Effective optical constants and effective optical properties of ultrathin trilayer structures

This work presents an extension of the characteristic effective medium approximation (CEMA) to ultrathin trilayer systems. The extension has been carried out analytically and is supported by corresponding calculations of the effective optical constants of Cu-Au-Cu and Ag-SiO-Ag trilayer systems using the CEMA approximation. This work is in essence a generalization of the characteristic effective medium approximation introduced earlier for ultrathin bilayer structures. This method is used to derive the effective optical constants of a trilayer system, consisting of three thin layers with each constituent layer of thickness much less than the wavelength of the incident radiation. Within this regime a trilayer system is viewed as one effective layer referred to as an effective stack (ES) with well defined effective optical constants, which can be used to calculate the optical properties of the trilayer stack within a specified wavelength range. The CEMA based calculations of the effective optical constants are applied to two trilayer systems with a total of five stacks. Three are Cu-Au-Cu and two are Ag-SiO-Ag stacks. The thicknesses of the parent layers in the Cu-Au-Cu stack range from 3 to 30 nm for Cu and 4 to 40 nm for Au; in the Ag-SiO-Ag stack the constituent layers are 6 nm for Ag, but range from 5 to 10 nm for SiO. This study is for normal or near normal incidence spectroscopy in a wavelength range that extends from visible to near infrared. The agreement between CEMA based ES stack results and those of the standard CMT technique is very satisfactory.     

Optical characteristics of nickel and boron carbonitride films in Si(100)/Ni/BC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> structures

The optical characteristics of nickel films deposited on Si(100) substrates by vacuum thermal evaporation have been studied. The thickness and optical constants of the films are determined using monochromatic zero ellipsometry, while the inverse problems are solved within the three-layer optical model of the samples. It is shown that thermal annealing leads to a change in the optical constants of nickel films in the heating-temperature range of 500–900°C. Boron carbonitride layers deposited on silicon substrates with a nickel sublayer are analyzed within multilayer optical models, which make it possible to determine the refractive index and absorption coefficient distributions along the thickness of the synthesized Si(100)/Ni/BC _x N _y structure.     

Ellipsometric studies of annealing of SiO2 layers during the formation of light-emitting Si nanocrystals in them

Annealing of SiO₂ layers with excessive Si leading to the formation of silicon nanocrystals capable of fluorescing in the visible region owing to quantum-dimensional limitations is studied by the ellipsometry method. Excessive Si was introduced in SiO₂ layers by ion implantation with an energy of 25 keV and a dose of 5× 10¹⁶ cm^?2. Isochronous (10³ s) annealings were carried out in a temperature interval of 200–1150°C with a step of 100°C. An LÉF-2 ellipsometer with a 70° angle of incidence at a wavelength of 632.8 nm was used for the measurements. Fluorescence excited by a nitrogen laser was monitored concurrently. It is found that variations in optical constants of the layers at each step of annealing over the entire temperature range studied are clearly detected by ellipsometry. Variations in optical parameters of excessive Si are calculated in the Bruggeman approximation. They are found to correspond to individual stages of the formation of nanoprecipitates revealed earlier by other techniques. Nanocrystals proper producing intense visible photoluminescence are formed at annealing temperatures of 1000°C and higher.     

Optical constants of nanostructured layers of copper,nickel, palladium,and some oxides in the UV and visible spectral regions

It is found that a significant spread in the optical constants of metals reported by different authors is caused by differences in the sample preparation methods, measurement conditions, and methods of calculation of sought parameters, as well as by the oxidation effect. It is shown that the optical constants of metals in films 80–120 nm thick on silicon substrates with scattering below 10⁻⁴ are determined with minimal errors. The reflectance of these mirrors calculated from the optical constants found by the most accurate ellipsometric method coincides with the experimental value within the measurement accuracy. Low values of k(λ) obtained for thin layers in some works using the methods based on the measurement of the coherent transmittance and regular reflectance are explained by disregarded scattering and luminescence. The spectra of the imaginary part of the complex refractive index of copper, nickel, and copper oxide determined by us by the proposed methods for thin nanostructured layers taking into account the scattering and luminescence coincide with the most correct data for thick films in the spectral range of 325–633 nm. For thin palladium and palladium oxide layers, the variations in k(λ) are caused by the oxidation of metal granules and disregarded luminescence for thick oxide layers in the long-wavelength spectral region. The maximal difference in the imaginary part of the complex refractive index of copper and nickel for thin nanostructured layers are observed in the region of plasmon resonances, whose positions and amplitudes depend on the degree of asphericity, the shape, and the degree of order of particles and their aggregates, which shift the plasmon resonances of films to longer wavelengths with respect to spherical particles.     

