Molecular behavior in the vibronic and excitonic properties of hydrogenated silicon nanoparticles

The molecular behavior of silicon nanoparticles, produced via electrochemical etching of a bulk precursor, is studied. The smallest particle, 1 nm in diameter, is amenable to first principles modeling due to the manageable number of atoms in the structure. The ability to produce these particles in macroscope amounts allows for the testing of these models through various optical techniques. Raman spectroscopy measurements, performed on 1 nm silicon nanoparticles suspended in liquid, were found to agree well with vibrational modes calculated using Hartree-Fock theory through the GAMESS package. The Raman peaks offer direct evidence of stretched Si-Si surface dimers in the reconstructed particle, which have been suggested to be the source of its blue luminescence. The peak positions and full widths at half maximum, along with calculations of the normal modes, suggest that the nanoparticle exhibits strong molecular behavior despite its derivation from a bulk structure. Low temperature photoluminescence measurements show the involvement of the dimers in the luminescence characteristics.