Barrier SiO2-like coatings for archaeological artefacts preservation

Abstract

Thin film chemical vapour deposition technique has been used for more than 50 years. Introducing organo-silicones as precursors, e.g. hexamethyldisiloxane (HMDSO) or tetraethyl orthosilicate (TEOS), brought new possibilities to this method. Barrier properties of thin films have become an important issue, especially for army and emergency services as well as for food and drink manufacturers. Our work is focused on protective HMDSO thin films for encapsulating cleaned archaeological artefacts, preventing the corrosion from destroying these historical items.Thin films are deposited via plasma enhanced chemical vapour deposition (PECVD) technique using low pressure capacitively coupled pasma in flow regime. Oxygen transmission rate (OTR) measurement was chosen as the most important one for characterization of barrier properties of deposited thin films. Lowest OTR reached for 50 nm thin film thickness was 120 cm3 m-2 atm-1 day-1. Samples were also analyzed by Fourier Transform Infrared spectrometry (FTIR) to determine their composition. Optical emission spectra and thin film thickness were measured during the deposition process. We optimized the deposition parameters for barrier layers by implementation of pulsed mode of plasma and argon plasma pre-treatment into the process.