An investigation of the optical characteristics of a layer of Ag nanoparticles deposited from an AgNO3 solution on the surface of single-crystal Si is presented. The measurements were carried out using spectroscopic ellipsometry and spectrophotometry at the same tilt angle and sample probe location in a wide spectral range from 200 to 1700 nm. From the obtained experimental data, the parameters of the Drude-Lorentz model and the complex dielectric function were determined, which was compared with the pseudo-dielectric function. Both dependences revealed resonances of a bulk plasmon near the energy E = 3.8 eV, while a localized plasmon was detected in the pseudo-dielectric function at E = 1.65 eV, and in the dielectric function at E = 1.84 eV. Keywords: dielectric function, Drude-Lorentz model, silver nanoparticles, plasmon, pseudo-dielectric function, spectrophotometry, ellipsometry

In this study, we propose a method for creating a composite structure consisting of an array of vertical silicon nanowires (SiNWs) and silver nanoparticles (AgNPs). To obtain SiNWs, the process of two-stage metal-assisted chemical etching of c-Si was used, and to ob-tain a uniform distribution of AgNPs in the SiNW array over their entire height, the atomic layer deposition method was used. The structural and optical characteristics of the AgNPs/ SiNWs were studied by nondestructive spectroscopic ellipsometry and scanning electron mi-croscopy before and after the preparation of the composite structure. The thickness (from 2.7 to 7.8 nm) of AgNPs layers deposited on a c-Si substrate and their complex dielectric func-tions were determined within the framework of the Drude-Lorentz model, on which resonance peaks of localized and bulk plasmons are observed. For an array of SiNWs, using a multilayer model and the effective Bruggeman medium approximation, the height of sublayers and the Si fraction in them, as well as the Ag fraction in the Ag/SiNWs composite structure, are deter-mined. The c-Si:Ag composite structure has been characterized by comparing the calculation and experiment. The optical properties of Ag/SiNWs structures with complex spatial geometry are modeled using the COMSOL Multiphysics software package. The expected localization of the electric field is observed on the surface and near the AgNP as a result of the excitation of localized plasmon resonance. The calculated enhanced factor reached 1010, which suggests that composite AgNPs/SiNWs structure is promising to use as a substrate for surface-enhanced Raman scattering.

The optical properties of thin films and layers of Ag nanoparticles on a c-Si substrate are modeled by calculating the complex pseudo-dielectric function . The evolution of the imaginary part with an increase in the thickness of continuous layers from the dielectric function e of the substrate to e of bulk silver is studied, which demonstrates the appearance of optical characteristics of Ag and the suppression of c-Si features in the form of critical points. The data measured on the spectroscopic ellipsometer for Ag films produced by magnetron sputtering for several nominal thicknesses from 10 to 300 nm, and layers of Ag nanoparticles chemically deposited on a c-Si substrate, were interpreted using a pseudo-dielect ric function and by calculating the complex dielectric functions e using the Drude-Lorentz model. Morphological parameters obtained by atomic force microscopy and scanning electron microscopy were also used in the calculations. Since the Ag layers and films were deposited on the c-Si substrate without any additional layers (except for the native layer), the determined pseudo-dielectric functions for thicknesses in the range of 7-50 nm turned out to be close to the calculations of the dielectric functions using the Drude-Lorentz model. It was found that in the calculated and experimental spectra in the imaginary part of e2 and a peak appears at E -3.9 eV, which is interpreted as a plasmon resonance in the lon-gitudinal mode at oblique incidence of light. In the e2 spectrum of a layer of disordered Ag nanoparticles produced by chemical deposition, there is a broader localized surface plasmon resonance peak at E -2.5 eV, in contrast to thin films. Whereas, in a layer of larger nanoparticles, the peak is absent, and its e dependence is close to e for bulk Ag.

The reflectance spectra of Ag layers on a silicon substrate are interpreted using the approach based on the calculation of the reflectance Rcalc spectra of a thin film with variable thickness, which makes it possible to follow the effect of c-Si substrate critical points in the Brillouin zone and the formation of characteristics of bulk Ag at the edge of interband transitions. The calculated Rcalc spectra were compared with the experimental Rexp spectra of the Ag nanoparticle layers with different morphologies measured at the normal and oblique (45°) angle of incidence of light. For a layer consisting of coarser nanoparticles, one can observe a steep dip in the Rexp spectrum, which almost coincides with the edge of the interband transitions in bulk Ag in the UV range, and a broad dip in the Rexp spectrum with a minimum at λ = 382 nm, which demonstrates the maximum absorption of the localized plasmon resonance of Ag nanoparticles. For the samples consisting of finer particles, the dip of the interband transitions in the Rexp spectra is not observed at both angles of incidence, since the deposited Ag nanoparticles did not form a structure with the optical properties of bulk Ag, but the bulk plasmon resonance appeared at λ ~ 335 nm in the longitudinal mode at the oblique angle of incidence.

