This paper revies the preparation and properties of hard forms of amorphous carbon and hydrogenated amorphous carbon, often known as diamond-like carbon. Properties such as the hydrogen content, sp 3 content, optical gap, refractive index, hardness, elastic modulus and friction and their dependence on the deposition conditions are described. Models of the electronic structure and mechanical properties are used to relate the physical properties to the atomic structure.

Properties of diamond-like carbon

Hard amorphous (diamond-like) carbons

Diamond-like carbon — present status

Deposition mechanisms for promoting sp3 bonding in diamond-like carbon

Diamond-like carbon (DLC) films combine several excellent properties like high hardness, low friction coefficients and chemical inertness. The DLC coating material can be further classified in two main groups, the hydrogenated amorphous carbon (a-C:H, ta-C:H) and the hydrogen free amorphous carbon (a-C, ta-C). By adding other elements like metals (a-C:H:Me) or non-metal elements like silicon, oxygen, fluorine or others (a-C:H:X), several modifications of the properties can be adjusted according to application requirements. First reports on hard amorphous carbon films were published in the 1950s and about 20 years later there began worldwide intensive research activities on DLC. In the following years the number of publications increased continuously and the importance for industrial applications became more and more evident. Several deposition techniques were applied to prepare a-C:H, ta-C, metal containing a-C:H:Me and non-metal containing a-C:H:X coatings. In parallel the structure and deposition mechanisms of DLC coatings were extensively studied. An essential obstacle for a broad industrial application was the high compressive stress level in a-C:H films causing delamination and limiting the film thicknesses. With metal based intermediate layer systems most adhesion problems could be solved satisfactorily and thus from the mid-1990s the pre-conditions for a broad application especially in the automotive industry were given. With modified a-C:H:X and a-C:X coatings a considerable friction reduction or surface energy adjustments could be achieved.

History of diamond-like carbon films — From first experiments to worldwide applications

Properties of tetrahedral amorphous carbon prepared by vacuum arc deposition

Amorphous carbon (a-C) prepared by plasma-arc deposition has been examined by neutron scattering. Comparison of the position of the first C-C peak of the radial distribution function with similar data for crystalline diamond shows the amorphous material to be predominantly tetrahedrally bonded with about 14% trigonal bonding. Structural data indicate that this particular form of a-C is essentially analogous to the other tetrahedral amorphous elemental semiconductors, amorphous silicon and amorphous germanium

P. H. Gaskell

Papers

Properties of tetrahedral amorphous carbon prepared by vacuum arc deposition

The structure of highly tetrahedral amorphous diamond-like carbon. I : Neutron scattering studies