Silicon Nanocylinders Research Articles

Photonic management of silicon nanocylinder arrays to enhance photovoltaic performance

The light–matter interaction of subwavelength and periodic silicon (Si) nanostructures strongly correlates with their geometrical features, resulting in them being highly unsuitable for the practical development of Si-based photovoltaic applications. In this study, the concepts of effective medium and retrieval methods are needed to deal with the subwavelength periodic dielectric structure. Using finite-difference time-domain simulations, we study the interactions of electromagnetic radiation with a square array of dielectric rods parallel to the incident light, and the effective optical properties such as refractive index, permittivity, and permeability are calculated. Furthermore, the electric field distributions are also plotted for a deeper understanding of the energy changes within Si nanocylinder arrays (SiNCAs) under different incident wavelengths of radiation. By employing calculated optimized SiNCAs for the construction of hybrid solar cells, improved cell performances showing a conversion efficiency of 13.79% are demonstrated, with further estimation by electrical chemical measurements for a better understanding of the carrier transition. These are numerically and experimentally interpreted by the involvement of excellent light-trapping effects, delivering a method to design correlated photovoltaic devices.

Optical trapping and manipulation of nanowires using multi-hotspot dielectric nanononamers

Semiconductor nanowires have demonstrated great potential in all-photonic integrated circuit applications. However, the development of a controllable multidimensional nanowire assembly technique is still arguably in its infancy. Here, we numerically demonstrate the optical trapping and manipulation of cylindrical zinc oxide nanowires using an all-dielectric silicon nanononamer for designing programmable nanolasers. The nanononamer is composed of nine identical silicon nanocylinders arranged in a square grid on top of a glass substrate. This is a suitable choice, as optical trapping with the proposed silicon nanononamer is envisioned as an effective technique for the contactless manipulation of suspended nanowires with multiple hotspots and with negligible heating generation. We determine optical forces and torques applied to nanowires using the Maxwell stress tensor method. We investigate the influence of light polarization on the field confining and laser tweezing properties. For this work, the simple nanowire-based silicon photonic platform is compatible with the complementary metal–oxide–semiconductor technology, which allows low-cost fabrication of such structures and the integration with other on-chip optical components.

Integrated Janus dipole source for selective coupling to silicon waveguide networks

The efficient selective and directional coupling of light to waveguiding circuitry at the nanoscale is one of the key challenges in nanophotonics, as it constitutes a prerequisite for many applications, including information processing, routing, and quantum technologies. Various exotic nanostructures and nanoparticle arrangements have been designed to achieve directional coupling with compact on-chip integration remaining one of the foremost hurdles to realizing many real-world devices. At the same time, selective coupling to one of several neighboring waveguides is much more difficult to achieve and control. To address this challenge, we demonstrate a subwavelength selective coupler integrated in a waveguide network, with selectivity controlled by wavelength, polarization, and angle of incidence. We utilize a Janus source, which is composed of a superposition of electric and magnetic dipoles, supported by a silicon nanocylinder. By placing the nanocylinder between identical single mode silicon waveguides, we successfully achieve selective coupling with a high contrast ratio between the waveguides. The operating wavelength of the Janus dipolar source can be easily tailored, and the coupling efficiency is also shown to be conveniently boosted by the addition of multiple nanocylinders. Our compact approach provides a direct path toward on-chip highly directional nanoscale sources for a plethora of applications, including information routing, metrology, and quantum technologies.

Non-Huygens transparent metasurfaces based on the novel Hybrid anapole state

In this work we studied the optical properties of the metasurfaces based on silicon nanocylinders experincing hybrid anapole. Our investigation shows the possibility of creating fully invisible metasurfaces consisting of silicon nanocylinders based on the novel state which in their properties can compete with the Huygens’ metasurfaces. These results can be used in various fields of nanophotonics and may have important outcome in the development of various photonic devices.

Ultrafast laser heating of non-plasmonic nanocylinders

We develop a model describing non-equilibrium processes under the excitation of resonant semiconductor nanostructures with ultrashort laser pulses with a duration of about 100 fs. We focus on the heating effects related to pulsed excitation with account on free carriers generation, thermalization, and relaxation. The heat exchange between the electron and phonon system is treated within the two-temperature model. We applied the developed model to describing pulsed heating of silicon nanocylinder on top of a dielectric substrate. We come up with estimations of the thermal damage threshold of the considered structures which provides the limits for the experimental conditions and ensures thermal stability of the samples.

