Unlike real diamonds, Diamond-Like Carbon has no crystalline structures. The term Diamond Like Carbon (DLC) was created to differentiate this coating from other graphite coatings, which are lamellar, or layered. Dissociated cubic carbon (sp3 or diamond carbon) and hexagonal carbon (sp2 or graphite carbon) structures deposit arbitrarily on a surface creating a completely amorphous material solid coating.
The amorphous organization of DLC means the coating appears smooth to the naked eye while resembling a layer of pebbles microscopically. It also means DLC has no brittle fracture planes, which makes it a very tough material which inspires the name “Diamond-Like.”
Here’s a Scanning Electron Microscope (SEM) image of a gold-coated replica of a ta-C “diamond-like” coating.
(Image from https://www.wikiwand.com/en/Diamond-like_carbon)
In addition to being exceptionally hard, DLC has several other attractive properties including:
- Low coefficient of friction
- Abrasion resistance
- Chemically inert i.e. it is resistant to salts, acids, alkalis, and most organic solvents
- Biologically compatible
- Electrically insulating
- Optically transparent
These properties combined with smooth surfaces make DLC attractive for a broad range of applications from machining tools to motor and other frictional components to biomedical equipment to electronics and semi-conductor to solar to optics.
DLC is especially well-suited for high-performance infrared (IR) optics. It adheres well to a variety of infrared and ultraviolet substrates including Germanium (Ge), Silicon (Si), Zinc Selenide (ZnSe), Zinc Sulfide (ZnS), Fused Silica and Chalcogenides. It is an anti-reflective (AR) coating with high hardness and good stress resilience causing only minor losses (between 5-10%) in transmission. As a single-layer coating, DLC can be adjusted to tune it for specific spectral ranges.