Self-assembled monolayers are a unique class of nanostructured materials, with properties determined by their molecular lattice structures, as well as the interfaces with their substrates and environments. As with other nanostructured materials, defects and dimensionality play important roles in the physical, chemical, and biological properties of the monolayers. In this review, we discuss monolayer structures ranging from surfaces (two-dimensional) down to single molecules (zero-dimensional), with a focus on applications of each type of structure, and on techniques that enable characterization of monolayer physical properties down to the single-molecule scale.

Patterning by Subtraction: Soft lithographic patterning is usually a “positive” inking process. A polymer stamp is cured on a hard master substrate and then inked with molecules such as alkane thiols, which can then be transferred to a second substrate (such as gold). However, the resolution of the transferred pattern is often degraded by surface diffusion. Liao et al. (p. 1517 ; see the Perspective by Rogers ) obtained higher resolution in a subtractive approach, in which oxygen-plasma–activated silicone stamps removed hydroxyl-terminated alkane thiols from gold surfaces. This lift-off process also removed the terminal gold atom bound to the alkane thiol. The bare regions could be backfilled with protein molecules, and multiple lift-off steps could create patterns with features as small as 40 nanometers.