M. Yu. Tsvetkov

Synthesis of silver nanocomposites by SCF impregnation of matrices of synthetic opal and Vycor glass by the Ag(hfac)COD precursor

Silver-containing nanocomposites were prepared by impregnating Vycor glass (a pore diameter of 4 nm) and synthesized opal matrices (an interstitial void size of 40 nm) with cyclooctadiene complex of silver hexafluoroacetylacetonate (Ag(hfac)COD), a silver precursor, dissolved in supercritical carbon dioxide and were examined by optical absorption spectroscopy, atomic force microscopy, and electron spin-resonance spectroscopy. It was demonstrated that the absorption spectra of Vycor glass and opal matrices impregnated with Ag(hfac)COD molecules and subjected to thermal treatment in air at temperatures above 50°C exhibit plasmon resonances characteristic of Ag nanoparticles at 420–430 nm. The peculiarities of the plasmon resonance band for both types of samples were attributed to the morphology of the pore space in which silver particles are formed. Paramagnetic Cu(hfac)2 molecules (copper hexafluoroacetylacetonate) were used as a spectroscopic probe for estimating the distribution of the precursor in the pores of Vycor glass and opal matrices during supercritical fluid impregnation.

Surface-enhanced raman scattering platforms on the basis of assembled gold nanorods

This study investigates the surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) on the surface of gold nanorods (GNRs) assembled on silicon. Two samples of GNRs were synthesized, notably, GNR-670 and GNR-810, with the average (length × thickness) dimensions of 64 × 23 and 45 × 11 nm and with plasmon resonances at 670 and 810 nm, respectively. Three types of substrates were fabricated, namely, a low-density monolayer (S1), a densely packed monolayer with regions of the side-by-side assembly of nanorods (S2), and a fractal film (S3). The extinction spectra of densely packed substrates showed the appearance of new maxima and the broadening and the red-shift of plasmon resonances, as was consistent with the typical behavior of plasmonic particles interacting at an interparticle distance of about 1–3 nm (data of transmission electron microscopy). The intensities of SERS peaks of the rhodamine 6G increased for substrates S1, S2, and S3 as 1: 6: 260, respectively. There was no significant difference in the SERS efficiency of the substrates based on GNR-670 and GNR-810 rods. The average enhancement of the signal over an area of 400 μm was about 105 with a reproducibility error of ±10%, thus making the obtained substrates promising platforms for sensitive SERS chemical and biological sensors.

Plasmon resonances of silver nanoparticles in silica based meso-structured films

The process of fabrication of plasmon mesostructures based on opal-like films (films consisting of silica spheres of similar diameters) and homogeneous and quasi-homogeneous sol-gel SiO2 films has been elaborated. The kinetics of formation of silver nanoparticles (NPs) in such films in the course of thermal treatment has been studied. Two mechanisms of the formation of the plasmon absorption bands in such structures have been revealed. The results of the plasmon amplification of the Raman scattering signal of the Rhodamine 6G dye on opal-like films containing silver NPs have been reported.

Routes to polymer-based photonics

AbstractThe advances in polymer materials and technologies for telecom applications are reported. The polymers include new highly halogenated acrylates, which possess absorption losses less than 0.25 dB/cm and refractive indices ranging from 1.3 to 1.5 in the 1.5 μm wavelength region. The halogenated liquid monomers are highly intermixable, photocurable under UV exposure and exhibit high contrast in polymerization.The polymer technologies developed at the Institute on Laser and Information Technologies of the Russian Academy of Sciences (ILIT RAS) include:UV contact lithography permitting creation of single-mode polymer waveguides and waveguide arrayssubmicron printing for fabricating corrugated waveguides and polymer phase masksUV laser holography for writing refractive index gratings in polymer materials. The technology for fabricating narrowband Bragg filters on the basis of single-mode polymer waveguides with laser-induced submicron index gratings is presented in detail. The filters possess narrowband reflection/transmission spectra in the 1.5 μm telecom wavelength region of 0.2–2.7 nm width, nearly rectangular shape of the stopband, reflectivity R > 99% and negligible radiation losses. They can be used for multiplexing/demultiplexing optical signals in high-speed DWDM fiber networks.

Optical, magnetic, and dielectric properties of opal matrices with intersphere nanocavities filled with crystalline multiferroic, piezoelectric, and segnetoelectric materials

The properties and structure of composites on the basis of the lattice packings of SiO2 nanospheres (opal matrices), containing in intersphere nanocavities clusters of the crystal phases of multiferroics and piezoelectric and ferroelectric materials.

