Effect of surface modification of hydrophilic organic molecules on the energy gap of Si nanoparticles

Abstract The effects of surface modification with hydrophilic molecules on the electronic structure of silicon nanoclusters were investigated by using density functional theory (DFT), with the aim of tuning the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap for potential bio-labeling applications. We performed DFT calculations performed on Si 10 , Si 39 , and Si 62 clusters terminated with representative acids like propionic and fumaric acid. Results revealed that while most acids caused only minor HOMO-LUMO gap reductions, fumaric acid termination led to a markedly greater reduction. This is attributed to a significant lowering of the LUMO energy level via interaction with its conjugated π-system. This effect was consistently observed and largely independent of the Si cluster size or number of attached fumaric acid molecules. These findings suggest this is a highly promising strategy for enabling the long-wavelength emission required for advanced applications.