Silicon Nanorings Research Articles

ITO-Based Electrically Tunable Metasurface for Active Control of Light Transmission.

In recent years, the rapid development of dynamically tunable metasurfaces has provided a new avenue for flexible control of optical properties. This paper introduces a transmission-type electrically tunable metasurface, employing a series of subwavelength-scale silicon (Si) nanoring structures with an intermediate layer of Al2O3-ITO-Al2O3. This design allows the metasurface to induce strong Mie resonance when transverse electric (TE) waves are normally incident. When a bias voltage is applied, the interaction between light and matter is enhanced due to the formation of an electron accumulation layer at the ITO-Al2O3 interface, thereby altering the resonance characteristics of the metasurface. This design not only avoids the absorption loss of metal nanostructures and has a large modulation depth, but also shows compatibility with complementary metal oxide semiconductor (CMOS) technology.

Metasurface cutoff perfect absorber in a solar energy wavelength band.

We report a metasurface cutoff perfect absorber (MCPA) in the solar energy wavelength band based on the double Mie resonances generated from the silicon and gallium arsenide nanoring arrays grown on the Al layer in the solar energy wavelengths. A high average absorption of 0.910 in the absorption band and almost eliminated absorption in the nonabsorption band are realized within only 120nm thick structures. The MCPA is of a sharp cutoff between the absorption and nonabsorption band, whose extinction ratio, extinction difference, and cutoff slope are 9.4dB, 0.8, and 0.0019n m -1, respectively. The proposed MCPA suggests an efficient way to design a solar thermal absorber, which is of great importance in renewable energy, such as for solar thermal applications.

Control of light emission of quantum emitters coupled to silicon nanoantenna using cylindrical vector beams

Light emission of europium (Eu3+) ions placed in the vicinity of optically resonant nanoantennas is usually controlled by tailoring the local density of photon states (LDOS). We show that the polarization and shape of the excitation beam can also be used to manipulate light emission, as azimuthally or radially polarized cylindrical vector beam offers to spatially shape the electric and magnetic fields, in addition to the effect of silicon nanorings (Si-NRs) used as nanoantennas. The photoluminescence (PL) mappings of the Eu3+ transitions and the Si phonon mappings are strongly dependent of both the excitation beam and the Si-NR dimensions. The experimental results of Raman scattering and photoluminescence are confirmed by numerical simulations of the near-field intensity in the Si nanoantenna and in the Eu3+-doped film, respectively. The branching ratios obtained from the experimental PL maps also reveal a redistribution of the electric and magnetic emission channels. Our results show that it could be possible to spatially control both electric and magnetic dipolar emission of Eu3+ ions by switching the laser beam polarization, hence the near field at the excitation wavelength, and the electric and magnetic LDOS at the emission wavelength. This paves the way for optimized geometries taking advantage of both excitation and emission processes.

Hybrid Dielectric-Plasmonic Nanoantenna with Multiresonances for Subwavelength Photon Sources

The enhancement of the photoluminescence of quantum dots induced by an optical nanoantenna has been studied considerably, but there is still significant interest in optimizing and miniaturizing such structures, especially when accompanied by an experimental demonstration. Most of the realizations use plasmonic platforms, and some also use all-dielectric nanoantennas, but hybrid dielectric-plasmonic (subwavelength) nanostructures have been very little explored. In this paper, we propose and demonstrate single subwavelength hybrid dielectric-plasmonic optical nanoantennas coupled to localized quantum dot emitters that constitute efficient and bright unidirectional photon sources under optical pumping. To achieve this, we devised a silicon nanoring sitting on a gold mirror with a 10 nm gap in-between, where an assembly of colloidal quantum dots is embedded. Such a structure supports both (radiative) antenna mode and (nonradiative) gap mode resonances, which we exploit for the dual purpose of out-coupling the light emitted by the quantum dots into the far-field with out-of-plane directivity, and for enhancing the excitation of the dots by the optical pump. Moreover, almost independent control of the resonance spectral positions can be achieved by simple tuning of geometrical parameters such as the ring inner and outer diameters, allowing us to conveniently adjust these resonances with respect to the quantum dots emission and absorption wavelengths. Using the proposed architecture, we obtain experimentally average fluorescence enhancement factors up to $654\times$ folds mainly due to high radiative efficiencies, and associated with a directional emission of the photoluminescence into a cone of $\pm 17\degree$ in the direction normal to the sample plane. We believe the solution presented here to be viable and relevant for the next generation of light-emitting devices.

