Three-Dimensional Laser Chemical Vapor Deposition of Nickel-Iron Alloys
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Mat. Res. Soc. Symp. Proc. Vol. 397 01996 Materials Research Society
Fig. 1 (a) Ni-Fe Needle grown at 300 mW and Fe(CO)5 and Ni(CO) 4 partial pressures of 20 mbar each. (b) Same needle sectioned longitudinally. Another interesting feature is that other modes of heat loss, such as radiation and natural convection, are only effective when the surface area of the deposit reaches a critical size. It can be shown that in the kinetic regime, the balance of heat losses to the input power of the beam ultimately determines the steady-state diameter of rods grown in this manner [12]. In this paper, we investigate the influence of precursor partial pressures and incident laser power on the growth rates and composition of 3-dimensional rods and bulbs grown from a mixture of nickel and iron carbonyls. Besides demonstrating the potential of 3D-LCVD for the prototyping of alloys, the purpose of the experiment was to determine variations in final deposit compositions-so that the temperature changes during rod growth can be determined-as well as the difference in activation energies (Ea) of the iron and nickel carbonyl precursors. We chose two deposit materials with
nearly identical thermal conductivities to simplify the analysis, and similar threshold decomposition temperatures, Td (see table I). Table I: Thermophysical Properties of Me, Me(CO)x.[Source: 13] Me
Me
Me (CO)x
Me(CO)x
Me
k [W/cm K]
M.P. [K]
Td [C]
Ea [kJ/mol]
Ni Fe
0.66 (@ 600 C) 0.55 (@600 C)
1726 1810
150 200
48-49 N/A
EXPERIMENTAL The 3D-LCVD reactor at Rensselaer consists of a custom quartz tube with several ports for viewing and laser input. The chamber is connected to a pumping station via a gate valve which sets the total system pressure during operation. The vacuum chamber and gas-delivery system are enclosed within a ventilated hood for safety purposes, and the quartz tube is suspended from a heavy superstructure to isolate the system from vibration. The iron pentacarbonyl was delivered to the reaction chamber via an evaporator. In this experiment, the room-temperature vapor pressure of Fe(CO) was used to fill the chamber. In most cases, a 20 mbar chamber partial pressure of the precursor was employed. The Fe(CO) 5 was transferred to the evaporator under subdued light, within a fume hood, and in an inert atmosphere. A burn-box and scrubber were used to dispose of the unused precursors after each experiment. 602
Following each Fe(CO) 5 fill, nickel tetracarbonyl was metered into the system from a commercial cylinder to achieve a desired total pressure and vapor composition; the sample cylinder was cooled to 12'C to reduce the chance of Ni(CO) 4 condensation at high pressures. A static fill was employed for all experiments, as the total volume of the chamber is large enough to neglect changes in ambient gas composition during the growth of a single rod (less than 1% increase in by-product volume percent). The chamber was evacuated and refilled following the growth of each sample microstructure, and the chamber windows were cleaned periodicall
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