a manner consistent with previous x-ray diffraction studies. This technique will also be useful in studying other processes where changes in molecular tilt impact function.

ACS Nano 3, 10.1021/nn901030x (2009).

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