Influence of target surface degradation on the properties of r.f. magnetron‐sputtered calcium phosphate coatings

Abstract

This paper reports a detailed study of how repeated r.f. magnetron sputtering from a hydroxyapatite (HA) powder target affects the nature and reproducibility of a sequential series of thin-film coatings deposited onto Ti6Al4V substrates. An evaluation of the effective lifespan of the HA sputter targets and the reproducibility of the calcium phosphate (CaP) coatings produced from them has been made from Fourier transform infrared spectroscopy, XPS and, as appropriate, atomic force microscopy and SEM/energy dispersive x-ray analyses. The annulus region of the target surface, from which sputtering under r.f. magnetron conditions normally occurs, showed severe surface degradation after only one deposition run, as indicated by significant PO 4 3− and OH − depletion. This deterioration continued after each subsequent deposition cycle but to a much lesser extent than that observed in the initial sputtering period. The layers produced from all of the sputter runs contained the expected Ca 2+ and PO 4 3− species characteristic of a CaP system but were OH − deficient in the as-deposited state. However, the chemical and morphological properties of the coatings did not change significantly until after the third consecutive sputter cycle. Hence, these data indicate that, even though a significant level of degradation of the HA target occurs at the outset of the sputtering procedure, the general plasma conditions employed here have a dominant influence on the coating properties until a critical degradation condition is met. As such, the compacted HA powder targets of interest can have a life-cycle greater than single usage without detriment to the chemistry and morphology of the coatings produced from them.

XPS Study of Apatite Formed from Simulated Body Fluid on a Titanium Substrate Surface Nitrided by an Atmospheric Pressure Nitrogen Microwave Plasma

“…The P2p spectral envelope could also be fit with two peaks, each of which comprises an unresolved doublet. The most intense of these bands is located at 132.72 eV (1), while the weaker band is centered at 133.99 eV (2), corresponding to P-O and P-O-H bonding in HPO 4 2-, respectively [8]. These data are consistent with the chemical structure of HAp.…”

“…4 indicates the presence of two distinct bands. The first of these contributions is located at 530.60 eV (1) and is attributed to O-P bonding and the second, found at 531.62 eV (2), is associated with oxygen bonded to OH -groups [8][9][10]. The P2p spectral envelope could also be fit with two peaks, each of which comprises an unresolved doublet.…”

Preparation of Calcium Phosphate Films by Radiofrequency Magnetron Sputtering

“…All the reflections from the target after sputtering for 630 ks were indexed to -TCP structure. The ICP analysis for ''annular race track'' 45) of the target surface revealed that the composition, Ca/P molar ratio, was almost the same as that before sputtering. Boyd et al 45) applied hydroxyapatite (HAp) targets pressed at 10 MPa for 7.2 ks using a pressure filtration die assembly in RF magnetron sputtering.…”

“…The ICP analysis for ''annular race track'' 45) of the target surface revealed that the composition, Ca/P molar ratio, was almost the same as that before sputtering. Boyd et al 45) applied hydroxyapatite (HAp) targets pressed at 10 MPa for 7.2 ks using a pressure filtration die assembly in RF magnetron sputtering. They indicated that the HAp degraded during sputtering with becoming hydroxyl ion deficient forming other calcium phosphate phases and Ca(OH) 2 accompanying an increase in Ca/P ratio.…”

“…Radiofrequency (RF) magnetron sputtering has been used in wide areas for coatings of thin films with excellent adherence to substrates, 43) and applied to coatings of calcium phosphate films on commercially pure titanium (CP-Ti) 23,37,38,40,44) and þ type titanium alloys. 33,35,36,41,42,45,[47][48][49][50] Ti and its alloys are known as biocompatible metals because of their low elastic modulus, high corrosion resistance and the appropriate combination of strength and ductility. Low processing temperature is also an advantage of RF magnetron sputtering for calcium phosphate coatings for Ti substrates because the mechanical properties of the substrates will be degraded by high processing temperatures.…”