Promising results in terms of moisture and oxygen permeation barrier properties have been reported for organic/inorganic multilayers, but the impact of the organic interlayer on the overall barrier performance is still under discussion. It is generally accepted that the organic interlayer acts as a smoothening layer, allowing for the decoupling between defects/pinholes present in the polymer substrate and the inorganic layer. It is, however, also hypothesized that the organic interlayer infiltrates into the nano-pores present in the inorganic barrier layer, therefore affecting the barrier properties at microstructural level. In the present work, the moisture permeation barrier performance of SiO2/organosilicon multilayers deposited by means of initiated- and plasma enhanced-chemical vapor deposition is investigated. Calcium test measurements were used to discriminate between the overall water permeation (effective water vapor transmission rate, WVTR) through the layer and the permeation through the matrix porosity (intrinsic WVTR). The improvement in terms of intrinsic barrier performance was found to correlate with the residual nano-porosity content, due to the filling/infiltration of the organosilicon monomer in the SiO2 nano-pores. However, such improvement upon the deposition of the organosilicon interlayer is limited to a factor four. These results, in combination with the analysis of the local defects present in the multilayer structure, lead to the conclusion that the main contribution of the organosilicon interlayer to the overall barrier performance is the decoupling of the above-mentioned local defects/pinholes.

Satisfactory results in term of moisture permeation barrier performance have been achieved for the encapsulation of organic electronic devices. However, further insight into the correlation between barrier performances and moisture permeation pathways are sought. This contribution focuses on the residual nanoporosity in the inorganic layer and its role in controlling the barrier performance. Inorganic barrier layers (i.e. Al2O3 and SiO2) prepared by plasma-enhanced atomic layer deposition (PE-ALD) and plasma-enhanced chemical vapor deposition (PE-CVD) have been extensively analyzed by means of IR spectroscopy, spectroscopic ellipsometry, Rutherford backscattering spectroscopy, elastic recoil detection and X-ray photoelectron spectroscopy. The calcium test has been performed to determine the intrinsic water vapor transmission rate (WVTR), as well as the effective WVTR values. Ellipsometric porosimetry (EP) has been adopted to determine the open porosity and pore size range in the structure of the layer. Trivinyltrimethyl cyclotrisiloxane (dv(3)D(3) = 1 nm) and water (d(H2O) = 0.3 nm) have been chosen as probe molecules. A correlation between the residual nanoporosity and the intrinsic barrier properties has been found, regardless of the chemistry of the layer and deposition method used. Pores larger than 1 nm with a relative content above 1% have been found responsible for mediocre barrier layers characterized by a WVIR in the range of 10(-2) to 10(-3) g m(-2) day(-1). Furthermore, the pore size range of 0.3-1 nm and its relative content have been found to control the transition in WVTR between the 10(-4) g M-2 day(-1) and the 10(-6) g m(-2) day(-1) regime, highlighting the role of residual nanoporosity in controlling the intrinsic barrier properties. (C) 2014 Elsevier Inc. All rights reserved.

Organosilicon layers have been deposited from 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane (V3D3) by means of the initiated-chemical vapor deposition (i-CVD) technique in a deposition setup, ad hoc designed for the engineering of multilayer moisture permeation barriers. The application of Fourier transform infrared (FTIR) spectroscopy shows that the polymerization proceeds through the scission of the vinyl bond and allows quantifying the degree of conversion of vinyl groups, which is found to be larger than 80% for all the deposited layers. In situ real-time spectroscopic ellipsometry (SE) allows following all the i-CVD growth stages, i.e., from the initial monomer adsorption to the layer bulk growth. Finally, the combination of SE and FTIR has allowed defining the process window for the deposition of stable and highly cross-linked poly(V3D3) layers by tuning a key process parameter, i.e. the surface monomer adsorption.

Although very promising results in terms of moisture and oxygen barrier properties have been achieved by alternating organic and inorganic layers composing a multilayer structure, the impact of the organic interlayer on the global barrier performance is still unraveled. Three main hypotheses have been reported in literature so far, although consistently applied to the case of a liquid-phase polymerization process of the organic layer: smoothening of the polymeric substrate surface by the organic layer; decoupling, by means of a tortuous path, of the defects present in two adjacent inorganic barrier layers; filling of the nano-defects present in the barrier layer during the (liquid phase) polymerization of the organic layer. Within this framework, this contribution reports on the adsorption/desorption study of an initiated-CVD (i-CVD) monomer (trimethyl-trivinyl-cyclotrisiloxane), V3D3, performed on plasma deposited SiO2-like layers by means of in situ spectroscopic ellipsometry measurements. The SiO2-like layers are used as moisture permeation barriers followed by an organic interlayer deposited by means of the i-CVD technique. The experimental evidence for the V3D3 molecule infiltration and filling in the open micro/meso porosity present in the inorganic layer underneath, confirms the hypothesis on the filling of nano-defects in the barrier layer upon organic layer deposition and shows that the defect filling occurs also in the case of a CVD-based approach.

In this paper, the characterization of the optical anisotropy of poly(ethylene-2,6-naphthalate) (PEN) by means of Transmission Generalized Ellipsometry coupled with reflection multi-angle Spectroscopic Ellipsometry (SE) measurements is presented. This study is functional to the determination of the refractive index of atmospheric pressure plasma-deposited SiO2-like layers deposited on PEN. The effect of the plasma duty cycle (DC) on the film properties is investigated. From the analysis of the optical properties, complemented with chemical and morphological studies, it is concluded that the increase in DC is responsible for the layer densification process, eventually causing an improvement in the PEN/SiO2 system barrier properties.

SiO2 layers have been deposited from Ar/O2/hexamethyldisiloxane mixtures in a remote expanding thermal plasma setup enabling a good control of both the ion flux (by changing the deposition chemistry and the arc plasma parameters) as well as the ion energy. This latter is achieved by an additional rf substrate biasing or a tailored ion biasing technique, i.e. a low frequency pulse-shaped bias. The role of the ion energy and ion-to-growth flux ratio on the film microstructure and densification at low substrate temperature (100oC) has been investigated by means of ellipsometric porosimetry. This technique monitors the refractive index change due to the adsorption (and desorption) of ethanol vapors in the volume of macro-meso-micro pores in the SiO2 layer. From the analysis of the adsorption isotherm and the presence of hysteresis during the desorption step as a function of the equilibrium partial pressure, the open porosity in the layer can be determined. It is found that both biasing techniques lead to densification of the deposited layer, which experiences a transition from micro-/ mesoporosity to microporosity and eventually non-porosity, as function of the increasing ion energy. Although both biasing techniques lead to a comparable critical ion energy value per deposited SiO2 unit (about 100 eV), the ion-to-growth flux ratio and ion energy are not found to be interchangeable parameters. In fact, in the case of the rf bias, the meso- and large micropores are first affected leading to a quantitative decrease of porosity, i.e. from 11% to 3% at an ion energy less than 20 eV. A further increase in ion energy eventually reduces the presence of smaller micropores leading to non porous films at energy of 45 eV. When the pulse-shaped biasing technique is adopted, the micro- and mesopores are simultaneously affected over the whole range of available ion energy, leading to a non porous layer only at very high energy values, i.e. 240 eV. This difference is attributed to the increasing ion-to-growth flux ratio accompanying the rf biasing, as a consequence of the rf plasma generation in front of the substrate.