Optical and magneto-optical properties of MBE grown Co/Au multilayers

The optical and magneto-optical properties of Co/Au multilayers, grown by molecular beam epitaxy (MBE), have been examined in the wavelength range 300 to 900 nm using ellipsometry and normal incidence Kerr polarimetry. The dispersion of fundamental optical and magneto-optical constants and the complex Kerr rotation are discussed in terms of the interaction of electromagnetic radiation with a multilayered structure. This is done on the basis of a single equivalent layer approach for dealing with multilayered media using values for the optical constants of cobalt and gold measured on single films of these materials grown by MBE. It is suggested that a restriction of the mean free path of the conduction electrons in the gold layers, of the order of the individual sub-layer thickness, accounts for some aspects of the observed optical spectra.     

Incidence angle dependence on structural and optical properties of UHV deposited copper nano layers

Copper nano-layers with different incident angles as vertical, 20 and 30 degrees, same 73.3 nm thicknesses, and same deposition rate, were deposited on glass substrates, at 373K temperature, under UHV conditions. Their nano-structures were determined by AFM and XRD methods. Their optical properties were measured by spectrophotometry in the spectral range of 300–1100 nm. Kramers–Kronig relations were used for the analysis of the reflectivity curves of Cu films to obtain the optical constants of the nano layers. Different incident angles show important effects on both structural and optical properties. The effective medium approximation was employed to establish the relation between structure zone model (SZM) and EMA predictions. By increasing incidence angle the separation of metallic grains increases, hence the volume fraction of voids increases. That is in agreement with AFM analysis. The predictions of Drude free-electron theory are compared with experimental results for dielectric functions of these nano layers. There is a good agreement between our optical results and Hangman's optical results for a bulk standard Cu sample.     

极薄银膜光学常数的研究

本文利用衰减全反射(ATR)法对磁控溅射和热蒸发制备的极薄Ag膜的光学常数和光学特性进行了研究和比较,得到了光学常数和光吸收随膜厚的变化规律.     

Spectroscopic ellipsometric characterization of TiAlN/TiAlON/Si3N4 tandem absorber for solar selective applications

Sputter deposited TiAlN/TiAlON/Si₃N₄ tandem absorber has been characterized by spectroscopic ellipsometry in the wavelength range of 450-1200 nm. Each layer of the tandem absorber viz., TiAlN, TiAlON and Si₃N₄ has been deposited separately on copper substrate (Cu) and ellipsometric measurements have been carried out on each of these layers. The measured ellipsometric spectra were fitted with theoretically simulated spectra and the sample structure and wavelength dispersion of optical constants of each layers have been determined. The ellipsometric measurements have also been carried out on the three-layer tandem absorber deposited on Cu substrate. By analyzing the ellipsometric data, depth profiling of the tandem absorber has been carried out using the derived optical constants of the individual layers.     

Optical and magneto-optical properties of Co–SiO<Subscript>x</Subscript> thin films

The optical and magneto-optical properties of hybrid Co–SiO_x systems are studied as a function of Co concentration. The structures were prepared by alternate depositions of SiO_x thin films and layers of 10-nm-diameter Co nanoparticles produced by an Ion Cluster Source. Both optical and magneto-optical constants of the system gradually increase with the amount of Co, though maintaining low optical absorption values in the visible range. The experimental results are well reproduced assuming that the nanoparticles have a cobalt core (7–8 nm in diameter) surrounded by a cobalt oxide shell (1–2 nm thick). The magneto-optical activity versus optical absorption figure of merit of this system is compared with other magneto-optical dielectric systems.     

