Dielectric Nanoparticles Research Articles

Temporal dynamics of surface phonon polaritons in polar dielectric nanoparticles with nonlocality

Surface phonon polaritons (SPhPs) supported by polar dielectrics have been a promising platform for nanophotonics in mid-infrared spectral range. In this work, the temporal dynamic behavior of polar dielectric nanoparticles without (or with) spatial dispersion/nonlocality driven by the ultrashort Gaussian pulses is carried out. We demonstrate that three possible scenarios for the temporal evolutions of the dipole moment including ultrafast oscillations with the decay, exponential decay, and keeping a Gaussian shape exist, when the pulse duration of the incident field is much shorter than, similar to, and much longer than the localized SPhP lifetime. Once the nonlocal effect is considered, the oscillation period becomes large slightly, and the exponential decay turns fast. Furthermore, nonlocality-induced novel temporal behavior is found such as the decay with long-period oscillations when the center frequency of the incident pulse lies at the frequency of adjacent longitudinal resonant modes. The positive and negative time-shifts of the dielectric response reveal that the excitation of the dipole moment will be delayed or advanced. These temporal evolutions can pave the way towards potential applications in the modulation of ultrafast signals for the mid-infrared optoelectronic nanodevices.

Optical force propelled by metamaterial surface waves excitation: pushing and tractor beam sources

Theoretical research on opto–mechanical interactions at sub–wavelength levels using surface waves (SWs) excitation has a great impact in both the academic knowledge and practical realm. In this letter we have revealed that the dynamic characteristics of the SWs excited along a metamaterial boundary, such as its forward or backward propagation nature, provide a direct demonstration about the direction of action of the optical force exerted on a dielectric nano–particle. In particular, by using a rigorous electromagnetic formalism based in the second Green identity, we have modeled the scattering problem of a Gaussian beam impinging on a metamaterial plane surface with a sub–wavelength localized defect. We have shown that depending on the nature of the excited SW, dielectric nano–particles placed near the surface can be pushed away or towards the localized defect. We believe that this work unveils the potential implementation of sub–wavelength defects as sources of pushing or pulling optical forces.

Surface recoil force on dielectric nanoparticle enhancement via graphene acoustic surface plasmon excitation: non-local effect consideration.

Controlling optomechanical interactions at sub-wavelength levels is of great importance in academic science and nanoparticle manipulation technologies. This Letter focuses on the improvement of the recoil force on nanoparticles placed close to a graphene-dielectric-metal structure. The momentum conservation involving the non-symmetric excitation of acoustic surface plasmons (ASPs), via near-field circularly polarized dipolar scattering, implies the occurrence of a huge momentum kick on the nanoparticle. Owing to the high wave vector values entailed in the near-field scattering process, it has been necessary to consider the non-locality of the graphene electrical conductivity to explore the influence of the scattering loss on this large wave vector region, which is neglected by the semiclassical model. Surprisingly, the contribution of ASPs to the recoil force is negligibly modified when the non-local effects are incorporated through the graphene conductivity. On the contrary, our results show that the contribution of the non-local scattering loss to this force becomes dominant when the particle is placed very close to the graphene sheet and that it is mostly independent of the dielectric thickness layer. Our work can be helpful for designing new and better performing large plasmon momentum optomechanical structures using scattering highly dependent on the polarization for moving dielectric nanoparticles.

Design of Multifunctional Color Routers with Kerker Switching Using Generative Adversarial Networks

AbstractTo achieve optoelectronic devices with high resolution and efficiency, there is a pressing need for optical structural units that possess an ultrasmall footprint yet exhibit strong controllability in both the frequency and spatial domains. For dielectric nanoparticles, the overlap of electric and magnetic dipole moments can scatter light completely forward or backward, which is called Kerker theory. This effect can expand to any multipoles and any directions, re‐named as generalized Kerker effect, and realize controllable light manipulation at full space and full spectrum using well‐designed dielectric structures. However, the complex situations of multipole couplings make it difficult to achieve structural design. Here, generative artificial intelligence (AI) is utilized to facilitate multi‐objective‐oriented structural design, wherein the study leverages the concept of “combined spectra” that consider both spectra and direction ratios as labels. The proposed generative adversarial network (GAN) is named as DDGAN (double‐discriminator GAN) that discriminates both images and spectral labels. Using trained networks, the simultaneous design for scattering color and directivities, RGB color routers, as well as narrowband light routers is achieved. Notably, all generated structures possess a footprint <600 × 600 nm indicating their potential applications in optoelectronic devices with ultrahigh resolution.

