Optical reflection from dielectric layers containing metal particles formed by ion implantation

Dielectric layers with silver nanoparticles, which are synthesized in a soda-silicate glass by implantation of 60-keV ions with a dose of 7.0×10¹⁶ Ag⁺/cm² at an ion current density of 10 μmA/cm², are analyzed. The depth of silver distribution was measured by Rutherford backscattering. Data on optical characteristics of composite layers were obtained from the transmission spectra and from the reflection, which were measured both from the side of an implanted glass surface and from the unimplanted side. To calculate reflection spectra, a multilayer plane-parallel film structure was considered, which was modeled on the basis of the matrix method using complex Fresnel coefficients. Dielectric functions of separate layers were determined using the Maxwell-Garnet theory of an effective medium. A qualitative agreement between the experimental and the model optical spectra was obtained taking into account a nonuniform depth distribution of metal nanoparticles in a composite material.     

Formation of silver nanoparticles in photothermorefractive glasses during electron irradiation

The formation of silver nanoparticles in photothermorefractive glasses during electron irradiation and subsequent heat treatment is experimentally studied. The optical density spectra of samples at various stages of heat treatment are compared. The formation of metallic nanoparticles is shown to occur during both electron irradiation and subsequent heat treatment. Nanoparticles are localized in layers parallel to the surface. At the initial stage of nanoparticle formation, the key role is played by the appearance of a negative bulk charge in the near-surface layer in glass, which results in the field-assisted migration of positive metal ions and a characteristic layered distribution of metallic nanoparticles in the glass volume.     

Ion synthesis of copper nanoparticles in sapphire and their modification by high-power excimer laser pulses: A review

Composite layers made in sapphire by implantation of 40-keV Cu⁺ ions at a dose of 1 × 10¹⁷ cm⁻² and an ion beam current density varying from 2.5 to 10 μA/cm² are studied. It is shown that ion implantation makes it possible to synthesize a composite layer containing copper nanoparticles at the surface of the insulator. However, the nanoparticle size distribution in this layer is nonuniform. The composite layer is exposed to high-power excimer laser radiation with the aim of modifying the size and size distribution of the metal nanoparticles in it. The resulting structures are examined by Rutherford backscattering, optical reflection spectroscopy, and atomic force microscopy. It is found that the laser irradiation diminishes copper nanoparticles in the composite layer. Experimental data on laser modification may be explained by photofragmentation and/or melting of the nanoparticles in the sapphire matrix under the action of nanosecond laser pulses.     

Magnetoelectric effect in an asymmetric layered magnet-piezoelectric structure

The magnetoelectric effect in magnet-piezoelectric layered composite structures is discussed. The magnetoelectric voltage and the magnetoelectric coefficient are calculated taking into account bending deformations that accompany tensile and compressive strains in structures with asymmetric positions of magnetic layers relative to the neutral plane. It is demonstrated that bending deformations lead to a nonuniform distribution of the electric field over the thickness of the piezoelectric layer and to a nonmonotonic dependence of the magnetoelectric coefficient on the thickness ratio of the layers in the structure.     

Synthesis and photo physical properties of Au @ Ag (core @ shell) nanoparticles disperse in poly vinyl alcohol matrix

Synthesis of core @ shell (Au @ Ag) nanoparticle with varying silver composition has been carried out in aqueous poly vinyl alcohol (PVA) matrix. Core gold nanoparticle (~15 nm) has been synthesized through seed-mediated growth process. Synthesis of silver shell with increasing thickness (~1–5 nm) has been done by reducing Ag⁺ over the gold sol in the presence of mild reducing ascorbic acid. Characterization of Au @ Ag nanoparticles has been done by UV–Vis, High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) spectroscopic study. The blue shift of surface plasmon resonance (SPR) band with increasing mole fraction of silver has been interpreted due to dampening of core, i.e. Au SPR by Ag. The dependence of nonlinear optical response of spherical core @ shell nanoparticles has been investigated as a function of relative composition of each metal. Simulation of SPR extinction spectra based on quasi-static theory is done. A comparison of our experimental and the simulated extinction spectra using quasi-static theory of nanoshell suggests that our synthesized bimetallic particles have core @ shell structure rather than bimetallic alloy particles.     

