We demonstrate optical readout and actuation of nanomechanical motion using plasmonic fields in a nanoscale gap waveguide. The top gold layer of the waveguide is free to vibrate like a drumhead, and patterned with an optical grating to facilitate efficient coupling to free-space radiation. The change of the plasmonic gap mode with the top layer position couples the plasmonic resonance to the mechanical displacement of the drum. We characterize optical and mechanical resonances of the system, and demonstrate sensing of nanomechanical vibrations with ∼10−14 m/Hz sensitivity. The mechanical resonators are actuated through plasmonic forces. Quantifying their magnitude shows that plasmonic forces can significantly exceed pure radiation pressure, indicating that their nature is dominated by a photothermoelastic effect. This work opens avenues to the use of plasmonic readout and control in nanomechanical sensing applications.

The use of noble metals within nanophotonics and nanoplasmonics in general is a well established practice. However, when the thickness of the metals used, in particular gold, decreases, their quality suffers. In particular, the influence of the adhesion layers becomes significant. In this papers we present our approach towards obtaining up to 10 periods of gold/alumina layers, with 20 nm period and 50% filling fraction. Using organic adhesion layers, the Au behaves very close to the theoretical limit, demonstrating that these layers minimally influence the Au properties. Initial attempts into patterning these multi-layer structures show the possibility of obtaining simple one-dimensional designs having down to ca. 100 nm linewidth. Results and challenges in using our approach are also presented.

The photonic spin Hall effect [1] or spin Hall effect of light [2] is the photonic analog of the spin Hall effect occurring with charge carriers in solid-state systems. Typically, this phenomenon takes place when a light beam refracts at an air-glass interface, or when it is projected onto an oblique plane, the latter effect being known as the geometric spin Hall effect of light [3]. In general, the photonic spin Hall effect leads to a polarization dependent transverse shift of a light peak intensity [3,4]. An example of the latter effect is the transverse Imbert-Federov beam shift [3], which happens for paraxial beams reflected or refracted at a sharp inhomogeneity of an isotropic optical interface. Potential applications of the photonic spin Hall effect in spin-dependent beam splitters, optical diodes [1], and surface sensors are considered in various fields in photonics, such as nanophotonics, plasmonics, metamaterials, topological optics, and quantum optics [1,2].

The capability to support optical waves with large wavevectors (high-k) is one of the principle features of hyperbolic metamaterials (HMMs). These waves play the key role in HMM applications such as imaging, sensing and lifetime engineering. To predict HMMs behavior a simple and convenient analytical effective medium approximation (EMA) is widely used. Theoretically, EMA is applicable to a deeply subwavelength unit cell of implicitly infinite periodic structures. So, in order to confidently use the EMA for the practical implementation HMMs, the question is what are constrains on the thickness, i.e. number of periods, of a realistic design to claim the validity of the EMA conclusions. We fabricated a series of stacks with 1, 2,. 10 periods of 10 nm gold - 10 nm alumina layers of exceptional quality keeping the roughness root mean square well below 1 nm. Characterization supported by modeling shows that starting from four periods, the multilayers properties are reasonably good expressed through EMA.

The capability to support optical waves with very large wave vectors (high‐k) is one of the principle features of hyperbolic metamaterials (HMMs). These waves play the key role in HMM applications such as imaging and lifetime engineering. Effective medium approximation (EMA) as widely used analytical method to predict HMMs behavior, has shortcomings in calculating high‐k modes of practical structures. EMA is applicable to a subwavelength unit cell of implicitly infinite periodic structures. Using conventional EMA, in the present paper, boundary effects and spatial dispersion are taken into consideration to properly compute the high‐k modes of finite‐thickness multilayer HMMs. Applying nonlocal homogenization to stacks of alternating metal‐dielectric layers, the corresponding effective medium is examined as a high‐k waveguide sandwiched between the substrate and an ambient superstrate. The developed theory enables us to recognize two types of bulk waves coined as short‐range and long‐range propagating modes. Number of such modes as well as their cutoff conditions are quantified for the first time. Validity of the developed theory is verified both numerically by rigorous simulations of the multilayer structures with the transfer matrix method and experimentally by optical characterization of the HMMs in infrared regime.

