Plasma-enhanced chemical vapor deposition (PECVD) processes have been developed to produce prototype barrier coatings for protection from detrimental gases. The strategy used is based on a combination of molecular precursor design and advanced plasma processing and represents a route to an effective, barrier solution. Silicon carbide room temperature deposition processes have been established on several reactor systems. The impact of process-operating factors on the structure and barrier performance has been analyzed and a wide range of tunability has been found. A metrology has been developed to estimate the optical, mechanical, and application-relevant barrier properties. In addition, coatings have been analyzed for subnanometer structural defects by positronium annihilation lifetime spectroscopy (PALS). None of the barriers present evidence of any mesopores or open porosity. Furthermore, the amount of nanostructural defects in layers has been found to depend on both plasma chemistry and power. Based on the PALS results, structural models of different types of barrier layers are proposed. Significant progress in barrier performance has been demonstrated in terms of water vapor transmission rate down in the range of 10(-4) g/m(2) d. (c) 2006 American Vacuum Society.