Anisotropic local-field effects of nanoparticles in plasmonic optics and magneto-optics

A theory of anisotropic optical local-field effects caused by resonantly polarizable small particles in multilayer polarizable media is developed. Considered is the model of a rectangular lattice of ellipsoidal nanoparticles with taking account of “image forces” at an interface in a layered medium. The lattice sums for anisotropic dipolar interactions are found using the Green’s function method in the quasi-point dipole approximation, and the effective polarizabilities of particles in a layer located near an interface are calculated self-consistently. The manifestation of an anisotropic local field of nanoparticles in optical radiation and propagation of evanescent waves responsible for optical near-field effects is investigated. Applications of the obtained results in the polar magneto-optical Kerr effect and reflectance anisotropy spectroscopy in propagating the polarized light along the normal to layers are considered. The resonant features in the spectra due to enhancement of the optical effects under excitation of surface (local) plasmons in nanoparticles of a noble metal are studied.     

Calculation of the electrostriction effect in thin-film metal-ferroelectric-metal structures

An analysis is made of the influence of electron injection from the cathode on the electrical conductivity and nonuniform thickness distribution of the piezoelectric properties of metal-insulator-metal structures using an electrostrictive, optically transparent FE ceramic such as lanthanum-containing lead zirconate titanate (PLZT). Because thin-film insulators, in contact with metal electrodes, exhibit semiconducting properties, the theory put forward by Mott and Gurney for insulating diodes can be used to calculate the electric fields and currents. The distribution of the polarization over the thickness of the piezoelectric layer was determined by means of an asymptotic solution, and relations were formulated for the electroelasticity of FE ceramic plates and shells. A detailed analysis was made of the electromechanical bending effect in homogeneous piezoelectric plates used as optical radiation modulators. It is shown that these formulas can be used for a computational and experimental determination of the distribution of the polarization over the thickness of thin-film piezoelectric structures. Zh. Tekh. Fiz. 69, 120–124 (July 1999)     

Optical properties of metal nanoparticles synthesized in a polymer by ion implantation: A review

Polymer composite layers irradiated by 30-keV Ag⁺ ions with doses from 3.1×10¹⁵ to 7.5×10¹⁶ cm^?2 and an ion current of 4 µA/cm² are investigated. The composites were examined using Rutherford backscattering (RBS), transmission electron microscopy (TEM), and optical spectroscopy. As follows from electron microscopy and electron microdiffraction data, ion implantation is a promising tool for synthesizing silver nanoparticles in the surface region. The optical density spectra taken of these composites demonstrate that the silver nanoparticles exhibit unusually weak plasma resonance. The formation of silver nanoparticles in layers carbonized by ion implantation is considered. Based on the Mie theory, optical extinction spectra for silver particles in the polymer and carbon matrices are simulated and optical spectra for complex silver core-carbon sheath nanoparticles are calculated. The physics behind the experimental optical spectra of the composite is discussed.     

Preparation, structure, and properties of metal nanocomposites in lithium niobate

Crystals of lithium niobate LiNbO₃ are implanted with 60-keV Cu^? ions at different ion fluxes to a fluence of 2 × 10¹⁷ ions/cm². The structure and the linear and nonlinear optical properties of the implanted layers are investigated. The optical transmission and ion-induced photon spectra of the LiNbO₃ crystals are measured in the course of implantation. It is revealed that the implantation brings about the formation of complex nanocomposites consisting of metallic copper nanoparticles and nanodomains of the matrix. The distributions of nanoparticles and nanodomains in the implanted layers do not correlate with each other. It is shown that the variations in the linear and nonlinear optical absorption of the nanocomposites are predominantly determined by the changes in the chemical composition and the structure of the matrix.     

The influence of low-temperature silver-ion exchange on the spectral-luminescent properties of fluorophosphate glasses doped with PbSe

Changes in the absorption and luminescence spectra of fluorophosphate glasses doped with PbSe caused by low-temperature Ag⁺–Na⁺ ion exchange are considered. It is found that the silver distribution gradient in a near-surface layer about 16 μm thick leads to two different processes of interaction between metal and semiconductor nanoparticles. PbSe molecular clusters and quantum dots more efficiently grow in deep layers with a low silver concentration. The near-surface glass layers with a high silver concentration exhibit formation of Ag metal nanoparticles, on the surface of which interaction with PbSe molecular clusters leads to the formation of Ag–Se–Pb bonds, which transform into Ag₂Se layers in the process of heat treatment. The appearance of the new phase is confirmed by X-ray diffraction.     