Multilayer hyperbolic metamaterials (HMMs) are highly anisotropic media consisting of alternating metal and dielectric layers with their electromagnetic properties defined by the effective medium approximation (EMA). EMA is generally applied for a large number of subwavelength unit cells or periods of a multilayer HMM. However, in practice, the number of periods is limited. To the best of our knowledge, a comparison between rigorous theory, EMA and experiments to investigate the minimum number of layers that allow for the low error of EMA results has not yet been investigated. In this article, we compared the reflectance response of the effective anisotropic HMMs predicted by the scattering matrix method (SMM) and EMA with optical characterization data, having the unit cell twenty times smaller than the vacuum wavelength in the visible range. The fabricated HMM structures consist of up to ten periods of alternating 10 nm thick Au and Al2O3 layers deposited by sputtering and atomic layer deposition, respectively. The two deposition techniques enable us to achieve a high quality HMM with low roughness: the root mean square (RMS) is less than 1 nm. We showed that the multilayer structure behaves like an effective medium from the fourth period onwards as the EMA calculation and experimental results agree well having below 4% mean square standard deviation of reflectance (MSDR) for the wavelength range from 500 to 1750 nm with a wide incident angle range. These results could have an impact on the design and development of active metamaterials and their applications ranging from imaging to nonlinear optics and sensing.

Hyperbolic metamaterials (HMMs) are hailed as one of the main advances in nano-optics in general and metamaterials in particular. Generally, HMMs are multi-layered structures where it is assumed that, due to geometric reasons, one can describe them as a uniform material with effective properties [1]. Their extraordinary characteristics come precisely from the extremely different values of their effective parameters. While the assumption of assigning material properties to these structures may be valid for a very large number of layers, it will start to fail when the number of layers diminishes. In practice, the number of periods these structures have is generally below 10, thus the investigation of the lower limit of such assumption is necessary.

We report here on our advances in fabrication and characterization of lamellas metamaterials. Such structures can exhibit effective properties with enhanced and even extreme anisotropy. The latter case exhibits hyperbolic dispersion. Typical hyperbolic metamaterials (HMMs) consist of alternative metal/plasmonic and dielectric layers. We have developed two types of lamellas metamaterials: planar multilayer and vertical trench structures. In the former case, we deposit ultrathin ultra-smooth gold layers with the assistance of organic material (APTMS) adhesion layer. The technology supports the stacking of such layers in a multi-periods construction with alumina spacers between gold films. While planar technology makes multilayer systems conventional nanostructures, vertical arrangement of nanolamellas requires a nontrivial fabrication processing. In the latter case, we apply the atomic layer deposition (ALD) technique to arrange vertical alignment of layers of heavily doped ZnO or TiN, which enables us to produce hyperbolic metamaterials in the visible or near- and mid-infrared ranges. Potential applications of such structured lamellas metamaterials are illustrated with examples of surface waves propagation and sensing.

