7 Micro-hole Arrays and Net-like Structure Fabrication …
223
Fig. 7.10 SEM images of the inlet hole (left) and the outlet hole (right) at different ambient pressures
[24]
by an increase in ambient pressure, which results in an increase in the amount of
redeposited material around the holes. When the ambient pressure is 5500 Pa or
higher, the re-deposited ablative material is confined into the ablation holes. This
will reduce the amount of ablative material around the hole.
Substrate temperature is an important parameter for controlling the properties of
femtosecond laser-induced surface structures besides traditional ways [25]. In 2014,
the S. K. Moon group of the School of Mechanical and Aerospace Engineering at
Nanyang Technological University evaluated the effects of the hole geometry and
the spatter area around the drilled hole on silicon with various temperatures [26].
Figure 7.11 is SEM images of the front side and back side micro-holes array drilled
by femtosecond laser with power of 200 mW at different temperatures. The laser
drilling efficiency is increased by 56% when the temperature is elevated from 300 to
873 K. The spatter area is found to continuously decrease with increasing substrate
temperature; the diameter of inlet holes was reduced by 25% when temperature is
873 K compared to 300 K. The reason for this change is that the elevated temperature
of the substrate leads to the increase of the laser energy absorption.
In 2004, P. Simon group of the Laser Laboratory in Göttingen in Germany fabricated a large number of micro-holes patterns on the titanium film using the ultraviolet
femtosecond laser interference technique as shown in Fig. 7.12 [27]. Diameter of
the holes is about 400 nm, and the micro-holes have good quality. This technology
223
Fig. 7.10 SEM images of the inlet hole (left) and the outlet hole (right) at different ambient pressures
[24]
by an increase in ambient pressure, which results in an increase in the amount of
redeposited material around the holes. When the ambient pressure is 5500 Pa or
higher, the re-deposited ablative material is confined into the ablation holes. This
will reduce the amount of ablative material around the hole.
Substrate temperature is an important parameter for controlling the properties of
femtosecond laser-induced surface structures besides traditional ways [25]. In 2014,
the S. K. Moon group of the School of Mechanical and Aerospace Engineering at
Nanyang Technological University evaluated the effects of the hole geometry and
the spatter area around the drilled hole on silicon with various temperatures [26].
Figure 7.11 is SEM images of the front side and back side micro-holes array drilled
by femtosecond laser with power of 200 mW at different temperatures. The laser
drilling efficiency is increased by 56% when the temperature is elevated from 300 to
873 K. The spatter area is found to continuously decrease with increasing substrate
temperature; the diameter of inlet holes was reduced by 25% when temperature is
873 K compared to 300 K. The reason for this change is that the elevated temperature
of the substrate leads to the increase of the laser energy absorption.
In 2004, P. Simon group of the Laser Laboratory in Göttingen in Germany fabricated a large number of micro-holes patterns on the titanium film using the ultraviolet
femtosecond laser interference technique as shown in Fig. 7.12 [27]. Diameter of
the holes is about 400 nm, and the micro-holes have good quality. This technology