Effect of nano-metric changes on morphology and optical constants of TiO2 thin films

Titanium dioxide films of different thicknesses, ranging from 10 to 110 nm were deposited on glass substrate, at room temperature by physical vapor deposition method. Topography, roughness and crystallography of produced layers were determined by AFM and XRD methods respectively. Optical properties were measured by transmission spectroscopy in the spectral range of 300–1100 nm wave length range. The optical constants were obtained using Kramers-Kronig analysis of the reflectivity curves. It was found that film thickness plays an important role on the nanostructures as well as optical properties of layers and cause significant variations in behavior of thin titanium oxide films.     

Optical characterization of porous silicon films and multilayer filters

Porous silicon (PS) has a great potential in optical applications due to the tunability of its refractive index. However, the electrochemical formation parameters of porous silicon have a great influence both on porosity and pore morphology and, hence, on the optical properties of the PS layers. In the present work, the optical constants of PS layers are determined in the visible-wavelength range for different electrolyte compositions and for a wide range of formation-current densities. Thus, the interval of refractive indices that can be achieved for each electrolyte composition is studied, for the further development of interference filters. In particular, it is demonstrated that a higher ethanol concentration in the electrolyte leads to a considerably higher tunability of the refractive index of PS while reducing absorption losses. In addition, the performance of PS-based multilayer interference filters is shown to improve when formed with an electrolyte of higher ethanol concentration, especially in the blue region of the visible spectrum. PACS 78.20.Ci; 78.40.-q; 78.55.Mb     

Optical constants of nanosized films of metal titanium

A new ellipsometric technique for optical measurements of the refraction and extinction indices and thickness of nanosized metal-titanium films in air is proposed and implemented. It is shown that the determination of optical constants of titanium films by measuring the ellipsometric parameters Ψ and Δ for a light beam incident upon the metal/substrate interface through the substrate of fused silica allows one to obtain optical constants of the metal, which correlate well with the results of the most reliable measurements performed in vacuum chambers. In this case, one can additionally determine the thickness and refractive index of the natural oxide film on the titanium surface. The obtained values of the optical constants of titanium, n ₂ = 3.42 ± 0.05 and k ₂ = 3.75 ± 0.05 (λ = 632.8 nm), agree well with the results of the measurements made in vacuum. The proposed technique makes it possible to measure the thicknesses of titanium films within the range 7–30 nm with an accuracy of 0.7 nm. The technique is tested on titanium films deposited onto fused silica substrates obtained by vacuum thermal evaporation. The possible error of determining the thickness due to various additional factors is estimated. The results of ellipsometric measurements of the thickness are compared with the data obtained from parallel measurements of electric resistance of the films.     

基于1stOpt求解光学玻璃折射率温度系数经验公式常量的方法

为了解决ZEMAX软件拟合计算折射率温度系数经验公式常量时,参量回归计算的折射率和折射率温度系数与实验值存在较大偏差的问题,用1stOpt差分进化法求解折射率温度系数经验公式常量.以氟冕D-FK61和特种火石H-TF3A光学玻璃为例,用该方法求解的λtk常量与其通用数值范围0.08~0.33相吻合,参量回归计算的折射率和折射率温度系数与实测值的偏差分别小于1×10~(-5)、2×10~(-7)/℃.该方法作为ZEMAX软件计算光学玻璃折射率温度系数的有效补充,计算的准确性高,可为热补偿光学系统设计提供准确的光学参量保障.     

Influence of surface topography and annealing temperature on the surface and volume of dissipation electrical energy and Spitzer–Fan model in Al doped ZnO films

The aim of this work is to investigate the optical constants of aluminum doped zinc oxide films annealed at different temperatures. With increasing temperature, due to decreasing unfilled inter-granular volume per unit thickness, the optical transmittance spectra of films were increased. The films have a normal dispersion in the spectral range 400?<?λ?<?500 nm and the anomalous dispersion in IR range. The lattice dielectric constants ε_L, the free charge carriers concentration, the plasma frequency, Spitzer–Fan model and the waste of electrical energy as heat of films can be analyzed using the refractive index n and the extinction coefficient k spectra. With increasing annealing temperature, the lattice dielectric constants ε_L of films decrease however the free charge carriers concentration of films increase. The free carrier electric susceptibility of films annealed at 600 °C has maximum value. The energy loss by the free charge carriers when traversing the bulk and surface of films annealed at 600 °C has a minimum value in the near fundamental absorption edge and it with increasing energy increases.     

