On the role of micro-porosity in affecting the environmental stability of atomic/molecular layer deposited (ZnO)a(Zn–O–C6H4–O)b films

Abstract

Atomic/molecular layer deposited (ALD/MLD) inorganic–organic thin films form a novel class of materials with tunable properties. In selected cases, hybrid materials are reported to show environmental instability, specifically towards moisture. In this article, we focus on zinc oxide/zincone multi-layers with the theoretical formula of (ZnO)_a(Zn–O–C₆H₄–O)_b. We show by means of ellipsometric porosimetry that micro-porosity in the range of 0.42 and 2 nm in the pristine zincone layer is responsible for its environmental degradation. During degradation, it is found that a relative micro-porosity content of 1.2 ± 0.1 vol% in the pristine zincone films evolves into micro-mesoporosity with a relative content of 39 ± 1 vol%. We also show that the micro-porosity in the zincone layer can be gradually suppressed when few cycles (a = 1–10) of ZnO are introduced. The resulting (ZnO)_a(Zn–O–C₆H₄–O)_{b = 1} periodic multilayer is an environmentally stable film with a = 10. It is found that the suppressed micro-porosity is due to the development of continuous ZnO layers with a ≥ 10.