Ultraviolet laser-induced liquid-phase palladium seeding on polymers

Excimer laser pulses with wavelength of 308 nm, repetition rates of 1–10 Hz, pulse energies of 300–400 mJ, and pulse width of 20 ns are used to selectively seed palladium aggregates from a liquid-phase solution on polymer (polyimide) surfaces. The precursors used are PdCl2 in hydrochloric acid and Pd(CH3CO2)2 in acetic acid. The coverage of the polyimide with palladium aggregates is determined by the analysis of scanning electron microscopy measurements. Qualitative and quantitative analyses of seeded particles on polyimide (PI) are investigated by x-ray diffraction and transmission measurements. The amount of deposited palladium showed a quadratic dependence on the laser fluence reaching the surface. On the other hand, the coverage versus number of laser shots shows a square-root-like dependence. The palladium deposits also appear as amorphous and Pd[111] crystallites forms depending on the number of laser pulses. The roughness of a PI surface prior to seeding is modified mechanically and characterized by its fractal dimension. The fractal dimension of the samples varies between 2.3 and 2.7 for all the parameters applied, and the palladium deposition is found to be dependent on this dimension of the PI film.