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M. Zhong and P. Fan
2.3 Fabrication of Metals Surface Micro-nano Structures
2.3.1 Fabrication of Metal Surface Nanoripples
and Nanoparticles
The formation of LIPSS (i.e., laser-induced periodic surface structures) under laser
irradiation is a well-known phenomenon and has been being studied since years
ago. As a special type of LIPSS, nanoripples with spatial periodicities obviously
shorter than the irradiation laser wavelengths have exhibited many unique physical
properties and thus attracted numerous research interests. With the high repetition
rate high power ultrafast lasers, we have also produced nanoripples on metal surfaces.
Figure 2.6a shows a typical SEM image of these nanoripples. Through continuous
laser scanning where the adjacent laser tracks were partially overlapped to each
other, continuous and long ripples perpendicular to the linear polarization vector of
the laser beam can be produced. Figure 2.6b shows a AFM image of the nanoripples,
which have clear contours. From the cross-sectional profile shown in Fig. 2.6c, it can
be seen that the nanoripples have an average height of 270 ± 22 nm and an average
periodicity of 750 ± 31 nm, which is significantly smaller than the wavelength of
laser utilized (1064 nm).
Another major type of nanoscale feature generated by the high repetition rate high
power ultrafast lasers is nanoparticles. Our investigations show that the nanoparticle distributions on metal surfaces can be effectively controllable by sequentially
changing the ultrafast laser processing parameters. Figure 2.7 demonstrates typical
morphologies of nanoscale features produced under ultrafast laser on copper, where
nanoparticles are found to be existing together with irregular surface nanostructures. Most nanoparticles are spherical in shape, with their diameters varying from
a few to over a hundred nanometers. Those nanoparticles distribute randomly over
the nanostructured copper surfaces, with no obvious orientations. With a relatively
lower scanning speed, like 2000 mm s
−1 , and correspondingly higher energy input
per area, more abundant nanoparticles tend to be produced, covering the areas both
around and among the surface nanostructures.
Statistical analysis on the radius distribution of the nanoparticles was made (see
Fig. 2.8). Most of nanoparticles on the nanostructured copper surfaces are smaller
than 100 nm in radii. Besides, the radius distributions are pretty narrow, with over
80% of the nanoparticles having a radius below 60 nm for all studied conditions. As
the scanning speed decreases, two evolution trends ban be observed. On the one hand,
the number densities of nanoparticles in all radius ranges increase simultaneously,
resulting in an obvious increase in the total number of nanoparticles from near 50 to
about 125 per 10 µm
2 . On the other hand, the mean radius of nanoparticles is kept
almost constant, showing only a slight increase from 42 to 48 nm. As a consequence,
the mean distance between these nanoparticles decreases obviously from ~400 to
~200 nm. Nanoparticle features with similar distributions have also been produced
on other metal surfaces like steel, titanium, aluminum, etc. It is well known that
metallic nanoparticles can induce unique localized surface plasmon resonance effect,
M. Zhong and P. Fan
2.3 Fabrication of Metals Surface Micro-nano Structures
2.3.1 Fabrication of Metal Surface Nanoripples
and Nanoparticles
The formation of LIPSS (i.e., laser-induced periodic surface structures) under laser
irradiation is a well-known phenomenon and has been being studied since years
ago. As a special type of LIPSS, nanoripples with spatial periodicities obviously
shorter than the irradiation laser wavelengths have exhibited many unique physical
properties and thus attracted numerous research interests. With the high repetition
rate high power ultrafast lasers, we have also produced nanoripples on metal surfaces.
Figure 2.6a shows a typical SEM image of these nanoripples. Through continuous
laser scanning where the adjacent laser tracks were partially overlapped to each
other, continuous and long ripples perpendicular to the linear polarization vector of
the laser beam can be produced. Figure 2.6b shows a AFM image of the nanoripples,
which have clear contours. From the cross-sectional profile shown in Fig. 2.6c, it can
be seen that the nanoripples have an average height of 270 ± 22 nm and an average
periodicity of 750 ± 31 nm, which is significantly smaller than the wavelength of
laser utilized (1064 nm).
Another major type of nanoscale feature generated by the high repetition rate high
power ultrafast lasers is nanoparticles. Our investigations show that the nanoparticle distributions on metal surfaces can be effectively controllable by sequentially
changing the ultrafast laser processing parameters. Figure 2.7 demonstrates typical
morphologies of nanoscale features produced under ultrafast laser on copper, where
nanoparticles are found to be existing together with irregular surface nanostructures. Most nanoparticles are spherical in shape, with their diameters varying from
a few to over a hundred nanometers. Those nanoparticles distribute randomly over
the nanostructured copper surfaces, with no obvious orientations. With a relatively
lower scanning speed, like 2000 mm s
−1 , and correspondingly higher energy input
per area, more abundant nanoparticles tend to be produced, covering the areas both
around and among the surface nanostructures.
Statistical analysis on the radius distribution of the nanoparticles was made (see
Fig. 2.8). Most of nanoparticles on the nanostructured copper surfaces are smaller
than 100 nm in radii. Besides, the radius distributions are pretty narrow, with over
80% of the nanoparticles having a radius below 60 nm for all studied conditions. As
the scanning speed decreases, two evolution trends ban be observed. On the one hand,
the number densities of nanoparticles in all radius ranges increase simultaneously,
resulting in an obvious increase in the total number of nanoparticles from near 50 to
about 125 per 10 µm
2 . On the other hand, the mean radius of nanoparticles is kept
almost constant, showing only a slight increase from 42 to 48 nm. As a consequence,
the mean distance between these nanoparticles decreases obviously from ~400 to
~200 nm. Nanoparticle features with similar distributions have also been produced
on other metal surfaces like steel, titanium, aluminum, etc. It is well known that
metallic nanoparticles can induce unique localized surface plasmon resonance effect,