Search

Electric field enhancement mediated through sharp tips in scattering-type scanning near-field optical microscopy (s-SNOM) enables optical material analysis down to the 10-nm length scale and even below. Nevertheless, the out-of-plane electric field component is primarily considered here due to the lightning rod effect of the elongated s-SNOM tip being orders of magnitude stronger than any in-plane field component. Nonetheless, the fundamental understanding of resonantly excited near-field coupled systems clearly allows us to take profit from all vectorial components, especially from the in-plane ones. In this paper, we theoretically and experimentally explore how the linear polarization control of both near-field illumination and detection can constructively be implemented to (non-)resonantly couple to selected sample permittivity tensor components, e.g., explicitly to the in-plane directions as well. When applying the point-dipole model, we show that resonantly excited samples respond with a strong near-field signal to all linear polarization angles. We then experimentally investigate the polarization-dependent responses for both non-resonant (Au) and phonon-resonant (3C-SiC) sample excitations at a 10.6 µm and 10.7 µm incident wavelength using a tabletop CO2 laser. Varying the illumination polarization angle thus allows one to quantitatively compare the scattered near-field signatures for the two wavelengths. Finally, we compare our experimental data to simulation results and thus gain a fundamental understanding of the polarization's influence on the near-field interaction. As a result, the near-field components parallel and perpendicular to the sample surface can be easily disentangled and quantified through their polarization signatures, connecting them directly to the sample's local permittivity. [ABSTRACT FROM AUTHOR]

Surging interests in point-of-device miniaturization have led to the development of metasurface-based optical components. Here, we demonstrate an electrically-driven ultracompact beam controller in the infrared spectral range. The effect benefits from diffraction gratings consisting of the commercially available conductive polymer PEDOT:PSS, which exhibits metal-to-insulator transition characteristics upon electrical biasing. By combining several metagratings with different superlattice periods in electrically isolated areas, our device enables diffraction beams at 16 and 33.5° when applying voltages of only ±1 V. Furthermore, no diffraction is realized by switching off the plasmonic property of the gratings. Dynamic control of electromagnetic wave via the presented platforms could be transformative for sensing, imaging, and communication applications.

Nanomaterials derive their electronic, magnetic, and optical properties from their specific nanostructure. In most cases, nanostructured materials and their properties are defined during the materials growth, and nanofabrication techniques, such as lithography, are employed subsequently for device fabrication. Herein, a perspective is presented on a different approach for creating nanomaterials and devices where, after growth, advanced nanofabrication techniques are used to directly nanostructure condensed matter systems, by inducing highly controlled, localized, and stable changes in the electronic, magnetic, or optical properties. Then, advantages, limitations, applications in materials science and technology are highlighted, and future perspectives are discussed. [ABSTRACT FROM AUTHOR]

Scalable methods to access single-photon sources on demand are highly sought after. As a potential strategy, we demonstrate the optical trapping and chemical anchoring of NaYF4 nanoparticles (NPs) and NaYF4 NPs doped with on average a single Er3+ ion. The anchoring method we present involves surface coating the NPs with thiol-functionalized phospholipids, where the thiol group is protected with a chemical group photoremovable at 340 nm 2-bromo-4′-hydroxyacetophenone. Functionalized NPs are trapped optically in a gold double-nanohole aperture using a 980 nm laser. A 340 nm light beam is focused on the particle, resulting in deprotection of the thiol groups and attachment of the thiols to the gold surface, permanently anchoring the NPs. Electron microscopic imaging proves the successful anchoring after removal of the trapping laser, 340 nm light source, and solvent. The approach is promising for reliably fabricating a single-photon emitting material in a scalable and potentially automatable manner. [ABSTRACT FROM AUTHOR]

The application of surface plasmon resonance microscopy for the time-continuous nondestructive control of thin dielectric coatings during their fabrication is considered. The high sensitivity of the method, in comparison with other photometric methods, and time-continuous optical control makes it possible to correctly restore the thickness profiles and optical constants for multilayer and gradient dielectric coatings. Adaptation of the ghost-imaging method to surface plasmon resonance microscopy makes it possible to measure the reflection coefficients locally for each surface point. It makes it possible to restore the spatial distribution of optical constants for planar optical elements. The operation of the method is described by the example of the Luneburg plasmon-lens model. One of the possible schemes of implementation of the proposed method in production (for a magnetron-sputtering unit) is presented. The superiority in the sensitivity of the surface plasmon resonance method over spectroreflectometry by 2 orders of magnitude in the case of the optical characterization of ultrathin dielectric films during their growth in thickness and in the case of the mutual diffusion of dielectric layers is demonstrated by examples. The source codes in Python of the numerical results are published in GitHub repository. The described approach of optical control is applicable both in the visible and infrared ranges of the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

