Electronic characteristics of PbS quantum dots passivated by halides on different surfaces

Abstract

The electron properties of PbS quantum dots (QDs) with different halogens passivation on different surfaces were studied by first principle calculation. The relaxation analysis showed that the vertical direction of the surface is the main relaxation direction for the PbS QDs surface. Energy analysis shows that the greater the surface energy induces higher adsorption energy. The positive adsorption energy implies that all adsorption models are exothermic and thermodynamically stable. Compared with the I atom with larger atomic number, the F atom with smaller atomic number releases more heat after adsorption on the surface, which makes the reaction easier. The energy level shift results suggest that the vacuum energy level has shifted, leading to the PbS band edge shift. The investigations dealing with the partial density of states (PDOS) show that trap state energy levels could be observed in the bandgap of PbS (110). Furthermore, with the smaller atomic number and more serious the orbital localization, more energy levels are introduced into the bandgap. It can be seen from the differential charge distribution that the S-I, I-I and Pb-I covalent bonds are formed on PbS(100), PbS(110) and PbS(111) respectively.