DLC Coating for Infrared Optics
Intro to DLC Coatings
A Diamond-Like Carbon or DLC coating is an amorphous nano-composite carbon material that exhibits properties similar to that of natural diamond including low friction, high hardness, and high corrosion resistance.
DLC is used throughout the Photonics industry where an external optic requires both Anti-Reflective (AR) properties and the durability to withstand the harshest environments.
DLC was introduced because of its Infrared (IR) optical and durability properties. It also addresses what every company, in any industry, strives to achieve – a superior, ultra reliable coating at reduced cost. The durability and reliability of DLC increases the longevity of your optical product, thereby reducing the total cost of ownership, which ultimately benefits your bottom line. DLC coatings are used in high-cost applications like thermal cameras, optical windows, and infrared optics – where the optic on the outside is subject to harsh environmental conditions.
There are several methods to produce amorphous DLC including, but not limited to, RF Discharge Plasma CVD, PIG Plasma CVD, Sputtering/Plasma CVD-composite, Sputter Vapor Deposition, Arc PVD method, Filtered Arc PVD, etc. With the many pros and cons associated with different types of DLC coatings, the end user must decide the best fit for their application. But, if your application requires low stress and virtually pinhole-free DLC coatings, then films produced from a hydrocarbon gas using the plasma CVD method would be preferred.
What Are Pinholes?
While inherent property concerns of DLC, such as compressive stress, can be controlled with process input settings, the real Achilles heel of a DLC coating is pinholes – tiny imperfections caused by poor design, chamber geometry, coating technique, temperature and vacuum settings. Pinholes almost certainly lead to a premature failure and rupture – improper adhesion, undue stresses, etc. – of the coating itself.
“It is always preferable to use a DLC process that coats up to ensure virtually pinhole-free coatings.”
Jadranka Lakic-Reljic
Principal Quality Engineer, DRS Technologies
How to Eliminate Pinholes From DLC Coatings
Omega’s DLC system uses Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) technique and deposits the carbon towards the top of the chamber which results in virtually zero pinholes – improving reliability, reducing failure rate and resulting in better performance of high-end optics.
Our custom-designed DLC system delivers coating repeatability and uniformity of ± 1% over a tooling diameter of 360mm and can be applied on typical IR materials including Germanium (Ge), Silicon (Si), as well as Zinc Selenide (ZnSe), Zinc Sulfide (ZnS), and Chalcogenides.
