Single-atom dopants in silicon have been a topic of high interest since the Kane quantum computer was first proposed in 1998. Much work has since been dedicated toward the single-atom doping of lighter group 15 atoms into silicon with atomic-scale precision, with notable success, though significantly less toward heavier dopant atoms owing to the lack of readily available precursor molecules. This thesis investigates two novel potential precursor molecules for atomic bismuth: triphenylbismuth (TPB) and bismuth trichloride (BiCl3). Bismuth is a promising heavy dopant species in silicon-based electronic devices thanks to its high quantum information storage capacity, but currently lacks a suitable precursor. Neither of these molecules has previously been studied on the Si(100) surface.
Using scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we demonstrate that TPB partially dissociates on Si(100) at room temperature, with bismuth atoms forming ad-dimers while phenyl remains on the surface. Annealing the surface causes complete molecular dissociation, followed by bismuth diffusion into the bulk. Phenyl desorption is not observed. We show that prior to dissociation, TPB bonds to the surface in a variety of configurations; using density functional theory calculations, we propose favorable bonding structures for the TPB molecule on Si(100).
We also show that BiCl3, contrastingly, undergoes complete and spontaneous dissociation on Si(100) at room temperature, with some bismuth atoms forming ad-dimers while others remain as monomers constrained by adjacent chlorine atoms. We pro- pose key steps in the reaction pathway for room-temperature BiCl3 dissociation. We also demonstrate the molecule’s post-dissociation chemical behavior on Si(100) at higher temperatures, at varying levels of surface coverage. Our results demonstrate that BiCl3 is a promising candidate for a single-atom bismuth precursor, while TPB is less likely to be suitable. In combination with chlorine lithography, this paves the way for single-atom doping of bismuth in silicon devices