Silver nanoparticles have unique optical properties due to resonance effects that arise due to the presence of conduction electrons in them. When these electrons interacte with photons, they can create localization of electric fields at the interfaces with the environment. Silver nanoparticles deposited on a transparent substrate are often used for research, while Ag nanostructures on Si are studied in this work. They have great potential for practical applications. The interaction of light with nanostructures can be described using various models (pseudo-dielectric functions, effective medium, thin-layer structures, etc.) and optical methods for the experimental determination of their parameters (refractometry, spectrophotometry). Bulk plasmon resonance is considered in this work, which is excited when plasmons are excited at their resonant frequency by an external electromagnetic wave. Calculations were performed for different diameters of silver nanoparticles on a silicon substrate with different structure periods. The calculated spectra are in good agreement with the experimental data of the obtained samples. As a result of the plasmon resonance modeling, the position of the plasmon resonance depends on the density of the arrangement of silver nanoparticles, with an increase in the displacement resonance towards the long-wavelength region.

To interpret the spectra of reflectivity of Ag layers on a silicon substrate, an approach with the use of calculation of the reflection spectra Rcalc of a thin film with varying thickness are used, as a result of which the influence of the critical points of the c-Si substrate in the Brillouin zone and the formation of characteristics bulk Ag near the edge of interband transitions are studied. The Rcalc spectra were compared with experimental Rexp spectra of the Ag nanoparticles layers of various morphologies, measured at normal and oblique (45°) angles of incidence of light. For a layer with larger nanoparticles, the formation of a sharp dip in the Rexp spectrum, which practically coincides with the edge of the interband transitions of bulk Ag in UV range, is observed, as well as a wide dip in the Rexp spectrum with a minimum at λ = 382 nm demonstrates absorption maximum of localized plasmon resonance of Ag nanoparticles. For samples with less the size of particles, there is no dip due to the interband transitions in the Rexp spectra for both of incidence angles, since the deposited Ag nanoparticles did not form into a structure with the optical properties of bulk Ag, but the bulk plasmon resonance appeared at λ= 335 nm in the longitudinal mode at an oblique angle incident light.

The method of metal-assisted chemical etching for obtaining silicon nanowires, which consists of two stages, was studied. The conditions and modes for producing layers at both stages of the implemented technology are established, which include (1) chemical deposition of an array of self-organizing Ag nanoparticles on a Si substrate as a catalyst mask and (2) chemical etching of SiNWs to various depths from 110 to 1200 nm. The optical properties and morphology of a metal-catalyst (Ag) film were studied depending on the deposition time and solution concentration. Spectral ellipsometry was used to characterize the samples at all stages of MACE. Using the measured ellipsometric angles, the dielectric functions were determined, as well as the thicknesses and parameters of the fractions of composite layers in a multilayer model by approximating the effective Maxwell Garnett and Bruggeman medium for two-component layers. Samples with Ag nanoparticles with different morphologies were studied using reflection spectrophotometry in the wavelength range from 200 to 600 nm. The results showed that composite Ag-Si structures are promising for obtaining plasmon effects in both the visible and IR spectral regions.

This study consisting of two parts is concerned with the features of the three-stage process of the metal-assisted chemical etching (MACE) of silicon. This process is used to fabricate silicon nanostructures. In the first part of this work, a layer of self-assembled Ag nanoparticles chemically deposited from a solution on the surface of single-crystal silicon (c-Si) (MACE stage 1) was studied, and the second part includes of investigation of Si nanostructures formed in stages 2 and 3. By means of spectroscopic ellipsometry (in the range of wavelengths λ = 250–900 nm), the pseudodielectric functions of the nanostructures were determined and compared for all the three stages of the MACE process. In addition, for the Si nanostructures, the parameters of layers (the thickness and void fraction) were calculated in the context of the multilayer optical model, with the use of Bruggeman’s effective-medium approximation and fitting procedures.

