Growth and structure of hyperthin SiO2 coatings on polymers

Abstract

Transparent inorganic oxide coatings on polymers are playing an increasingly important role in pharmaceutical, food, and beverage packaging, and more recently in encapsulation of organic, light-emitting display devices. Such coatings are being prepared by physical or by chemical vacuum-deposition methods. They possess barrier properties against permeation of gases or vapors when they are thicker than a certain critical thickness, dc; for d<dc, the “oxygen transmission rate” (in standard cm3/m2/day/bar), for example, is roughly the same as that of the uncoated polymer. This fact is commonly attributed in the literature to a “nucleation” phase of the coating’s growth, during which it is thought to present an island-like structure. In order to test this hypothesis, we have deposited hyperthin SiO2 coatings on various flexible polymeric substrates using plasma-enhanced chemical vapor deposition. The film thicknesses investigated here, well below dc (typically in the range 1–10 nm), were determined by Rutherfo...