Large electropositive cations as surfactants for the growth of polar epitaxial films

TL;DR

This study uses density functional theory to show that large electropositive cations like potassium and cesium can facilitate the epitaxial growth of polar LaAlO3 on SrTiO3 by stabilizing the interface and promoting electron transfer, offering a new growth method.

Contribution

It introduces a novel approach for growing polar epitaxial films using large alkali metal cations to stabilize interfaces and control electronic properties.

Findings

Large cations remain adsorbed on the surface during growth.

Potassium transfer electrons to the substrate, forming a 2D electron gas.

This method enables clean LAO/STO interface fabrication.

Abstract

Using density functional theory (DFT) we demonstrate that the adsorption of large cations such as potassium or cesium facilitates the epitaxial growth of polar LaAlO$_3$ (LAO) on SrTiO$_3$ (STO). The low ionization potential of K favors efficient electron transfer to the STO conduction band and results in a 2D electron gas which exactly compensates for the diverging potential with increasing layer thickness. For large cations like K or Cs, DFT total energy considerations show that they remain adsorbed on the LAO surface and do not enter substitutionally into LAO. These results suggest a novel scheme for growing clean LAO/STO interface systems, and polar systems in general, by performing the growth process in the presence of large, low ionization potential alkali metal ions.