We present our latest findings regarding the optical properties of thin Au films and their relation with currently available models, from classical Drude, with thickness correction, to non-local estimations and abinitio calculations predictions. Thin metallic layers, in particular Au, are the main building block in plasmonic and metamaterials community [1]. However, there have been very few measurements of their optical properties, especially regarding the dependence on the film thickness [2]. Using a non-metallic adhesion layer, we showed that we can obtain ultra-smooth and thin Au layers [3] supporting surface plasmon polariton propagation characteristics very close to the theoretical ones [4]. Here, we present their experimental permittivity and compare it to several available models from literature. The experimental data was obtained on layers between 8 and 22 nm thick, using ellipsometry measurements in the range of 675 to 1750nm to limit the influence of the interband transitions and use a simple Durde model. In general, the dependence of the collision energy with thickness tt is considered to be in the form of Γ(tt) = Γ0 + AA ∗ vvff tt ⁄ [5]. For nano-spheres, the free factor AA is assumed to be unity [6]. In the case of our nano-layers the best fit is for a factor AA of 0.06, significantly smaller (Fig 1(a)). As second finding, no clear trend in the behaviour of the plasma energy, as defined by the Drude model (Fig 1(b)) was observed. The GNOR non-local model [7] shows a variation of the plasma energy within the error of the measure and a general trend of the collision energy that matches our data. The model from [8] predicts a change of the plasma energy that does not consistently match our experimental data. Ab-initio calculations on particles with diameters smaller than 3 nm show collision energies having a similar trend as the one observed experimentally [9]. We present experimental data and their comparison to different theoretical models for Au layer permittivity with no other metallic influence. Involving metallic adhesion layers would complicate the problem manifold [10]. To conclude, the size-dependent damping of Au was much smaller than expected, and there was no measurable plasmon energy change. Further analysis, especially for thicknesses below 10nm is required. Fig. 1 The fitted values of the collision (a) and plasma (b) energy from the measured ellipsometer data. The full line is the best fit with the 1/tt dependence. Dotted lines show the 95% confidence interval. The computed error bars (red lines) are too small to be visible. The fitting was made between 675 to 1750nm, to minimise the influence of the Lorentz terms. References [1] R. Malureanu and A. Lavrinenko, "Ultra-thin films for plasmonics: a technology overview," Nanotechnol. Rev. 4, 259–275 (2015). [2] D. I. Yakubovsky, A. V. Arsenin, Y. V. Stebunov, D. Y. Fedyanin, and V. S. Volkov, "Optical constants and structural properties of thin gold films," Opt. Express 25, 25574 (2017). [3] L. Leandro, R. Malureanu, N. Rozlosnik, and A. Lavrinenko, "Ultrathin, ultrasmooth gold layer on dielectrics without the use of additional metallic adhesion layers.," ACS Appl. Mater. Interfaces 7, 5797–5802 (2015). [4] J. Sukham, O. Takayama, A. V. Lavrinenko, and R. Malureanu, "High-Quality Ultrathin Gold Layers with an APTMS Adhesion for Optimal Performance of Surface Plasmon Polariton-Based Devices," ACS Appl. Mater. Interfaces 9, (2017). [5] U. Kreibig and C. v. Fragstein, "The limitation of electron mean free path in small silver particles," Zeitschrift fur Phys. 224, 307–323 (1969). [6] J. A. Gordon and R. W. Ziolkowski, "The design and simulated performance of a coated nano-particle laser.," Opt. Express 15, 2622– 2653 (2007). [7] N. A. Mortensen, S. Raza, M. Wubs, T. Søndergaard, and S. I. Bozhevolnyi, "A generalized non-local optical response theory for plasmonic nanostructures," Nat. Commun. 5, 3809 (2014). [8] I. V. Bondarev and V. M. Shalaev, "Universal features of the optical properties of ultrathin plasmonic films," Opt. Mater. Express 7, 3731 (2017). [9] Y. He and T. Zeng, "First-Principles Study and Model of Dielectric Functions of Silver Nanoparticles," J. Phys. Chem. C 114, 18023– 18030 (2010). [10] M. Todeschini, A. Bastos da Silva Fanta, F. Jensen, J. B. Wagner, and A. Han, "Influence of Ti and Cr Adhesion Layers on Ultrathin Au Films," ACS Appl. Mater. Interfaces 9, 37374–37385 (2017). (a) (b)

Hyperbolic metamaterials (HMMs) consisting of alternating dielectric and metal layers are playing a key role in the field of nanophotonics due to their wide range of potential applications including thermal emission engineering, photonic density states engineering, super resolution imaging and sensing. Gold is a practical plasmonic material to fabricate HMMs in the visible to near- infrared range due to its high chemical stability. As a noble metal, Au needs an adhesion promoter and recently amino-propyl-trimethoxy-silane (APTMS) was used instead of metallic adhesion layers. We showed that these latter ones, classically Ti or Cr, increase the losses of the propagating plasmons as compared with APTMS. In this work, we have successfully fabricated and characterized HMMs with various number of periods . The gold layer was 10 nm and the dielectric 12 nm thick, thus allowing for hyperbolic dispersion in the near-infrared range. We have used APTMS adhesion layer on each interface between Au and alumina to provide a better adhesion and also to obtain high quality smooth layers. The Au and alumina layers were fabricated using sputtering and atomic layer deposition techniques, respectively. The use of these techniques helps to obtain a high HMM quality, having a final roughness of 0.80 nm RMS, even after the tenth period. Using these structures, we show that the effective medium approach (EMA) may be used even for a structures with as little as 3 periods. The optical characterization shows very good agreement with the theoretically predicted ones, both rigorous approach, as well as EMA ones.

