Adjacent to the groove on both sides are hills that can be seen from both surface profile in
figure 2, and 3D image in figure 3. This indicates that the irradiated area, where the light
intensity has a maximum, has been undergone a melting-re-solidifying process, left behind the
features with hill-crater form, under the influence of plasma pressure, surface tension and
temperature gradient.
Using three instead of two laser beam interference, two dimensional structures are obtained.
Figure 4 and 5 show two kinds of structures, by different laser energy density on the surface
of c-Si. They are characterized by dot- and net-shape structures.
Figure 4. dot-shape structure by three- Figure 5. Net-shape structure by three-
beam interference with lower energy density ~~ beam interference with higher energy density
the structures have the same period but the form of the feature is completely different
Qualitatively speaking, in the case of dot-shape structure the energy density is just
above the melting threshold of the material; while in the case of net-shape structure the
energy density is well above the melting threshold. It is this feature that makes the
controlling of feature size through energy density possible.
Similar structure with net-shape of Au on the plastic PMMA is made by three beam
interference, as shown in figure 8..
Zn Ws
Se
ba“
ate
Figure 6 Net-shape structure of Au coating on the substrate of PMMA: (a) image of
WLI and (b) surface profile
h The sample is prepared by vacuum sputtering of Au onto the substrate of PMMA; the
re on the thickness of the Au coating is approximately 100 nm. After the structuring with three
YAG beam interference, craters with diameter 2 um, depth 13 nm appeared with period of 5.4
um, as shown in figure 6. By varying the energy density one can change the diameter
and depth of the crater; combined with the different period, one can obtain various gold
pattern on PMMA substrate with nano-and micrometer resolution. This is of special
interest for electrical applications.
{b)
33
