30 May 2019

GROWTH

Boron doped nanocrystalline diamond growth process

The synthesis of boron doped nano- micro-crystalline diamond films on carbon fiber (based on PAN: polyacrylonitrile) to obtain modified carbon fiber reinforced polymer (CFRP) materials can make this material stiffer, tougher  and more mechanically resistant.  In addtion, the addtion of boron transforms it in thermal and electrical conductive. However, grain size and geometrical configuration, proportion of sp2/sp3 as well as CF/diamond interface bonding are fundamental issues that can vary the latter properties. The surface characterization of CFRP materials, their  surface functionalization as well as  the nucleations and growth mechansims of the diamond phase are some of these questions.  

Some studies have showed that the presence of graphitic carbon on the growth surface is related to the high quality of the nanocrystalline diamond film formationThe graphite and the unsaturated aromatic compounds serve as sites for the diamond nucleations and enhance the nucleation centers due to the preferential growth of the diamond nuclei on graphite prism planes. 

In this context, the roughness of CF materials could assist the graphitic phase nucleation, so the higher the values of roughness you have the more specific sites with high surface enery would be provided. This energy could be used to enhance the surface proportion of sp2 carbon through physical adhesion and/or chemical bonding of diamond seeds or different organic groups. Therefore the CF carbon fiber charaterization becomes a crucial step in the boron doped diamond growth process. 

To set the role of CF surface, the b-doped diamond growth could be optimized to get grain size of the order of several microns. It’s known that the syntehsis of nanocrsytalline diamond (NCD) is a result of a new growth and nucleation mechanis, which involve the insertion of C2, carbon dimmer, into C/C and C/H bonds. By changing the gas phase chemistry of the chemical vapor deposition process (CVD), it is possible to change the diamond grain size. Nevertheless different questions about the LAPECVD growth process  remain open yet, such as those related to the influence of surface energy of diamond seeds  in the B-NCD nucleation and growth, as well as,  the relation between the gas fluxes and optimum diamond size grains. In the CFRP composite materials, the size of the particles play an important role into adherence mechanisms inside the epoxy matrix which are responsible of final mechanical behaviour.  It is required to establish desing rules to achieve a compromise between mechanical-electrical properties of such materials and its aerospace applications. 

In summary, our research group could contribute to improving the electrical-thermal-mechanical properties of carbon fiber and to understanding the impact of this diamond coating at nanometer scale.