Real-time volumetric growth rate measurements and feedback control of three-dimensional laser chemical vapor deposition
A method for controlling the reaction rate during laser-induced chemical vapor deposition was developed, which allows accurate reproduction of high-quality films and three-dimensional forms. From specific emission spectra generated during the heterogeneous reaction, a measure of the volumetric growth rate was obtained. By using this rate measure to modulate the laser power in real time, direct feedback control of the reaction rate was realized. High-aspect-ratio axi-symmetric forms of desired shape and microstructure were grown from vapor-phase precursors with this technique. Three-dimensional rods, cones, hyperboloids, and spheroids were prototyped. Materials deposited include: pyrolytic graphite, nickel, iron, and nickel-iron superalloys. These were grown from ethylene, nickel tetracarbonyl, iron pentacarbonyl, and mixtures of the nickel and iron carbonyls, respectively. Graphite and iron axial growth rates of up to 45 μm/s were obtained. By means of the feedback method, both layered and continuous prototyping on the micro-scale is feasible, since real-time compensation for growth rate perturbations can be made.