Understanding Stress Profiles in Multilayer PVD Coatings

Please note that this is an EngD studentship (sponsored by Pilkington Technology Management) - see our web pages for programme background www.surrey.ac.uk/MiNMaT.

You will spend around 75% of your time on this project based on campus at Surrey, with the balance at the sponsor premises in Ormskirk Lancs.

Thin film coatings, consisting of multiple layers of a various materials, are used around to world to tailor the properties of glass. These coatings are designed to modify thermal insulation, alter reflectivity, and also impart properties such as the ability to ‘self-clean’.

The presence of some stress in a multi-material thin film is unavoidable. This will in part begin with lattice mismatch during initial thin film deposition and become more intricate with the trapping of defects and the possibility of phase transformations. This scenario becomes more complex when multiple material systems are combined to create a ‘coating stack’. As thin films subject to excessive tensile stresses will crack, while thin films with heightened compressive stresses will buckle or blister, understanding and controlling the stresses generated during thin film production is vital to improve reliability and durability.

This project aims to improve understanding of the stress profiles of thin films generated using physical vapour deposition (PVD).

While at NSG’s European Technical Centre in West Lancashire, the research engineer will work alongside the Materials Properties and Surface Analysis team and liaise with the Thin Film Technology group. Initial work at NSG could include the production and characterisation of test coating stacks to improve the research engineer’s understanding of how PVD coatings are deposited. This project will include the use of the dual beam focussed ion beam scanning electron microscope (FIB-SEM) at Surrey University to obtain imaging datasets using ion beam layer removal. This will involve the selective removal of the coating layer(s) from a micro-cantilever, which will be used to determine the residual stress profiles of different coating materials. This work, complemented by stress measurements obtained using X-ray diffraction, will evolve from single layer coating materials to more complex multilayer systems as the project develops.

It is envisaged that there would be approximately a 75 % / 25 % split between the time at Surrey and time at NSG Lathom, with the majority of the time spent here at Surrey. This split could be approximately the same over each of the whole 4 years, but will depend on project progress etc.