title: Analysis of Nanoporosity in Moisture Permeation Barrier Layers by Electrochemical Impedance Spectroscopy.
abstract: Water permeation in inorganic moisture permeation barriers occurs through macroscale defects/pinholes and nanopores, the latter with size approaching the water kinetic diameter (0.27 nm). Both permeation paths can be identified by the calcium test, i.e., a time-consuming and expensive optical method for determining the water vapor transmission rate (WVTR) through barrier layers. Recently, we have shown that ellipsometric porosimetry (i.e., a combination of spectroscopic ellipsometry and isothermal adsorption studies) is a valid method to classify and quantify the nanoporosity and correlate it with the WVTR values. Nevertheless, no information is obtained about the macroscale defects or the kinetics of water permeation through the barrier, both essential in assessing the quality of the barrier layer. In this study, electrochemical impedance spectroscopy (EIS) is shown as a sensitive and versatile method to obtain information on nanoporosity and macroscale defects, water permeation, and diffusivity of moisture barrier layers, complementing the barrier property characterization obtained by means of EP and calcium test. EIS is performed on thin SiO2 barrier layers deposited by plasma enhanced-CVD. It allows the determination of the relative water uptake in the SiO2 layers, found to be in agreement with the nanoporosity content inferred by EP. Furthermore, the kinetics of water permeation is followed by EIS, and the diffusivity (D) is determined and found to be in accordance with literature values. Moreover, differently from EP, EIS data are shown to be sensitive to the presence of local macrodefects, correlated with the barrier failure during the calcium test.
authors.affiliation: †Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.|‡Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
authors.forename: Alberto
authors.initials: A
authors.lastname: Perrotta
authors.affiliation: §Delft University of Technology, Novel Aerospace Materials, Kluyverweg 1, 2629 HS Delft, The Netherlands.
authors.forename: Santiago J
authors.initials: SJ
authors.lastname: García
authors.affiliation: ∥Max Planck Institute for Polymer Research (MPIP), Ackermannweg 10, D-55128 Mainz, Germany.
authors.forename: Jasper J
authors.initials: JJ
authors.lastname: Michels
authors.affiliation: †Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Anne-Marije
authors.initials: AM
authors.lastname: Andringa
authors.affiliation: †Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.|⊥Solar Research SOLLIANCE, High Tech Campus 21, 5656 AE Eindhoven, The Netherlands.
authors.forename: Mariadriana
authors.initials: M
authors.lastname: Creatore
keywords: EIS; PE-CVD; macrodefects; moisture permeation barrier; nanoporosity