This work reports on (i) the gas barrier properties of a-C:H films rf-sputtered in Ar–H2 plasmas from a graphite target on polyethylene terephthalate (PET)and (ii) the influence of the film chemical structure and defect properties on the gas permeability. The intrinsic permeabilities of the films to He, CO2,O2, N2 gases and H2O vapour were determined and found to be orders of magnitude lower than that of the bare PET. Indirect evidence was given to a solubility–diffusion process as the more probable permeation mechanism, over a gas flow through microdefects or gas transport through nanodefects by a Knudsen diffusion mechanism. The barrier capability of the films was found to scale as the gas molecular diameter within the He, CO2, O2 and N2 series, and inversely with the gas critical temperature for the CO2, O2, N2 and H2O series. A correlation between the film Urbach energy, Eu, and the gas permeability was established, except for H2O. Such findings further favour a bulk diffusion contributing mechanism to permeation over the gas state transport. Conversely, this Eu-permeability relation shed more light on the origin of the valence band tailing of the amorphous carbon electron structure.
Production and characterization of thin a-C:(H) films for gas permeation barrier functionality against He, CO2, N2, O2 and H2O
Bensaada Laidani, Nadhira;Bartali, Ruben;Gottardi, Gloria;Anderle, Mariano;
2006-01-01
Abstract
This work reports on (i) the gas barrier properties of a-C:H films rf-sputtered in Ar–H2 plasmas from a graphite target on polyethylene terephthalate (PET)and (ii) the influence of the film chemical structure and defect properties on the gas permeability. The intrinsic permeabilities of the films to He, CO2,O2, N2 gases and H2O vapour were determined and found to be orders of magnitude lower than that of the bare PET. Indirect evidence was given to a solubility–diffusion process as the more probable permeation mechanism, over a gas flow through microdefects or gas transport through nanodefects by a Knudsen diffusion mechanism. The barrier capability of the films was found to scale as the gas molecular diameter within the He, CO2, O2 and N2 series, and inversely with the gas critical temperature for the CO2, O2, N2 and H2O series. A correlation between the film Urbach energy, Eu, and the gas permeability was established, except for H2O. Such findings further favour a bulk diffusion contributing mechanism to permeation over the gas state transport. Conversely, this Eu-permeability relation shed more light on the origin of the valence band tailing of the amorphous carbon electron structure.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
