Supporting Information
Plasmonic spectral engineering
via interferometric illumination of colloid sphere monolayers
Áron Sipos, Anikó Somogyi, Gábor Szabó, Mária Csete*
Department of Optics and Quantum Electronics, University of Szeged,
H-6720 Szeged, Dóm tér 9, Hungary
*mcsete@physx.u-szeged.hu
The absorptance and reflectance spectra were also inspected to uncover all nanophotonical
phenomena responsible for the modulation on the optical response of hole doublet arrays with
hexagonal and rectangular symmetry. General tendencies on absorptance and reflectance
signals are that extrema on both arrays shift to larger wavelength in symmetric environment,
on larger objects, and at larger azimuthal angle, with the largest extent in case of  = 90°
azimuthal orientation, with few exceptions described below.
The absorptance spectra of all hexagonal arrays exhibit only single maxima, these maxima are
shifted towards smaller wavelengths in comparison to transmittance maxima, and appear in
between the transmittance extrema, when the transmittance signal exhibits also a minimum.
(Fig. S1a, c, Fig. S3a). The amount of the back-shift is larger and on larger hole doublets,
except at  = 90° azimuthal orientation in symmetrical environment, where the sparse hole
doublet array results in larger backshift.
The absorptance spectra for rectangular hole doublet arrays exhibit single maxima at  = 0° in
symmetric environment, while at  = 90° azimuthal orientation a local-global minimummaximum pair develops in symmetric environment and a local perturbation appears in
asymmetric environment (Fig. S1b, d, Fig. S3b). All global absorptance maxima are
backward shifted with respect to global maxima in transmittance, and appear always in
between the maximum and the local minimum/perturbation on the transmittance, moreover at
a wavelength larger than that of the global minimum at  = 90° azimuthal orientation. For
larger hole doublets one can observe slightly larger difference between the wavelengths of
absorptance and transmittance maxima, except at  = 0° azimuthal orientation.
At  = 90° azimuthal orientation all local extrema appearing on the absorptance of rectangular
hole doublet-arrays are observable in spectral intervals, where the p/g = plas condition is met.
1
This indicates that the Rayleigh scattering of propagating plasmons on the rectangular hole
doublet arrays modulates the absorptance related to localized plasmon excitation.
Fig. S1. Absorptance spectra of (a, b continuous lines) compact and (c, d dashed lines) sparse
hole doublet arrays with (a, c) hexagonal and (b, d) rectangular symmetry, embedded into
gold films having a thickness of 45 nm. The presented two azimuthal orientation angles of the
patterns are  = 90° (wine/orange in symmetric/asymmetric environment), and  = 0° (red in
symmetric environment). The effect of (gold) 1 protein layer, (light brown) 3 protein layers,
and (brown) complete protein filling on the spectra of (c) hexagonal and (d) rectangular hole
doublet arrays in asymmetric environment at  = 90° azimuthal orientation is also presented.
The mismatch between the corresponding global maxima reveals that the phenomena
involved in transmittance and absorptance modifications are different [25]. Further inspection
of the near-field at the absorptance extrema revealed that the wavelength dependent extrema
in the normalized E-field intensity correlate most exactly with the absorptance (Fig. S1, S3a).
The absorptance maxima gather gradually larger spectral shift on both hexagonal and
rectangular hole doublet arrays, when larger amount of protein layer is seeded onto the
surface (Fig. S1c, d).
2
However, in all cases, regardless the hole doublets are filled by one or three protein layers or
completely, the shift is smaller than the corresponding shifts observable on the transmittance
(Fig. S3a).
The negative values observed on reflectance curves indicate that all hole doublet arrays,
regardless of their type, exhibit reflectance smaller than the reflectance of a thin continuous
film used as a reference in rectification (Fig. S2).
