Disordered plasmonic nanocavity for entropy embedded structural color

Abstract

Engineering nanoscale disorder with high information density is essential for next-generation optical security systems, particularly for physically unclonable functions (PUFs) that rely on intrinsic randomness to generate unique and irreproducible keys [1]. However, conventional approaches for embedding such entropy, including chemical vapor deposition and crystal growth, offer limited control over correlation length and spatial entropy distribution, restricting achievable information density. To address this, we demonstrate a physically engineered short- range disordered plasmonic nanocavity using glancing angle deposition (GLAD) technique [2]. The structure consists of a Cu mirror, an HfO₂ dielectric gap layer (~20 nm), randomly distributed Cu nanoparticles, and an HfO₂ capping layer, where stochastic nanoparticle distributions are directly embedded into the cavity resonance. Notably, the capping layer thickness enables independent tuning of reflective color without degrading entropy. Compared to conventional methods, the system achieves a shorter correlation length (~44 nm) and higher surface coverage (~49.5%), enabling dense information encoding with over 800 PUF keys and ~5.3 × 10⁷ bits per mm², along with strong security performance (bit uniformity of 0.505 and inter-Hamming distance of 0.492 ± 0.008).