Effect of particles size on the optical constants of iron/polystyrene composites via UV-radiation

The present study deals with the optical characteristics of polystyrene (PS) composites containing iron particles of different sizes: 5, 40, 110, and 250 μm. The optical absorption spectra were collected in the wavelength range 300–800 nm using a UV-spectrophotometer. The optical results obtained were analyzed in terms of the absorption formula for non-crystalline materials. The optical energy gap and other basic optical constants such as refractive index, dielectric constants, and optical conductivity were investigated and showed a clear dependence on the iron particles size. It was found that the optical energy gap for the iron-filled composites is less than that for the neat PS, and it decreases as the iron particle size decreases. The refractive index of the prepared composites was determined from the collected transmittance and reflectance spectra. It was found that the calculated dielectric constant and refractive index of the composites increase when the iron particles size decreases. The optical dispersion behavior of the composites was described by the single-oscillator model. Enhancement in the optical conductivity was observed with decreasing the iron particles size.     

Über die Temperaturabhängigkeit optischer Eigenschaften kleiner Silberteilchen

The influence of low temperature on the spectral light absorption of small silver particles has been investigated in the spectral range between 3500 and 4500 Å. Measurements of the absorption coefficient were taken at 293, 77, and 4.2 K. For this purpose a method was developed to obtain silver particles (mean diameter between 20 and 300 Å) inside a matrix of polymethylmethacrylate. This highpolymer allowed measurements of optical transmission at low temperatures and the exact determination of form and size distribution of the inbedded particles by electron microscopy. Using the Kramers-Kronig-analysis modified by Kreibig the optical constants were obtained. The results show relatively good agreement with constants calculated for the Drude free electron gas taking into account temperature dependend electron collision frequency.     

Optical constants of single-crystal GeS in the photon energy range 0.04–4 eV

The optical constants of crystalline GeS have been determined in the range from just beyond reststrahlbands to 4 eV for two light polarizations lying in the plane of crystal layers. The electronic parts of the principal components of the dielectric tensor are evaluated and discussed from the viewpoint of interband transitions (anisotropy) and index-of-refraction family of sum rules and related spectroscopic theory of the chemical bond.     

Effect of indium incorporation on the optical properties of spray pyrolyzed Cd0.22Zn0.78S thin films

In this study, effect of indium incorporation on the optical properties is investigated for the spray pyrolyzed onto glass substrates at 275°C substrate temperature undoped and indium doped Cd_0.22Zn_0.78S thin films. The average optical transmittance of all the films was over 77% in the wavelength range between 450 and 800 nm. The optical band gap energies of the thin films have been investigated by the measurement of the optical absorbance as a function of wavelength. The optical absorption studies reveal that the transitions are direct band gaps of 3.02 and 3.05 eV for undoped and doped indium Cd_0.22Zn_0.78S thin films, respectively. The Urbach tail parameter and optical constants such as refractive index, extinction coefficient, and dielectric constants were calculated for these films. The dispersion parameters such as single-oscillator energy and dispersive energy were discussed in terms oft he single-oscillator Wemple—DiDomenico model.     

纳米纤锌矿氮化硼的同步辐射真空紫外反射光谱与光学性质

对冲击波法合成的纳米纤锌矿氮化硼（ｗＢＮ）进行了同步辐射真空紫外区的反射光谱测量，得到波长范围１００一２４０ｎｍ区间的反射光谱．利用Ｋｒａｍｅｒｓ－Ｋｒｏｎｉｇ关系计算获得了它的光学常数和介电函数谱，并导出了光电导谱．获得了纳米ｗＢＮ的光学禁带宽度实验值，为８．７±０．５ｅＶ．将以上结果和最新的理论计算进行了比较．观察到了经不同退火温度处理的纳米ｗＢＮ样品结构及尺寸变化对反射光谱和光学性质的影响． 关键词：