Effect of Continuous-to-Discontinuous Layer Transition on the Interface Evolution and Dielectric Response in...

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 (t_s) 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 t_s 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 t_s 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 (t_s ≈ 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 t_s 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.