Factors influencing the distribution of charge in polar nanocrystals

TL;DR

This study uses first-principles calculations to investigate how surface termination influences charge distribution and dipole moments in polar GaAs nanorods, revealing mechanisms that can be used to tune nanocrystal properties.

Contribution

It identifies how surface termination controls dipole moments and charge distribution in polar nanocrystals, independent of spontaneous polarization.

Findings

Dipole moment direction and magnitude depend on surface termination.

Excess charge at nanorod ends is not strongly localized.

Surface termination mechanisms influence nanocrystal properties.

Abstract

We perform first-principles calculations of wurtzite GaAs nanorods to explore the factors determining charge distributions in polar nanostructures. We show that both the direction and magnitude of the dipole moment $\mathbf{d}$ of a nanorod, and its electic field, depend sensitively on how its surfaces are terminated and do not depend strongly on the spontaneous polarization of the underlying lattice. We identify two physical mechanisms by which $\mathbf{d}$ is controlled by the surface termination, and we show that the excess charge on the nanorod ends is not strongly localized. We discuss the implications of these results for tuning nanocrystal properties, and for their growth and assembly.