Electric field enhancement mediated through sharp tips in scattering-type scanning near-field optical microscopy (s-SNOM) enables optical material analysis down to the 10-nm length scale and even below. Nevertheless, the out-of-plane electric field component is primarily considered here due to the lightning rod effect of the elongated s-SNOM tip being orders of magnitude stronger than any in-plane field component. Nonetheless, the fundamental understanding of resonantly excited near-field coupled systems clearly allows us to take profit from all vectorial components, especially from the in-plane ones. In this paper, we theoretically and experimentally explore how the linear polarization control of both near-field illumination and detection can constructively be implemented to (non-)resonantly couple to selected sample permittivity tensor components, e.g., explicitly to the in-plane directions as well. When applying the point-dipole model, we show that resonantly excited samples respond with a strong near-field signal to all linear polarization angles. We then experimentally investigate the polarization-dependent responses for both non-resonant (Au) and phonon-resonant (3C-SiC) sample excitations at a 10.6 µm and 10.7 µm incident wavelength using a tabletop CO2 laser. Varying the illumination polarization angle thus allows one to quantitatively compare the scattered near-field signatures for the two wavelengths. Finally, we compare our experimental data to simulation results and thus gain a fundamental understanding of the polarization’s influence on the near-field interaction. As a result, the near-field components parallel and perpendicular to the sample surface can be easily disentangled and quantified through their polarization signatures, connecting them directly to the sample’s local permittivity.

The problem of plane electromagnetic wave diffraction on an infinite plasmon nanocylinder with a core-shell structure is considered. The solution is based on the computational scheme of the discrere sources method. This takes into account the presence of nonlocal effect in both core and shell of the cylinder. Conjugation conditions accounting for plasmonic properties of metals are employed as additional boundary conditions on the metal-metal interface. Numerical investigation of the nonlocal effect influence on the optical properties of cylindrical particles with their deformation is carried out. [ABSTRACT FROM AUTHOR]

Given an arbitrarily complicated object, it is often difficult to say immediately how it interacts with a specific illumination. Optically small objects, e.g., spheres, can often be modeled as electric dipoles, but which multipole moments are excited for larger particles possessing a much more complicated shape? The T-matrix answers this question, as it contains the entire information about how an object interacts with any electromagnetic illumination. Moreover, a multitude of interesting properties can be derived from the T-matrix such as the scattering cross section for a specific illumination and information about symmetries of the object. Here, we present a method to calculate the T-matrix of an arbitrary object numerically, solely by illuminating it with multiple plane waves and analyzing the scattered fields. Calculating these fields is readily done by widely available tools. The finite element method is particularly advantageous, because it is fast and efficient. We demonstrate the T-matrix calculation at four examples of relevant optical nanostructures currently at the focus of research interest. We show the advantages of the method to obtain useful information, which is hard to access when relying solely on full wave solvers.

Semiconductor nanoparticles (SNPs), such as quantum dots (QDs) and core/shell nanoparticles, have proven to be promising candidates for the development of next-generation technologies, including light-emitting diodes (LEDs), liquid crystal displays (LCDs) and solar concentrators. Typically, these applications use a sub-micrometer-thick film of SNPs to realize photoluminescence. However, our current knowledge on how this thin SNP layer affects the optical efficiency remains incomplete. In this work, we demonstrate how the thickness of the photoluminescent layer governs the direction of the emitted light. Our theoretical and experimental results show that the emission is fully outcoupled for sufficiently thin films (monolayer of SNPs), whereas for larger thicknesses (larger than one tenth of the wavelength) an important contribution propagates along the film that acts as a planar waveguide. These findings serve as a guideline for the smart design of diverse QD-based systems, ranging from LEDs, where thinner layers of SNPs maximize the light outcoupling, to luminescent solar concentrators, where a thicker layer of SNPs will boost the efficiency of light concentration.

The plasmon resonance of a metal nanoparticle increases the optical field amplitude in and around the particle with respect to the incoming wave. In consequence, optical effects that are nonlinear in their field amplitude profit from this increased field. In general, a plasmonic structure can react nonlinearly by itself and it can also enhance the effect of the nonlinearity in its environment, which we consider as plasmonic nanoantenna. In this paper, we review third-order nonlinear effects such as third-harmonic generation, pump-probe spectroscopy, coherent anti-Stokes Raman scattering and four-wave mixing of and near plasmonic nanostructures. All these processes are described by very similar equations for the nonlinear polarization, but the underling physics differs.

