Synthesis of PECVD a-SiCXNY:H membranes as molecular sieves for small gas separation

Plasma enhanced chemical vapor deposition (PECVD) a-SiCXNY:H thin films have been studied as molecular sieve membranes for light (hydrogen, helium) gas separation at room temperature up to 150 °C. The microstructure of the deposited materials and their thermal stability have been characterized as a function of the electric plasma power and the ratio between the vapor precursors - hexamethyldisilazane and ammonia - using SEM, Fourier transformed infrared spectroscopy (FTIR), EDS, thermo-gravimetric analysis (TGA) and ellipsometry. Single gas permeation tests have also been carried out. An ideal selectivity of helium over nitrogen of 50 has been obtained at 150 °C with a helium permeance of about 10−7 mol m−2 s−1 Pa−1. These promising PECVD materials developed for gas separation also revealed a chemical stability up to 500 °C, even in oxidative atmosphere.