Fig. S2. Reflectance spectra of (a, b continuous lines) compact and (c, d dashed lines) sparse
hole doublet arrays with (a, c) hexagonal and (b, d) rectangular symmetry, embedded into
gold films having a thickness of 45 nm. The presented two azimuthal orientation angles of the
patterns are  = 90° (plum/pink in asymmetric/symmetric environment), and  = 0° (purple in
symmetric environment). The effect of (violet) 1 protein layer, (peach) 3 protein layers and
(dark blue) complete protein filling on the spectra of (c) hexagonal and (d) rectangular hole
doublet arrays in asymmetric environment at  = 90° azimuthal orientation is also presented.
The reflectance extrema are slightly forward and backward shifted with respect to the
corresponding extrema observed on the absorptance and transmittance curves, respectively
(Fig. S2, 3).
3
The global reflectance minima almost coincide with the global absorptance maxima, except
for larger hole doublets in symmetric environment, where the reflectance minima appear at
slightly larger wavelengths (Fig. S2, S3). This reveals that the absorptance maxima are related
to resonant excitation of different plasmonic modes, which modes are accompanied by
reflectance decrease.
On hexagonal hole doublet arrays, a single reflection minimum appear in between the
absorptance and transmittance maxima, very close to the former. The amount of backshift
with respect to transmittance maxima becomes slightly larger in case of larger objects except
at  = 90° in symmetric medium.
In rectangular hole doublet arrays in symmetric environment the global reflectance minimum
appears always between the global absorptance and transmittance extrema, very close to the
former. The backshift with respect to the transmittance maxima is slightly larger at  = 90°
azimuthal orientation for all extrema on larger objects, while at  = 0° the global minimum is
shifted backward with smaller extent on larger hole doublets. The counterpart local extrema
are completely coincident in absorptance and reflectance at  = 90° azimuthal orientation.
The global transmittance minima in rectangular arrays are accompanied by medium
absorptance and reflectance, indicating the co-existence of radiant and subradiant resonant
modes.
The reflectance minima exhibit larger spectral shift on both hexagonal and rectangular hole
doublet arrays, when larger amount of protein layer is seeded onto the surface (Fig. S2c, d).
Fig. S3. Comparison of different types of extrema on the transmittance, absorptance and
reflectance signals in (a) hexagonal and (b) rectangular hole doublet arrays. For the sake of
completeness, spectral positions of local perturbations are also indicated.
4
On the hexagonal hole doublet array the shifts in reflectance are smaller than the shifts in
absorptance, while on the rectangular hole doublet array the corresponding shifts are equal,
accordingly, the shifts in all cases of protein filling are smaller than the shifts in transmittance
(Fig. S3b).
In summary, although the optical responses exhibit similar tendencies in case of hexagonal
and rectangular hole doublet arrays, rectangular arrays have important advantages (Fig. S3).
In hexagonal arrays one global extremum governs the entire optical signal in every case and
each studied optical quantity, except the transmittance, where a local perturbation appears in
case of  = 90° azimuthal orientation, which turns into a global minimum in symmetric
environment or after filling the doublets completely by protein (Fig. S3a). This minimum is
far apart from the global extremum, as a consequence cannot reduce the FWHM with
appropriately large extent.
In rectangular arrays a local perturbation appears in transmittance similarly to that observed
on hexagonal array, which turns into a local minimum on larger objects, in symmetric
environment, and after filling the doublets completely by protein (Fig. S3b). In addition to
this, in close proximity of the global extremum governing the optical signals, a local
extremum appears, which becomes more pronounced in symmetric environment and on larger
objects, moreover in transmittance turns into a global extremum at  = 90° azimuthal
orientation. This global minimum is capable of resulting in reduced FWHM on the Fanoshaped transmittance signal.
Although, the difference in spectral shifts observable in case of partial and complete protein
filling is commensurate on the absorptance, reflectance and transmittance curves, indicating
that all these signals are sensitive to the amount of material, the absolute sensitivity of the
transmittance signal is the largest, proving that observation of transmittance is the most
appropriate to realize bio-detection. Although, partial or complete filling of hole doublets in
both arrays results in well defined shifts, larger FOM is attainable on rectangular arrays due to
the significantly smaller FWHM of transmittance maxima.
5