Andrey V. Ivanov

The field enhancement and optical sensing in the array of almost adjoining metal and dielectric nanorods

The surface plasmon (SP) excitations in the periodical array of the nanorods have attracted a lot of attention in the recent years due to the numerous potential applications in nanoplasmonics including transmitting and processing optical signals on a scale much smaller than the wavelength. In our work the plasmonic and dielectric systems consisting of twodimensional periodic arrays of nanorods are considered. We use computer simulation as well as exact analytical solution to find reflectance and transmittance the plane array of the nanorods, which have various diameters and inter-particle spacing. As the metal nanorods approach each other, series of surface plasmon resonances are excited. The resonances are strongly localized between nanorods due to its collective nature. It is shown that the local electric field is much enhanced in the interparticle gap and it concentrates at a scale much smaller than the diameter of the rod. The reflectance and transmittance have sharp minima and maxima corresponding to the excitation of various SP resonances. The computer simulations are in an agreement with our analytical theory. In the case of the dielectric nanorods the phenomenon of the whispering gallery modes effect is considered. The resonance frequencies and field enhancement can be tuned by variation of the shape and arrangement of the nanorods. The system of nanorods that almost touched each other by their generatrices can be used to develop plasmon and dielectric substrates, which are the basic elements of high sensitive SERS bio and chemical sensors.

Metallation of N-vinylpyrroles and -indoles with Hg(OAc)2: N-vinyl vs. pyrrole nucleophilic sites

N-Vinylpyrroles and -indoles bearing electron-withdrawing substituents at the pyrrole ring are mercurated, with 1 equivalent of Hg(OAc)(2) in dry MeCN (20-80 °C), regioselectively at the vinyl group (yields are almost quantitative), while their congeners without electron-withdrawing functions are mercurated both at the N-vinyl group and the pyrrole ring.

Light localization and SERS in tip-shaped silicon metasurface

Optical properties of two dimensional periodic system of the silicon micro-cones are investigated. The metasurface, composed of the silicon tips, shows enhancement of the local optical field. Finite element computer simulations as well as real experiment reveal anomalous optical response of the dielectric metasurface due to excitation of the dielectric resonances. Various electromagnetic resonances are considered in the dielectric cone. The metal-dielectric resonances, which are excited between metal nanoparticles and dielectric cones, are also considered. The resonance local electric field can be much larger than the field in the usual surface plasmon resonances. To investigate local electric field the signal molecules are deposited on the metal nanoparticles. We demonstrate enhancement of the electromagnetic field and Raman signal from the complex of DTNB acid molecules and gold nanoparticles, which are distributed over the metasurface. The metasurfaces composed from the dielectric resonators can have quasi-continuous spectrum and serve as an efficient SERS substrates.

Systematic investigations of 3D acoustic receptivity with respect to steady and unsteady disturbances. Experiment and DNS

In the present paper, the linear 3D acoustic-roughness receptivity of the 2D boundary layer of an airfoil is investigated systematically with respect to main influence parameters by means of wind tunnel experiments and Direct Numerical Simulations (DNS). A plane acoustic wave with frequency f ac scatters at a specially designed localized roughness element, that is capable to vibrate with frequency f v . The resulting Tollmien-Schlichting (TS) waves appear at combination frequencies (f 1,2 = f ac ∓ f v ) and develop as a wave train downstream of the surface roughness. The complex receptivity function is evaluated by normalization of the initial TS-spectra with the related amplitudes and phases of the surface vibrator and the acoustics. The main influence parameters investigated are the frequency (of the acoustic and the TS wave), the pressure gradient (given by the streamwise position of the surface roughness) and the influence of surface vibrations on the acoustic receptivity. Additionaly pure vibrational receptivity is studied. The main goal of this investigation is to study and compare systematically different types of receptivity in the same base flow developing on an airfoil at a Reynolds number typical for glider applications.

