ABSORPTION SPECTROSCOPIC MEASUREMENTS OF PLUME DENSITY AND TEMPERATURE IN PRODUCTION OF NANOCRYSTALLINE NBAL3 BY LASER-ABLATION DEPOSITION

Nanocrystalline NbAl3 powders were synthesized via ablation of a sintered NbAl3 target by a KrF excimer laser. Laser absorption spectroscopy employing a tunable dye laser was used to measure the density distributions of several electronic states of neutral niobium atoms within the ablation plume. Comparisons between these level populations exhibit the degree to which local thermodynamic equilibrium is satisfied. Peak values of measured densities were in the range 1011-1012 cm-3. Atomic velocities perpendicular to the target of (1-7.5)×105 cm/sec were measured by time-of-flight calculations based on arrival time of the absorption signal. Doppler widths of the absorption transitions were used to estimate the transverse velocities. Mean velocities varied over (3.9-9.2)×105 cm/sec. Correlations between the observed plume characteristics and the process yield and mean particle size were proposed. © 1995 The American Physical Society.