Hydroxyapatite (HA) is an important class of biomaterial which has been extensively researched as a coating on metallic implant devices and/or as a model for the study of cells on bioactive surfaces. The composition of such coatings, when compared with the raw HA target powder, has led to them being termed as calcium phosphate (CaP) thin films with varying "HA-like" properties. The ability of the coating to deliver some or all of the properties of the sources material is limited by the unit cell composition that originates from the crystallinity of the coating during its growth. Although structural models exist for HA as a powder, the unit cell composition of CaP thin films has not yet been determined at the level necessary to understand the influences that effects from substrate topography and thermal annealing have on these properties. This work describes a detailed investigation of the evolution of the microstructure that occurs via grain growth in sputter deposited CaP thin films. The approach taken here utilises a multi-source RF magnetron sputter deposition system to create the relevant CaP surfaces and the application of advanced characterisation techniques and data analysis methodologies to investigate the structural properties. The effects of the key operational aspect of the process, most particularly the sputtering parameters and subsequent thermal processing on the extent of stress incorporation determined from crystallographic data and quantitative phase analysis have indicated that the choice of deposition parameters is the most critical consideration in terms of coating reproducibility and quality. The relationship between quality of the precursor HA (target) powder, thickness of the deposited layer and the unit cell composition of coating have all been addressed. It has been shown that the composition of the coating and its evolving microstructure are determined through preferred crystallographic orientation in the plane of lowest surface energy which limits the size and angle of curvature of the grains present in the coating. The size and shape of the grains produced influences the distribution of residual stress levels, i.e. the mechanical stal)1ity of the coating and also the concentration of the various atoms that are distributed across and within the thin film.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:550567 |
| Date | January 2011 |
| Creators | Duffy, Hugh |
| Publisher | Ulster University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0022 seconds