Space filling by nucleation and growth in chemical vapor deposition of diamond
- PDF / 530,317 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 34 Downloads / 193 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Space filling by nucleation and growth in chemical vapor deposition of diamond J. Stiegler, Y. von Kaenel, M. Cans, and E. Blank D´epartement de Mat´eriaux, Ecole Polytechnique F´ed´erale de Lausanne, CH-1015 Lausanne, Switzerland (Received 18 November 1994; accepted 6 November 1995)
Phase transformations, including chemical vapor deposition (CVD) of diamond, taking place by nucleation and growth are commonly described by Avrami or Johnson-Mehl type models. In order to avoid the restrictions of such models with respect to assumptions concerning nucleation rates and growth velocities, the variation with time of nucleation and growth of diamond particles during the deposition of microwave plasma-assisted CVD was studied. The size distributions obtained from image analysis enabled us to trace back details of the nucleation and growth history. Three sources of particle formation were operating during deposition. A general growth law suitable for all particles did not exist. These observations limited the applicability of Avrami-type models to describe space filling. Computer simulation of surface coverage and particle growth was successful because one particular mode of particle formation and growth dominated surface coverage. Based on image analysis and the determination of the film growth rate, the evolution of the diamond volume fraction with time, starting from three-dimensional particle growth followed by a continuous transition to one-dimensional film growth, was described.
I. INTRODUCTION
In chemical vapor deposition (CVD) of diamond films on non-diamond substrates, surface coverage occurs by island growth; i.e., nucleation is followed by grain growth and coalescence. The most common method to enhance the nucleation density is to abrade the surface with diamond powders, either by manual scratching or ultrasonic treatment.1–6 The effect of substrate pretreatment is still a matter of debate. Iijima et al. have shown that seeds of less than a few tens of nanometers are implanted in the substrate surface during sonicating with diamond powders,2 providing local seed densities as high as 1011 cm22 . Similarly, geometric features protruding from the substrate surface like sharp edges or apexes, as opposed to sharp valleys or flat regions, and carbonaceous phases in scratches have been reported to favor nucleation.4,5 During deposition nucleation centers can also disappear as a result of thermal annealing and erosion by atomic hydrogen.6 Recently, Molinari and co-workers, investigating nucleation and growth of hot filament CVD of diamond, have proposed a very detailed model describing the kinetics of heterogeneous nucleation on foreign substrates.7–10 The model, which is an extension of Avrami’s11 statistical treatment of the kinetics of phase change applied to diamond CVD, involves the time evolution of active sites, germs, and nuclei.7 By applying a uniform growth law for all particles, which has not 716
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 3, Mar
Data Loading...
