Diamond Like Carbon
Diamalite is coated with a revolutionary Diamond Like Carbon (DLC) treatment for the enhancement of the CZ core. CZ gemstones are excellent candidates for treatment.
The term Diamond Like Carbon describes a group of materials with a wide range of properties. DLC films are generally amorphous, having no overall crystal structure as do graphite and diamond. Many DLC films have hydrogen, nitrogen or other elements incorporated into the film to tailor their properties. Hydrogen for example reduces the internal stress of the DLC making it less susceptible to peeling. The ideal type of DLC and method of application depends upon the use to which it will be put. C3Jewelry Inc. has done extensive research into the best DLC coating for our new Diamalite product.
Carbon is the primary element in Diamond Like Carbon, graphite and diamond. The difference between these forms of carbon is the crystal structure, if present, and the carbon to carbon chemical bonds. Diamond and graphite are crystalline allotropes of carbon with cubic and hexagonal sheet crystal forms respectively. A very rare form of diamond is lonsdaleite which has a hexagonal crystal lattice. DLC can be thought of as a mixture of these crystal forms at the nano-scale along with amorphous carbon. Amorphous carbon, which means non-crystalline carbon can also have a variety of structures depending upon the nature of its carbon-carbon bonds. Amorphous carbon has no long-range crystal structure.
Carbon to carbon bonds are defined by their ‘hybridization’ as sp1, sp2, or sp3. These bonds are determined by the quantum mechanics of the carbon atom and its neighboring atoms. The sp3 bond is found in diamond and the sp2 bond in graphite. DLC has a variety of bonds and one of the defining properties of DLC is the amount of the types of bonds in it particularly the sp3 to sp2 ratio. The greater the proportion of sp3 bonding in a DLC film the more close its properties will generally be to diamond.
Other elements may be present in small quantities in the carbon and are called dopants. Nitrogen present in natural or synthetic diamond may cause a yellow or brown color. Boron in diamond can yield a blue color. DLC films are also commonly doped with hydrogen, nitrogen and various metals such as silicon, tungsten and molybdenum. The incorporation of these dopants allows the optical, chemical and physical properties to be adjusted to the needs of the application.
DLC films may contain any mixture of bonding, crystal structure and doping ingredients. These may be organized into 7 basic forms. They are:
1) Hydrogen free amorphous carbon. Symbol: a-C
2) Tetrahedral hydrogen free amorphous carbon. Symbol: ta-C
3) Metal containing hydrogen free amorphous carbon. Symbol: a-C:Me
4) Hydrogenated amorphous carbon. Symbol: a-C:H
5) Tetrahedral hydrogenated amorphous carbon. Symbol: ta-C:H
6) Metal containing hydrogenated amorphous carbon. Symbol: a-C:H:Me
7) Modified hydrogenated amorphous carbon. Symbol: a-C:H:X
Each of these forms of DLC has its own range of properties and applications. In general the more the sp3/sp2 bonding and lower dopant level the more diamond like are its properties. High sp3/sp2 sure carbon films have extreme hardness, high refractive index, are brittle and usually have high internal stress levels. They tend to be expensive to deposit and may have adhesion problems with some substrates.
The hardness of DLC films may be measured by a device called a nano-indenter. This machine has a very tiny diamond point or stylus rather like an old phonograph needle. This diamond point is driven into the DLC film and the force required relates to the film hardness. Some DLC films with sp3 nano crystalline phases have zones that actually measure harder than diamond. The diamond tip, being softer than this ultra-hard carbon phase may actually shatter during the measurement. This is an amazing result because no known bulk material is harder than diamond.
For gemstone coating, the following parameters are important: Hardness, Transparency, Color, Film stress, Thickness Uniformity, Film Adhesion to the stone, and Cost. DLC films require sophisticated and expensive equipment so the cost of deposition is usually an important issue. On the plus side DLC processes are very ‘Green”. They are vacuum processes using small quantities of safe gasses and so are environmentally benign.
There are many ways to deposit DLC films. The most common methods involve a vacuum chamber and a power supply. Common methods are Chemical Vapor Deposition (CVD) Physical Vapor Deposition (PVD) and Ion Beam Assisted Deposition (IBAD). Extra energy for ionization or chemical disassociation may be applied by high frequency power such as microwaves or radio waves. Microwave Assisted Chemical Vapor Deposition (MACVD) or Inductively Coupled Plasma (ICP) methods are often used for DLC coating.
The DLC film is condensed from a vaporized form of carbon onto the gemstones. Carbon vapor may be either pure carbon gas from an arc or ion source or a chemical precursor such as acetylene or methane. The vapor is usually ionized to a greater or lesser degree by the energy of the source power supply. This energetic carbon rich vapor is extremely reactive and will coat surfaces inside the chamber. The energy of the arriving carbon species causes bombardment of the depositing DLC layer. The impact of the incoming carbon material profoundly affects the film properties. Adhesion of the film is also affected. The various deposition processes each have an optimal bombarding energy which is usually measured in electron volts.
The cleanliness of the gemstone immediately prior to coating is very important. Because the film is very thin all contaminants such as fingerprints and polishing compound must be removed. Clean room practices similar to semiconductor manufacturing are used to prevent contamination of the pristine gemstone by air bourn dust. The result of this careful control is a perfect gem of exceptional sparkle, durability and beauty.
Additional Information can be found at;
http://en.wikipedia.org/wiki/Diamond-like_carbon
