Active magnetoplasmonic ruler.

Plasmon rulers are an emerging concept in which the strong near-field coupling of plasmon nanoantenna elements is employed to obtain structural information at the nanoscale. Here, we combine nanoplasmonics and nanomagnetism to conceptualize a magnetoplasmonic dimer nanoantenna that would be able to report nanoscale distances while optimizing its own spatial orientation. The latter constitutes an active operation in which a dynamically optimized optical response per measured unit length allows for the measurement of small and large nanoscale distances with about 2 orders of magnitude higher precision than current state-of-the-art plasmon rulers. We further propose a concept to optically measure the nanoscale response to the controlled application of force with a magnetic field.

Magnetoplasmonic design rules for active magneto-optics.

Light polarization rotators and nonreciprocal 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.

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 1 order of magnitude smaller than those for intensity based measurements. As this phase change 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.

Plasmon line shaping using nanocrosses for high sensitivity localized surface plasmon resonance sensing.

The detection of small changes in the wavelength position of localized surface plasmon resonances in metal nanostructures has been used successfully in applications such as label-free detection of biomarkers. Practical implementations, however, often suffer from the large spectral width of the plasmon resonances induced by large radiative damping in the metal nanocavities. By means of a tailored design and using a reproducible nanofabrication process, high quality planar gold plasmonic nanocavities are fabricated with strongly reduced radiative damping. Moreover, additional substrate etching results in a large enhancement of the sensing volume and a subsequent increase of the sensitivity. Coherent coupling of bright and dark plasmon modes in a nanocross and nanobar is used to generate high quality factor subradiant Fano resonances. Experimental sensitivities for these modes exceeding 1000 nm/RIU with a Figure of Merit reaching 5 are demonstrated in microfluidic ensemble spectroscopy.

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.

Multiscale conformal pattern transfer.

We demonstrate a method for seamless transfer from a parent flat substrate of basically any lithographic top-down or bottom-up pattern onto essentially any kind of surface. The nano- or microscale patterns, spanning macroscopic surface areas, can be transferred with high conformity onto a large variety of surfaces when such patterns are produced on a thin carbon film, grown on top of a sacrificial layer. The latter allows lifting the patterns from the flat parent substrate onto a water-air interface to be picked up by the host surface of choice. We illustrate the power of this technique by functionalizing broad range of materials including glass, plastics, metals, rough semiconductors and polymers, highlighting the potential applications in in situ colorimetry of the chemistry of materials, anti-counterfeit technologies, biomolecular and biomedical studies, light-matter interactions at the nanoscale, conformal photovoltaics and flexible electronics.

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.

Quasi-isotropic surface plasmon polariton generation through near-field coupling to a penrose pattern of silver nanoparticles.

Quasicrystals are structures that possess long-range order without being periodic. We investigate the unique characteristics of a photonic quasicrystal that consists of plasmonic Ag nanodisks arranged in a Penrose pattern. The quasicrystal scatters light in a complex but spectacular diffraction pattern that can be directly imaged in the back focal plane of an optical microscope, allowing us to assess the excitation efficiency of the various diffraction modes. Furthermore, surface plasmon polaritons can be launched almost isotropically through near-field grating coupling when the quasicrystal is positioned close to a homogeneous silver surface. We characterize the dispersion relation of the different excited plasmon modes by reflection measurements and simulations. It is demonstrated that the quasicrystal in-coupling efficiency is strongly enhanced compared to a nanoparticle array with the same particle density but only short-range lateral order. We envision that the system can be useful for a number of advanced light harvesting and optoelectronic applications.