Study on plasmonic near field scanning nanoscope and its application

다국어 초록 (Multilingual Abstract)

In this thesis, We introduce a plasmonic resonance ridge aperture capable of
sensing changes in refractive index and absorption with nanoscale resolution.
Using this aperture, we devised a plasmonic near-field scanning nanoscope
(PNSN) to record images of heterogeneous nanostructures. Compared to a
conventional near-field scanning optical microscope that measures light scattered
by the sample, the PNSN directly measures the change in a beam reflected from
the aperture to detect buried objects. Using the PNSN we recorded images of
nanoscale rectangular groove arrays on a SiO2 substrate with patterns typical of a
dynamic random access memory circuit. By comparing the experimental and
calculated image of the nanostructure, we estimate the resolution of PNSN to be
20 nm, which is 50% smaller than the near-field spot generated by the aperture.
Also, we theoretically analyzed the feasibility of the PNSN detecting an object
underneath a metal film.
Also, we apply a plasmonic near-field scanning nanoscope using a resonant
ridge aperture to measure the thickness of a metal thin film. We determine an
appropriate design of the resonant ridge aperture to obtain high measurement range and sensitivity for the measurement. As a proof of concept, we measure the
thickness of gold thin films with thicknesses ranging between 5 nm and 30 nm.
We demonstrate that the experimental and calculated results are in good
agreement with one another. Also, we find that any observed errors are caused by
uncertainties in the material properties of the metal and by tolerances in the
fabrication of the ridge aperture. By comparing these thickness measurements with
those taken by atomic force microscopy, we are able to obtain an uncertainty of
~5% for our thickness measurements. Regarding the spatial resolution, theoretical
analysis indicates that the thickness of a metal thin film should be detectable
below 40 nm.
And then, we introduce the problem of asymmetric ridge nano-aperture for
nano-scale imaging. To show clearly this problem, we measure gold
nano-particles with 100 nm diameter. We measure the gold nano-particles with
rotation of nano-aperture and sample to confirm the effect of asymmetric
nano-aperture. Meausred image of nano-particle has asymmetric shape and it is
rotated with rotation of bowtie nano-aperture. Imaging result with bowtie
nano-aperture has 1.17 ratio between width of x and y axis but that with clover
nano-aperture has 1.0 ratio. Through these results, we can expect that the clover
nano-aperture can be used for near-field imaging and patterning for more accurate
imaging and patterning.