ABSTRACTA systematic study of the composition of Ni-Fe steel microstructures grown from iron pentacarbonyl and nickel tetracarbonyl by direct laser-induced pyrolysis is presented. The partial pressures of both precursors were varied from 2 to 40 mbar, resulting in needles of iron, nickel, and iron-nickel alloys. An Ar+ laser was employed at incident powers of 100 to 600 mW. Auger Spectroscopy and a microprobe were used to determine the composition of the needles vs. partial pressure and laser power. Composition was also measured along the length of the rods to determine temperature changes during needle growth. This latter effect is useful in modelling the heat flow mechanisms during 3-dimensional laser CVD, as the threshold decomposition temperatures of Fe(CO)5 and Ni(CO)4 differ and the composition of the rods affects their thermal conductivity. In some iron samples, periodic banded structures were observed along the length of the rods, indicative of periodic melting. Axial deposition rates were also measured relative to laser power density, and rates up to 40 μm/s were achieved. Photolysis in the gas phase was observed for the iron-nickel carbonyl mixture, and was largely eliminated with a high-pass UV filter at 420nm. Additional disassociation of the carbonyl groups produced carbon soot near the reaction zone, but only for high nickel carbonyl concentrations. Convective cooling of the needles during growth was determined to be the primary heat transfer mechanism.
High-Speed Deposition of Highly-Oriented Calcium Titanate Film by Laser CVD