A plasmonic Raman sensor using periodic hole arrays was investigated numerically and experimentally. In previous
work, we fabricated a hole array in a thin metal film on a dielectric substrate using focused ion beam lithography and
succeeded in observing surface plasmon resonance. We demonstrated the effectiveness of hole shape dependency (i.e.,
cylindrical or tapered hole structures) for electric field enhancement, transmittance, and reflectance spectra obtained by
numerical simulation using the finite-difference time-domain method. Those simulation results for an array of tapered
holes agreed well with experimental results. Moreover, we numerically determined the optimized structure in terms of
metal film thickness, tapered hole diameter, and hole period. However, optimal structure of a tapered hole array provides
insufficient sensitivity (i.e., electric field enhancement) for measuring surface-enhanced Raman scattering. Therefore, we
enhanced the electric field by using further structural parameters such as differs from tapered and incident light direction,
which we expected to would give us a larger electric field. When the incident light coming from Si3N4 side, the electric
field enhancement was increased markedly. The electric field enhancement was more likely to be uninvolved in metal
film thicknesses using 300 nm and 500 nm.
A plasmonic Raman sensor using periodic hole arrays was investigated numerically and experimentally. In previous
work, we fabricated a hole array in a thin metal film on a dielectric substrate using focused ion beam lithography and
succeeded in observing surface plasmon resonance. Those experimental results agreed well with simulation results (for
an array of cylindrical holes) obtained using the finite-difference time-domain method. However, a cylindrical hole array
provides insufficient sensitivity (i.e., electric field enhancement) for measuring surface-enhanced Raman scattering
(SERS). Therefore, we enhanced the electric field by using focusing holes (tapered structure), which we expected to
would give us a larger electric field than the cylindrical holes. Furthermore, for a hole array, we optimized the structural
design in terms of metal film thickness, hole diameter, and hole period on the basis of theoretical predictions. We
successfully designed and fabricated an arbitrary localized surface plasmon resonance for the optimized array for the
excitation wavelength (λ= 632.8 nm) for the target molecule rhodamine 6G for SERS.
A novel plasmonic Raman sensor using periodic nano-hole and, potentially, nanofocusing arrays is investigated
numerically and experimentally. The effect of structural parameters (such as periodicity of the structure, hole
dimensions, etc.) is determined and investigated. The analysed structures are fabricated in thin gold films by means of
focused ion beam lithography. Optical characteristics of the fabricated arrays are determined experimentally and
compared with the theoretical predictions. Experimental field enhancements are determined and also compared with the
theoretical predictions.
Analysis of adiabatic and non-adiabatic nano-focusing in tapered metal nano-rods leads to the determination of optimal taper angles and rod lengths as functions of material parameters (for gold, silver, and aluminum) at frequencies from the optical and near infra-red ranges. The considered nano-focusing structures appear to be highly tolerant to such structural and fabrication imperfections as variations of length of the rod and taper angle around their optimal values. However, the major parameter that tends to sig-nificantly affect the nano-focusing capabilities of the rods is the radius of the tip, and this is the parameter that should be carefully reproduced in the experiments. Comparison of the numerical results with the adiabatic theory of nano-focusing for different metals and different wavelengths demonstrates the validity of the adiabatic theory in a much wider range of taper angles (up to tens of degrees) than it was previously expected. Major predicted local field enhancements of up to ~ 2,500 times in the considered structures within nano-scale regions as small as a few nanometers will make tapered metal rods highly promising for single molecule detection and development of a new generation of sensors, measurement and nano-manipulation techniques.
We have measured the propagation distances of wedge plasmons and two-dimensionally localized gap plasmons (GPW)
at a vacuum wavelength of 632.8nm. The measured propagation distances of the wedge plasmons increased from
2.2μm to 3.1μm with increasing the wedge tip radius from 20nm to 125nm. The GPW has the measured propagation
distance of 8.2μm for a gap width of 100nm and 900nm height.
We have developed a finite-difference time-domain (FDTD) method represented by the spherical coordinates which is
applicable for numerical calculations of nonlinear optical responses. This FDTD technique gives information about
time-dependent spatial distributions of light intensity in nonlinear metallic particles and we can deeply understand
nonlinear optical phenomena related with localized surface plasmons in a spherical particle.
We have numerically investigated characteristics of plasmonic waveguides for coupled wedge plasmons (CWPs)
consisting two silver wedges separated by a nano gap all on a glass substrate. Three types of waveguides for CWPs on
a glass substrate are considered: (1) two metallic wedges on a planar substrate, (2) two metallic wedges built into the
substrate and (3) two-folded free-standing metallic wedges. For numerical calculation, we have employed the Drude
model for the dielectric constant of silver and the excitation light with the vacuum wavelength of 632.8 nm. The
refractive index of the glass ns is fixed at ns = 1.5. We have calculated field distributions in the waveguide as well as
dependence on changing the gap w between wedges and the wedge angle θ. CWPs eigenmodes of such structures are
shown to exist and propagate along waveguides structures employed here. The propagation constant k//, propagation
distance L and the beam area of a CWP depends on w and θ. L and the beam area size for waveguide employed here are
in the order of 10 μm and in the range from 10-4 μm2 to 10-1 μm2, respectively. These values mean that waveguides for
CWPs have a potential to be utilized for the nano optical waveguides in future.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.