7 Micro-hole Arrays and Net-like Structure Fabrication …
239
Fig. 7.28 Optical micrographs of microfluidic channels. a After direct writing; b enlarged image
of figure a; c after selective chemical etching; d enlarged image of figure c; e fabricated net-like
triangular microfluidic channels [47]
It can be easily found that there were a handful of recasts around the ablation area,
besides the embossment and scallops that existed on the straight channels which seriously impact the roughness of microfluidic channels. After the etching process, top
view optical micrographs of microfluidic channels are shown in Fig. 7.28c, d. Recasts
have almost disappeared, and besides the microfluidic channels have become more
homogeneous. By comparing the optical micrographs of microfluidic channels after
direct writing with post-chemical etching, it can be easily found that the roughness
and morphology of microfluidic channels both effectively improve after etching.
Meanwhile, after etching, the width of microfluidic channels increased to some
extent.
The SEM images of the surface morphology of the sample after etching are shown
in Fig. 7.29. The overall profile of the net-like microfluidic channel is shown in
Fig. 7.29a. Figure 7.29b is an enlarged image of the microfluidic channels with
the focus located on the substrate surface. Figure 7.29c shows the morphology of
microfluidic channel when the focus is located at the bottom of the microfluidic
channel. It is clear that the microfluidic channel after selective chemical etching still
shows relatively high surface roughness, which can be attributed to the fact that the
SEM has a greater depth of field compared with an optical microscope, and there
is always a certain inclination in internal face of the channel particularly near the
surface of the substrate (silver zonal region in Fig. 7.29c). The reason why the silver
zonal region existed is that the focus position is fixed in the FLDW process; thus, the
spot becomes larger with the increase of machining depth. Furthermore, the areas
reached the damage threshold will become smaller when the Gaussian femtosecond
laser beam becomes larger, and then the width of the channel will decrease with
depth increase of channel. Eventually, the fabricated microfluidic channel presents
a slope feature in the direction of microfluidic channel depth.
239
Fig. 7.28 Optical micrographs of microfluidic channels. a After direct writing; b enlarged image
of figure a; c after selective chemical etching; d enlarged image of figure c; e fabricated net-like
triangular microfluidic channels [47]
It can be easily found that there were a handful of recasts around the ablation area,
besides the embossment and scallops that existed on the straight channels which seriously impact the roughness of microfluidic channels. After the etching process, top
view optical micrographs of microfluidic channels are shown in Fig. 7.28c, d. Recasts
have almost disappeared, and besides the microfluidic channels have become more
homogeneous. By comparing the optical micrographs of microfluidic channels after
direct writing with post-chemical etching, it can be easily found that the roughness
and morphology of microfluidic channels both effectively improve after etching.
Meanwhile, after etching, the width of microfluidic channels increased to some
extent.
The SEM images of the surface morphology of the sample after etching are shown
in Fig. 7.29. The overall profile of the net-like microfluidic channel is shown in
Fig. 7.29a. Figure 7.29b is an enlarged image of the microfluidic channels with
the focus located on the substrate surface. Figure 7.29c shows the morphology of
microfluidic channel when the focus is located at the bottom of the microfluidic
channel. It is clear that the microfluidic channel after selective chemical etching still
shows relatively high surface roughness, which can be attributed to the fact that the
SEM has a greater depth of field compared with an optical microscope, and there
is always a certain inclination in internal face of the channel particularly near the
surface of the substrate (silver zonal region in Fig. 7.29c). The reason why the silver
zonal region existed is that the focus position is fixed in the FLDW process; thus, the
spot becomes larger with the increase of machining depth. Furthermore, the areas
reached the damage threshold will become smaller when the Gaussian femtosecond
laser beam becomes larger, and then the width of the channel will decrease with
depth increase of channel. Eventually, the fabricated microfluidic channel presents
a slope feature in the direction of microfluidic channel depth.