Efficient Third Harmonic Generation from Magnetic Resonance in Low-Index Dielectric Nanopillars

Boosting the harmonic generation of light in nanostructures through efficiently enhancing the light–matter interaction has received enormous attention and applications. Low-index dielectric nanoparticles, as one of the crucial members of nanophotonics, have not been successful in nonlinear enhancement due to weak Mie resonance and poor light confinement. Here, we designed efficient third harmonic generation (THG) in low-index dielectric nanopillars sandwiched by double layers of metal dressing (Au/polymer/Au), where the polymer offers essential nonlinear susceptibility. The resonance of the low-index nanopillars significantly enhanced the scattering and had a strong magnetic response that could boost the THG effect. We predict that the THG efficiency reaches up to 3 × 10−6 (six orders of enhancement) at a third harmonic wavelength of 300 nm. The efficient THG in low-index dielectric nanopillars may open the possibility for the development of a new type of efficient nonlinear coherent source.

Self-hybridisation between interband transitions and Mie modes in dielectric nanoparticles

Abstract We discuss the possibility of self-hybridisation in high-index dielectric nanoparticles, where Mie modes of electric or magnetic type can couple to the interband transitions of the material, leading to spectral anticrossings. Starting with an idealised system described by moderately high constant permittivity with a narrow Lorentzian, in which self-hybridisation is visible for both plane-wave and electron-beam excitation, we embark on a quest for realistic systems where this effect should be visible. We explore a variety of spherical particles made of traditional semiconductors such as Si, GaAs, and GaP. With the effect hardly discernible, we identify two major causes hindering observation of self-hybridisation: the very broad spectral fingerprints of interband transitions in most candidate materials, and the significant overlap between electric and magnetic Mie modes in nanospheres. We thus depart from the spherical shape, and show that interband–Mie hybridisation is indeed feasible in the example of GaAs cylinders, even with a simple plane-wave source. This so-far unreported kind of polariton has to be considered when interpreting experimental spectra of Mie-resonant nanoparticles and assigning modal characters to specific features. On the other hand, it has the potential to be useful for the characterisation of the optical properties of dielectric materials, through control of the hybridisation strength via nanoparticle size and shape, and for applications that exploit Mie resonances in metamaterials, highly-directional antennas, or photovoltaics.

Controllable shaping of high-index dielectric nanoparticles by exploiting the giant optical force of femtosecond laser pulses

Nanoparticles made of different materials usually support optical resonances in the visible to near infrared spectral range, such as the localized surface plasmons observed in metallic nanoparticles and the Mie resonances observed in dielectric ones. Such optical resonances, which are important for practical applications, depend strongly on the morphologies of nanoparticles. Laser irradiation is a simple but effective way to modify such optical resonances through the change in the morphology of a nanoparticle. Although laser-induced shaping of metallic nanoparticles has been successfully demonstrated, it remains a big challenge for dielectric nanoparticles due to their larger Young’s modulus and smaller thermal conductivities. Here, we proposed and demonstrated a strategy for realizing controllable shaping of high-index dielectric nanoparticles by exploiting the giant optical force induced by femtosecond laser pulses. It was found that both Si and Ge nanoparticles can be lit up by resonantly exciting the optical resonances with femtosecond laser pulses, leading to the luminescence burst when the laser power exceeds a threshold. In addition, the morphologies of Si and Ge nanoparticles can be modified by utilizing the giant absorption force exerted on them and the reduced Young’s modulus at high temperatures. The shape transformation from sphere to ellipsoid can be realized by laser irradiation, leading to the blueshifts of the optical resonances. It was found that Si and Ge nanoparticles were generally elongated along the direction parallel to the polarization of the laser light. Controllable shaping of Si and Ge can be achieved by deliberately adjusting the excitation wavelength and the laser power. Our findings are helpful for understanding the giant absorption force of femtosecond laser light and are useful for designing nanoscale photonic devices based on shaped high-index nanoparticles.

Scattering characteristics of silicon nanoprisms: A theoretical investigation across monomeric to hexameric structures

Dielectric nanostructures exhibit intriguing optical properties and outstanding advantages in designing optical nanoantennas and metasurfaces compared to plasmonic nanostructures. This study employs classical electrodynamic methods to comprehensively explore the scattering characteristics of silicon triangular nanoprisms in monomer and oligomer forms. For monomeric nanoprisms, the scattering spectra reveal two distinct and prominent resonance peaks attributed to magnetic dipole (MD) and electric dipole (ED) modes. Reducing interparticle gaps within dimeric structures leads to noticeable blueshifts in MD resonance peaks with stable intensities, in contrast to the nearly constant position and significantly reduced intensities of the ED resonance peaks. A pronounced Fano-like resonance was observed upon transitioning to tetrameric and hexameric configurations, resulting from the coupling between MD and ED modes. A broad resonance peak also emerges in the long-wavelength region due to MD-to-MD coupling. The simulations conducted herein hold significant theoretical implications, advancing our comprehension of the scattering properties of dielectric nanoparticles and contributing valuable insights into fundamental nanophotonics.

