Thermal grafting of aniline derivatives to silicon (1 1 1) hydride surfaces

Abstract

Through a series of aniline derivatives with para-substituents possessing different electron donating/withdrawing characteristics, we examined the nature of thermal grafting of these nucleophilic anilines onto planar Silicon (111) surfaces via detailed XPS and AFM analysis. Based on our current results, para-positioned electron withdrawing group (4-Trifluoromethylaniline) would draw electron density away from the nucleophilic NH2 site which consequently reduces surface grafting. We also concluded that para-positioned halide (Cl and Br) may produce inductive effect that significantly reduces nucleophilic grafting of the NH2 to the silicon hydride while their bulky distal groups may further limited packing density on the surface. On the other hand, 1,3-diaminopropane (control) as well as Phenylenediamine were found to be highly reactive to the surface due to high electron density confinement at the NH2 groups. Furthermore, grafting of aromatic phenylenediamine was observed to have significantly lowered the underlying Si-Si back bonding lysis. Our results and proposed mechanisms were complemented by AFM surface interrogation, contact angle measurements, ATR-FTIR as well as DFT optimized electrostatic potential presentation. Herein, this study presents an in-depth view on molecular grafting through deliberate modulation of the electron density distribution around aromatic system and this may present an important insight towards producing useful bifunctional monolayers.