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S. Bashir, M. Rafique, C. Nathala, W. Husinsky:
"The formation of nanodimensional structures on the surface of Tin exposed to femtosecond laser pulses in the ambient environment of ethanol";
Applied Surface Science, 290 (2014), 53 - 58.

The formation of nanodimensional structures on the surface of Tin (Sn) has been explored as a function
of the laser fluence and pulse duration. The targets were exposed by employing femtosecond pulses of
a Ti: Sapphire laser (wavelength of 800 nm, pulse length of 25 fs and pulse repetition rate of 1 kHz) in
ethanol. In order to investigate the effect of fluence, the targets were exposed to 1000 succeeding pulses
for four various fluences ranging from 4.7 to 11.8 J cm−2 with the pulse duration of 25 fs. To probe the
effect of pulse duration, targets were exposed for various pulse durations ranging from 25 fs to 100 fs
at a constant fluence of 11.8 J cm−2 (i.e. maximum). Nano sized structures including globules, droplets,
craters and grooves were observed by SEM analysis. The dependence of structure formation on the laser
fluence and pulse duration has been explored both for central as well as peripheral ablated areas. For
increasing fluences, the more energy deposition is responsible for the growth of distinct features. For
increasing fluence, the size distribution of nanostructures reduces and their number density increases
after fragmentation. As the pulse width increases, the size distribution of structures increases significantly
due to enhanced thermal effects. The development of nanostructures has been correlated with structural
analysis carried out by micro-Raman spectroscopy. The formation of various bands e.g. SnO, SnO2, C2H5
Sn, Sn-CO complexes after laser irradiation of Sn in a liquid-confined environment (ethanol) has been
observed. For higher fluences more energy deposition takes place which enhances the chemical reactivity
and is responsible for an appearance of additional and strong bands. However, with increasing pulse
width more thermal effects are responsible for bond breaking and disappearance of those peaks which
are identified for the shortest pulse duration. It is found first time that both the pulse duration as well
as laser fluence are promising parameters to be explored for the modification of the Sn surface. The
optimum growth of smallest structures is possible only for the highest fluence and the shortest pulse
duration within the utilized range of parameters where the maximum chemical reactivity takes place.

Femtosecond laser pulses Fluence Pulse width Surface structures SEM Raman spectroscopy