Effects of surface termination on the band gap of ultrabrightSi29nanoparticles: Experiments and computational models

A ${\mathrm{Si}}_{29}{\mathrm{H}}_{24}$ particle, with five atoms constituting a tetrahedral core and 24 atoms constituting a H-terminated reconstructed Si surface was recently proposed as a structural prototype of ultrasmall ultrabright particles prepared by electrochemical dispersion from bulk Si. We replace the H termination with a N linkage (in butylamine) and O linkage (in pentane). The emission band for N-termination downshifts by ∼0.25 eV from that of H termination, whereas it blueshift ∼0.070 eV for C termination. We use density-functional approaches to calculate the atomic structures and correction from the quantum Monte Carlo method to estimate the highest occupied–lowest unoccupied molecular-orbital band gap. We find a downshift of 0.25 eV for N termination and very little for C termination. These features are discussed in terms of exciton penetration in the capping material.