Tail effect on trihydroxysilanes dimerization: A dispersion-corrected density functional theory study

We present Density Functional Theory calculations on the intrinsic arrangement capabilities of Self Assembled Monolayers (SAMs) at the light of tail effects: nature of end groups and alkyl chain length. We show that in the second case London interactions are critical for a realistic description of SAM behavior. We have further analyzed the influence of polar end groups in structuring the deposited layers by investigating five terminations: propyl, bromopropyl, mercaptopropyl, acetoxyethyl and aminopropyl. The examination of the effect of alkyl chain has allowed a better understanding of the experimental results. We establish, in particular, that chain lengths from C18 and over can lead to well ordered SAMs, in terms of parallelism of grafted molecules and uniformity of substrate coverage, in agreement with experimental observations. Finally, using thermodynamic and kinetic arguments, we discuss the nature of possible defects in the investigated layers.