In our work for producing silicon nanowires, deposition
was performed at a pressure between 10 and 15 Torr with a
constant flow rate of 5 sccm of 10% silane in argon. Continuouswave
(cw) and femtosecond (fs) laser systemswere tested
to compare the results. The cw laser used was a ND:yttrium–
aluminum–garnet laser with a wavelength of 532 nm and
a maximum power of 10 W. The femtosecond laser used
was a mode-locked Ti:sapphire laser with a wavelength of
800 nm, about 100 fs pulse duration, 14 nJ per pulse maximum,
and a repetition rate of 86 MHz. The femtosecond
laser output was then frequency-doubled to 400 nm using a
0.5-mm thick barium borate (BBO) crystal and then focused
onto the substrate surface with high numerical aperture Fresnel
phase zone plates. These phase zone plates aremade from
hydrogen silsesquioxane (HSQ) coated on a quartz substrate
and patterned by electron beam lithography (EBL). Indium
tin oxide (ITO) is coated on the quartz substrate to avoid
charging during EBL, and a hexamethyldisilazane (HMDS)
layer is used to improve the adhesion of the developed HSQ
to the ITO. In order to produce nanoscale structures, a small
laser spot is desirable. The size of the spot produced by the
zone plate is calculated as13