Self-assembled hexagonal double fishnets as negative index materials

We show experimentally the successful use of colloidal lithography for the fabrication of negative index metamaterials in the near-infrared wavelength range. In particular, we investigated a specific implementation of the widely studied double fishnet metamaterials, consisting of a gold-silica-gold layer stack perforated by a hexagonal array of round holes. Tuning of the hole diameter allows us to tailor these self-assembled metamaterials both as single- ({\epsilon} < 0) and double ({\epsilon} < 0 and {\mu} < 0) negative metamaterials

Dimer-on-mirror SERS substrates with attogram sensitivity fabricated by colloidal lithography

Nanoplasmonic substrates with optimized field-enhancement properties are a key component in the continued development of surface-enhanced Raman scattering (SERS) molecular analysis but are challenging to produce inexpensively in large scale. We used a facile and cost-effective bottom-up technique, colloidal hole-mask lithography, to produce macroscopic dimer-on-mirror gold nanostructures. The optimized structures exhibit excellent SERS performance, as exemplified by detection of 2.5 and 50 attograms of BPE, a common SERS probe, using Raman microscopy and a simple handheld device, respectively. The corresponding Raman enhancement factor is of the order 10(11), which compares favourably to previously reported record performance values

Boosting the Figure Of Merit of LSPR-based refractive index sensing by phase-sensitive measurements

Localized surface plasmon resonances possess very interesting properties for a wide variety of sensing applications. In many of the existing applications only the intensity of the reflected or transmitted signals is taken into account, while the phase information is ignored. At the center frequency of a (localized) surface plasmon resonance, the electron cloud makes the transition between in- and out-of-phase oscillation with respect to the incident wave. Here we show that this information can experimentally be extracted by performing phase-sensitive measurements, which result in linewidths that are almost one order of magnitude smaller than those for intensity based measurements. As this phase transition is an intrinsic property of a plasmon resonance, this opens up many possibilities for boosting the figure of merit (FOM) of refractive index sensing by taking into account the phase of the plasmon resonance. We experimentally investigated this for two model systems: randomly distributed gold nanodisks and gold nanorings on top of a continuous gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5 for the respective nanoparticles

Magnetoplasmonic design rules for active magneto-optics

Light polarization rotators and non-reciprocal optical isolators are essential building blocks in photonics technology. These macroscopic passive devices are commonly based on magneto-optical Faraday and Kerr polarization rotation. Magnetoplasmonics - the combination of magnetism and plasmonics - is a promising route to bring these devices to the nanoscale. We introduce design rules for highly tunable active magnetoplasmonic elements in which we can tailor the amplitude and sign of the Kerr response over a broad spectral range

Plasmonic Metamaterials for Sensing Applications (Plasmonische metamaterialen voor sensortoepassingen)

Metamaterials are man-made artificial materials of which the optical properties can be engineered to generate the desired response to an incident electromagnetic wave.They consist of sub-wavelength sized structures which can be thought of as the atoms in conventional materials. The collective response of a randomly or periodically ordered ensemble of such meta-atoms defines the properties of the metamaterial, which can be described in terms of effective material parameters such as the permittivity,permeability, refractive index and impedance. Here we show how these metamaterials can be exploited for sensing experiments in the visible and near-infrared wavelength ranges of the electromagnetic spectrum. The meta-atoms used in this work consist of nanostructures defined in gold and silica, which are both very stable and biocompatible materials. At the interface between nano-sized noble metal particles and dielectric media, collective oscillations of the electron cloud in the metal particles can be resonantly excited, which are known as plasmon resonances. In this work we deal with two types of plasmon resonances: localized surface plasmon resonances (LSPRs) and propagating surface plasmon polaritons (SPPs). The investigated sample structures are manufactured by combining conventional lithography (top-down) and self-assembly based colloidal lithography (bottom-up) protocols with standard microprocessing techniques. In that way, we fabricated a self-assembled version of the widely studied double fishnet negative refractive index metamaterials and benchmarked this structure to e-beam lithography based reference structures. We proved that these self-assembled metamaterials can be produced on large scales with a small number of defects and similar performance as the reference structures. In the second part of this work, we focused on self-assembled randomly distributed nanoparticle arrays on top of a continuous gold layer and a thin silica spacer for refractive index sensing applications. We proved that we can reduce the line widths of intrinsically broad dipole resonances in gold nanoparticle arrays by measuring both the amplitude and phase of the reflected waves in spectroscopic ellipsometrymeasurements. By spectrally detuning the electric dipole LSPR for P- and S-polarized waves we can pick up the transition between in- and out-of-phase oscillation of the free electrons in the metal nanoparticles with respect to the incident wave. As a result the line width of the LSPRs is largely reduced, resulting in a major boost of the Figure-Of-Merit (FOM) for refractive index sensing which could eventually result in much lower detection limits. In the third part of this work we optimized the plasmonic metamaterial substrates for refractive index sensing by changing from random particle distributions towards periodic arrays on top of a continuous gold layer and a thin silica spacer. We clearly observe that the eects of inhomogeneous broadening are largely reduced, giving rise to narrower line widths both in amplitude- and phase sensitive measurements,resulting in even larger values for the FOM. The grating structure allows for very efficient excitation of propagating SPP modes on the gold film below, which interact strongly with the localized modes. As we scan the angle of incidence, we clearly observe anti-crossing of the SPP and LSPR modes resulting in highly asymmetric line shapes and increased phase dierences due to Fano-interference. We show thatthe interaction between the SPP mode and the LSPR mode can be used to increase the refractive index sensitivity of the LSPR mode dramatically, which in combination with the reduced line widths results in extremely high values for the FOM.status: publishe

Highly conformal fabrication of nanopatterns on non-planar surfaces

While the number of techniques for patterning materials at the nanoscale exponentially increases, only a handful of methods approach the conformal patterning of strongly non-planar surfaces. Here, using the direct surface self-assembly of colloids by electrostatics, we produce highly conformal bottom-up nanopatterns with a short-range order. We illustrate the potential of this approach by devising functional nanopatterns on highly non-planar substrates such as pyramid-textured silicon substrates and inherently rough polycrystalline films. We further produce functionalized polycrystalline thin-film silicon solar cells with enhanced optical performance. The perspective presented here to pattern essentially any surface at the nanoscale, in particular surfaces with high inherent roughness or with microscale features, opens new possibilities in a wide range of advanced technologies from affordable photovoltaics and optoelectronics to cellular engineering

Angular tuning of plasmonic inter-particle coupling probed by spectroscopic ellipsometry

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Design and modeling of self-assembled hexagonal double fishnets

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Boosting the Figure of Merit of LSPR based refractive index sensing by phase sensitive measurements

status: publishe