Giant field fluctuations in dielectric metamaterial and Raman sensor

New dielectric metamaterial based on the Bragg filter comprising ten dielectric bilayers was investigated. Each bilayer is the thin films of silicone dioxide (SiO2) and another film of zirconium dioxide (ZrO2). The surface of the multilayer film is profiled. It has a form of periodic system of rectangles separated by the open gaps. We use the computer simulation as well as analytical solution to find the reflectance of the multilayer as a function of the wavelength and electromagnetic (em) field distribution. The multilayer system reveals the enhancement of em fields at the surface. The considered Bragg filter was modified by Raman-active structure made of gold nanoparticles with chemically attached 3,3-thio-bis(6- nitrobenzoic acid) - (TNB). The high Surface Enhanced Raman Scattering (SERS) signal was detected.

Metal-dielectric resonances in tip silicon metasurface and SERS based nanosensors

Optical properties of two-dimensional periodic systems of the dielectric micro bars and micro cones are investigated. Computer simulations as well as real experiment reveal anomalous optical response of the dielectric metasurface due to excitation of the dielectric and metal-dielectric resonances, which are excited in-between metal nanoparticles and dielectric cones and bars. In the metal-dielectric resonance local electric field can be orders on magnitude larger than the field in the plasmon resonance only. To investigate local electric field the signal molecules were deposited on the metal nanoparticles. We demonstrate the enhancement of the electro- magnetic field by detecting the Raman signal from the of organic acid molecules deposited on the investigated metasurface.

Laminar-turbulent transition delay on a swept wing

The paper describes the results of experiments on robustness of laminar-turbulent transition control on a swept-wing using distributed micro-sized roughness (DMSR) elements. These elements introduce controlled stationary vortices which are able to significantly modify the base flow and its stability characteristics. We have performed parametric study first varying height and period of the DMSR elements in order to find the most stabilizing effect on boundary later flow in compare to uncontrolled reference case without DMSR. Significant downstream shift of laminar-turbulent transition position due to application of DMSR is found and well documented with help of thermography. The robustness of this flow control method was studied by variation of the wind-tunnel flow quality introducing significant sound background or introducing enhanced turbulence level (applying turbulizing grids). The wind-tunnel tests performed with turbulence-generating grids (at enhanced turbulence levels) have shown that laminar-turbulent transition moves upstream in this case, while DMSR-elements loose their effectiveness for transition control (no matter in quiet sound conditions or at elevated sound background). The experiments on acoustic influence have shown that without DMSR acoustic does not effect transition location. However, in case then laminar-turbulent transition is delayed by presence of DMSR, an additional transition delay was observed when harmonic acoustic waves of certain frequency were excited.The paper describes the results of experiments on robustness of laminar-turbulent transition control on a swept-wing using distributed micro-sized roughness (DMSR) elements. These elements introduce controlled stationary vortices which are able to significantly modify the base flow and its stability characteristics. We have performed parametric study first varying height and period of the DMSR elements in order to find the most stabilizing effect on boundary later flow in compare to uncontrolled reference case without DMSR. Significant downstream shift of laminar-turbulent transition position due to application of DMSR is found and well documented with help of thermography. The robustness of this flow control method was studied by variation of the wind-tunnel flow quality introducing significant sound background or introducing enhanced turbulence level (applying turbulizing grids). The wind-tunnel tests performed with turbulence-generating grids (at enhanced turbulence levels) have shown that laminar-turb...

Characteristics of 3D instability of a 35-degree swept wing to CF and TS modes. Experiment and theory

An extensive experimental investigation of linear evolution of Cross-Flow (CF) and Tollmien-Schlichting (TS) modes of 3D boundary layer oscillations on a swept wing has been carried out. TS-instability characteristics have been studied experimentally for the first time. The characteristics of development of the two kinds of instability modes are compared with calculations and display a very good agreement. The whole dataset may be used for promotion of theoretical methods of investigation of laminar-turbulent transition in swept wing boundary layers.