Giant conductivity switching of LaAlO3/SrTiO3 heterointerfaces governed by surface protonation.

Keith A Brown,Hyungwoo Lee,Mengchen Huang,Daniel J Eichelsdoerfer,Shu He,Patrick Irvin,Jose Mendez-Arroyo,Ishan Levy,Sangwoo Ryu,Chang-Beom Eom,Jeremy Levy,Chad A Mirkin

doi:10.1038/ncomms10681

Abstract

Complex-oxide interfaces host a diversity of phenomena not present in traditional semiconductor heterostructures. Despite intense interest, many basic questions remain about the mechanisms that give rise to interfacial conductivity and the role of surface chemistry in dictating these properties. Here we demonstrate a fully reversible >4 order of magnitude conductance change at LaAlO3/SrTiO3 (LAO/STO) interfaces, regulated by LAO surface protonation. Nominally conductive interfaces are rendered insulating by solvent immersion, which deprotonates the hydroxylated LAO surface; interface conductivity is restored by exposure to light, which induces reprotonation via photocatalytic oxidation of adsorbed water. The proposed mechanisms are supported by a coordinated series of electrical measurements, optical/solvent exposures, and X-ray photoelectron spectroscopy. This intimate connection between LAO surface chemistry and LAO/STO interface physics bears far-reaching implications for reconfigurable oxide nanoelectronics and raises the possibility of novel applications in which electronic properties of these materials can be locally tuned using synthetic chemistry.

Highlights

Complex-oxide interfaces host a diversity of phenomena not present in traditional semiconductor heterostructures
X-ray photoelectron spectroscopy (XPS) and solvent immersions, we find that LAO/STO conductivity is correlated with the protonation of the LAO surface
R increased by 44 orders of magnitude over the 3 total minutes of immersion. This insulating state was stable in the dark under ambient conditions (Supplementary Fig. 2), measurements of R following sequential 15 s exposures to broadband light revealed a decrease in R commensurate with the solvent-driven increase (Fig. 1b—right)

Summary

Introduction

Complex-oxide interfaces host a diversity of phenomena not present in traditional semiconductor heterostructures. The proposed mechanisms are supported by a coordinated series of electrical measurements, optical/solvent exposures, and X-ray photoelectron spectroscopy This intimate connection between LAO surface chemistry and LAO/STO interface physics bears far-reaching implications for reconfigurable oxide nanoelectronics and raises the possibility of novel applications in which electronic properties of these materials can be locally tuned using synthetic chemistry. By immersing the samples in various solutions including different pH aqueous solutions, solvents with a range of pKa, and solutions of molecules that function as proton sponges, we find that a solvent’s ability to render the LAO/STO layer insulating is dictated by its ability to deprotonate the LAO surface Based on these results, we propose a model in which LAO surface protonation dictates the electronic state of the LAO/STO interface. We find that the conductive state can be directly patterned by illuminating selected regions of the LAO/STO surface, suggesting a future method for realizing reconfigurable electronics based upon LAO/STO interfaces

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Results

Conclusion