Silicon particles are created via anodic or platinum catalyzed etching of bulk
silicon. A peroxide and HF etchant provides uniform surface termination, and
results in discrete stable sizes for particles below 3 nm in size. The smallest
of these are 1 nm silicon particles, which is amenable to rst principles quan-
tum calculations of the structure, electronic levels, and ionic interactions.
The vibrational modes of several candidate structures of the 1 nm particles
are calculated at the Hartree-Fock level, and compared to previously acquired
Raman spectra to determine the structure. The vibrational modes are also
compared to the vibrational structure in low temperature photo-luminescence
to indicate surface reconstruction bonds play a role in the
uorescence. The
uorescence mechanism is explored further with calculations of the excited
state potential energy surface using time dependent density functional theory,
which show radiative traps accessible via direct excitation at the band edge
of the ground state geometry. The self-trapped excitons proposed by Lannoo
et al. [1, 2] are found to be unstable for the Si29H24 structure, with the
outer-well leading to non-radiative recombination via conical intersection of
the excited state with the ground state. Absorption measurements indicate
the silicon nanoparticles may form charge complexes with iron ions in aque-
ous solutions. Calculations including solvation e ects provide a proposed
structure for the complex, with a binding energy of 0.49 eV. The binding
mechanism is quite general and suggests many other ions could form charge
complexes with the silicon particles in aqueous solutions, potentially leading
to new applications
