Sergey Scherbak

Electric Properties of Hemispherical Metal Nanoparticles: Influence of the Dielectric Cover and Substrate

We described the distribution of electric potential and field generated by a planar electromagnetic wave in the vicinity of a hemispherical metal nanoparticle deposited on a dielectric substrate and covered with a dielectric layer of arbitrary thickness using the solution of the Laplace equation. The developed solution is applied to calculate the position of surface plasmon resonance and the distribution of electric field near a hemispherical silver nanoparticle placed on a soda–lime glass surface and covered with titania layer. The position of the surface plasmon resonance as a function of the thickness of TiO2 cover of the silver hemisphere is computed and compared with corresponding experimental data. Developed approach can be applied to evaluate the efficiency of Raman scattering enhanced by metal island films with a protective dielectric spacer.

Second harmonic generation from hemispherical metal nanoparticle covered by dielectric layer

Using hydrodynamic theory of electron gas motion in metals, we obtain hyperpolarizability of the metal hemisphere in the framework of the quasistatic approach. For a silver hemisphere placed on a glass substrate and covered with TiO2 shell, we demonstrate analytically that conduction electrons in the vicinity of the hemisphere sharp edge dominate the nonlinear optical response of the nanoparticle. The developed theory is verified by numerical simulation in COMSOL. Numerical analysis reveals that rounding of the sharp edge affects the linear polarizability and first hyperpolarizability of the hemisphere differently. We also discuss dependence of the hyperpolarizability on the dielectric shell thickness and show that both lacking of the inversion symmetry and presence of the glass–air-TiO2 interface essentially contribute to the polarizability of the hemisphere at the frequency of the second harmonic.

3.5-μm radius race-track microlasers operating at room temperature with 1.3-μm quantum dot active region

We present detailed studies of optically pumped InAs/InGaAs quantum dot based racetrack microlasers with 3.5-μm bend radius operating at room temperature. Q factor over 8000 and room temperature threshold power in the mW-range were achieved in the racetrack microlasers with straight section length ranging from 0 to 4 μm. A systematic investigation of the influence of the racetrack straight section length on spatial distribution of optical modes is presented. The microcavity eigenmodes and electromagnetic field distribution calculated by means of three-dimensional numerical simulation demonstrate a good agreement with the experimental results obtained by micro-photoluminescence and scanning near-field optical microscopy. The racetracks demonstrate zigzagging behavior of the modes inside the cavity and the energy switching between the radial maxima in second-order modes. Higher-order modes are found to be suppressed in micro-photoluminescence spectra.

Dark-field spectroscopy of plasmon resonance in metal nanoislands: effect of shape and light polarization

We present the experimental dark-field scattering studies and the simulation of plasmonic properties of isolated silver nanoislands. The nanoislands were fabricated on a soda- lime glass substrate using silver-sodium ion exchange, subsequent thermal poling and annealing of the processed glass substrate in hydrogen. The morphology of the nanoislands was characterized with atomic force microscopy and scanning electron microscopy; the dimensions were 100-180 nm in base and 80-160 nm in height. We measured and modeled dark-field scattering spectra of the silver hemiellipsoidal nanoparticles differing in size and shape. The SPR position varied from 450 nm to 730 nm depending on the particle shape and dimensions. Both experiments and simulation showed a red shift of the SPR for bigger nanoislands of the same shape. Losing the axial symmetry in nanoislands resulted in the resonance splitting, while their elongation led to an increase in the scattering of p-polarized light.

Plasmonic properties of metal nanoislands: Practical guide

We propose a simple approach to describe plasmonic properties of a metal hemisphere placed on a dielectric substrate and covered by another dielectric. Very simple analytical expressions and numerical data presented allow avoiding numerical calculations in finding the spectral position of the surface plasmon resonance and the dispersion of the polarizability of the hemisphere. The expressions are obtained using semi-analytical solution of the related problem in the quasistatic approximation. They are valid for most of the metals and for a wide variety of dielectric substrate and cover materials. The maps allowing to find the surface plasmon resonance wavelength and spectral dispersion of the polarizability of Ag,Au,Cu, and Al hemispherical nanoparticles are also presented. The maps are plotted in the coordinates of the substrate and the surrounding media dielectricpermittivity. The results of the study can be applied to describe the polarizability of isolated or weakly interacting metal nanoislands and metal island films.

Enhanced light outcoupling in microdisk lasers via Si spherical nanoantennas

High-index dielectric (Si) nanoantennas providing outcoupling of light from InAs/Ga(Al)As quantum dot (QD) microdisk lasers have been designed. The spatial distribution of light emitted from optically pumped QD microdisk lasers with a single Si spherical nanoantenna placed on the top surface of the microdisk was studied experimentally by confocal optical microscopy. Dependences of the emission intensity on the size and position of the Si nanoantenna were investigated. It was found that the laser mode to be outcoupled can be selected by choosing the nanosphere position with respect to the mode electromagnetic field maximum. Optimization of the Si nanoantenna parameters resulted in a 23-fold increase of the emission intensity at the location of the Si nanoantenna (whereas the total intensity enhanced 4 times) compared to the emission intensity from the initial microdisk laser without significant deterioration of the resonator quality factor.High-index dielectric (Si) nanoantennas providing outcoupling of light from InAs/Ga(Al)As quantum dot (QD) microdisk lasers have been designed. The spatial distribution of light emitted from optically pumped QD microdisk lasers with a single Si spherical nanoantenna placed on the top surface of the microdisk was studied experimentally by confocal optical microscopy. Dependences of the emission intensity on the size and position of the Si nanoantenna were investigated. It was found that the laser mode to be outcoupled can be selected by choosing the nanosphere position with respect to the mode electromagnetic field maximum. Optimization of the Si nanoantenna parameters resulted in a 23-fold increase of the emission intensity at the location of the Si nanoantenna (whereas the total intensity enhanced 4 times) compared to the emission intensity from the initial microdisk laser without significant deterioration of the resonator quality factor.

Resonant properties of coupled silver hemispheroids

Abstract. We present a study of resonant optical properties of paired silver hemispheroids grown on a glass substrate using out-diffusion technique combined with thermal poling of the glass. Atomic force microscopy was used to characterize the morphology of the grown nanostructures. Dark-field spectroscopy and numerical simulation were applied to study the optical properties of the coupled nanoparticles (NPs) depending on the interparticle gap and size difference of the hemispheroids in a pair. Raman spectroscopy testing of the coupled hemispherical NPs showed that they can provide signal enhancement factor exceeding one of a single hemispherical NP.

Plasmonic properties of metal nanoislands: surface integral equations approach

The surface integral equations method is used to analyse the surface plasmon resonance position in a metal island film formed by non-interacting axisymmetrical prolate/oblate hemispheroids placed on a dielectric substrate. The approach is verified via the comparison of results obtained for a hemisphere on a substrate with the ones obtained using the multipole expansion method. The preference of the integral equations method is in obtaining a simple final analytical expression for a particle polarizability in which any dielectric function of a metal can be substituted. Such simple formulae for the hemispherical particle on the substrate and calculated dependences of the hemispheroid resonant wavelength on its aspect ratio are presented.