M. Bystrzejewski et al. / Chemical Physics Letters 444 (2007) 113–117
117
ble to evaluate the relative content of amorphous nanopar-
ticles. High surface area and small Lc size reveal that sam-
ple 4 is the most rich in the amorphous phase. Since the
carbon coating on the magnetic nanoparticles is thin and
well graphitized (Fig. 2b) the CEMNPs should be more
resistant to the laser beam action. Thus, one can conclude
that the OL response is mostly caused by amorphous car-
bon nanoparticles. The optical limiting threshold (Table
1) is enhanced with the increase of the amorphous carbon
content. This observation is consistent to the results
obtained by Chen et al. [24]. It follows from that the car-
bon-encapsulated magnetic nanoparticles are rather very
poor optical limiters and the observed optical limiting
response results from the amorphous carbon phase. It
was recently reported that the suspensions of well crystal-
lized nanoparticles exhibit enhanced thermal conductivity
and mass transport [25,26]. Hence, it cannot be excluded
that CEMNPs may favor the heat transfer and mass trans-
port. It can also influence on the generation of bubbles and
expansion of shockwaves during laser irradiation.
thanks DFG (Grant No DFG 436POL) and the Founda-
tion for Polish Science (FNP) for the financial support.
Tartu Technologies (Tartu, Estonia) is acknowledged for
BET measurements.
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Acknowledgements
This work was supported by the Ministry of Science and
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