X-ray photoelectron spectroscopy of uv laser irradiated sapphire and alumina

Abstract

X-ray photoelectron spectroscopy (XPS) was performed in as-received, thermally annealed, and laser-irradiated sapphire and alumina specimens in order to study the effects of the different treatments on surface chemistry and properties. Laser irradiations with a 308 nm wavelength laser were performed in air and in a reducing atmosphere consisting of a mixture of Ar and 4% of hydrogen. The atomic percentages of carbon, aluminum, and oxygen were measured in all the specimens. Particular attention was paid to the percentages of oxygen in the oxide and in a hydroxyl state. The XPS analyses clearly established that a very thin film of metallic aluminum is formed on the surface of both alumina and sapphire substrates when they are irradiated under a reducing atmosphere. However, the film is discontinuous because it is electrically insulating. Substrates irradiated in air have metallic aluminum only for fluences below 0.4 J/cm2. The valence band photoemission spectra of as-received, annealed, and laser-irradiated specimens were measured. In irradiated specimens, the width of the valence band spectra was found to decrease by ∼10%. One possible cause of this decrease is the generation of point defects during laser irradiation. Electroless copper deposition occurs on sapphire and alumina substrates if their surface has been activated by laser irradiation. The time required for copper deposition was monitored by measuring the electrical resistivity in the irradiated area while the substrates were immersed in an electroless bath. The kinetics of deposition on laser-activated substrates and the XPS results show that the presence of metallic aluminum accelerates the deposition process. However, the presence of aluminum is not the sole reason for laser activation in alumina. Very strong metal-ceramic bonding is produced after thermal annealing of samples having preirradiated substrates. This result is explained in terms of the excess oxygen that is present at the ceramic surface after irradiation.