Dielectric metasurface for emission control of magnetic dipole in the near-IR wavelength range

Developing active dielectric systems is in high demand due to growing the internet of things. Such systems can control the optical properties of nanoemitters which leads to an increase in the performance of the telecommunication networks. Here we numerically investigate metasurface consists of all-dielectric erbium-doped silicon nanocylinders. We demonstrate that such a structure can effectively control and enhance 320-folds spontaneous emission in the near-IR wavelength range. The results of this paper can be used for creating new telecommunication systems.

Metal, dielectric and hybrid nanoantennas for enhancing the emission of single quantum dots: A comparative study

The confinement of electromagnetic energy to subwavelength volumes through nanoscale antennas can be used to enhance the spontaneous emission of quantum emitters. With this aim, different configurations of metallic and high refractive index dielectric nanoparticles have been explored. Here, we carry out a comparative analysis of planar metallic, high refractive index dielectric, and hybrid nanoantennas considering three different parameters: the Purcell factor enhancement, radiation efficiency, and directionality properties. We focus our study on different geometries and material combinations of a dimer of cylinders. A dimer made of two gold nanocylinders is the most promising candidate for improving the spontaneous emission. While most previous works have paid attention to the redirection of the scattered emission in the nanoparticle plane, our proposed nanostructure of two large gold cylinders (R=λ/4) emits most of the radiation upwards. This effect is due to the strong quadrupolar electric contribution to the resonant mode. With the aim to further improve the directionality properties, additional silicon nanocylinders are used as directors of the scattered radiation, increasing the directivity by a factor of 2.4 with respect to the gold dimer without directors. All in all, a hybrid structure composed of a gold dimer and silicon nanoparticles is proposed to enhance the spontaneous emission of a single quantum dot and to govern its emission pattern. The results shown in this work could be useful in fluorescence enhancement or in quantum photonics. They are particularly interesting for the development of single-photon sources based on quantum dots and other nanoscale emitters.

Compact Optical Polarization‐Insensitive Zoom Metalens Doublet

AbstractMetasurface‐based lenses (metalenses) offer specific conceptual advantages compared to ordinary refractive lenses. For example, it is possible to tune the focal length of a metalens doublet by varying the relative angle between the two metalenses while fixing their distance, leading to an extremely compact zoom lens. An improved polarization‐insensitive design based on silicon nanocylinders on silica substrates is presented. This design is realized and characterized experimentally at 1550 nm wavelength. By varying the relative angle between the metalenses in steps of 10°, tuning of the doublet focal length is demonstrated from −54 mm to ±3 mm to +54 mm. This results in a zoom factor of an imaging system varying between 1 and 18. For positive focal lengths, the doublet focusing efficiency has a minimum of 34% and a maximum of 83%. Experiment and theory are in very good agreement.

Evolution of multipole moments in silicon nanocylinder while varying the refractive index of surrounding medium

Here we use multipole decomposition approach to study optical properties of a silicon nanocylinder in different lossless media. We show that resonant peaks of multipole moments experience red shift, smoothing and broadening. Worth noting that electric multipoles experience bigger red shift than their magnetic counterparts. Our results can be applied to design optical devices within a single framework.

Enhanced Chiral Sensing with Dielectric Nanoresonators.

Chiro-sensitive molecular detection is highly relevant as many biochemical compounds, the building blocks of life, are chiral. Optical chirality is conventionally detected through circular dichroism (CD) in the UV range, where molecules naturally absorb. Recently, plasmonics has been proposed as a way to boost the otherwise very weak CD signal and translate it to the visible/NIR range, where technology is friendlier. Here, we explore how dielectric nanoresonators can contribute to efficiently differentiate molecular enantiomers. We study the influence of the detuning between electric (ED) and magnetic dipole (MD) resonances in silicon nanocylinders on the quality of the CD signal. While our experimental data, supported by numerical simulations, demonstrate that dielectric nanoresonators can perform even better than their plasmonic counterpart, exhibiting larger CD enhancements, we do not observe any significant influence of the optical chirality.

Unravelling the Role of Electric and Magnetic Dipoles in Biosensing with Si Nanoresonators.

