Characterising a Custom-Built Radio Frequency PECVD Reactor to Vary the Mechanical Properties of TMDSO Films.

Racim Radjef,Sally L Mcarthur,Colin Hall,Andrew Ang,Karyn L Jarvis,Bronwyn L Fox

doi:10.3390/molecules26185621

Abstract

Plasma-polymerised tetramethyldisiloxane (TMDSO) films are frequently applied as coatings for their abrasion resistance and barrier properties. By manipulating the deposition parameters, the chemical structure and thus mechanical properties of the films can also be controlled. These mechanical properties make them attractive as energy adsorbing layers for a range of applications, including carbon fibre composites. In this study, a new radio frequency (RF) plasma-enhanced chemical vapour deposition (PECVD) plasma reactor was designed with the capability to coat fibres with an energy adsorbing film. A key characterisation step for the system was establishing how the properties of the TMDSO films could be modified and compared with those deposited using a well-characterized microwave (MW) PECVD reactor. Film thickness and chemistry were determined with ellipsometry and X-ray photoelectron spectroscopy, respectively. The mechanical properties were investigated by nanoindentation and atomic force microscopy with peak-force quantitative nanomechanical mapping. The RF PECVD films had a greater range of Young’s modulus and hardness values than the MW PECVD films, with values as high as 56.4 GPa and 7.5 GPa, respectively. These results demonstrated the varied properties of TMDSO films that could in turn be deposited onto carbon fibres using a custom-built RF PECVD reactor.

Highlights

Protective coatings have been created using organosilane coatings, predominately for polymer substrates
The MW TMDSO films were deposited with O2 concentrations in the monomer flow of 55–90%, whereas the radio frequency (RF) TMDSO films were deposited without O2 to determine if the film properties were controllable in the absence of oxygen by varying only the deposition power
Dual electrodes were utilized for the deposition of TMDSO films to optimise radial film thickness uniformity, under the assumption that this would lead to greater uniformity in film chemistry and mechanical properties

Summary

Introduction

Protective coatings have been created using organosilane coatings, predominately for polymer substrates Siloxane precursors, such as hexamethyldisiloxane (HMDSO) [1,2,3] and tetramethyldisiloxane (TMDSO) [4,5,6], have been used to safely deposit these organosiloxane coatings via plasma-enhanced chemical vapour deposition (PECVD) for many years. TMDSO films can be deposited with controllable mechanical properties by increasing the O2 concentrations in the monomer feed, which results in harder films and higher Young’s moduli because of the increase of Si-O-Si bonds within the film [4,5,7]. Harder TMDSO films with higher Young’s moduli have been deposited with higher O2 concentrations in the monomer feed because of the increase of Si-O-Si bonds within the film [4,5,7]. MW TMDSO films have been produced with hardness and Young’s modulus values of 0.014 to 1.2 GPa and 0.23 to 15.7 GPa, respectively

Objectives

Results

Conclusion