posted on 2021-08-03, 15:45authored byYulun Han, Kweeni Iduoku, Gena Grant, Bakhtiyor Rasulev, Alexey Leontyev, Erik K. Hobbie, Sergei Tretiak, Svetlana V. Kilina, Dmitri S. Kilin
We provide a case-study for thermal
grafting of benzenediazonium
bromide onto a hydrogenated Si(111) surface using ab initio molecular dynamics (AIMD) calculations. A sequence of reaction steps
is identified in the AIMD trajectory, including the loss of N2 from the diazonium salt, proton transfer from the surface
to the bromide ion that eliminates HBr, and deposition of the phenyl
group onto the surface. We next assess the influence of the phenyl
groups on photophysics of hydrogen-terminated Si(111) slabs. The nonadiabatic
couplings necessary for a description of the excited-state dynamics
are calculated by combining ab initio electronic
structures and reduced density matrix formalism with Redfield theory.
The phenyl-terminated slab shows reduced nonradiative relaxation and
recombination rates of hot charge carriers in comparison with the
hydrogen-terminated slab. Altogether, our results provide atomistic
insights revealing that (i) the diazonium salt thermally decomposes
at the surface allowing the formation of covalently bonded phenyl
group, and (ii) the coverage of phenyl groups on the surface slows
down charge carrier cooling driven by electron–phonon interactions,
which increases photoluminescence efficiency at the near-infrared
spectral region.