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We investigate the impact of the substrate on the structural properties andthe morphology of alkanethiol self-assembled monolayers (SAMs) on gold, usingfirst principles calculations and atomistic molecular dynamics simulations. Weconsider hexadecanethiols on Au(211), Au(221) and Au(311) surfaces whichcontain few-atom wide terraces separated by monoatomic steps similar to thecomplex Au surfaces used in experiments. The structure of the SAMs is probedvia several structural properties including tilt angles, mean C atom heightsfrom the surface, precession angles, gauche defects, gyration tensors andrelative shape anisotropy. Comparing these properties to those of thewell-studied SAMs on Au(111), we observe similarities but also strikingdifferences. A clear order to disorder transition is observed by changing thesubstrate: well-ordered SAMs on (111) and (211) surfaces become mixedordered-disordered structures on (311) and fully disordered on (221). Thepresence of steps on the Au surfaces also results in preferential tiltorientations with long-range order. Our results show that in addition to theexpected grafting density dependence, the transition from order to disordercrucially depends on substrate morphology. The onset of ordering behavior isrelated to the atomic structure of the surface. The key parameter that affectslong-range order is the energy for changing the dihedral angle betweenAu-S-$\mathrm{C^{(1)}-C^{(2)}}$ of the adsorbed alkanethiol.

From Order to Disorder of Alkanethiol SAMs on Complex Au (211), (221) and (311) Surfaces: Impact of the Substrate