A complete characterization of Ca5(PO4)3OH sputter-deposited films by ion beam analysis: RBS and ERD

Abstract

RF magnetron sputter deposition was used to deposit thin calcium phosphate (hydroxyapatite) layers on titanium alloy substrate material. We determined the precise amount of calcium, phosphorus, oxygen, and hydrogen in these films by combining two ion-beam analysis techniques: Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD). Variables were power level, partial oxygen pressure, or additional water vapor. Also examined was the influence of additional bias power to the substrates during deposition and the effect of annealing on the final composition of the deposited layers. Measurements showed that the Ca/P ratio decreased with increasing oxygen pressure or decreasing sputtering power. In addition, the Ca/P ratio increased when a bias was applied to the substrates. The O/P ratio of the films decreased with additional oxygen pressure but increased when additional water vapor was applied during deposition. All as-deposited films showed a higher hydrogen content than stoichiometric HA. The hydrogen content in the films deposited with water vapor was more than 7 times higher than in the films deposited under pure argon conditions. After annealing, the hydrogen content decreased to about 3.5 at % whereas in stoichiometric HA the hydrogen content amounts to 4.5 at %. After annealing, the oxygen concentration in the film also decreased. We assume that hydrogen disappears out of the film as H2O during annealing. For the targets used in these experiments, sputter deposition at 400 W, with additional water vapor and annealing at 500 degrees C, produced films with a stoichiometry closest to that of hydroxyapatite.

Composition and Crystallization of Hydroxyapatite Coating Layer Formed by Electron Beam Deposition

“…The Ca/P ratio of the coating layer is known to vary widely depending on the deposition procedures. 5,[12][13][14] The dissolution rate of the coating layer in the physiologic saline solution decreased with increasing Ca/P ratio until it reached the value for stoichiometric HA. However, when the Ca/P ratio exceeded 1.67, the dissolution rate increased again.…”

Development of a Biologically Relevant Calcium Phosphate Substrate for Sum Frequency Generation Vibrational Spectroscopy

“…The calcium content of the target was determined to be 36% as compared to a theoretical value of 40% for stoichiometric hydroxyapatite. As discussed above, previous studies of RF magnetron sputtered hydroxyapatite have indicated that it is difficult to reproduce the exact stoichiometry of hydroxyapatite following deposition, , and therefore the quoted deficiency in calcium content of the target was deemed acceptable.…”

“…Further, the adherence of the coating to the substrate, the uniformity of the coating thickness, and the integrity of the structure are often poor . The plasma spraying technique has an additional drawback in the creation of a composite SF substrate; the coatings produced are at least a micrometer thick, far larger than the 100 nm or less required for SFG.…”

“…For example, van Dijk et al have investigated the influence of argon pressure, discharge power level, and the addition of oxygen on the film composition. The stoichiometry of the coatings was found to differ from bulk HA; specifically the Ca/P ratio remained too high even after rigorous optimization of the protocol . This was attributed to the target itself being a plasma sprayed layer of HA on a copper base plate, which as mentioned above is expected to have a stoichiometry that deviates from bulk HA.…”

“…After annealing at 500 °C, the water content disappeared and O−H bands became visible in the vibrational spectrum. Consequently, annealing at 500 °C was included in the final protocol . Biological evaluations of the sputtered HA layers revealed their biocompatibility to be excellent with the coating enhancing the growth of hydroxyapatite in a cell culture.…”