Enhanced nucleation of diamond on three dimensional tools via stabilized colloidal nanodiamond in electrostatic self-assembly seeding process.

Nanocrystalline diamond particles are promising candidates for copious applications in materials science, biology and electronics. In this work, diamond nucleation density was unprecedentedly enhanced via a non-invasive electrostatic self-assembly seeding approach. By addition of glutamic acid to the nanodiamond seeding solution, the positively charged amino-group of glutamic acid, which is adsorbed on nanodiamond particles, enhances the adsorption on negative charged cemented carbide substrate. The highest nucleation density (1.0×1010 cm-2 ) was achieved by utilizing glutamic acid at pH 4 as well as DI water at pH 2.2. This density was 20-1000 times higher than most earlier published results on WC-Co substrate. The concentration of the organic molecule, pH, concentration of ND particles and ultrasonication seeding time were found to be important for the seeding process. The colloidal stability was tweaked by pH of the dispersion and concentration of glutamic acid. The optimized parameters for nanodiamond adsorption on WC-Co substrate were found to be pH 4 at a concentration of 7×10-5 M of glutamic acid at a nanodiamond concentration of 0.005wt%, while the seeding was conducted for 30min. The short ultrasonication time inhibits aggregation and void formation due to peeling off of nanodiamond patches at prolonged seeding times. Moreover, diamond thin films were deposited uniformly and densely on end mills made of cemented carbide. This work indicates that electrostatic induced adsorption of diamond nanoparticles is crucial for the development of ultra-high nucleation densities for the growth of high performance nanocrystalline diamond films, especially for micro sized tools with sharp cutting edges. It may serve as an approach for pinhole-free ultra-thin films deposition on micro-electromechanical system, and encapsulation coating in harsh environment.