Structuring of Metal Surfaces by Ultra-Short Pulsed Laser Irradiation

STRUCTURING OF METAL SURFACES BY ULTRA-SHORT PULSED LASER IRRADIATION 

The morphology of the surface topography depends on the laser processing parameters in addition to the material properties. It is noteworthy that all structures are formed on the surfaces long after the laser pulse absorption has taken place. 

For ultra-short pulsed laser irradiation of metals, with pulse duration smaller than 1 ps, two different ablation regimes, termed gentle and strong ablation, are observed (Nolte et al., 1997). At laser fluences (laser pulse energy per unit area) just above the ablation threshold, the average ablation rate is determined by the optical penetration depth (for example, 13 nm for copper) of laser radiation in metal. The average ablation rate is low. The processed area is relatively smooth with nanometer-sized 

Surfaces containing spike structures show promise for the fabrication of superhydrophobic metallic surfaces due to their particular shape (concave structure with high aspect ratio, covered with nanoroughness). Note that the spikes that have been generated on semiconductor surfaces have been intensively studied in the past, inter alia, because of their superhydrophobic properties (Baldacchini et al., 2006 Zorba et al., 2006,2008). 

The first tier is composed of spikes. The second tier, generated on the spike surface, contains nanostructures that are typical for the gentle ablation regime and redeposited ablation nanoparticles. The hierarchical surface structures of this type have been shown to be one of the key factors for a surface to exhibit superhydrophobic properties (Bhushan et al.,2009). 

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