Magnetron Sputtering Deposition of Calcium Phosphate Films with Nanoscale Grain Morphology in their Surface

Hydroxyapatite (HA) is a calcium phosphate mineral analogous to the mineral part of bone. This similarity makes this material bioactive and suitable to coat medical implants. However, at present, there is not a coating technique which gives the coated implant the desired properties and long life required for medical implants.In an effort to produce HA coatings with improved properties, calcium phosphate films were prepared using magnetron sputtering deposition on a silicon substrate at 600°C. Initial efforts resulted in the deposition of amorphous films with a distinctive grain-like surface morphology. The morphological grain size was studied using SEM and found that it was possible to control the average diameter value of the round shaped grains by adjusting the deposition time. Increasing the deposition time increases the mean grain diameter. EDS spectra showed the unintentional addition of carbon, iron and nickel to the samples during deposition. After eliminating the impurities, it was possible to prepare calcium phosphate films in the HA phase but without the grain-like surface morphology. These results suggested that the impurities prevented the formation of the calcium phosphate HA phase while acting as nuclei for the heterogeneous nucleation of the grains. This is an important result where the deposition process parameters can be controlled to functionalize the films in order to produce distinctive nanoscale features in the surface morphology.