Effects of high contents of dielectric inclusions on ferroelectricity in dielectric-ferroelectric nanocomposites with dimethylammonium aluminum sulfate hexahydrate

The present study is devoted to analyzing effects of high contents (85 wt.%) of dielectric inclusions, including nanocellulose and silicon dioxide nanoparticles, on ferroelectricity of composites which are made by combining dimethylammonium aluminum sulfate hexahydrate with each of them. The obtained results revealed that in the case of using nanocellulose, the ferroelectricity was not detected in fresh composite samples, but then gradually appeared over time. Meanwhile, the ferroelectricity was not observed in the composite with silicon dioxide during the observation time.

Optical clearing agents based on metallic and dielectric nanoparticles for caries diagnostic by optical coherence tomography.

This study aimed to assess the effect of titanium dioxide (TiO2) and silver (Ag) nanoparticles dispersed in glycerol or water, serving as optical clearing agents nanocolloids (OCAs-NC), for improving optical coherence tomography (OCT) images and highlighting incipient lesions in ex vivo human teeth. Twelve human teeth with incipient lesions were divided into seven groups according to the OCA-NC; they were subjected to G1 (air), G2 (glycerol), G3 (TiO2 0.1%), G4 (TiO2 0.01%), G5 (TiO2 0.001%), G6 (AgNO3 10%), and G7 (AgNO3 100%). The OCA-NC was applied to the occlusal surface, and two-dimensional images of the specimens were analyzed using OCT (930nm central wavelength; 100nm bandwidth; 5 mW output power; axial resolution of 7/5.3μm in water and air, respectively; lateral resolution of 8μm; and light penetration depth of 1.6mm inside the sample). The findings demonstrated that the utilization of OCAs-NC containing metallic or dielectric nanoparticles (AgNO3 and TiO2) led to improved differentiation between sound and demineralized enamel on occlusal surfaces. Additionally, it enhanced the depth of image penetration when analyzing this hard tissue with OCT. In the current context of minimally invasive dentistry, the use of OCAs-NC in conjunction with OCT can provide clinicians with early diagnosis, allowing for the determination of less/more invasive therapies and consequently halting the disease before cavitation of dental tissues occurs.

Quantum engineering of the radiative properties of a nanoscale mesoscopic system.

Despite the recent advances in quantum technology, the problem of controlling the light emission properties of quantum emitters used in numerous applications remains: a large spectral width, low intensity, blinking, photodegradation, biocompatibility, etc. In this work, we present the theoretical and experimental investigation of quantum light sources - mesoscopic systems consisting of fluorescent molecules in a thin polydopamine layer coupled with metallic or dielectric nanoparticles. Polydopamines possess many attractive adhesive and optical properties that promise their use as host media for dye molecules. However, numerous attempts to incorporate fluorescent molecules into polydopamines have failed, as polydopamine has been shown to be a very efficient fluorescence quencher through Förster resonance energy transfer and/or photoinduced electron transfer. Using the system as an example, we demonstrate new insights into the interactions between molecules and electromagnetic fields by carefully shaping its energy levels through strong matter-wave coupling of molecules to metallic nanoparticles. We show that the strong coupling effectively suppresses the quenching of fluorescent molecules in polydopamine, opening new possibilities for imaging.

The Impact of Electromagnetic Waves Propagation to the Dielectric Nanoparticles on Crude Oil Interfacial Tension Reduction for Oil Recovery: A Review

The presence of interfacial tension (IFT) force between crude oil and other fluids in reservoirs is one of the critical parameters that restrict the effective mobility of the oil and is continuously entrapped in reservoir pores. Reducing binding forces between oil and such fluids is one of the methods employed to improve oil productivity known as enhanced oil recovery (EOR). Various nanoparticles (NPs) have been utilized to reduce IFT. However, NPs encountered a challenge in terms of successful operation under a high temperature. Consequently, the NPs tend to segregate at the oil/ water interface which diminishes the IFT influences and more oil continuously entrapped. Recently, an innovative approach to enhance oil mobility was proposed by activating the charges of the NPs via electromagnetic (EM) wave propagation. Few analyses were reported using dielectric NPs with reasonable reductions to IFT. The dielectric properties of NPs are essential attributes corresponding to EM waves. During the EM wave exposure, the extra disruptions were generated at the fluid/oil interface that function as activating agents for the NPs resulting in the additional reduction for IFT. The present study provides a comprehensive review of the few results available, challenges that confronted the success of this novel approach, and admirable recommendations to improve the process in the future.

