Diamond Veneer Technology Diamond Carbon Coating

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Diamond Carbon Coating:

 Diamond Veneer Technology produces a revolutionary Carbon Diamond treatment for the enhancement of gemstones, such as Cubic zirconia (CZ),

The term Carbon Diamond describes a group of materials with a wide range of properties. Diamond Veneer is generally amorphous, having no overall crystal structure as do graphite and diamond. The Veneer may have hydrogen, nitrogen or other elements incorporated into it. Hydrogen for example reduces the internal stress of the Coating making it less susceptible to peeling. The ideal type of coating and method of application depends upon the use to which it will be put.

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. Diamond veneer can be thought of as a mixture of these crystal forms at the nano-scale along with amorphous carbon. Amorphous carbon, which means noncrystaline carbon can also have a variety of structures depending upon the nature of it’ carbon-carbon bonds. Amorphous carbon has no long-range crystal structure.

Carbon to carbon bonds are defined by their ‘hbridization’ 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. DV has a variety of bonds and one of the defining properties of DV 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 the 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.

DV 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

 

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 coated 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 coated film and the force required relates to the film hardness. Some coated films with sp³ nano crystalline phases have zones that actually measure harder than diamond. The diamond tip, being softer than this ultrahard carbon phase may actually shatter during the measurement. This is an amazing result because no known bulk material is harder than diamond.

Diamond Veneer coating requires sophisticated and expensive equipment so the cost of deposition is usually an important issue.  On the plus side the process is very ‘Green”. They are vacuum processes using small quantities of safe gasses and so are environmentally benign.

 

The Diamond Veneer 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 Carbon Diamond  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.

 

Diamond Veneer  uses the Microwave Assisted Chemical Vapor Deposition (MACVD) method of depositing DV film. Hydrogen and nitrogen are used as dopants to make hard, transparent well adhering films. Our films thus fall into the modified hydrogenated amorphous carbon (a-C:H:X) category. Cost is kept low with a custom coating machine using components from conventional microwave oven technology. This allows us to accurately control all of the relevant process parameters such as plasma energy, process pressure, gas composition and coating geometry. The resulting process produces very uniform, consistently hard and durable films with excellent adhesion at an affordable price.  

 

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.