C-band operating plasmonic sensor with a high Q-factor/figure of merit based on a silicon nano-ring.

In this paper, we take advantage of the high refractive index property of silicon to design a practical and sensitive plasmonic sensor on a photonic integrated circuit (PIC) platform. It has been demonstrated that a label-free refractive index sensor with sensitivity up to 1124nm/RIU can be obtained using a simple design of a silicon nano-ring with a concentric hexagonal plasmonic cavity. It has also been shown that, with optimum structural parameters, a quality factor (Q-factor) of 307 and a figure of merit (FOM) of 234R I U -1 can be achieved, which are approximately 8 times and 5 times higher than the proposed sensors counterparts, respectively. In addition, the resonance mode of the hexagonal cavity with Si nano-ring (HCS) sensor can be adjusted to operate in the C-band, which is a highly desirable wavelength range in terms of compatibility with devices in PIC technology.

Two-dimensional silicon nanoring array enabled polarization-independent narrow spectral linewidth optical filter

In this paper, we investigate a new, to the best of our knowledge, type of guided-mode resonance optical filter with polarization-independence at normal incidence and relatively narrow spectral linewidth in the near-infrared regime. The new optical spectral filter consists of a 2D array of silicon nanorings on silicon film on silica substrate. Using finite difference time domain (FDTD) simulations, it is found that the spectral linewidth of the optical filter is primarily controlled by nanoring width and is tolerant to the variations of the size and height of silicon nanorings. FDTD simulations also reveal that the excited guided mode is more tightly confined in the nanoring structures with smaller ring widths. It is explained that the narrow spectral linewidth of the nanoring structure filter is due to the smaller scattering cross-section of the silicon nanorings and tighter confinement of the guided mode. Our optimally designed optical reflection filter exhibits a 2.4 nm spectral linewidth with nearly 100% peak reflectance at the resonance wavelength.

Strong dipole and higher multi-pole Mie resonance modes with all-dielectric nanoring metasurfaces structure

Strong electric and magnetic dipole in infrared region and higher order multi-pole resonance at visible wavelengths are observed in all-dielectric nanoring metasurfaces. We discuss some of the parameters that influence the optical response of the dielectric nanoring. Adjustment of nanoring radius (inner radius and outer radius) and height can change the absorption intensity and the resonance peaks. Dipole, quadrupole, six-pole and ten-pole resonance modes can be found in the silicon nanoring at resonance wavelength. The transmission spectrum of nanoring with high Q-factor and contrast is achieved with appropriate parameters. Further the nanoring is used to application of sensing in which the sensitivity reaches 228 nm/RIU. This research is an important step to understand resonance in silicon nanoring and paves way for designing some optic devices such as sensor, nanoantennas, and photovoltaics.

Templated fabrication of periodic arrays of metallic and silicon nanorings with complex nanostructures

Here we report a scalable colloidal templating approach for fabricating periodic arrays of metallic and silicon nanorings with complex nanostructures. Non-close-packed monolayer silica colloidal crystal prepared by a simple spin-coating technology is first used as template for making periodic arrays of mushroom-like composite nanostructures consisting of silica spherical caps and polymer stems. Subsequent metal sputtering and reactive ion etching lead to the formation of ordered asymmetric nickel nanorings which can be further utilized as etching masks for patterning periodic arrays of symmetric silicon nanorings. Moreover, periodic arrays of metallic and silicon concentric double nanorings can be fabricated by using the asymmetric nickel nanorings as templates. We have also demonstrated that gold concentric double nanorings show strong surface-enhanced Raman scattering (SERS) with a SERS enhancement factor of ∼9.5 × 107 from adsorbed benzenethiol molecules. The SERS enhancement and the electric field amplitude distribution surrounding gold concentric double nanorings have been calculated by using finite element electromagnetic modeling. This new colloidal templating technique is compatible with standard microfabrication and enables wafer-scale production of a variety of periodic nanorings with hierarchical structures that could find important technological applications in plasmonic and magnetic devices.

