The role of nanodefects in gas barrier layers

The performance of gas barrier layers for applications, for example, in flexible optoelectronics, depend upon the defects in the barrier layer through which the permeant passes.  This paper explores the understanding of both microscopic defects, but also nano-defects that are not directly resolvable either by microscopy or by calcium test.  In particular, examples are presented of sputtered AlOx barrier layers in which a significant proportion of the permeation is through nanodefect populations, as signified by an increase in the activation energy of water vapour transport above that of the substrate polymer.  Often, an increase in activation energy has been associated with a decrease in population of the larger defects (and hence a decrease in overall permeation) but effects such as substrate interactions and process conditions can give rise to changes in the character and population of nanodefects giving rise to cases in which decreased permeation can be associated with an increase in activation energy.  As materials with high barrier properties are further developed, this understanding of the role of nanodefect populations will be crucial to the further progress in the field.