Structural Phases of Alkanethiolate Self-Assembled Monolayers (C1-12) on Cu[100] by Density Functional Theory

The structure and as such the properties of alkanethiolate self-assembled monolayers (SAMs) on metal surfaces depend on the surface structure, thiolate coverage and chain length. The chain length dependence of alkanethiolate phases on Au surfaces is extensively documented. Much less insight exists for alkanethiolate SAMs on Cu surfaces, despite the relevance for area-selective deposition (ASD) applications. This work therefore studies the phase behavior of alkanethiolates on Cu through density functional theory (DFT) modelling. Short chain thiolates (C1,2) display no phase behavior and their saturation coverage is determined by steric hindrance. Longer thiolates (C6,12) show distinct lying-down and standing-up phases. The substrate-adsorbate interactions become weaker with increasing thiolate content, but still dominate in the standing-up phase at the saturation content of 5.1∙1014 thiolates∙cm-2. This is in contrast to Au[100] surfaces, where intermolecular interactions dominate at the saturation content...