Reaction of Bis(pinacolato)diboron with H-Si(100): The Pursuit of On-surface Hydrosilane Borylation Reactions

Abstract

On-surface solution phase chemical reactions, which are inherently amenable to scale-up, provide a pathway towards overcoming challenges present in gas phase processes for ultradoping of Si, a process that introduces unprecedented concentration of dopant. Ultradoping, which can only be achieved with a direct chemical bond between dopant and Si, fundamentally changes the electronic properties of Si, making it a promising next-generation electronic material. Traditional processes for solvent-based chemical functionalization attach species to the Si surface through carbon or oxygen linkers, which limits activated dopant density. This prevents solution phase chemistry from being useful for applications involving ultradoped Si. Recent work has focused on forming a direct on-surface Si-dopant bond to provide a scalable ultra-doping pathway. In this work, we expand upon that goal by demonstrating that well-known homogeneous chemistries can be usefully applied to surface reactions for ultradoping Si. By adapting a hydrosilane borylation reaction used to synthesize silyl boranes into a surface chemistry reaction, we successfully incorporate 1.3e14 cm<sup>-2 </sup>B using scalable on-surface solvent based chemistry. This density is high enough to produce the overlap of dopant wavefunctions required for achieving unprecedented conductivity in Si. Using computational studies, performed with the assumption that catalyst interaction was negligible, we predict the reaction straightforwardly occurs through a Si-B bond. However, with extensive experimental characterization including infrared spectroscopy, x-ray photoelectron spectroscopy, and secondary ion mass spectroscopy we elucidate cross-reactivity between the substrate, B<sub>2</sub>Pin<sub>2</sub> and catalyst. The reaction complexity indicates that radical initiating catalysts are not benign in surface chemistry systems.