Strain-Stabilized Interfacial Polarization Enables >1 eV Work-Function Tuning in RuO2/TiO2 Heterostructures

Researchers at the University of Minnesota Twin Cities showed that ruthenium dioxide (RuO2) films on titanium dioxide (TiO2) sustain interfacial polarization, allowing the surface work function to be tuned by over 1 eV when the RuO2 thickness is near 4 nm. Strain-induced lattice distortions create electric dipoles at the interface, providing a controllable “knob” for metallic electronic properties. Published in *Nature Communications* (9 Feb 2026).

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Metals are thought to screen internal electric fields, preventing stable polarization, which is typical of insulators and ferroelectrics. Theory has suggested “polar metals,” but experimental evidence has been scarce. The present work demonstrates that interface strain can generate a polar state in a conductor.

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When RuO2 layers are thinner than ~4 nm, the work function rises by more than 1 eV; above this thickness the value drops as the film relaxes. The 4 nm critical thickness corresponds to the diameter of a DNA strand. Multislice electron ptychography reveals picometre-scale ion displacements and interfacial dipoles only in the strained regime. Precise work-function control is vital for charge injection in transistors, catalytic electron transfer, and quantum devices. Achieving >1 eV shifts without surface chemistry offers a scalable design knob for semiconductor contacts, electrocatalysts, and buried-interface architectures, though integration of ultrathin layers remains challenging.

A Four-Nanometre Sweet Spot Lets Scientists Reprogram How Metals Handle Electricity

Jalan said the work “challenges the traditional notion that polarization is incompatible with metals.” Jeong noted the work-function shift “defied our expectations,” highlighting its unexpected magnitude.

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Analysts point out the effect is strongest only below 4 nm, a scale hard to integrate, and that it has been demonstrated for a single metal-oxide pair, leaving broader applicability uncertain.

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All sources agree on the >1 eV shift; the main gap is data on other systems and long-term stability.

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• “We anticipated modest interface-induced changes, but observing such a robust and tunable shift in work function defied our expectations,” — Seung Gyo Jeong, lead researcher

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• “We often think of polarization as something that belongs to insulators or ferroelectrics—not metals,” — Bharat Jalan, Shell Chair, University of Minnesota

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• “Our work shows that, through careful interface design, you can stabilize polarization in a metallic system and use it as a knob to tune electronic properties. This opens an entirely new way of thinking about controlling metals.” — Bharat Jalan, Shell Chair, University of Minnesota

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• “We expected subtle interface effects, but not such a large and controllable change in work function.” — Seung Gyo Jeong, first author

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The team will explore other metal/oxide heterostructures, assess durability, and test buried-interface integration.

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