Self-assembled monolayers of oligophenylenes stiffer than steel and silicon, possibly even stiffer than Si3N4

To quantify charge transport through molecular junctions fabricated using the conducting probe atomic force microscopy (CP-AFM) platform, information on the number of molecules.. per junction is absolutely necessary... can be currently obtained only via contact mechanics, and the Young's modulus.. of the self-assembled monolayer (SAM) utilized in a key quantity for this approach. The experimental determination of.. for SAMs of CP-AFM junctions fabricated using oligophenylene dithiols (OPDn, 1 <= n <= 4) and gold electrodes turned out to be too challenging. Recent measurements (Z. Xie et al, J. Am. Chem. Soc. 139 (2017) 5696) merely succeeded to provide a low bound estimate (E approximate to 58 GPa). Supplying this missing experimental information is the aim of the present theoretical investigation. Our microscopic calculations yield values E approximate to 240 +/- 6 GPa for the OPDn SAMs of the aforementioned experimental study, which are larger than those of steel (E approximate to 180 - 200 GPa) and silicon (E approximate to 130 - 185 GPa). The fact that the presently computed.. is much larger than the aforementioned experimental lower bound explain why experimentally measuring.. of OPDn SAM's is so challenging. Having E approximate to 337 +/- 8 GPa, OPDn SAMs with herringbone arrangement adsorbed on fcc (111)Au are even stiffer than Si 3N 4 (E approximate to 160 - 290 GPa).