Berlin 2012 – scientific programme

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DS: Fachverband Dünne Schichten

DS 21: Micro- and nanopatterning (jointly with O)

DS 21.8: Talk

Wednesday, March 28, 2012, 13:30–13:45, H 0111

Time and space resolved pump-probe investigations on induced ablation of thin films with femtosecond laser pulses — •Stephan Rapp, Matthias Domke, and Heinz P. Huber — Munich University of Applied Sciences

An about 500 nm thin molybdenum film acts as p-contact for CIGS thin film solar cells, which has to be separated to serially interconnect the sub cells of a solar panel. The Mo can be structured either by irradiating the Mo from the front side or from the glass substrate side, resulting in a selective removal or a lift-off of an intact Mo cap, respectively. To investigate the underlying physical effects, a pump-probe setup is used for time- and space resolved microscopy. Several series of pictures are taken with time delays between femto- and microseconds, showing the complete temporal evolution of laser ablation (lift-off). The front side irradiation with fluences up to 5.0 J/cm² leads to thermal effects after a few picoseconds and after 100 ps ring systems appear. This suggests a bulging of the material. After 3 ns a shock wave crosses the sample with velocities from 675 to 3950 m/s. The substrate side irradiation with fluences up to 1.0 J/cm² initiates a decrease of the sample reflectivity due to heating for delay times up to 10 ps. Ring systems are formed after 4 ns and a model was created to determine the bulging height by analyzing these Newton′s rings. After the bulging a lift-off of an intact Mo cap can be observed at times between 10 and 40 ns for fluences above the ablation threshold which was determined to 0,6 J/cm².