Heterostructure with extended optical waveguide for diode lasers

The thickness and composition of diode heterolaser layers are optimized with respect to the ratio of the optical beam width d to the optical confinement factor Γ. The stability of the vertical near field distribution and the most important waveguide parameters to static changes and dynamic variations of the refractive indices of heterostructure layers is tested in the laser operation mode.     

Fabrication of composite based on GeSi with Ag nanoparticles using ion implantation

Comparative analysis of the structural and optical properties of composite layers fabricated with the aid of implantation of single-crystalline silicon (c-Si) using Ge⁺ (40 keV/1 × 10¹⁷ ions/cm²) and Ag⁺ (30 keV/1.5 × 10¹⁷ ions/cm²) ions and sequential irradiation using Ge⁺ and Ag⁺ ions is presented. The implantation of the Ge⁺ ions leads to the formation of Ge: Si fine-grain amorphous surface layer with a thickness of 60 nm and a grain size of 20–40 nm. The implantation of c-Si using Ag⁺ ions results in the formation of submicron porous amorphous a-Si structure with a thickness of about 50 nm containing ion-synthesized Ag nanoparticles. The penetration of the Ag⁺ ions in the Ge: Si layer stimulates the formation of pores with Ag nanoparticles with more uniform size distribution. The reflection spectra of the implanted Ag: Si and Ag: GeSi layers exhibit a sharp decrease in the intensity in the UV (220–420 nm) spectral interval relative to the intensity of c-Si by more than 50% owing to the amorphization and structuring of surface. The formation of Ag nanoparticles in the implanted layers gives rise to a selective band of the plasmon resonance at a wavelength of about 820 nm in the optical spectra. Technological methods for fabrication of a composite based on GeSi with Ag nanoparticles are demonstrated in practice.     

Layered structure of epitaxial yttrium iron garnet films

The layered structure of yttrium iron garnet films, ranging in thickness from 0.7 to 4.1 μm, grown epitaxially on single-crystal gallium-gadolinium garnet substrates, was investigated by x-ray spectral microanalysis. The ferrite films were chemically etched layer by layer in a mixture of orthophosphoric and sulfuric acids at T=353–423 K. It was established that the chemical composition of the films varies over the thickness because of the nonuniform distribution of gadolinium, gallium, lead, and platinum ions; the film-substrate transitional layer and the surface layer of the film differ most greatly with respect to the composition and magnetic properties. It was shown that the thickness of the transitional layers and their negative effect on the magnetic characteristics of ferrite films decrease appreciably if at the time of immersion of the substrate and pulling of epitaxial structure out of the fluxed solution the substrate holder together with a special mixer rotate at a rate of 50 rpm and the pulling velocity is 20 cm/min. Zh. Tekh. Fiz. 69, 62–64 (December 1999)     

Comparative study of cathode and magnetron sputtering methods for depositing Pb(TiZr)O<Subscript>3</Subscript> ferroelectric film

The radial distribution of the composition and thickness of lead zirconate titanate films deposited in several modes of magnetron and diode sputtering was measured. It was shown that the effects of deposited film resputtering with preferential lead sputtering are pronounced during ion-plasma sputtering of Pb(Zr,Ti)O₃. During magnetron sputtering, this leads to a nonuniform distribution of the film composition over the substrate, which cannot be compensated by varying the target composition. During diode sputtering with a short target-substrate distance, resputtering has no significant effect on the film composition.     

Nanostructural composites of phthalocyanine and metals

Thin composite films of metal nanoparticles incorporated into a phthalocyanine matrix were prepared by simultaneous vacuum deposition of copper and phthalocyanine from two evaporation sources. Absorption spectra in both the IR and UV/VIS regions were measured in order to study changes of structure and properties with different volume fractions of copper in the films. The effective medium theory (EMT) approach was used to model optical spectra. A pronounced aging of composite layers was observed after the deposition.     

Spectra of resonance light scattering of gold nanoshells: Effects of polydispersity and limited electron free path

