We present a novel optomechanical antenna design that directly converts near-infrared (lambda=1.55 mu m) light into mechanical motion using a tuning fork architecture with an integrated optical transmission line (OTL). The design consists of two parallel nanocantilever arms, made of gold-coated silicon nitride, forming a lateral tuning fork, with a plasmonic nanodipole antenna at the free end. Upon focused NIR laser illumination, our simulation results indicate that the nanodipole's feed gap concentrates the optical field and induces an oscillating voltage across the gap. This produces a strong DC electrostatic attraction between the tuning fork arms, causing an inplane deflection. The integrated coplanar optical transmission line significantly enhances the antenna's performance by improving impedance matching, leading to nearly an order-of-magnitude higher gap voltage compared to designs without OTL. We verified the static mechanical response using COMSOL multiphysics simulations. An optimized design exhibits a lateral displacement up to 24.6 nm at 8 mW optical power, which corresponds to a responsivity of 3 nm/mW at 1.55 mu m, outperforming previous NIR optomechanical transducers.

We present a systematic investigation of the optical response to circularly polarized illumination in twisted stacked plasmonic nanostructures. The system consists in two identical, parallel gold triskelia, centrally aligned and rotated at a certain angle relative to each other. Sample fabrication was accomplished through a novel multilevel high-resolution electron beam lithography. This stack holds two plasmonic modes of multipolar character in the near-infrared range, showing a strong dependence of their excitation intensities on the handedness of the circularly polarized incident light. This translates into a large circular dichroism which can be modulated by adjusting the twist angle of the stack. Fourier-transform infrared (FTIR) spectroscopy and numerical simulations were employed to characterize the spectral features of the modes. Remarkably, in contrast to previous results in other stacked nanostructures, the system’s response exhibits a behavior analogous to that of two interacting dipoles only at small angles. As the angle approaches 15°, where maximum dichroism is observed, more complex modes of the stack emerge. These modes evolve towards two in-phase multipolar excitations of the two triskelia as the angle increases up to 60°. Finally, simulations for a triangular array of such stacked elements show a sharp mode arising from the hybridization of a surface lattice resonance with the low-energy mode of the stack. This hybridized mode demonstrates the capability to be selectively switched on and off through the light polarization handedness.

The design of a plasmomechanical actuator based on an optical nanodipole antenna integrated in the overlapped free moving end of two micro-nanocantilevers is presented here. The static steady state deflection of the cantilevers, which defines the actuator response, is produced by means of two transduction phenomena activated by a continuous power NIR illumination: a desired opto-electromechanical (OEM) mechanism, in which the cantilevers are mutually attracted directly by the electrostatic force induced in the nanodipole feed gap, and a non-desired parasitic opto-thermomechanical (OTM) mechanism associated to the bimetallic effect induced by the optical heating of the structure. COMSOL Multiphysics has been chosen to carry out a design of the actuator based on an optimized optical response of the nanodipole antenna to the 1.55 μm wavelength radiation. COMSOL simulations have been also performed to evaluate the parasitic OTM response and the responsivity, defined as the OEM signal per unit radiation power. Predicted responsivity values of 0.67 nm/mW are of the same order of magnitude as in similar state-of-the-art transducers.

In this study we present a novel device for the direct transduction of optical radiation in the near-infrared region into mechanical actuation, which is based on a plasmonic optical nanoantenna integrated in a microcantilever. We propose and demonstrate the feasibility of a simple fabrication process consisting in the nano-tailoring of a commercially available Atomic Force Microscope (AFM) cantilever by means of the Focused Ion Beam (FIB) milling technique. Furthermore, the comprehensive analysis of the device performance characteristics included in this work reveals the different sensitivity values of these characteristics to the fabrication process tolerances of the most relevant geometric design parameters.

This work studies the effect of introducing a rhomboidal apodization pattern in the interdigital transducers (IDT) of 30°YX-cut Lithium Niobate-On-Insulator (LNOI) Shear Horizontal SH 0 resonators. To demonstrate the effect of IDT apodization, this work presents a set of manufactured resonators with different apodization ratios and compares their performance with non-apodized resonators.