A three dimensional problem of plane wave diffraction on a plasmonic nanoparticle is considered, with account for the nonlocal effect. A solution is constructed on the basis of a modified computational scheme of the discrete sources method. A numerical study of the nonlocal effect influence on the scattering properties of spherical nanoparticles upon their deformation is conducted. [ABSTRACT FROM AUTHOR]

Titanium nitride (TiN) is a novel refractory plasmonic material which can sustain high temperatures and exhibits large optical nonlinearities, potentially opening the door for high-power nonlinear plasmonic applications. We fabricate TiN nanoantenna arrays with plasmonic resonances tunable in the range of about 950-1050 nm by changing the antenna length. We present second-harmonic (SH) spectroscopy of TiN nanoantenna arrays, which is analyzed using a nonlinear oscillator model with a wavelength-dependent second-order response from the material itself. Furthermore, characterization of the robustness upon strong laser illumination confirms that the TiN antennas are able to endure laser irradiation with high peak intensity up to 15 GW/cm² without changing their optical properties and their physical appearance. They outperform gold antennas by one order of magnitude regarding laser power sustainability. Thus, TiN nanoantennas could serve as promising candidates for high-power/high-temperature applications such as coherent nonlinear converters and local heat sources on the nanoscale. [ABSTRACT FROM AUTHOR]

The article provides information on a study which observed the chemical degradation process of black phosphorus and the effectiveness of passivation coatings using infrared scattering type scanning near-field microscopy. Topics discussed include identification of oxidized phosphorus species at the onset of degradation by nanoscale spectroscopic imaging at mid-infrared frequencies, and effectiveness of aluminium oxide coating.

We introduce the concept of nonlinear plasmonic sensing, relying on third harmonic generation from simple plasmonic nanoantennas. Because of the nonlinear conversion process we observe a larger sensitivity to a local change in the refractive index as compared to the commonly used linear localized surface plasmon resonance sensing. Refractive index changes as small as 10-3 can be detected. In order to determine the spectral position of highest sensitivity, we perform linear and third harmonic spectroscopy on plasmonic nanoantenna arrays, which are the fundamental building blocks of our sensor. Furthermore, simultaneous detection of linear and nonlinear signals allows quantitative comparison of both methods, providing further insight into the working principle of our sensor. While the signal-to-noise ratio is comparable, nonlinear sensing gives about seven times higher relative signal changes. [ABSTRACT FROM AUTHOR]

Owing to their surface plasmon-based operation, arrays of subwavelength holes show extraordinary electromagnetic transmission and intense field localizations of several orders of magnitude. Thus they were proposed as the basic building blocks for a number of applications utilizing the enhancement of nonlinear optical effects. We designed and simulated nanometer-sized subwavelength holes using an analytical approach. In our experiments we used the scanning probe method for nanolithographic fabrication of subwavelength hole arrays in silver layers sputtered on a positive photoresist substrate. We fabricated ordered nanohole patterns with different shapes, dispositions and proportions. The smallest width was about 60 nm. We characterized the fabricated samples by atomic force microscopy.

The detailed investigation has been made of the lens effect in plane multilayered metal-dielectric structures (Ag-TiO2). The optical scheme of the lens has been studied with the radiation focusing in free space. The transfer function is calculated, where the phase profile determines definitely the possibility of focusing. The condition for far-field image formation is found using a flat lens. This condition is used for a numerical simulation of several lens designs with a various number of metal layers. It is found that considered flat lenses have close to limiting angular aperture and therefore the subwavelength resolution. It is established that at increase of a number of metal layers the object and image distances grow.

Investigating new materials plays an important role for advancing the field of nanoplasmonics. In this work, we fabricate nanodisks from magnesium and demonstrate tuning of their plasmon resonance throughout the whole visible wavelength range by changing the disk diameter. Furthermore, we employ a catalytic palladium cap layer to transform the metallic Mg particles into dielectric MgH2 particles when exposed to hydrogen gas. We prove that this transition can be reversed in the presence of oxygen. This yields plasmonic nanostructures with an extinction spectrum that can be repeatedly switched on or off or kept at any intermediate state, offering new perspectives for active plasmonic metamaterials. [ABSTRACT FROM AUTHOR]

We report on the dynamics of spatial temperature distributions in aligned semiconducting carbon nanotube array devices with submicrometer channel lengths. By using high-resolution optical microscopy in combination with electrical transport measurements, we observe under steady state bias conditions the emergence of time-variable, local temperature maxima with dimensions below 300 nm, and temperatures above 400 K. On the basis of time domain cross-correlation analysis, we investigate how the intensity fluctuations of the thermal radiation patterns are correlated with the overall device current. The analysis reveals the interdependence of electrical current fluctuations and time-variable hot spot formation that limits the overall device performance and, ultimately, may cause device degradation. The findings have implications for the future development of carbon nanotube-based technologies. [ABSTRACT FROM AUTHOR]

