Thursday, February 7, 2008

PVD Diamond Like Carbon Thin Films

Continuing our discussion of diamond thin films, we move on to PVD diamond-like-carbon (DLC) films. The main advantages of PVD DLC over CVD diamond are lower temperature deposition (room temperature versus 400C at best for CVD), lower cost typically and a benign environmental footprint. The best PVD DLC is deposited using cathodic arc and can be 3 times harder than sputtered DLC. Cathodic arc produces carbon ions which, with careful substrate bias control, allow the ideal energetic conditions for optimizing diamond, sp3 bonding in the growing film. High sp3 bond ratio correlates with high hardness, up to about 90 GPa, or about the same hardness as CVD diamond (http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=2574&DID=118953&action=detail). Some DLC films have been reported to be even harder than natural diamond; natural diamond nano-indentors can break during hardness measurements.
The main drawback of PVD versus CVD diamond is the difficulty in growing thick films due to compressive stress. CVD "diamond-sheet" films can be 50 microns thick, compared to about 2 microns maximum for the best PVD DLC films. Numerous process modifications have been developed for the relief of stress, including post deposition annealing and substrate high voltage pulsing, but no one has yet brought a high sp3 DLC film to market that is as easy to widely implement as other more standard PVD films, such as titanium-nitride.

2 comments:

Flippe said...

Dear Sir/Madam
Would you please introduce some papers about PVD DLC coatings?
Regards
F. Noba

ionman said...

flippe, Cambridge University online is probably the best place to find papers about PVD DLC coatings. Otherwise, a handbook, such as "Diamond Films Handbook" by Jes Asmussen is recommended.