Regensburg 2002 – wissenschaftliches Programm
DS 20.1: Vortrag
Donnerstag, 14. März 2002, 11:45–12:00, HS 31
Mass transport mechanisms during excimer laser nitriding of aluminum — •Ettore Carpene and Peter Schaaf — Zweites Physikalisches Institut,Universität Göttingen, Bunsenstrasse 7/9, D-37073, Göttingen, Germany
Surface layers of aluminum nitride were formed by irradiating pure aluminum substrates in nitrogen atmosphere with a pulsed excimer laser. The beam was focused on the sample placed inside a chamber filled with nitrogen gas. The irradiation was carried out at various laser fluences, nitrogen gas pressures and numbers of pulses in order to investigate the influence of each parameter on the nitrogen incorporation and the mass transport mechanisms. The thermal simulations and the experimental evidence show that for fluences higher than 3 J/cm2 the temperature of the substrate exceeds 2900 K. This value is higher than the dissociation temperature (∼2400 K) and close to the melting point (∼3070 K) of AlN, which can therefore dissociate or melt. The atomic nitrogen can rapidly diffuse to greater depths in the liquid Al matrix or it can degas (outgas) through the surface of the sample, leading to the formation of rather homogeneous concentration profiles. For fluences lower than 3 J/cm2 the temperature of the substrate is not sufficient to destroy the present AlN grains and they can move inside the molten Al. In this case, the material transport can be attributed to Brownian motion and thermophoretic drift, which in turn are correlated with the chemical and thermal gradient, respectively .
 E. Carpene and P. Schaaf, Phys. Rev. B, submitted.