Ultra-Dense, Highly Ordered and Thermally Stable Anthracene Monolayers on Ag(111)─The Impact of the Anchoring Group

Aromatic self-assembled monolayers (SAMs) are commonly used to tune the properties of metal electrodes in organic electronics, with their structural quality and thermal stability being of key importance. As demonstrated before for the gold electrodes, the use of anthracenethiol or -selenol SAMs provides template layer which can be used for the growth of organic semiconductors such as pentacene. Here, we show that the use of silver instead of gold and carboxylate instead of thiol/selenol allows to fabricate highly ordered anthracene monolayers with unprecedentedly high packing density (an area per molecule of ∼0.226 nm²), which even exceeds that of anthracene single crystal in the (001) plane (an area per molecule of ∼0.256 nm²) and, for the first time, provides 2D structure commensurate with the pentacene single crystal. Moreover, we show that these modifications lead to a radical improvement in the thermal stability (by ∼100 K) of anthracene-based SAMs. Consequently, the obtained results open up the possibility of using carboxylate-anchored anthracene monolayers on silver as a molecular template for facilitating the growth of high-quality anthracene and pentacene films for organic electronics.