Diamond nucleation and growth in the combustion-flame method were monitored in real time using thermionic emission current from the deposited diamond films. It was observed that the emission current evolved over three periods, the incubation, the fast increase, and the saturation periods. Ball-shaped diamond particles, faceted diamond crystals, and diamond films with well-faceted crystals were formed in the three periods. The current from a diamond-seeded substrate started to increase immediately without an incubation period, continuing that the current is from the diamond. Therefore, the current could be used for real-time monitoring of the diamond nucleation and growth. (c) 2007 Elsevier B.V. All rights reserved.