Effect of Continuous-to-Discontinuous Layer Transition on the Interface Evolution and Dielectric Response in Subnanometric Al2O3/TiO2 Laminates Grown by Atomic Layer Deposition.

Recently, Al2O3/TiO2 nanolaminates (ATA NLs) have emerged as promising materials because of their excellent optical, mechanical, and dielectric properties. However, as individual sublayer thicknesses (ts) decrease into the subnanometer range, the impact of interfacial structure evolution on performance degradation remains poorly understood. Here, we have fabricated a series of amorphous subnanometric ATA NLs, with ts values ranging from ∼1 to 0.17 nm, using atomic layer deposition (ALD) and systematically investigated how interfacial evolution affects their structural, electronic, and dielectric properties, particularly their Maxwell-Wagner (M-W) relaxation behavior. The XRR and TEM measurements of NLs confirm the formation of artificial periodic structures with discrete sublayers as thin as ∼0.67 nm. The NL with a ts of  0.67 nm exhibited enhanced M-W interfacial polarization-assisted high k (∼230) and low loss (∼0.07) values, whereas the submonolayer systems suffered from degraded dielectric performance. A comprehensive suite of characterization techniques revealed a critical transition in interface morphology, sublayer density, interface chemistry, and functionality in dielectric behavior near the monolayer thickness regime (ts ≈ 0.35 nm), marking a transition from continuous-to-discontinuous layer growth with an increased level of intermixing. Electronic structure analyses revealed an associated redistribution of Ti3+ and oxygen vacancy-induced in-gap states and strong interfacial interdiffusion-driven Al-Ti-O compound formation in the submonolayer regime. These chemical changes from the hybridized electronic environments detrimentally affect dielectric properties due to compromised interfacial confinement. These findings establish a ts of ≈0.35 nm as the practical lower bound for maintaining atomically discrete oxide layers, underscoring the pivotal role of nanoscale interface engineering and defect control in optimizing dielectric behavior in ultrathin oxide heterostructure-based devices.