The effects of the polydispersity of the structure of gold nanoshells and of the limited electron free path in a thin metal layer on the spectra of resonance light scattering of a suspension of two-layer nanoparticles are studied theoretically and experimentally for the first time. It is shown theoretically that both factors lead to a broadening of the plasmon resonance in light scattering and to a change in its magnitude. To experimentally test the calculations, two samples of nanoshells based on gold and silicon dioxide (silica) were synthesized. Nanoshells of sample 1 have a diameter of the core of 90 nm and a broad thickness distribution of shells (with an average value of 30 nm), whereas nanoshells of sample 2 have a diameter of the core of 70 nm and a narrow thickness distribution of shells (with an average value of 12 nm). The core diameter, the shell thickness, and the polydispersity of the structure of nanoparticles are estimated by dynamic light scattering. It is shown that the simulation of the optical properties of nanoparticles with their parameters estimated from the dynamic light scattering data makes it possible to obtain good agreement between experimental and theoretical spectra of light scattering. For nanoshells of sample 1, the inhomogeneous broadening of the scattering spectrum is completely determined by the polydispersity; therefore, the bulk constants of gold can be used in simulation of the spectra of such nanoshells. The main mechanism of the broadening for nanoshells of sample 2 is connected with the limitation of the free path length of electrons, whereas the contribution from the thickness distribution of shells can be neglected.     

Simulation on effect of metal/graphene hybrid transparent electrode on characteristics of GaN light emitting diodes

In order to decrease the Schottky barrier height and sheet resistance between graphene(Gr) and the p-GaN layers in GaN-based light-emitting diodes(LEDs), some transparent thin films with good conductivity and large work function are essential to insert into Gr and p-GaN layers. In this work, the ultra-thin films of four metals(silver(Ag), golden(Au), nickel(Ni), platinum(Pt)) are explored to introduce as a bridge layer into Gr and p-GaN, respectively. The effect of a different combination of Gr/metal transparent conductive layers(TCLs) on the electrical, optical, and thermal characteristics of LED was investigated by the finite element methods. It is found that both the TCLs transmittance and the surface temperature of the LED chip reduces with the increase of the metal thickness, and the transmittance decreases to about 80% with the metal thickness increasing to 2 nm. The surface temperature distribution, operation voltage, and optical output power of the LED chips with different metal/Gr combination were calculated and analyzed. Based on the electrical, optical, and thermal performance of LEDs, it is found that 1.5-nm Ag or Ni or Pt, but 1-nm Au combined with 3 layered(L) Gr is the optimal Gr/metal hybrid transparent and current spreading electrode for ultra-violet(UV) or near-UV LEDs.     

菱形金属纳米粒子光学性质的研究

金属纳米粒子的光学性质与金属纳米粒子的组成、形状、尺寸及周围的介电常数有关。利用时域有限差分法研究菱形纳米粒子的尺寸与其消光特性关系, 发现粒子尺寸的大小对其消光谱共振峰有较大影响, 随着粒子尺寸的增大, 消光谱共振峰可分裂成两个或多个共振峰。而且在可见光范围内波长大于480 nm的区域, 表面等离子体共振峰是偶极子激发模式; 而在波长小于480 nm的区域, 共振模式则比较复杂, 有偶极子模式, 也有多极子模式。计算表明, 波长为480~ 600 nm区间与波长大于600 nm的区间, 菱形纳米粒子的尺寸对消光光谱的峰值和谱线宽度影响不同。在波长为480~600 nm之间, 短轴为140 nm时, 其消光效率最高。     

Optical Spectra of Metal-Dielectric Nanocomposites with a Layered Subwave Structure

The results of theoretical and experimental investigations of the optical spectra of layer-periodic nanocomposites consisting of alternating tightly packed monolayers of silver nanoparticles and separating KCl layers of subwave thickness are presented. The characteristic features of the spectral dependence of the transmission and reflection coefficients of this type of nanocomposites have been analyzed for the case where the photon forbidden bands are located near the plasmon-absorption band. Experimental samples were prepared by successive thermal evaporation of silver and KCl in vacuum. Theoretical calculations were carried out using the quasi-crystalline approximation of the theory of multiple scattering of waves. It is shown that the spectral position, shape, and intensity of absorption and reflection bands can be regulated by changing the optical thickness of the intermediate dielectric films in a layered metal-dielectric composite.     

Photoluminescence characterization of silicon nanostructures embedded in silicon oxide

This paper describes a simple method to analyze the photoluminescent characteristics of materials based on embedded light-emitting nanoclusters. Photoluminescence spectra of deposited silicon sub-oxide layers with the same composition and different thicknesses have been obtained. A saturation of the total luminescence intensity is observed with increase in thickness. By analyzing the photoluminescence spectra several optical and structural parameters can be evaluated. We thus propose a model in which the absorption of light from a nanostructure layer implies the possibility of subsequent luminescence and affects the underlying layers as well. By fitting the data to the developed model, two fundamental parameters are extracted: nanostructures absorption probability, which is independent of the emission energy and the spectra of emission probability of an excited nanostructure which fits a Gaussian shape.