| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 95 === By using transmission near-field scanning optical microscopy (NSOM),
near-field optical distributions are studied when green laser source (532 nm) is
illuminated on the substrate side of the sample.
Three types of structures: macroslits, nanowire array and nanodot array, are
fabricated for the study of near-field intensity distributions. The structures of single
and multiple macroslits are made by atomic force microscopy (AFM) nanomachining
on Au-deposited glass substrate with the thickness of 57.05 nm. The structures has
slits with averaged width of 2.72 μm and the period of 10~15 μm. For the fabrication
of nanowire array and nanodot array, PMMA is spincoated on the quartz substrate as
a single layer resist first. Using nanomachining, subsequent Au deposition of 18 nm
thickness, and finally lift-off, nanowire array and nanodot array are fabricated.
By illuminating the sample from the substrate side with the 532 nm green laser
source, the near-field intensity is collected by home-made NSOM fiber probe. For
slits, two types of intensity distributions, namely stripes and concentric circles, on the
air-gold interface are observed. Stripe patterns appear at two locations, inside slit and
metal surface without polarization dependence. Concentric circular patterns which
have 470 nm period, on the other hand, are observed on the air-gold interfaces of the
one-slit structure with transverse electric (TE) polarized light, two-slit structure with
transverse magnetic (TM) polarized light, and three-slit structure with TE polarized
light, respectively. The period of 470 nm is in good agreement with the wavelength of
surface plasmons. For nanowire array, the interference inside array has the same
period of 1μm as structure and outside array is the contributions of scattering of each
gold nanowire plus normal incident intensity. Interference patterns also appeared on
the broken nanowire array due to scattering of metal gap. For nanodot array, however,
near-field intensity distributions don’t show interference pattern.
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