Direct Feedback Control of Gas-Phase Laser-Induced Deposition

Three-dimensional laser Chemical vapor deposition (3D-LCVD) or SALD, was used to prototype metallic and ceramic microstructures. Iron, nickel, and steel metal forms were grown from organic and halogen based precursors. Through the simultaneous use of multiple precursors, specific nickel-iron based alloys were produced. By observing the emission spectra during growth, a measure ofthe volumetric growth rate, was obtained. Direct, PID control ofthe process was then possible using the growth rate measurement as real-time feedback. Calibrated infrared photographs of evolving microstructures were taken at various wavelengths, giving a measure of the temperature gradient over the growth zone. While radiation contributes to heat losses at high temperatures, enhanced convection is the dominant heat transfer mechanism due to the small dimensions of the heated area. Enhanced growth rates, induced by convective flow, were also observed. The heat and mass transfer coefficients were determinedfor various processing conditions, and compare well with experimental data. Axi-symmetric rods may also be grown in both the kinetic and transport-limited regimes, and a systematic study of the precursor pressure and deposit temperature during growth yielded distinct growth regimes, influn, ced by the interplay of heat losses and diffusive transport.