AbstractThis study consisting of two parts is concerned with the features of the three-stage process of the metal-assisted chemical etching (MACE) of silicon. This process is used to fabricate silicon nanostructures. In the first part of this work, a layer of self-assembled Ag nanoparticles chemically deposited from a solution on the surface of single-crystal silicon (c-Si) (MACE stage 1) was studied, and the second part includes of investigation of Si nanostructures formed in stages 2 and 3. By means of spectroscopic ellipsometry (in the range of wavelengths λ = 250–900 nm), the pseudodielectric functions of the nanostructures were determined and compared for all the three stages of the MACE process. In addition, for the Si nanostructures, the parameters of layers (the thickness and void fraction) were calculated in the context of the multilayer optical model, with the use of Bruggeman’s effective-medium approximation and fitting procedures.

In this work it was shown the applicability of the spectroscopic ellipsometry technique for characterization of an optically inhomogeneous polymer film with silver NPs. The histogram of silver NPs distribution based on SEM images shows the largest number of NPs have a size in the range 15-35 nm and the filling factor as large as 6%. By using the possibilities of ellipsometry it was suggested a 3-layer inhomogeneous structure with different sizes of silver NPs covered by thin polyamide-6 film. Also existence of localized plasmon resonance in such NPs was observed by optical absorption measurements.

In this work, the optical constant films of amorphous hydrogenated carbon (a-C: H) and a hybrid structure based on it with a granulated gold film before and after their annealing at 300 °C were studied by spectral ellipsometry. The dispersions n (λ) and k (λ) of the a-C:H film were established using the Cauchy approximation and its thickness. The spectral features of the Au plasmon nanoparticle layer deposited on the a-C:H surface were modeled as an effective medium and a Lorentz oscillator. The parameters of the films and their thickness were determined by fitting the calculated spectra to the ellipsometric spectra  (λ) and  (λ). The obtained data were used to determine the parameters of the Lorentz oscillator in the model of a-C:H / Au two-layer structure. As a result of the a-C:H / Au structure annealing, the intensity of the maxima in the spectra n and k increased, their position shifted to the blue region, and the half-width of the bands decreased. The observed changes in the ellipsometric spectra are completely consistent with the spectrophotometric data of this structure.

In this work, the preparation of c-Si nanowires was investigated using a two-stage metal-assisted chemical etching process. For characterization of structures at all stages of the process, spectroscopic ellipsometry was used and two approaches were used: a) determining and analysing the complex pseudo-dielectric function ε and b) determining parameters of simulated multilayer structures using the effective medium approximation. Taking into account the structure parameters measured from SEM images the spectra of ψ and Δ were calculated and fitted to the experimental ones to obtain best convergence. The study of metal-assisted chemical etching process the Si process is intended for the development of silicon technology for obtaining structures of various topology (morphology) with functional components and creating on their basis sensory elements for bio and chemical reagents, taking into account the possibility of integration with micro and nanodevices on the chip.

Optical сonstants of an amorphous hydrogenated carbon (a-C:H) film and its hybrid structure with granular gold film before and after annealing at 300°C have been investigated by spectral ellipsometry. Dispersions n(λ) and k(λ) of the a-C:H film and its thickness have been identified using the Cauchy approximation. The spectral features of the layer of Au plasmon nanoparticles deposited on the a-C:H surface have been modeled in the form of an effective medium and Lorentz oscillator. The parameters of the films and their thickness have been determined by fitting the calculated spectra to the ψ(λ) and Δ(λ) ellipsometric spectra. The obtained data have been used to determine the Lorentz oscillator parameters in the model of an a‑C:H/Au two-layer structure. The intensity of the maxima in the n and k spectra increased, their position shifted to the blue region, and the half-width of the bands decreased as a result of the a-C:H/Au structure annealing. The observed changes in ellipsometric spectra are fully consistent with the spectrophotometric data of this structure.

It is established that the magnetron sputtered thin PbZr54Ti46O3 (PZT) films contain a certain amount of pores, which makes it impossible to investigate their properties by traditional methods. It is shown that the boundaries of polycrystalline blocks in PZT films have an increased values of appearing transient currents associated with grain boundaries traps recharging. It is also found that the values of transient currents differ for oppositely polarized domains in the PZT films. The thickness of studied films was determined by the ellipsometry method as well as the dielectric function epsilon in the energy range E = 1.4-5 eV.

