• Sputter deposition and characterization of calcium phosphate coatings

    This project by Dr. Otaño explores the properties of Hydroxyapatite (HA), a bioactive coating material that is being used to coat medical implants as a result of its similarity with the ceramic constituent of bone.  Commercial HA is being produced using a technique that yields low adhesion coatings, satisfactory when the longevity of the coating is not an issue.  As the average longevity time of the medical implants increases due to increased life expectancy of the population, these coatings are no longer satisfactory. The HA coatings will be prepared using the controlled balance sputtering technique.  The success if this deposition technique is a result of its flexibility to provide energetic bombardment to the growing film, while at the same time providing the necessary substrate temperature and stoichiometry.  The goals of this research project are the following:

    1) synthesis of a highly crystalline HA coating on silicon and Ti6Al4V substrates, with defined control of the crystalline
    phase(s) and stoichiometry, and with excellent adhesion to the coated surface,

    2) modeling of the HA coating using the competitive growth mechanism to study the evolution of their microstructure and
    texture, and the effect of process parameters selected to modify the growth of crystals, and

    3) incorporation of carbon to the HA matrix with the hypothesis that it is possible to produce type B substitution also
    known as biological apatite.

    The first objective of the proposed research is to define the deposition process parameter–characteristics/properties profile of the coatings.  The profile will be analyzed using the statistical method known as Response Surface Modeling.  The development of microstructure and crystallographic-texture will be modeled (second objective) to elucidate the influence of selected growth parameters. The hypothesis of the proposed project is that it is possible to form a single-phase hydroxyapatite coating, with high crystallinity and density, and excellent adhesion to the coating surface using magnetron sputtering deposition.  The addition of carbon to the HA coating (third objective), the incorporation of O2 to the sputtering gas, and changes in deposition pressure and in the target composition will be used to influence the crystal growth.  The long-term goal is to correlate the physical and chemical properties of the deposited HA coating with process parameters affecting the self-organization process of the crystal.  The aim is to produce a uniform bioactive HA coating with excellent adhesion and longevity.