Thermostimulated formation of silver and gold nanoparticles in porous silicon dioxide matrices

Manifestations of thermostimulated formation and subsequent transformation of silver and gold nanoparticles in porous opal and Vycor glass matrices are studied using optical spectroscopy. Two temperature ranges for silver nanoparticles are revealed, where first-type particles transform into another type of particles. With gold nanoparticles in these matrices, a temperature range in which one type of particles transforms into another type is established. An effect of complete blackening of Vycor glass samples, caused by their annealing, is revealed, and a rationalization of this effect is given.

Improving the efficiency of laser-induced backside wet etching of optically transparent materials as a result of generation of carbon and silver nanoparticles

The processes of laser-induced backside wet etching (LIBWE) and microstructuring of silicate glass by laser impulses with a wavelength of 527 nm and a duration of about 5 ns have been studied in different aqueous solutions that provide different etching modes, namely, volume (in a solution of dye), volume + surface (in a solution of dye and polyethylene glycol (PEG)), and surface modes (in an aqueous solution of AgNO3). It is shown that the etching rate and the quality of the obtained structures depend on two different processes: the chemical etching of the material surface by water in the supercritical state (fluid produced at fast laser heating) and the shockwave or cavitational destruction of a material. The LIBWE rate and the quality of the formed microstructures are determined by a dominating mechanism of the process. In the case of an aqueous dye solution, the shockwave and cavitational destruction dominates, which makes it impossible to create well-replicated craters and tracks with smooth walls. Upon the addition of PEG to a solution of dye and, especially, upon using an aqueous solution of the silver precursor (AgNO3), the laser-induced processing of carbon or silver nanoparticles gives rise to a strong absorption on the surface of the formed structure, the undesirable cavitational destruction of a material is suppressed, and the process of etching of the glass surface by supercritical water becomes a dominating mechanism of LIBWE. As a result, it is possible to create highly effective and well-reproducible LIBWE technology for the fabrication of precision optical microstructures on the surface of advanced optical materials on the basis of high-performance and reliable lasers with a wavelength of 527 nm.

Gold nanorods as a perspective technology platform for SERS analytics

We discuss the application of gold nanorods for forming SERS substrates for chemical and biological sensing. Two approaches are considered: (1) formation of planar arrays on silicon wafers by using suspensions of gold nanorods; and (2) a new approach based on gold nanorod powders that can be easily dissolved in aqueous media. Both SERS platforms are characterized and their SERS enhancement factors are compared.

Etching of Sapphire in Supercritical Water at Ultrahigh Temperatures and Pressures under the Conditions of Pulsed Laser Thermoplasmonics

The method of thermoplasmonic laser-induced backside wet etching (TPLIBWE) is applied for effective and well-controlled microstructuring of sapphire. The method is based on the generation of highly absorbing silver nanoparticles in the course of the pulsed-periodic laser irradiation. The silver nanoparticles are formed as a result of the reduction of a water-dissolved precursor, AgNO3. The process of sapphire etching occurs via the formation of supercritical water at ultrahigh temperatures and pressures (which significantly exceed the critical values for water) and the formation of silver nanoparticles at the sapphire/water interface as a result of the absorption of laser radiation. The mechanism of TPLIBWE is considered and the etching rate, which reaches ~100 nm/pulse, is determined. The formation of aluminum nanoparticles, which indicates a deep destruction of Al2O3 as a result of TPLIBWE, is observed.

On the Role of Supercritical Water in Laser-Induced Backside Wet Etching of Glass

The features and mechanisms of microcrater formation in optical silicate glass by laser-induced backside wet etching (LIBWE) are determined in a wide range of energy densities (Φ) from 4 to 103 J/cm2 for laser pulses of 5 ns length and 1 kHz repetition rate. The existence of two different mechanisms of laserinduced microcrater formation is revealed: (i) chemical etching in supercritical water (SCW), and (ii) cavitation. At Φ > 102 J/cm2 irregular craters of 1–20 μm in depth with rough walls and distinct cracks around microcrater are formed testifying that in such mode (“hard”) laser induced cavitation plays a dominant role in glass removal. At Φ < J/cm2 neat glass craters with smooth walls are formed, their size and shape are easily reproducible, cracks are not formed, and the processing area is limited to the laser spot area. In this mode (“soft mode with active cavitation”), a microcirculation of water is stimulated by cavitation without causing undesirable shock breakage. The latter is achieved thanks to the fast removal of glass etching products by microcirculation, and the inflow of “fresh” etchant (SCW) to the glass surface in the vicinity of the formed microcraters. Such mode is optimal for highly controlled laser microstructuring of glass and other optically transparent materials.