Plasmonic lattice nanostructures are of technological interest because of their capacity to manipulate light below the diffraction limit. Here, we present a detailed study of dark and bright modes in the visible and near-infrared energy regime of an inverted plasmonic honeycomb lattice by a combination of Au+ focused ion beam lithography with nanometric resolution, optical and electron spectroscopy, and finite-difference time-domain simulations. The lattice consists of slits carved in a gold thin film, exhibiting hotspots and a set of bright and dark modes. We proposed that some of the dark modes detected by electron energy-loss spectroscopy are caused by antiferroelectric arrangements of the slit polarizations with two times the size of the hexagonal unit cell. The plasmonic resonances take place within the 0.5-2 eV energy range, indicating that they could be suitable for a synergistic coupling with excitons in two-dimensional transition metal dichalcogenides materials or for designing nanoscale sensing platforms based on near-field enhancement over a metallic surface.

In this work, we report on the fabrication of fluidic devices with hollow, suspended nanochannels, made by a combination of nanoimprint lithography and gas-phase deposition. We fabricated and characterized complete fluidic devices with arrays of nanochannels in the range of 500 nm x 500 nm to 700 nm x 700 nm, 30 µm long, with wall thickness just few tens of nm thick. We also developed a COMSOL model to predict the motion and resonance frequency range of the hollow beams with different materials, geometries, and investigate the relevant damping conditions.

We present an innovative contactless method suitable to study in-plane thermal transport based on beam-offset frequency-domain thermoreflectance using a one-dimensional heat source with uniform power distribution. Using a one-dimensional heat source provides a number of advantages as compared to point-like heat sources, as typically used in time- and frequency-domain thermoreflectance experiments, just to name a few: (i) it leads to a slower spatial decay of the temperature field in the direction perpendicular to the line-shaped heat source, allowing to probe the temperature field at larger distances from the heater, hence, enhancing the sensitivity to in-plane thermal transport; (ii) the frequency range of interest is typically < 100 kHz. This rather low frequency range is convenient regarding the cost of the required excitation laser system but, most importantly, it allows the study of materials without the presence of a metallic transducer with almost no influence of the finite optical penetration depth of the pump and probe beams on the thermal phase lag, which arises from the large thermal penetration depth imposed by the used frequency range. We also show that for the case of a harmonic thermal excitation source, the phase lag between the thermal excitation and thermal response of the sample exhibits a linear dependence with their spatial offset, where the slope is proportional to the inverse of the thermal diffusivity of the material. We demonstrate the applicability of this method to the cases of: (i) suspended thin films of Si and PDPP4T, (ii) Bi bulk samples, and (iii) Si, glass, and highly-oriented pyrollitic graphite (HOPG) bulk samples with a thin metallic transducer. Finally, we also show that it is possible to study in-plane heat transport on substrates with rather low thermal diffusivity, e.g., glass, even using a metallic transducer.

This work discusses how apodization of the interdigital transducers (IDT) of shear horizontal (SH 0 ) acoustic wave resonators allows to avoid the presence of spurious modes between resonances and enhance the achieved electromechanical coupling and quality factor. Achieving spurious-free resonators is fundamental to face the design of ladder filters with flat passbands. The proposal is demonstrated with manufactured resonators on a 30°YX-cut lithium niobate-on-insulator (LNOI) structure comparing the performance of apodized and non-apodized devices. Clean resonators without transverse spurious modes have been obtained showing an improvement in quality factor and electromechanical coupling coefficient, attaining $k_{t}^2=17 \%, Q_{\max } \sim 800$ and impedance ratios of 69 dB.

This work demonstrates manufactured microacoustic resonators exploiting the shear horizontal (SHo) mode on a 30 o YX-cut lithium niobate-on-insulator (LNOI) structure. Moreover, the work shows how the careful selection of electrode thickness is key to avoid the excitation of spurious longitudinal modes above the anti-resonance frequency. The manufactured resonators are in the 1.5 GHz frequency range and exhibit an electromechanical coupling coefficient of 14.3% and a quality factor of 615.