High refractive index dielectric nanoresonators are attracting much attention due to their ability to control both electric and magnetic components of light. Due to the combination of confined modes with reduced absorption losses, they have recently been proposed as an alternative to nanoplasmonic biosensors. In this context, we study the use of semirandom silicon nanocylinder arrays, fabricated with simple and scalable colloidal lithography for the efficient and reliable detection of biomolecules in biological samples. Interestingly, electric and magnetic dipole resonances are associated with two different transduction mechanisms: extinction decrease and resonance red shift. By contrasting both observables, we identify clear advantages in tracking changes in the extinction magnitude. Our data demonstrate that, despite its simplicity, the proposed platform is able to detect prostate-specific antigen in human serum with limits of detection meeting clinical needs.

Tailoring Photoluminescence from MoS2 Monolayers by Mie-Resonant Metasurfaces

We experimentally investigate coupling of the photoluminescence (PL) from monolayers of MoS2 to Mie-resonant metasurfaces consisting of silicon nanocylinders. By a systematic variation of the nanocylinder diameter, we sweep the metasurface resonances over the excitonic emission band of monolayer MoS2. We observe strong enhancement, as well as spectral and directional reshaping of the emission. By a comprehensive optical characterization, we unveil the different physical factors, including electronic, photonic, and mechanical influences, responsible for the observed PL changes. Importantly, we show that by geometrical tuning of the nanocylinder resonances, the emission can be tailored from occurring under very large angles to being directed out of the substrate plane. Our results highlight the need and potential of controlling not only the photonic, but also electronic and mechanical environmental factors for tailoring PL from TMD monolayers by integrating them in nanophotonic architectures.

Disorder-Induced Phase Transitions in the Transmission of Dielectric Metasurfaces.

Light interaction with disordered materials is both complex and fascinating at the same time. Here, we reveal disorder-induced phase transitions in a dielectric Huygens' metasurface made from silicon nanocylinders that simultaneously support an electric and magnetic dipole resonance. Depending on the degree of positional disorder and the spectral detuning of the two resonances, the phase angle of the transmission coefficient exhibits a clear phase transition from normal to anomalous dispersion. Combined with the considerations of whether the resonances of spectrally detuned particles appear as separated or overlapping, we distinguish four different phase states. We study this phenomenon analytically by employing dipole particles and disclose the entire phase diagram, support our insights with full-wave simulations of actual structures, and corroborate the findings with experimental results. Unveiling this phenomenon is a milestone simultaneously in the growing fields of metamaterial-inspired silicon nanophotonics, photonics in disordered media, and the fundamental physics of phase transitions.

Manipulation of Magnetic Dipole Emission from Eu3+ with Mie-Resonant Dielectric Metasurfaces.

Mie-resonant high-index dielectric nanoparticles and metasurfaces have been suggested as a viable platform for enhancing both electric and magnetic dipole transitions of fluorescent emitters. While the enhancement of the electric dipole transitions by such dielectric nanoparticles has been demonstrated experimentally, the case of magnetic-dipole transitions remains largely unexplored. Here, we study the enhancement of spontaneous emission of Eu3+ ions, featuring both electric and magnetic-dominated dipole transitions, by dielectric metasurfaces composed of Mie-resonant silicon nanocylinders. By coating the metasurfaces with a layer of an Eu3+ doped polymer, we observe an enhancement of the Eu3+ emission associated with the electric (at 610 nm) and magnetic-dominated (at 590 nm) dipole transitions. The enhancement factor depends systematically on the spectral proximity of the atomic transitions to the Mie resonances as well as their multipolar order, both controlled by the nanocylinder size. Importantly, the branching ratio of emission via the electric or magnetic transition channel can be modified by carefully designing the metasurface, where the magnetic dipole transition is enhanced more than the electric transition for cylinders with radii of about 130 nm. We confirm our observations by numerical simulations based on the reciprocity principle. Our results open new opportunities for bright nanoscale light sources based on magnetic transitions.