Electric field geometries dominate quantum transport coupling in silicon nanoring

Investigations on the relation between the geometries of silicon nanodevices and the quantum phenomenon they exhibit, such as the Aharonov–Bohm (AB) effect and the Coulomb blockade, were conducted. An arsenic doped silicon nanoring coupled with a nanowire by electron beam lithography was fabricated. At 1.47 K, Coulomb blockade oscillations were observed under modulation from the top gate voltage, and a periodic AB oscillation of ΔB = 0.178 T was estimated for a ring radius of 86 nm under a high sweeping magnetic field. Modulating the flat top gate and the pointed side gate was performed to cluster and separate the many electron quantum dots, which demonstrated that quantum confinement and interference effects coexisted in the doped silicon nanoring.

Structural and Optical Characterization of Pr<SUB>2</SUB>O<SUB>3</SUB> and Yb Doped and Co-Doped Silicon Nanorings

Structural and Optical Characterization of Pr<SUB>2</SUB>O<SUB>3</SUB> and Yb Doped and Co-Doped Silicon Nanorings

Top-down fabrication of vertical silicon nano-rings based on Poisson diffraction

Vertical Si nano-rings with a uniform thickness of about 100 nm have been fabricated byconventional optical photolithography with a low cost based on Poisson diffraction.Moreover, the roughness of the Si nano-rings can be effectively reduced by sacrificialoxidation. In order to increase the density of the nano-rings, coaxial twin Si nano-ringshave been fabricated by the Poisson diffraction method combined with the spacertechnique. The thickness of both the inner and outer Si nano-rings is about 60 nm, and thegap between the twin nano-rings is about 100 nm.

Structural and Nonlinear Optical Properties of Self-Assembled SnO[sub 2]-Doped Silicon Nanorings Formed by Pulsed Laser Ablation

SnO 2 -doped Si nanorings with an outer diameter of 25 nm and an average width of 5 nm are grown by pulsed laser deposition. Atomic force microscopy reveals several interesting self-assembling forms of polycrystalline as well as an amorphous type of silicon nanorings. Depending on the width of the ring, the optical bandgap and photoluminescence can be tuned from the near infrared (1.38 eV) to the ultraviolet (3.02 eV), giving evidence for the strong quantum confinement effect along the width of ringlike quantum states. From Z-scan studies, the two-photon absorption coefficient is determined to be 2.2 X 10 -6 m/W.

Novel silicon nanorings: Persilacyclacenes at DFT

AbstractStructures, energies, and aromatic characters are compared and contrasted for a series of [n]persilacyclacenes with n = 6–12: Si24H12, Si28H14, Si32H16, Si36H18, Si40H20, Si44H22, and Si48H24, respectively, at B3LYP levels (n, number of fused benzenoid rings). These are a brand of silicon nanorings that bear a resemblance to the shortest zig‐zag silicon nanotubes (SiNTs), henceforth referred to as SiNRs. The NBO results show nearly sp2‐hybridization for virtually all Si atoms of our SiNRs. This is in contrast to most reports where sp3‐hybridization is proposed for typical SiNTs. Comparison between the optimized SiNRs and their corresponding planar (polyacenic) forms shows longer bond lengths for the former, due to their curvatures. Except for sterically hindered Si24H12 (n = 6), all even SiNRs (n = 8, 10, and 12), are more aromatic than the odd ones (n = 7, 9, and 11). Such a higher aromaticity is witnessed inside, outside, and on the surface of the scrutinized SiNRs. Also, except for Si44H22 (n = 11), the energy gaps (ΔEHOMO−LUMO) for the odd set of SiNRs, as well as the even set, appear inversely proportional to their corresponding diameters, per se. Except for the sterically hindered SiNRs with n = 6 or 7, all the even SiNRs enjoy a higher stability (aromaticity) and conductivity for showing lower ΔEHOMO−LUMO than the odd ones. Evidently, the ideal diameter for persilacyclacenes (SiNRs) studied is from 0.92 to 1.42 nm, corresponding to n = 8–12, respectively. Higher than 1.42 nm causes structural disorders while lower than 0.92 brings about bond localization due to the high‐steric effects. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Silicon nanorings and nanotubes: a full-potential linear-muffin-tin-orbital molecular-dynamics method study

Using full-potential linear-muffin-tin-orbital molecular-dynamics method, we have studied the geometric and electronic structures of short possible silicon nanotube consisting of silicon rings. All atoms in the ring structures have fourfold coordination. The stacked tubes are stable.