In this paper, we will present the fabrication possibilities developed within our group for obtaining multilayer hyperbolic metamaterials (HMMs). The minimum metallic layer thickness reproducibly obtainable with our current technology is down to 6 nm, while the dielectric layer can be as low as 4 nm. During the talk we will present our approach for obtaining Au layers with better optical properties than the standard techniques. This is achievable by using an adhesion layer whose influence of the metallic properties is lower than the one of the classical Cr or Ti adhesion layers. These organic adhesion layers behave as dielectrics and thus do not contribute more to the metallic response. Since the imaginary part of permittivity of these layers is negligible and the real part is very close to the silica one, their contribution to the behaviour of the HMMs is minimal. The optical properties of Au with organic adhesion layers showing a closer to theory response than Au with metallic adhesion layer as well as a possible explanation for this behaviour will be presented. This technique can be further used to obtain metal-dielectric multi-layers that lead to HMMs behaviour. Both fabrication possibilities and optical characterisation will be shown and discussed during the talk.

The photonic spin Hall effect in transmission is a transverse beam shift of the out-coming beam depending on polarization of the incoming beam. The effect can be significantly enhanced by materials with high anisotropy. We report, to the best of our knowledge, the first experimental demonstration of the photonic spin Hall effect in a multilayer hyperbolic metamaterial at visible wavelengths (wavelengths of 520 and 633 nm). The metamaterial is composed of alternating layers of gold and alumina with deeply subwavelength thicknesses, exhibiting extremely large anisotropy. The angle-resolved polarimetric measurements showed the shift of 165 μm for the metamaterial of 176 nm in thickness. Additionally, the transverse beam shift is extremely sensitive to the variations of the incident angle changing theoretically by 270 μm with 1 milli-radian (0.057°). These features can lead to minituarized spin Hall switches and filters with high angular resolution.

The propagation of electromagnetic waves can be manipulated at the nanoscale by surface plasmons supported by ultra thin metal layers. An adhesion layer, with thickness in the order of few nanometerss is used for depositing ultra thin metal gold layers. Cr and Ti are the most popular metallic adhesion layers. Apart from them, a non metallic silane based wetting layer like (3-Aminopropyl)trimethoxysilane (APTMS) can be used. The behaviour of the propagating surface plasmons due to the influence of these adhesion layers has not been thoroughly investigated. To study the influence of the adhesion layers on propagating plasmons for use in plasmonic and metamaterial applications,we experimentally compared the performances of the ultra-thin gold layers using Cr and APTMS adhesion layers and without any adhesion layer. We show that the gold layers using APTMS adhesion exhibit short range surface plasmon polaritons (SR-SPPs) with characteristics close to the theoretical calculations, considering an ideal gold film.

Hyperbolic metamaterials can provide unprecedented properties in accommodation of high-k (high wave vector) waves and enhancement of the optical density of states. To reach such performance the metamaterials have to be fabricated with as small imperfections as possible. Here we report on our advances in two approaches in fabrication of optical metamaterials. We deposit ultrathin ultrasmooth gold layers with the assistance of organic material (APTMS) adhesion layer. The technology supports the stacking of such layers in a multiperiod construction with alumina spacers between gold films, which is expected to exhibit hyperbolic properties in the visible range. As the second approach we apply the atomic layer deposition technique to arrange vertical alignment of layers or pillars of heavily doped ZnO or TiN, which enables us to produce hyperbolic metamaterials for the near- and mid-infrared ranges.

A low-absorption adhesion layer plays a crucial role for both localized and propagating surface plasmons when ultrathin gold is used. To date, the most popular adhesion layers are metallic, namely, Cr and Ti. However, to the best of our knowledge, the influence of these adhesion layers on the behavior of propagating plasmon modes has not been thoroughly investigated nor reported in the literature. It is therefore important to study the effect of these few- to several-nanometers-thick adhesion layers on the propagating plasmons because it may affect the performance of plasmonic devices, in particular, when the Au layer is not much thicker than the adhesion layers. We experimentally compared the performances of the ultrathin gold films to show the pivotal influence of adhesion layers on highly confined propagating plasmonic modes, using Cr and 3-aminopropyl trimethoxysilane (APTMS) adhesion layers and without any adhesion layer. We show that the gold films with the APTMS adhesion layer have the lowest surface roughness and the short-range surface plasmon polaritons supported on the Au surface exhibit properties close to the theoretical calculations, considering an ideal gold film.

The design of a free-standing (substrate-less) metallic hole array is proposed for Terahertz frequencies. The bandpass filtering effect through free standing perforted Aluminium (Al) films is demonstrated using a square array of circular holes on Al films having thickness of ∼ 11 μm. The effect of variation of periodicity and hole diameter on the transmittance due to excitation of surface plasmons and coupling between resonant and non-resonant modes is studied.