Thermal and plasma-enhanced ALD for the synthesis of inverse opal Al2O3 and its composite materials

Abstract

This study explores the synthesis and characterization of inverse opal photonic crystals (IOPC) composed of Al₂O₃ and its composites, coated with ultra-thin ZnO and TiO₂ layers using thermal atomic layer deposition (TALD) and plasma-enhanced ALD (PEALD). Polystyrene (PS) opal nanospheres (460 nm) served as a template on a silicon wafer. Al₂O₃ was infiltrated into a PS opal template and subsequently calcined to remove the template. Ultra-thin ZnO and TiO₂ layers were deposited via TALD/PEALD to form composite IOPCs. Characterization by SEM/EDX, TG, UV–Vis spectroscopy, atomic force microscopy (AFM), photoluminescence (PL), and XPS confirmed the periodic, interconnected IO structures. The Al₂O₃ IOPC demonstrated template removal and a reduced sphere diameter to ∼433 nm. Composite structures-maintained periodicity, with TALD yielding smoother surfaces compared to PEALD. The incorporation of ZnO and TiO₂ layers increased surface roughness. UV–Vis spectroscopy revealed absorption peaks at 275 nm for Al₂O₃, with additional peaks at 400 nm and 529 nm related to the photonic band gap and slow photon effects. XPS analysis reveals characteristic peaks for Al₂O₃, ZnO, and TiO₂, along with oxygen vacancies and aluminum hydroxide formation, while elemental data highlight successful ZnO and TiO₂ incorporation with PEALD outperforming TALD in ZnO deposition. In this study PEALD enhanced film growth and tailored properties, while TALD offered smooth, conformal coatings and precise control over IOPC properties, both contributing to the design of advanced IO-based photonic materials.