We present an efficient refractive index sensor consisting of a heterostructure that contains an Au inverted honeycomb lattice as a main sensing element. Our design aims at maximizing the out-of-plane near-field distributions of the collective modes of the lattice mapping the sensor surroundings. These modes are further enhanced by a patterned SiO2 layer with the same inverted honeycomb lattice, an SiO2 spacer, and an Au mirror underneath the Au sensing layer that contribute to achieving a high performance. The optical response of the heterostructure was studied by numerical simulation. The results corresponding to one of the collective modes showed high sensitivity values ranging from 99 to 395 nm/RIU for relatively thin layers of test materials within 50 and 200 nm. In addition, the figure of merit of the sensor detecting slight changes of the refractive index of a water medium at a fixed wavelength was as high as 199 RIU−1. As an experimental proof of concept, the heterostructure was manufactured by a simple method based on electron beam lithography and the measured optical response reproduces the simulations. This work paves the way for improving both the sensitivity of plasmonic sensors and the signal of some enhanced surface spectroscopies.

Understanding defects is of paramount importance for the development of stable halide perovskite solar cells (PSCs). However, isolating their distinctive effects on device efficiency and stability is currently a challenge. We report that adding the organic molecule 3-phosphonopropionic acid (H3pp) to the halide perovskite results in unchanged overall optoelectronic performance while having a tremendous effect on device stability. We obtained PSCs with similar to 21% efficiency that retain similar to 100% of the initial efficiency after 1,000 h at the maximum power point under simulated AM1.5G illumination. The strong interaction between the perovskite and the H3pp molecule through two types of hydrogen bonds (H center dot center dot center dot I and O center dot center dot center dot H) leads to shallow point defect passivation that has a significant effect on device stability but not on the non-radiative recombination and device efficiency. We expect that our work will have important implications for the current understanding and advancement of operational PSCs.

Silicon based single photon avalanche diodes (SPAD) are able to detect single photons in the visible part of the spectrum with high detection efficiency and high timing resolution. They also provide both single-photon sensitivity and fast responsivity in large-area detectors if arranged in extended arrays as Silicon Photomultipliers (SiPM). However, in applications exploiting near infrared light like light detection and ranging (LiDAR), the detector performance is hindered by the limited Si absorption coefficient. The latter implies absorption depths much larger than the typical active thickness of these devices (10-100 μm against few micrometers) resulting in a quantum efficiency (QE) too low for most of the previous applications. The exploitation of Surface Plasmon Polaritrons (SPP) can convert light in highly-confined modes and enhance the absorption of NIR photons. In this contribution, the first results on the integration of plasmonics nanostructures on thin silicon photodiodes are reported. Electro-optical measurements were carried out and the QE has been measured in the full 400-1100 nm spectrum. The resulting QE on the first prototypes is higher than 7% at 950 nm, an enhancement of about 45% with respect to the reference structure, paving the way for the application of metallic nanograting to SPADs and SiPMs devices.

A methodology based on the use of Electron Beam Lithography for contacting individual nanowires on top of non-flat micromembranes and microhotplates has been implemented, and the practical details have been exhaustively described. The different fabrication steps have been adapted to the substrate's topology, requiring specific holders and conditions. The methodology is demonstrated on individual SnO2 nanowires, which, after fabrication, have been characterized as functional resistive gas nanosensors towards NH3 and benchmarked against similar devices fabricated using more conventional Dual Beam Focused Ion Beam techniques, demonstrating the superior properties of the here presented methodology, which can be further extended to other non-conventional suspended substrates and nanomaterials.

