Depth Profiling of a Titanium Doped Diamond-Like-Carbon (DLC) Coated Silicon Disk

Diamond-like carbon films are amorphous carbon films containing a significant fraction of diamond like bonds. The interest in diamond like carbon films has been growing over the last two decades due to their unique properties such as high hardness, low friction and wear, high corrosion resistance, chemical inertness, optical transparency, high band gap and biocompatibility. In addition the physical, mechanical and chemical properties of DLC can be tailored to specific applications by the addition of other elements during growth of the film. All these properties make DLC films ideal candidates for a wide range of applications such as low wear, low friction coatings for machine parts, protective coatings for optical windows and fibres, hard disks and magnetic media, medical prostheses, stents, invasive probes, catheters and biosensors.

There are factors which may limit the performance of DLC coatings. Poor adhesion caused by high compressive stresses and mismatch between DLC and the substrate are critical amongst these. For this reason an interlayer is often introduced separating the DLC and substrate. Cr and Ti are the most common interlayer.

The example illustrated below is from a much larger investigation on doped DLC and interface structures necessary to give the best adhesion, whilst maintaining low friction and low wear in coatings on a micro electrical mechanical actuator component.

AES depth profile for Ti doped DLC with TiC/Ti interlayer

The overall structure of coating and interface is the most important factor in determining properties. The test work was to characterize the samples for elemental and chemical state information using high spatial resolution and high energy resolution Auger spectroscopic analysis.

Above is shown an Auger depth profile of a Ti doped DLC on Si substrate with a Ti interlayer. This particular arrangement gave very good coating adhesion and reduction of interfacial stresses. The Ti doping in the DLC layer improved tribological properties and the interface structure produced good adhesion. Overall the coating structure performed exceptionally well in mechanical test conducted by MSA and in the practical application.

By investigating a number of such coating interface arrangements and correlating structural information to mechanical performance, the work helped the client optimise systems and deposition parameters to give the best overall results for any specific application.

Ti Auger spectra from DLC, TiC and Ti layers

C Auger spectra from DLC and TiC layers

This technique can also be invaluable in the investigation the causes of interface failures, where the chemistry at the interface may be unequivocally determined and causes of failure, whether they be due to contamination or to material mismatch can be identified.

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