Reaction of Bis(pinacolato)diboron with H-Si(100): The Pursuit of On-surface Hydrosilane Borylation Reactions
2021
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-2 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, B2Pin2 and catalyst. The reaction complexity indicates that radical initiating catalysts are not benign in surface chemistry systems.
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