Tuning Optical Properties of Al₂O₃/ZnO Nanolaminates Synthesized by Atomic Layer Deposition

Abstract

Nanolaminates are of great interest for their unique properties such as high dielectric constants and advanced mechanical, electrical, and optical properties. Here we report on the tuning of optical and structural properties of Al 2 O 3 /ZnO nanolaminates designed by atomic layer deposition (ALD). Structural properties of nanolaminates were studied by SEM, GIXRD, and AFM. Optical characterization was performed by transmittance and photoluminescence (PL) spectroscopy. Complex study of monolayer properties was performed by ellipsometry. Optical constants for Al 2 O 3 and ZnO monolayer were calculated. The band gap of ZnO single layers and the excitonic PL peak position were shifted to the UV region related to quantum confinement effects. No peaks in the UV region were observed in nanolaminates with 2 nm ZnO single layer thickness due to fully depleted region in small crystalline grains (<2 nm). The improved room temperature photoluminescence of nanolaminates makes them prominent materials for optical biosensors applications.

An innovative approach for the preparation of confined ZIF-8 membranes by conversion of ZnO ALD layers

“…The amount of the deposited ZnO has been directed by the number of ZnO cycles. The growth rate of ZnO on Al 2 O 3 is 0.2 nm per cycle as it has been determined elsewhere [21,26]. It was verified by measuring the thickness of ZnO deposited on Si/Al 2 O 3 wafers placed in the reactor.…”

“…The selected pulse, exposure and purge times were chosen both to ensure completion of the ALD surface reactions and to prevent mixing of the reactive species. The growth rate was typically 0.2 nm/cycle [21,25,26]. ZnO films with different thicknesses (5, 10, 30 and 50 nm) have been deposited in order to study their conversion to ZIF-8.…”

“…The growth per cycle for ZnO layer (ZnO thickness) has been controlled by deposited ZnO on Si/Al 2 O 3 substrates as reported elsewhere [21].…”

“…The ZnO layer serves as a unique zinc source which is subsequently converted to a confined ZIF-8 material during the solvothermal synthesis. In fact, the ALD provides significant advantage over other types of "reactive seeding" methods thanks to its atom-by-atom deposition mechanism enabling homogeneous ultra-thin coverage of high surface area materials with different chemical compositions [21][22][23]. The "eco-friendly" character of the proposed synthesis protocol bears on both the possible capturing of harmful by-products and gas recycling during ALD deposition of ZnO, followed by potential repetitive reutilization of the Zn-free solution used for growing ZIF-8 by a solvothermal treatment.…”

Effects of rapid thermal annealing on properties of HfAlO films directly deposited by ALD on graphene

“…4b, HfAlO on graphene had an absorption edge in the ultra-violet region while it was transparent in the visible light region. Both refractive index and absorption coefficients were related to the microstructure of HfAlO films [18][19][20]. After post-RTA, no obvious changes of refractive index or absorption coefficients were detected, indicating HfAlO maintained amorphous during the RTA process.…”