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Abstract
Rapid progress in the performance of organic devices has increased the demand for advances in the technology of thin-film permeation barriers and understanding the failure mechanisms of these material systems. Herein, we report the extensive study of mechanical and gas barrier properties of Al2O3/ZnO nanolaminate films prepared on organic substrates by atomic layer deposition (ALD). Nanolaminates of Al2O3/ZnO and single compound films of around 250 nm thickness were deposited on polyethylene terephthalate (PET) foils by ALD at 90 °C using trimethylaluminium (TMA) and diethylzinc (DEZ) as precursors and H2O as the co-reactant. STEM analysis of the nanolaminate structure revealed that steady-state film growth on PET is achieved after about 60 ALD cycles. Uniaxial tensile strain experiments revealed superior fracture and adhesive properties of single ZnO films versus the single Al2O3 film, as well as versus their nanolaminates. The superior mechanical performance of ZnO was linked to the absence of a roughly 500 to 900 nm thick sub-surface growth observed for single Al2O3 films as well as for the nanolaminates starting with an Al2O3 initial layer on PET. In contrast, the gas permeability of the nanolaminate coatings on PET was measured to be 9.4 × 10−3 O2 cm3 m−2 day−1. This is an order of magnitude less than their constituting single oxides, which opens prospects for their applications as gas barrier layers for organic electronics and food and drug packaging industries. Direct interdependency between the gas barrier and the mechanical properties was not established enabling independent tailoring of these properties for mechanically rigid and impermeable thin film coatings.
Highlights
The growing performance and use of organic devices has required the development of efficient and ultra-thin gas barrier layers with adequate mechanical properties
The exceptional thickness control, and the excellent uniformity and high conformality allowed by atomic layer deposition (ALD), enabled this route to emerge as a key technology for the deposition of thin films for numerous applications, from microelectronics [2] to photovoltaics [3], and from biosensing [4] to membranes [5]
The results show that the critical tensile strain is higher for thinner thicknesses of the Al2 O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates
Summary
The growing performance and use of organic devices has required the development of efficient and ultra-thin gas barrier layers with adequate mechanical properties. Nanomaterials 2019, 9, 88 a vapor phase deposition technique, is suited for the preparation of ultrathin films of inorganic materials with sub-nanometer thickness control [1]. It is based on sequential pulses of precursors and co-reactants within the reactor chamber, enabling for self-limiting chemical reactions to take place at the substrate surface. The exceptional thickness control, and the excellent uniformity and high conformality allowed by ALD, enabled this route to emerge as a key technology for the deposition of thin films for numerous applications, from microelectronics [2] to photovoltaics [3], and from biosensing [4] to membranes [5]. ALD films are very attractive candidates as gas barrier layers due to the conformal nature of the films on non-planar surface topographies [6]
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