Excitation of surface plasmons with a long oscillation lifetime using silicon nanophotonic devices: A strong coupling system

We report the excitation of surface plasmons by silicon nanophotonic devices. An array of silicon nanocylinders is fabricated on the top of corresponding silica nanopillars. The whole dielectric structure is placed on the surface of a gold film. Surface plasmons with a long oscillation lifetime are excited under light illumination. By adjusting geometry parameters, resonant peaks are tailored and the anticrossing phenomenon is observed in the spectra, demonstrating the strong coupling between surface plasmons and magnetic dipole mode. The presented findings reveal the potential of the development of silicon nanophotonic devices for plasmonic applications.

Broadband Electromagnetic Dipole Resonance by the Coupling Effect of Multiple Dielectric Nanocylinders

Broadband resonant scattering in a visible region that can be obtained by coupled multiple silicon nanocylinders. For a single high refractive index silicon nanocylinder, the electric dipole and magnetic dipole resonances can be observed. By constructing a silicon nanocylinder dimer, the interaction between the particles plays an important role in broadband scattering. Interestingly, due to magnetic-magnetic dipole interaction, a splitting phenomenon of magnetic resonance mode is revealed. A new magnetic resonant mode emerges at a longer wavelength in dimer and trimer by changing the diameter of one nanocylinder in dimer or trimer, and the gap size between nanocylinders. The scattering bandwidth can further increase with the effect of substrate, which is attributed to the extension of resonant mode into substrate. The broadband optical response can be revealed by the calculated scattering resonant spectra and the spatial electromagnetic field distributions. Furthermore, the transmission of periodic nanocylinder structure, including single nanocylinder and dimer, is demonstrated. By decreasing the gap between nanocylinders in dimer for periodic array structure, a new electric resonant mode occurs. These results can provide a guideline to realize broadband resonant optical elements.

Efficient colored silicon solar modules using integrated resonant dielectric nanoscatterers

We demonstrate photovoltaic modules with a bright green color based on silicon heterojunction solar cells integrated with arrays of light scattering dielectric nanoscatterers. Dense arrays of crystalline silicon nanocylinders, 100–120 nm wide, 240 nm tall, and 325 nm pitch, are made onto module cover slides using substrate-conformal soft-imprint lithography. Strong electric and magnetic dipolar Mie resonances with a narrow linewidth (Q ∼ 30) cause strong (35%–40%) specular light scattering on resonance (∼540 nm). The green color is observed over a wide range of angles (8°–75°). As the resonant nanoscatterers are transparent for the major fraction of the incident solar spectrum, the relative loss in short-circuit current is only 10%–11%. The soft-imprinted nanopatterns can be applied on full-size solar modules and integrated with conventional module encapsulation. The dielectric Mie resonances can be controlled by geometry, opening up a road for designing efficient colorful or white building-integrated photovoltaics.

Magnetic field concentration with coaxial silicon nanocylinders in the optical spectral range

Possibility of magnetic energy accumulation inside silicon nanoparticles at the conditions of resonant optical responses is investigated theoretically. The magnetic field distributions inside silicon nanocylinders with and without coaxial through holes are calculated using full-wave numerical approach. It is demonstrated that such systems can be used for control and manipulation of optical magnetic fields providing their enhancement up to 26 times at the condition of optical resonances. Obtained results can be used for realization of nanoantennas and nanolasers, in which magnetic optical transitions play significant roles.

Magnetic hot-spots in hollow silicon cylinders

Silicon nanoparticles can possess magnetic Mie-resonant response in the visible and near infrared wavelength ranges. In this paper, we consider numerically the features of magnetic hot-spots realized inside silicon nanocylinders at the conditions of the optical magnetic resonances, and show that the intensity of the magnetic field inside nanoparticles with a coaxial through hole can be much stronger than the intensity of incident light waves.

Controlling magnetic and electric dipole modes in hollow silicon nanocylinders.

We propose a dielectric nanoresonator geometry consisting of hollow dielectric nanocylinders which support geometrical resonances. We fabricate such hollow Si particles with an outer diameter of 108-251 nm on a Si substrate, and determine their resonant modes with cathodo-luminescence (CL) spectroscopy and optical dark-field (DF) scattering measurements. The scattering behavior is numerically investigated in a systematic fashion as a function of wavelength and particle geometry. We find that the additional design parameter as a result of the introduction of a center gap can be used to control the relative spectral spacing of the resonant modes, which will enable additional control over the angular radiation pattern of the scatterers. Furthermore, the gap offers direct access to the enhanced magnetic dipole modal field in the center of the particle.