Electronic and optical properties of agglomerated hydrogen terminated silicon nanoparticles

Abstract

Ab initio studies of silicon nanoparticles (NP) are ample in literature. We present the results of ab initio computations based on density functional theory (DFT) for the chemically interacting hydrogen terminated silicon (Si-H) NPs. This is considered to be the initial stage of agglomeration. Consequences of these combinations on the electronic and optical properties of the resulting cluster are discussed. The fully passivated Si-H NPs do not react with other NPs. The reaction is possible only between two NPs with one or more surface hydrogen being removed or replaced by other atom/molecule. Variety of bonding configurations are observed. An electron deficient three way bonding for oxygen is observed when OH replacing H on one NP interacts with dangling bond on the other NP. The reactions between NPs are sensitive to the presence of unpaired electrons on the dangling bonds. The defects introduce energy levels within the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of the NPs. The combination of these NPs lead to a band of defect states within the HOMO-LUMO gap. The presence of such states is detected through scanning tunnelling spectroscopy. Our experimental results support such a scenario. The absorption optical spectra of individual NPs shows detectable changes after two NPs react.