In this two-part work, nanostructures formed in a three-step process of metal-assisted chemical etching of silicon are investigated. In the first part (present publication), the process of the chemical deposition of a layer of self-assembled silver nanoparticles on the surface of a silicon wafer (the first stage of metalassisted chemical etching) is studied. This layer, on the one hand, serves as a catalyst for the subsequent etching of silicon, and, on the other hand, represents a kind of mask for the formation of a certain topology of the emerging Si nanowires. The morphology of the obtained 40- to 60-nm-thick silver nanoparticle layers is investigated by scanning electron microscopy. The spectral dependences of the ellipsometric angles Ψ and Δ are measured using spectroscopic ellipsometry (λ = 250–900nm), and the complex dielectric function of the silver nanolayers is determined from these spectra. The dielectric function features a characteristic plasmon resonance peak in the ultraviolet spectral range. The study of the optical properties of Si nanofilament layers which form during the early stages of metal-assisted chemical etching will be reported as the second part of this work in a separate publication.

The formation of the dielectric function c of Ag nanolayers on the silicon surface has been studied and spectral features associated with the surface plasmon resonance (SPR) have been revealed. The real cl and imaginary c2 functions, ellipsometric angles, and polarization reflection spectra Rp and Rs were calculated using the basic equation of ellipsometry, Fresnel formulas, transfer -matrix method, and Lorentz oscillator model. The Bruggeman and Maxwell -Garnett effective -medium approximation was used for the composite layer (Ag-air).

In this study, we obtained c-Si arrays by the method of metal-assisted chemical etching (MACE), which includes 3 stages, among which two are the main ones: (1) formation of a catalyst-mask from a layer of Ag nanoparticles and (2) chemical etching in which voids appear under Ag particles and nanowires are formed from the unetched part of the c-Si surface. In all the three stages, the properties of the structures were examined by scanning electron and atomic-force microscopy and also by multiple-angle spectroscopic ellipsometry.

AbstractIn this two-part work, nanostructures formed in a three-step process of metal-assisted chemical etching of silicon are investigated. In the first part (present publication), the process of the chemical deposition of a layer of self-assembled silver nanoparticles on the surface of a silicon wafer (the first stage of metalassisted chemical etching) is studied. This layer, on the one hand, serves as a catalyst for the subsequent etching of silicon, and, on the other hand, represents a kind of mask for the formation of a certain topology of the emerging Si nanowires. The morphology of the obtained 40- to 60-nm-thick silver nanoparticle layers is investigated by scanning electron microscopy. The spectral dependences of the ellipsometric angles Ψ and Δ are measured using spectroscopic ellipsometry (λ = 250–900nm), and the complex dielectric function of the silver nanolayers is determined from these spectra. The dielectric function features a characteristic plasmon resonance peak in the ultraviolet spectral range. The study of the optical properties of Si nanofilament layers which form during the early stages of metal-assisted chemical etching will be reported as the second part of this work in a separate publication.

The theoretical and experimental investigations of photonic band gaps in one-dimensional photonic crystals created by micromatchining silicon, which have been performed by the author as part of his doctoral dissertation, are presented. The most important result of the work is the development of a method of modeling photonic crystals based on photonic band gap maps plotted in structure–property coordinates, which can be used with any optical materials and in any region of electromagnetic radiation, and also for nonperiodic structures. This method made it possible to realize the targeted control of the optical contrast of photonic crystals and to predict the optical properties of optical heterostructures and three-component and composite photonic crystals. The theoretical findings were experimentally implemented using methods of micromatchining silicon, which can be incorporated into modern technological lines for the production of microchips. In the IR spectra of a designed and a fabricated optical heterostructure (a composite photonic crystal), extended bands with high reflectivities were obtained. In a Si-based three-component photonic crystal, broad transmission bands and photonic band gaps in the middle IR region have been predicted and experimentally demonstrated for the first time. Si–liquid crystal periodic structures with electric-field tunable photonic band-gap edges have been investigated. The one-dimensional photonic crystals developed based on micromatchining silicon can serve as a basis for creating components of optical processors, as well as highly sensitive chemical and biological sensors in a wide region of the IR spectrum (from 1 to 20 μm) for lab-on-a-chip applications.

We investigate the feasibility of using laser deposition to produce Pt and lead zirconate titanate layers. Optical microscopy, electron microscopy, and atomic-force microscopy of the lead zirconate titanate layer reveal surface roughness on these layers. The optical parameters of the resulting layers were studied by spectral ellipsometry, including the dispersion in the index of refraction and absorption coefficient of the Pt and lead zirconate titanate surface layer. X-ray crystallography indicates that the lead zirconate titanate layer produced has the classical (111) perovskite crystallographic orientation. Similar heterostructures are used as ferroelectric memory elements.