Aluminum Adhesion Layers Improve Gold-Based Zero-Reflection Metasurfaces

By Dr. Noopur JainReviewed by Sarah KellyJun 25 2026

*Important notice: This news reports on an unedited version of an accepted paper and is awaiting final editing. Therefore, the paper should not be regarded as conclusive or treated as established information.

Aluminum (Al) has been identified as an effective adhesion layer for the preservation of both optical performance and mechanical stability in gold-based zero-reflection optical metasurfaces. These findings suggest that aluminum adhesion layers could support the development of more robust, sensitive biosensing and device integration. These findings were published in Communications Materials.

Adhesion Challenges in Metasurfaces

Zero-reflection optical metasurfaces based on gold metal-insulator-metal (MIM) architectures enable perfect light absorption, which is crucial for applications such as ultrasensitive biosensing and thermal emission control.

These structures, composed of thin metallic films or nanoantenna structures separated by dielectric spacers, achieve zero reflection through precise impedance matching and critical coupling. Gold is preferred for its plasmonic and chemical stability, but requires adhesion layers to ensure mechanical stability on dielectric substrates.

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Conventional adhesion materials such as titanium (Ti) and chromium (Cr) introduce significant optical losses, degrading resonance quality and shifting absorption features. Alternative low-loss materials like indium tin oxide (ITO) and oxide layers have been explored, yet they risk disrupting zero-reflection by acting as unintended dielectrics within MIM stacks.

Addressing this challenge, the study identifies aluminum, with its native oxide layer, as an optimal adhesion layer that provides mechanical robustness while preserving optical performance, offering a practical solution for high-performance, zero-reflection metasurfaces.

Fabrication and Characterization Techniques

The study systematically assessed the impact of adhesion layers on gold-based zero-reflection metasurfaces using experimental and computational methods in the near-infrared range. The model system featured a narrowband nanodisc antenna MIM perfect absorber composed of a 100 nm gold bottom reflector, a 40 nm SiO₂ spacer, and a top layer of 40 nm gold nanodiscs (180 nm diameter, 650 nm pitch) fabricated on silicon substrates.

Adhesion layers of aluminum, titanium, or indium tin oxide were deposited beneath the dielectric, below the nanodiscs, or both, at thicknesses of 2.5 or 5 nm.

Optical properties were characterized by reflection spectroscopy at normal incidence, with absorption calculated as A = 1-R, given the negligible transmission through the thick gold. Adhesion layer thicknesses were confirmed via atomic force microscopy.

Finite-difference time-domain (FDTD) simulations with periodic boundaries replicated the structures, using precise optical constants and incorporating native oxide layers on ultrathin Al and Ti films modeled as approximately 60%-oxidized stacks. This inclusion was critical for accurate resonance prediction.

Additional analyses included near-field intensity simulations at the gold/air interface, biosensing tests monitoring resonance shifts from protein A/G binding, and mechanical stability assessments under fluid flow and ultrasonic sonication, linking adhesion layer robustness to preserved optical performance [T3–T6, T8–T9].

Adhesion Layer Impact Analysis

The study revealed that adhesion layer placement critically affects metasurface optical performance, with bottom adhesion layers beneath the dielectric spacer causing significantly greater absorption losses and resonance degradation than layers below the top nanodiscs.

For instance, a 5 nm bottom Ti layer reduced absorption by over 10% and near-field enhancement by 80%, whereas top-layer adhesion caused an absorption loss of under 5%. This is due to the bottom interface’s pivotal role in impedance matching for perfect absorption.

Among the materials tested, aluminum with its native Al₂O₃ oxide exhibited minimal optical losses and preserved resonance near 700 nm by balancing metallic-induced blue shifts with oxide-induced red shifts.

Titanium layers degraded the resonance quality and increased damping due to their lossy metallic nature and TiO₂ formation. ITO’s effectiveness depended on deposition; oxygen-poor amorphous ITO behaved metallically, causing damping, while oxygen-rich films had better resonance but poorer mechanical stability compared to Al.

Near-field simulations showed 2.5 nm Al layers maintained near-field intensity comparable to adhesion-free structures, while Ti layers reduced it markedly. Biosensing with protein A/G confirmed higher resonance shifts (~2.84 nm) for Al versus Ti (~2.18 nm), reflecting superior sensitivity.

Mechanically, Al-based metasurfaces withstood harsh PBS flow and sonication without damage, unlike those without adhesion.

Overall, aluminum’s native oxide provides a favorable dielectric-metal balance that minimizes optical losses while ensuring robust adhesion, underscoring adhesion layer engineering as key to optimizing metasurface optical and mechanical performance.

Aluminum-Enabled Robust Metasurfaces

This study demonstrates that ultrathin aluminum adhesion layers with their native oxide are optimal for zero-reflection gold-based optical metasurfaces. Aluminum outperforms conventional materials like titanium and indium tin oxide by minimizing optical losses and preserving resonance quality, near-field enhancement, and reflection spectra similar to adhesion-free structures.

Achieving perfect absorption depends not only on the metasurface’s design but, crucially, on the optical and physical properties of adhesion layers. Aluminum’s unique dielectric-metal balance sustains impedance matching while ensuring strong mechanical bonding.

The interplay between metallic Al and insulating Al₂O₃ yields a stable resonance near 700 nm, ideal for near-infrared sensing. Combining optical modeling, experimental validation, and biosensing tests, this work provides a practical route to robust, high-performance zero-reflection metasurfaces and presents a promising strategy for durable, ultrasensitive optical and photonic devices.

Journal Reference

Koc, N., Belarouci, A., et al. (2026). Adhesion layer engineering for zero reflection optical metasurfaces. Communications Materials. https://www.nature.com/articles/s43246-026-01237-3.