40
A. Hu et al.
Fig. 1.26 SEM images of Ag film photoreduced by a 365 nm light and (b) 615 nm light [132]
short-wavelength illumination (Fig. 1.26a). In opposite, the shape of nanoparticles
converted to a plate (disk) under long-wavelength illumination (Fig. 1.26b).
This phenomenon can be explained by the surface plasmon-enhanced photonic
reduction. Briefly, in the case of short-wavelength illumination, the surface plasmon
mode is dominantly transverse. Thus, short-wavelength light acts as feedback irradiation making the particle grow spherical. Conversely, as the longitudinal plasmon
absorbs the longer wavelength irradiation more strongly, this longer particle axis
grows preferentially, resulting in a plate-like shape [138].
1.4.4 Laser Direct Writing and Interference Lithography
Laser Direct Writing Laser direct writing provides high flexibility with non-contact
and maskless fabrication processes, which significantly reduces the fabrication cost.
Since laser direct writing can achieve a one-step fabrication combing local processing
with patterning, the manufacturing efficiency is significantly enhanced. Figure 1.27
shows one schematic for laser direct writing setup. The setup has four basic elements
to realize direct writing, including laser source, beam expander, focus lens (objective
Fig. 1.27 Schematic for
laser direct writing setup