Detection of microplastics and nanoplastics: Are Raman tweezers and enhanced Raman methods the solution for sub 20 μm particles?

Despite the significant progress in the detection of nano and small microplastics, the detection of such particles still faces problems caused by the limitations of current detection methods and instruments. Herein, we present the optical methods for detection of sub 20 μm microplastics. We introduce optical methods for the analysis of individual microplastics and the fabrication of a substrate using plasmonic particles to detect plastic nanoparticles. We summarize recent experimental activities involving the construction of portable Raman tweezers that can be used for optical trapping and analysis of microplastics with size from a few hundred nanometers to lower tens of micrometers. Optical trapping is complemented by another optical manipulation method: nanoimprinting of plasmonic nanoparticles that enables create the “active” aggregates that can be used for Surface Enhanced Raman Spectroscopy (SERS) detection in microfluidic circuits and as plasmon-enhanced thermoplasmonic concentrators for nanoscale particulate matter such as nanoplastics. The principle of nanoimprinting is based on the dominance of the scattering force (compared to the gradient force) for plasmonic particles, this force pushes the particles in the direction of propagation of the light beam. This phenomenon enables the preparation of an aggregate comprising of plasmonic particles that can serve as a substrate for SERS and as a source of the temperature gradient that is able to attract dielectric nanoparticles. In both cases, enhanced sensitivity is demonstrated, allowing the detection of nanoplastics/molecules of size/concentration orders of magnitude lower than what can be achieved by Raman spectroscopy. This study demonstrates that the combination of two optical manipulation techniques with Raman spectroscopy is capable of filling the technological gap in the detection of plastic particles ranging in size from a few tens of nanometers to 20 micrometers. This is an ideal solution for the detection of very small microplastics, which currently lacks a suitable technology.

Tunable emission from H-type supramolecular polymers in optical nanocavities.

H-type supramolecular polymers with preferred helicity and highly efficient emission have been prepared from the self-assembly of chiral tetraphenylene-based monomers. Implementation of the one-dimensional fibers into dielectric nanoparticle arrays allows for a significant reshaping of fluorescence due to weak light-matter coupling.

Mean Electric Field of Dielectric Nanoparticle

The nanoscale effect of the formation of an electric field near the surface of a dielectric nanoparticle is discussed within the framework of the proposed model based on the reconstruction of the crystal surface, including the splitting of the surface atomic layer into two parallel sublayers consisting of atoms with only positive or only negative effective static electric charges, respectively. The mean electric field potential and strength are obtained depending on the distance from the surface and the numerical values of their parameters for hexagonal boron nitride are estimated.

Measurement of electrical conductivity of transformer oil based nanofluid

In this article, an attempt was made to evaluate the electrical conductivity of ananofluid based on transformer oil. For this purpose, several nanofluid samples with different concentrations of dielectric silicon dioxide nanoparticles and conductive zinc nanoparticles were prepared. The dielectric permittivity and electrical conductivity of the obtained nanofluids were measured experimentally. After processing the experimental results, a theoretical calculation was made using the Nielsen formula. After the calculation, the results were compared with the experimental data. In the process of comparative analysis, the correspondence of the calculated and experimental values of the dielectric permittivity was noted. There was also a discrepancy between the experimental and calculated values of electrical conductivity. An explanation is proposed for the discovered discrepancy between the calculated and experimental values. Presumably, the main reason for the decrease in electrical conductivity in the experiment is the adsorption of ion particles in the dielectric.

