Laser Encapsulation of Metallic Films in SiO 2
- PDF / 2,095,130 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 81 Downloads / 213 Views
2
A. J. PEDRAZA S. CAO*, D. H. LOWNDES** AND L. F. ALLARD * Dept. of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996-2200, [email protected] ** Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6056 High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, "TN37831-6064 ABSTRACT Thin films of gold, copper and iron deposited on silica were driven into the substrate by a laser pulse. This transport takes place only when the irradiation is performed at a laser energy density of 0.7 J/cm 2 or lower. Cross sectional transmission electron microscopy (TEM) of the irradiated specimens reveals two distinctive stages in the encapsulation process. In the first, the film melts and clusters into small particles and in the second one the particles are driven into the substrate by the laser pulse. The particle size of encapsulated metal varies from 5 to 50 nm. Selected area diffraction of the large particles and lattice fringe images of the smaller particles reveal pure metals, e.g., gold, copper or iron. Titanium films laser irradiated are not encapsulated in silica; instead, these films react with silica forming an amorphous compound. Apparently, one of the conditions required for encapsulation is that the metal should not react with the substrate material. On subsequent irradiation at a laser energy density of 1.5 J/cm 2 , ablation of silica partially exposes the metallic particles. Strong bonding between a new film deposited after irradiation and the substrate is obtained because these particles anchor the freshly deposited film. Anchoring is clearly revealed by cross sectional TEM. The mechanisms of encapsulation are discussed using results from TEM and adhesion testing. INTRODUCTION The research presented here is part of a study on the effects of pulsed-laser irradiation on ceramic substrates and metal/ceramics couples. In previous studies we have seen that the near surface regions of alumina and of aluminum nitride are strongly modified by pulsed laser irradiation.[ 1-4] For laser irradiations at or below I J/cm 2 the surface of alumina is amorphized, and in sapphire a-A12 0 3 is transformed into -y-A12 0 3 at laser energy densities of the order of 4 J/cm 2 [5]. Thermal decomposition of AIN takes place during laser irradiation and metallic aluminum is left on the substrate surface [6]. The amount of aluminum produced by laser irradiation of AlN is a function of the irradiation atmosphere. After irradiation in a reducing atmosphere, the amount of metallic aluminum present on these substrates is significantly larger than the amount present when the irradiation is performed in air or in an oxygen-rich atmosphere. Part of the metallic aluminum produced during thermal decomposition forms A12 0 3 during irradiation in an oxidizing atmosphere. Reduction takes place in the near-surface region of A1203 when laser irradiation is performed in Ar-4% H2. Transmission electron microscopy shows that very small particles of metallic aluminum ranging in size from 2 t
Data Loading...
