Subplantation

The reactions taking place at the growing surface of plasma-deposited a-C H were reviewed by Jacob [29], and from this discussion emerged a framework to understand the a-C H film deposition mechanism. This framework is to some extent equivalent to the subplantation model, since it emphasizes the role of energetic molecular ions. In addition, it takes into account the role of neutral radicals. 

Another possibility to explain the ion assisted c-BN deposition is the subplantation model. The nucleation of c-BN crystals takes place under the surface of the substrate caused by sub-plantation of the ions and stress. The sub-plantation and high nucleation rates result in the nano-cBN coatings. 

It was suggested by Spencer et al. in 1976 that the diamond like films are formed due to preferential sputtering of sp sites compared to sp sites. Later in 1990, Lifshitz et al. observed that this was unlikely due to the low sputtering yield of carbon and suggested the subplantation model . This model proposes that film growth from hyperthermal species occurs via the... 

Gerber et al. [221] investigated the nucleation density of diamond on Si, which was placed on a heated stage, by changing the BEN parameters the CH4 concentration c< 15%CH4/H2, V, the biasing time, and T. The nucleation density became maximum of approximately 10 °/cm for 7],. >740°C at F = -250V, and did not depend on the CH4 concentration. Indeed, c = 5 and 15%CH4/H2 resulted in the same saturated nucleation density. An estimated ion energy for optimum nucleation was 70-80 eV, and hence it was concluded that the BEN process proceeds by a subplantation of hydrocarbon ions. 

Several models are presently under discussion to explain the formation of highly tetrahedrally coordinated carbon ta-C. According to one of these theories the ta-C deposition can be described as a subplantation process [19, 29]. The principle of this process is that carbon ions penetrate the first atomic layers and enter interstitial positions, thereby increasing the local density and inducing local compressive... 

The deposition mechanism of a-C and a-C H with ion beams involves subplantation of incident atoms. The ion bombardment produces a denser but a less stable sp a-C phase. An atom s hybridization will readily adjust to the local density where the density and the sp fraction pass through a maximum as a function of the ion energy [25], It is not yet clear how the flux of carbon controls the sp lsp ratio in ion beam or in chemical vapor deposition. It is found that a-C films deposited from a pure C" ion beam have a maximal density and sp content for ion energies between 30 and 50 eV. As the collisions between C ions create vacancies. 

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