In this communication, we show preliminary results on transmissive TiO2 wire-grid polarizers (WGP) operating in the deep ultraviolet (DUV) range. WGP are devices based on strips of materials with large values of the modulus of the dielectric constant along with high absorption in the operational range. The merit function Pi is introduced as a new tool to find the optimum material for WGPs in a given spectral range. The experimental dielectric constant of TiO2 thin films deposited by pulsed laser deposition are obtained through spectroscopic ellipsometry, and the Pi function indicates that TiO2 is the best candidate for WGP in the DUV range when it is compared with other oxides. Once the material selection for WGP is done, we present and compare two different design approaches for WGP: one using an effective medium theory for the periodic structure, and the second using finite-difference time-domain (FDTD) analysis. A prototype of WGP is fabricated by electron beam (e-beam) lithography followed by lift-off process; the topography of the sample is analyzed by AFM, and we found noticeable deviations in the grating from the designed values. In preliminary characterization work the effective dielectric constant in two perpendicular orientations is obtained by ellipsometry and the contrast is compared with the design.

We present the fabrication, operation, and CMOS integration of arrays of suspended silicon nanowires (SiNWs). The functional structures are obtained by a top-down fabrication approach consisting in a resistless process based on focused ion beam irradiation, causing local gallium implantation and silicon amorphization, plus selective silicon etching by tetramethylammonium hydroxide, and a thermal annealing process in a boron rich atmosphere. The last step enables the electrical functionality of the irradiated material. Doubly clamped silicon beams are fabricated by this method. The electrical readout of their mechanical response can be addressed by a frequency down-mixing detection technique thanks to an enhanced piezoresistive transduction mechanism. Three specific aspects are discussed: (i) the engineering of mechanically coupled SiNWs, by making use of the nanometer scale overhang that it is inherently-generated with this fabrication process, (ii) the statistical distribution of patterned lateral dimensions when fabricating large arrays of identical devices, and (iii) the compatibility of the patterning methodology with CMOS circuits. Our results suggest that the application of this method to the integration of large arrays of suspended SiNWs with CMOS circuitry is interesting in view of applications such as advanced radio frequency band pass filters and ultra-high-sensitivity mass sensors.

We introduce the concept of geometric frustration in plasmonic arrays of nanoelements. In particular, we present the case of a hexagonal lattice of Au nanoasterisks arranged so that the gaps between neighboring elements are small and lead to a strong near-field dipolar coupling. Besides, far-field interactions yield higher-order collective modes around the visible region that follow the translational symmetry of the lattice. However, dipolar excitations of the gaps in the hexagonal array are geometrically frustrated for interactions beyond nearest neighbors, yielding the destabilization of the low energy modes in the near infrared. This in turn results in a slow dynamics of the optical response and a complex interplay between localized and collective modes, a behavior that shares features with geometrically frustrated magnetic systems.

Arrays of silicon nanowires with height gradients fabricated using metal-assisted chemical etching act as tunable metamirrors enabling light focusing the reflected light in arbitrary shapes. Metamirrors with non-cylindrical nanowires can simultaneously focus the reflected light and induce strong polarization conversion effect. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Micro-patterned surfaces with alternate hydrophilic and hydrophobic rectangular areas effectively confine water droplets down to attolitre volumes. The contact angle, volume, and geometry of the confined droplets as a function of the geometry and physico-chemical properties of the confining surfaces have been determined by phenomenological simulations, validated by atomic force microscopy measurements. The combination between experiments and simulations can be used for the purposeful design of arrays with surface-addressable hydrophobicity employed in digital microfluidics and high-throughput screening nanoarrays.

This paper presents the study of the dynamics of the formation of polymer-assisted highly-orientated polycrystalline cubic structures (CS) by a fractal-mediated mechanism. This mechanism involves the formation of seed Ag@Co nanoparticles by InterMatrix Synthesis and subsequent overgrowth after incubation at a low temperature in chloride and phosphate solutions. These ions promote the dissolution and recrystallization in an ordered configuration of pre-synthetized nanoparticles initially embedded in negatively-charged polymeric matrices. During recrystallization, silver ions aggregate in AgCl@Co fractal-like structures, then evolve into regular polycrystalline solid nanostructures (e.g. CS) in a single crystallization step on specific regions of the ion exchange resin (IER) which maintain the integrity of polycrystalline nanocubes. Here, we study the essential role of the IER in the formation of these CS for the maintenance of their integrity and stability. Thus, this synthesis protocol may be easily expanded to the composition of other nanoparticles providing an interesting, cheap and simple alternative for cubic structure formation and isolation.