Systematic spatial and stoichiometric screening towards understanding the surface of ultrasmall oxygenated silicon nanocrystal

TL;DR

This study uses density functional theory to systematically analyze how different oxygen bonding configurations on silicon nanocrystals affect their electronic properties and stability, revealing significant impacts of surface oxidation.

Contribution

It provides a comprehensive theoretical analysis of various oxygen bonding modes on silicon nanocrystals, highlighting their effects on electronic structure and stability, which was previously underexplored.

Findings

Bridge-bonded oxygen nanocrystals have higher binding energies.

Oxygen configurations significantly alter HOMO-LUMO gaps.

Presence of hydroxyl groups further reduces electronic gaps.

Abstract

In most of the realistic ab initio and model calculations which have appeared on the emission of light from Si nanocrystals, the role of surface oxygen has been usually ignored, underestimated or completely ruled out. We investigate theoretically, by density functional theory (DFT/B3LYP) possible modes of oxygen bonding in hydrogen terminated silicon quantum dots using as a representative case of the Si29 nanocrystal. We have considered Bridge-bonded oxygen (BBO), Doubly-bonded oxygen (DBO), hydroxyl (OH) and Mix of these oxidizing agents. Due to stoichiometry, all comparisons performed are unbiased with respect to composition whereas spatial distribution of oxygen species pointed out drastic change in electronic and cohesive characteristics of nanocrytals. From an overall perspective of this study, it is shown that bridge bonded oxygenated nanocrystals accompanied by Mix have higher binding energies and large electronic gap compared to nanocrystals with doubly bonded oxygen atoms. In addition, it is observed that the presence of OH along with BBO, DBO and mixed configurations further lowers electronic gaps and binding energies and trends. It is also demonstrated that oxidizing constituent besides their spatial distribution significantly alters binding energy and highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap (HOMO-LUMO gap up to 1.48 eV) within same composition.