The main objective of first phase of this project was to assess the effect of Ti-Au composition on the mechanical properties and biocompatibility of deposited thin films. This will help to understand if the Ti-Au alloy has the reported biocompatibility features while exhibiting extremely high hardness, making it suitable for this project. To do this 6 sets of thin films were deposited on Ti and glass substrates, ranging from pure Ti films to increasing amount of Ti-Au composition up to pure Au films. For each composition run, 2 glass and 4 Ti coupons were prepared and loaded into a Moorfield nano PVD magnetron sputter coating system. The chamber was prepared and loaded with 2-inch diameter circular, high purity, Ti and Au targets supplied by Pikem Ltd, UK. The chamber was pumped down to a high level vacuum pressure of less than 0.5 mPa. Pure Ti thin films were deposited by powering up Ti target only. In the subsequent runs, power was increased gradually on the Au target to increase the amount of Au in the Ti-Au matrix. The final run was performed with power only on the Au target to achieve pure Au thin films. The deposition time was kept constant to achieve final film thicknesses in a similar region for all samples.
After each deposition run, the substrates were taken out of the chamber and the Kapton were tapes removed from the glass substrates to measure the thickness of thin films. After measuring the thickness, the samples were analysed using EDX to determine the exact amount of Ti and Au present in each thin film. These two initial tests give idea good indication if the deposited thin film is suitable or if another deposition needs to be performed.
It can be seen that all the films deposited have a thickness value that lies between 550 to 660nm. The lowest thickness is observed for the pure Au thin film. The sputter deposition rate of Au is 4 times that of Ti, therefore the power had to be decreased on the Au target substantially to achieve a similar thickness in a constant time. However, sputter deposition rate is influenced by interactions between many other chamber and deposition conditions making it difficult to predict the final thickness value of the film. The thickness value of 550 nm for the Au thin film is still within 10% of the set target of 600 nm, and is included in the batch to perform further tests so as not to waste the more expensive Au target. EDX results show that the Au concentration from TF1 to TF6 cover most of the composition spectrum from 0 to 100 at.%. It is expected that a Ti:Au ratio of 3:1 gives rise to the beta phase which exhibits the peak of hardness value. Though some wider composition gaps exist between TF1 to TF2 and TF5 to TF6, if the Ti-Au thin films show improvement of mechanical/biocompatibility properties for any composition range, then it would be considered advantageous to do further deposition runs around that particular composition range.
Now we know the set of 6 thin films deposited are suitable for further structural, morphological, mechanical and biological characterization to see if any suitable properties exist with variation in Au concentration. Please visit us again to read about the surface and cross-sectional characterization of thin films using SEM and AFM tools….
Kommentarer