Strain-Stabilized Interfacial Polarization Tunes Work Function Over 1 eV in RuO2/TiO2 Heterostructures

TL;DR

This study demonstrates that interfacial polarization in RuO2/TiO2 heterostructures can significantly modulate the metal's work function by over 1 eV, revealing a new method to control electronic properties in metallic systems.

Contribution

It reveals that interfacial polarization can be used to tune the work function of metals, a concept previously explored mainly in semiconductors, using advanced imaging and measurement techniques.

Findings

Over 1 eV work function modulation achieved

Polar displacements visualized near the interface

Critical thickness of 4 nm for polarization transition

Abstract

Interfacial polarization-charge accumulation at the heterointerface-is a well-established tool in semiconductors, but its influence in metals remains unexplored. Here, we demonstrate that interfacial polarization can robustly modulate surface work function in metallic rutile RuO2 layers in epitaxial RuO2/TiO2 heterostructures grown by hybrid molecular beam epitaxy. Using multislice electron ptychography, we directly visualize polar displacements of transition metal ions relative to oxygen octahedra near the interface, despite the conductive nature of RuO2. This interfacial polarization enables over 1 eV modulation of the RuO2 work function, controlled by small thickness variation (2-4 nm) as measured by Kelvin probe probe microscopy, with a critical thickness of 4 nm - corresponding to the transition from fully strained to relaxed film. These results establish interfacial polarization as a powerful route to control electronic properties in metals and have implications for designing tunable electronic, catalytic, and quantum devices through interfacial control in polar metallic systems.