Organosilicon Coatings Deposited in Atmospheric Pressure Townsend Discharge for Gas Barrier Purpose: Effect of Substrate Temperature on Structure and Properties

Abstract

Organosilicon plasma polymer and silicalike layers are deposited at different temperatures in a dielectric barrier discharge at atmospheric pressure operating in the Townsend regime. Final properties of these two kinds of layers can be finely tuned by the plasma process conditions. In particular, influence of deposition temperature is investigated when hexamethyldisiloxane based monolayers are deposited on poly(ethylene naphtalate) substrate. Coating chemical structure is tested by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Their thickness, topography, and mechanical properties are evaluated by ellipsometry, scanning electron microscopy observation of coatings cross sections, atomic force microscopy, and nanoscratch testing. Permeability of coated polymer is measured for transparent silicalike layers, and the effect of coating structure on the oxygen gas permeability is discussed. The deposition temperature of coatings at 90 °C provides a strong improvement in barrier property compared to room temperature deposition, thanks to a densification of the SiO₂ matrix and to a decrease in the silanol group content.

Synthesis of SiOC(–H) Films by the Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition Method

“…Peaks attributed to Si-O-Si symmetric stretching vibrations and bending mode was observed around 1100 cm −1 and 800 cm −1 , respectively [27,28]. In the case of SiOC(-H) films, the intense band between 1020 cm −1 and 1250 cm −1 is related to Si-O-Si and Si-O-C asymmetric stretch modes [29]. The Si-O-Si bond angle is flexible and varies within a wide range from 120…”

The role of carrier gas flow in roll-to-roll AP-PECVD synthesized silica moisture barrier films

“…A higher network porosity was observed for a short gas residence time and high precursor partial pressure, while denser layers were deposited in the region with a longer gas residence time and low precursor partial pressure. The network porosity in silica-like films is correlated with the presence of hydroxyl groups in the network structure [6,[29][30][31][32][33]. This observation is particularly relevant for the moisture barrier film, because within the discharge region these variable film properties translate into a vertical porosity gradient when the silica films are (dynamically) deposited on a moving substrate.…”

“…The dielectric barrier discharge (DBD) reactor type, widely employed in surface treatment applications [1] is nowadays subject of intense research for the synthesis of functional thin films either in a plane parallel or in a cylindrical electrode geometry [2][3][4][5][6][7][8][9]. In the DBD reactor with the gas mixture injected parallel to the electrodes and operating in precursor deficiency regime, the precursor depletion results in a non-uniform deposition rate profile along the gas flow [10,11].…”

“…The tailored surface can be either highly hydrophilic and possess adhesive properties with specific chemical reactive sites, or can be repellent to liquids with hydrophobic or oleophobic properties [13,14]. In addition, the vertical variation in the film properties can be exploited in anti-reflection coatings [15] by creating a gradient in the refractive index, in membrane layers by producing a gradient in the size and inter-connectivity of the porosity or in films with a gradient in the chemical composition for the synthesis of ultra-low moisture barrier films [6,16,17]. In other applications the vertical gradient properties can be highly undesirable, for example, in silicon microstructures used for electronic devices demanding uniform electrical properties [3].…”

“…In a recent study [11] the gradient film properties of films deposited on static substrate in an AP-PECVD reactor were investigated using spatially resolved ATR-FITR analysis. As ATR-FTIR has proved to be a valuable technique to study the intrinsic microstructure of amorphous silica films, with a focus on the relative content of hydroxyl (eOH) impurities [5,6,[29][30][31][32]. A clear variation in the film microstructure has been observed within the discharge region.…”