Silver Nanoparticle Thin Films with Nanocavities for Surface‐Enhanced Raman Scattering

The formation of nanometer‐sized gaps between silver nanoparticles is critically important for optimal enhancement in surface‐enhanced Raman scattering (SERS). A simple approach is developed to generate nanometer‐sized cavities in a silver nanoparticle thin film for use as a SERS substrate with extremely high enhancement. In this method, a submicroliter volume of concentrated silver colloidal suspension stabilized with cetyltrimethylammonium bromide (CTAB) is spotted on hydrophobic glass surfaces prepared by the exposure of the glass to dichloromethysilane vapors. The use of a hydrophobic surface helps the formation of a more uniform silver nanoparticle thin film, and CTAB acts as a molecular spacer to keep the silver nanoparticles at a distance. A series of CTAB concentrations is investigated to optimize the interparticle distance and aggregation status. The silver nanoparticle thin films prepared on regular and hydrophobic surfaces are compared. Rhodamine 6G is used as a probe to characterize the thin films as SERS substrates. SERS enhancement without the contribution of the resonance of the thin film prepared on the hydrophobic surface is calculated as 2×10⁷ for rhodamine 6G, which is about one order of magnitude greater than that of the silver nanoparticle aggregates prepared with CTAB on regular glass surfaces and two orders of magnitude greater than that of the silver nanoparticle aggregates prepared without CTAB on regular glass surfaces. A hydrophobic surface and the presence of CTAB have an increased effect on the charge‐transfer component of the SERS enhancement mechanism. The limit of detection for rhodamine 6G is estimated as 1.0×10^?8 M . Scanning electron microscopy and atomic force microscopy are used for the characterization of the prepared substrate.     

On a technique for determining the predominant orientation of crystal particles in clouds by virtue of polarization measurements in the MM-wave band

We propose a technique for analyzing polarization characteristics of microwave radiation scattered by cloud particles with different distributions over sizes, shape, and spatial orientation. We have found a combination of Stokes parameters that is weakly sensitive to the distribution of the scattering particles over sizes and eccentricities but very sensitive to their distribution over spatial orientation. Institute, of Applied Physics, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 9, pp. 839–844, August 1999.     

On The “Nonresonance” Parametric Cyclotron Radiation

We study the effect of amplification of coherent bichromatic radiation due to its cyclotron parametric interaction with a modulated ensemble of classical electron oscillators. The mechanism of energy exchange between the radiation and the electrons in the absence of partial synchronism of the waves and particles is analyzed. The features of the energy exchange in the course of interaction of the waves with relativistic and nonrelativistic particles are pointed out.     

Readjustment of ferroelectric domain structure under the action of polarized light

Change in the 180 domain structure of a gyrotropic ferroelectric produced by circularly polarized light is considered. Due to circular dichroism the photoinduced polarization differs in adjacent domains with different spontaneous polarization directions, as a result of which the domain dimensions change, the period of the structure is decreased, and the crystal as a whole becomes photopolarized.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 17–20, June, 1984.     

Applicability of alkanet (Alkanna tinctoria) extract for the histological staining of liver tissue

Staining of tissue is a significant process in histotechnology and staining techniques are used in the examination and diagnosis of diseases. The increase of international awareness for the environment, ecology, and health directed people to reduce toxic effluents and stop usage of dangerous chemical dyes. The present trend throughout the world is shifting towards to use of natural products over their synthetic alternatives. Therefore, in this study, the dyeing ability of alkanet plant on the cells of unstained sections taken from Wistar rat liver was investigated. The extract of Alkanna tinctoria contain naphthaquinone group of dyestuff. Chemical characterization of A. tinctoria extract was performed with HPLC-TOF/MS and UV spectra analysis, respectively. Different metal salts were used in the staining processes in order to obtain different colors. In the staining of without adding mordant (metal salt) to the extract, pale brown staining was obtained in the cytoplasm. Light pink color was obtained with the addition of CuSO₄ mordant. Dark pink-red color was achieved by adding alum, and also NiSO₄ was added for light purple staining. The staining of cytoplasm of different cells in liver tissue was achieved successfully with the extract of A. tinctoria and different colors were obtained using various mordants.     

Preparation and Optical Characterization of Sol-Gel Deposited Pb(Zr0.45Ti0.55)O3 Films

Homogeneous crack-free lead zirconate titanate (Pb(Zr_0.45Ti_0.55)O₃: PZT 45/55) films were prepared by a chemically modified sol-gel process using lead acetate trihydrate, zirconium n-propoxide, and titanium isopropoxide precursors. The coating solutions were modified by the addition of diethanolamine. Single and multilayer films were deposited with a 2000 rpm spin rate on fused silica and MgO(100) substrates. Multiple spin coating with an intermediate heat treatment in air at 400°C for 3 min between coatings was performed to obtain films up to 2 m in thickness. The formation of the tetragonal perovskite structure was found to depend on the intermediate firing temperature, final annealing temperature, and annealing time. A 650°C rapid thermal annealing treatment in oxygen was required to crystallize the PZT film into the perovskite structure. The films were characterized using optical spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermo-gravimetry and differential scanning calorimetry (TG-DSC). The optical constants of the PZT films were evaluated from spectral transmittance and reflectance measurements. Optical constants are presented over the visible and near infrared region.     

Stochastic Stability of Lyapunov Exponents and Oseledets Splittings for Semi‐invertible Matrix Cocycles

We establish (i) stability of Lyapunov exponents and (ii) convergence in probability of Oseledets spaces for semi‐invertible matrix cocycles subjected to small random perturbations. The first part extends results of Ledrappier and Young to the semi‐invertible setting. The second part relies on the study of evolution of subspaces in the Grassmannian; the analysis developed here is based on higher‐dimensional Möbius transformations and is likely to be of wider interest. © 2015 Wiley Periodicals, Inc.     

Photomagnetization of polydomain magnetic insulators by circularly polarized light

A new effect of magnetization of magnetic insulators due to light absorption by magnetic ions is proposed. The estimates for an yttrium ion garnet crystal are made.