Pressure Solid State Source LPSSS

Although the LPSSS method, invented by Roy s group in 1992, has not generated single crystal diamond films, it provides with useful information for diamond creation in metals. Indeed, the concept was already described in Section 9.2.1 for diamond heteroepitaxy on Ni. It seems that the LPSSS method will find practical applications in the fnture. It would thus be worthwhile to review the LPSSS method here. The LPSSS method using various carbon sources and metals (Mn, Fe, Co, Ni, Pt, Ag, Au, Cu) were published in Refs. [175, 391, 392, 412, 413], but only typical two techniques will be described below. 

The first is the method to use carbon, diamond powder, and hydrogen plasma [392] but without metals. The initial material was a gel that consisted of a mixture 

The second is an LPSSS method using Ni [412]. In this case, carbon (Aquadag), 10wt% Ni powder, and 1 wt% diamond of 1 pm in size were mixed, and a less than 10-pm thick layer of this material was applied on an Si or Mo substrate. By treating the specimen in a plasma of 1%CH4/H2, well-facetted diamond particles were grown. By contrast, no diamond was formed, if Ni had not been added. This experiment is different from the first case in that metallic catalyst is used. It is thus inferred that Ni plays an important role in the second case. 

In Ref. [414], a slurry of graphite powder was sprayed on a polycrystalline Pt substrate to form a 1-mm thick carbon layer. The specimen was first treated in hydrogen plasma at P = 40Torr, and 7 s==900°C for 30 min, which was followed by a high temperature treatment up to 1400 °C for 3 min to make a Pt-H-C phase. The specimen was then treated in the plasma of 0.5%CH4/H2 for lOh to grow out diamonds. Diamond partieles were grown on the Pt substrate, and notably, azimuthally (111(-oriented diamond partieles were formed in loeal areas. 

The mechanism of diamond formation by the LPSSS method using metal catalyst is considered to be similar to that of heteroepitaxial growth of diamond on Pt(lll) and Ir(lOO) described in Sections 12.1 and 12.2, because a metal-C H complex seems to be involved in the nucleation process. An advantage of the LPSSS method in view of engineering is that substrates with complex shapes could be coated with diamond. 

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Related to the CVD process is the low-pressure solid-state source (LPSSS) process, where preformed mixtures of carbon and diamond seeds [7] or carbon and metal [8] are treated in a H2 plasma, thus forming compact diamond ceramics. 

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