Vacuum-field-induced state mixing

By engineering the electromagnetic vacuum field, the induced Casimir-Polder shift (also known as Lamb shift) and spontaneous emission rates of individual atomic levels can be controlled. When the strength of these effects becomes comparable to the energy difference between two previously uncoupled atomic states, an environment-induced interaction between these states appears after tracing over the environment. This interaction has been previously studied for degenerate levels and simple geometries involving infinite, perfectly conducting half-spaces or free space. Here, we generalize these studies by developing a convenient description that permits the analysis of these non-diagonal perturbations to the atomic Hamiltonian in terms of an accurate non-Hermitian Hamiltonian. Applying this theory to a hydrogen atom close to a dielectric nanoparticle, we show strong vacuum-field-induced state mixing that leads to drastic modifications in both the energies and decay rates compared to conventional diagonal perturbation theory. In particular, contrary to the expected Purcell enhancement, we find a surprising decrease of decay rates within a considerable range of atom-nanoparticle separations. Furthermore, we quantify the large degree of mixing of the unperturbed eigenstates due to the non-diagonal perturbation. Our work opens new quantum state manipulation possibilities in emitters with closely spaced energy levels.

Electric field enhancement for triboelectrification-induced electroluminescence via micro electrode units and BaTiO3 nanoparticles

Intelligent terminals demand motion sensors with high intensity and low energy consumption. Motion sensors relied on the conversion of mechanical signals into electrical signals usually need complex electric circuits. Alternatively, novel motion sensors that can convert mechanical signals into optical signals represent an intuitive way of motion sensing. Here, a high-intensity luminescent composite film is proposed with utilization of micro electrode units and high dielectric BaTiO3 nanoparticles aiming at electric field enhancement for the electroluminescence process of triboelectrification-induced electroluminescence (TIEL). It is found that the existing of electrode units would effectively enhance the produced electric field along the edge of the electrode units and thus promote the luminescent intensity. Besides, the BaTiO3 nanoparticles would elevate the dielectric constant of the luminescent composite film and a proper ratio of BaTiO3 would significantly improve the luminescent intensity. The dielectric constant of the luminescent layer would rise as the driving frequency decreases, which indicates its suitability for low frequency mechanical movement sensing. Visualized motion sensing with high intensity and excellent stability thereby can be stimulated under ultra-low pressure and low frequency mechanical movement. Hand motion and water flow can be real-timely tracked via luminescent composite films with micro electrode arrays, demonstrating its great potential in self-powered motion sensors for the broad applications in biometrics, liquid sensing, anti-counterfeiting identification, surveillance and many others.

Three Orthogonal Polarization Distribution Mapping of the Tightly Focused Fields with a Dual‐Mode Waveguide Probe

AbstractStrongly confined electromagnetic (EM) fields generated by tightly focused light beams are applied widely in nano‐optics due to their vectorial characteristics. The inclusion of the longitudinal polarized component plays a crucial role in both the physical characteristics and practical uses of tightly focused vector beams. The acquisition of the distributions of the three orthogonal polarized components of these fields is advantageous for the comprehensive examination of their captivating physical phenomena and possible applications. However, this continues to pose a noteworthy obstacle, especially in the case of the fields that are generated by high numerical aperture objectives. A novel approach is proposed to quantifying the three mutually perpendicular polarizations simultaneously in the focal plane. The method utilizes a dual‐mode waveguide probe that is composed of a dielectric nanoparticle and a metal‐dielectric waveguide. This design allows for the simultaneous support of both transverse electric (TE) and transverse magnetic (TM) modes. Consequently, it enables the polarization recognition of scattering light in k‐space. Importantly, this method effectively eliminates any interference originating from the background light. The work involves an analysis of the theoretical notion of the probe and followed by experimental investigations. This approach holds promise for augmenting optical nanoscopy methodologies and their associated applications.

Determining the Optical Geometry of a Gold Semi-Shell under the Kretschmann Configuration

Dielectric nanoparticles coated with metals (half-shell or semi-shell structures) have attracted attention as potential composite plasmonic nanomaterials with large optical anisotropy and absorption cross-sections. Structures approximately 100 nm in size can excite plasmons in the visible and near-infrared ranges, highlighting their distinct optical properties. This study employed metal semi-shell structures (metal: gold, dielectric: silica) in the Kretschmann configuration to experimentally and numerically demonstrate the optical determination of single-structure orientations through a finite-difference time-domain method. Gold semi-shell structures were fabricated through deposition and etching. These structures were removed from their substrate in ultrapure water and randomly dropped onto a thin gold substrate. In the single structure, we experimentally observed changes in the scattering light spectrum based on the optical geometry of the gold semi-shell at wavelengths ranging from 530 to 700 nm. The obtained results closely resembled those of a simulation and confirmed the presence of eigenmodes in the orientation through electric field analysis. These observations allow for the cost-effective and rapid determination of the orientations of numerous structures that are approximately 100 nm in size, solely through optical methods. This technique is a valuable development for measurement applications in nanostructure orientation control and functionality enhancement.