Light, incident on a supported dielectric film, undergoes absorption, scattering, and reflection that can be analyzed by standard optical techniques to determine the complex index of refraction, crystalline phase, residual stress, and film thickness. Subjecting metal oxide films to Q-switched laser irradiation above the bandgap at moderate fluence induces metal-oxygen bond breaking, release of oxygen from the lattice and formation of free carriers leading to permanent n-type conductivity in the film. At somewhat higher fluence, non-linear optical effects turn on as evidenced by 2nd (SHG) and 3rd (THG) harmonic generation. At still higher fluence, irreversible film modification occurs that includes compaction due to a “peening” effect, transformation to a different crystalline phase, and eventual catastrophic damage owing to material ablation from the surface. This presentation summarizes our nsec pulsed laser irradiation studies of these effects in aluminum doped ZnO films deposited on silica from solution or by means of rf sputtering. The formation of a persistent conducting state upon pulsed laser irradiation above the bandgap has implications to the field of transparent conducting oxides.
Bio: http://www.pnl.gov/science/staff/staff_info.asp?staff_num=5507
Refreshments will be served half an hour before the start of the colloquium in Weniger 305.