Date of Award
Doctor of Philosophy (PhD)
Three-dimensional laser chemical vapor deposition (3D-LCVD) has been used to grow rods of carbon, tungsten, titanium, and hafnium from a variety of hydrocarbons and metal halide-based precursors. A novel computerized 3D-LCVD system was designed and successfully used in the experiments. A focused Nd:Yag laser beam (λ = 1.06 μm) was utilized to locally heat up a substrate to deposition temperature. The rods, which grew along the axis of the laser beam, had a typical diameter of 30–80 μm and a length of about 1 mm. The precursors for carbon deposition were the alkynes: propyne, butyne, pentyne, hexyne, and octyne. Propyne gave the highest deposition rate, in excess 3 mm/s at high laser powers (0.45 W) and high partial pressures (3000 mbar). the temperature dependence and pressure dependence were both non-linear functions of the growth rate. the temperature dependence could be separated into two regions—the kinetically limited region, which obeys the Arrhenius relationship, and the transport limited region, which is explained by diffusion of the precursors to the reaction zone. The pressure dependence showed that the reaction order for the different precursors varied from 2.5 for propyne to 1.3 for octyne.
The precursors used deposit the refractory metals were tungsten hexafloride, titanium tetraiodide and hafnium chloride. The only successful precursor was tungsten hexafluoride, which readily produced tungsten rods when mixed with hydrogen. Rod diameters typically ranged from 50 μm to 400 μm and the average length of the rods were about 1 mm. Much lower deposition rates, less than 4.5 μm/s were obtained in this case as compared to carbon deposition. By an optimization of the LCVD process, it was possible to deposit high-quality single crystal tungsten rods. They were all oriented in the ⟨100⟩ direction.
Gao, Feng, "" (2000). Dissertation. 164.