Reduction of surface plasmon-polariton losses due to their scattering on metal surface roughness still remains a challenge in the fabrication of plasmonic devices for nanooptics. To achieve smooth silver films, we study the dependence of surface roughness on the evaporation temperature in a physical vapor deposition process. At the deposition temperature range 90 to 500 K, the mismatch of thermal expansion coefficients of Ag, Ge wetting layer, and sapphire substrate does not deteriorate the metal surface. To avoid ice crystal formation on substrates, the working temperature of the whole physical vapor deposition process should exceed that of the sublimation at the evaporation pressure range. At optimum room temperature, the root-mean-square (RMS) surface roughness was successfully reduced to 0.2 nm for a 10-nm Ag layer on sapphire substrate with a 1-nm germanium wetting interlayer. Silver layers of 10- and 30-nm thickness were examined using an atomic force microscope (AFM), X-ray reflectometry (XRR), and two-dimensional X-ray diffraction (XRD2). PACS: 63.22.Np Layered systems; 68. Surfaces and interfaces; thin films and nanosystems (structure and nonelectronic properties); 81.07.-b Nanoscale materials and structures: fabrication and characterization [ABSTRACT FROM AUTHOR]

We investigate numerically the effect of axial rotation and the presence of a dielectric intralayer on the spectral behavior of the optical force on a gold nanorod pair. The frequency spectrum of the optical force is obtained through the Maxwell stress tensor formulation and the full vectorial solution of electromagnetic waves. The common and the relative forces, which are defined through the optical force acting on each nanorod, are computed for different axial rotations and for different permittivity and thickness of the dielectric intralayer. We found that both the misalignment and the dielectric intralayer can be utilized to tailor the magnitude and direction of the relative optical force, providing a tunable attractive or repulsive response between the nanorods. [ABSTRACT FROM AUTHOR]

Recent experimental progress in localized excitation with nanofields and localized detection for various observables (light intensities, photo electrons, etc.) at nanometer scales, suggest to rethink conventional spectroscopic schemes in terms of localized excitation and detection. In this paper, a systematic overview will be given, how the observables and Hamilton operators in case of localized excitation and detection need to be modified. The implications of localized excitation and detection are also illustrated using linear optics and pump probe spectroscopy. [ABSTRACT FROM AUTHOR]

Recent developments in the area of resonant dielectric nanostructures have created attractive opportunities for concentrating and manipulating light at the nanoscale and the establishment of the new exciting field of all-dielectric nanophotonics. Transition metal dichalcogenides (TMDCs) with nanopatterned surfaces are especially promising for these tasks. Still, the fabrication of these structures requires sophisticated lithographic processes, drastically complicating application prospects. To bridge this gap and broaden the application scope of TMDC nanomaterials, we report here femtosecond laser-ablative fabrication of water-dispersed spherical TMDC (MoS 2 and WS 2 ) nanoparticles (NPs) of variable size (5 to 250 nm). Such NPs demonstrate exciting optical and electronic properties inherited from TMDC crystals, due to preserved crystalline structure, which offers a unique combination of pronounced excitonic response and high refractive index value, making possible a strong concentration of electromagnetic field in the NPs. Furthermore, such NPs offer additional tunability due to hybridization between the Mie and excitonic resonances. Such properties bring to life a number of nontrivial effects, including enhanced photoabsorption and photothermal conversion. As an illustration, we demonstrate that the NPs exhibit a very strong photothermal response, much exceeding that of conventional dielectric nanoresonators based on Si. Being in a mobile colloidal state and exhibiting superior optical properties compared to other dielectric resonant structures, the synthesized TMDC NPs offer opportunities for the development of next-generation nanophotonic and nanotheranostic platforms, including photothermal therapy and multimodal bioimaging.

Abstract: For numerous applications, the computation and provision of exact derivative information plays an important role for optimizing the considered system. This paper introduces the technique of algorithmic differentiation, a method to compute derivatives of arbitrary order within working precision. This derivative information will be combined with a calculus-based optimization algorithm to optimize a non-trivially shaped laser pulse which coherently steers the electron dynamics in a semiconductor quantum wire. Numerical results illustrating the cost for the derivative computation and the optimization process are presented and discussed. [Copyright &y& Elsevier]

We discuss an optimization of a nanooptical transmission spectral filter. The structure designed takes into account that the filter is to be subsequently fabricated by nanoimprint lithography. The optimization of the filter is conducted on a computing cluster by means of the parallel asynchronous stochastic technique. The analysis of the designed nanostructure fabrication errors peculiar to the nanoimprint lithography is offered. [ABSTRACT FROM AUTHOR]