Ellipsometric Parameters Research Articles

X-ray analysis and optical properties of nickel oxide thin films

Nanoparticles of NiO were prepared by a homogeneous precipitation method with an aqueous solution of nickel nitrate hexahydrate and citric acid. The microstructure and surface morphology of NiO powder were characterized by thermogravimetric (TGA) analysis, differential scanning calorimeter (DSC), X-ray diffraction (XRD), and infrared (IR) spectroscopy. Different thicknesses of nickel oxide (NiO) thin films were deposited onto highly cleaned glass substrates by the electron beam technique. Their structural characteristics were studied by X-ray diffraction (XRD) and scan electron microscope (SEM). The XRD investigation shows that NiO films are polycrystalline with an cubic type structure. The microstructure parameters, e.g., crystallite size and microstrain were calculated. The optical constants (n, k) and film thicknesses of NiO thin films were obtained by fitting the ellipsometric parameters (ψ and Δ) data using three layer model systems in the wavelength range 300–1100nm. It is found that the refractive index, n increases with the increase of the film thickness. The possible optical transition in these films is found to be allowed direct transitions. The direct energy gaps increase with increasing of the film thickness.

The preparation and characterization of nanoparticle Ag–SiO2 composite films with super low refractive index

The spin coating technique is used to prepare the porous Ag–SiO2 composite films, and the subsequent annealing process makes the nanoparticle Ag–SiO2 composite films formed. As the increase of the annealing temperature from 300°C to 500°C, the size of Ag–SiO2 composite nanoparticles gradually decreases. The SEM, TEM and XRD measurements of Ag–SiO2 composite films indicate that the single crystal metal nanoparticles are uniformly embedded into the SiO2 particles, forming Ag–SiO2 composite nanoparticles. The SPR absorption spectra of the Ag–SiO2 composite films show the content of metal Ag increases with the increase of annealing temperature, but when the annealing temperature increases to 500°C, the SPR absorption is not observed on the absorption spectra although the total absorption of Ag–SiO2 composite films is enhanced. Furthermore, the optical constants of Ag–SiO2 composite films have been determined based on the measurement of ellipsometric parameters. It is more important the refractive index lower than 1 is obtained after annealing process of Ag–SiO2 composite films under 300 and 400°C, but the extinction coefficient is low, which makes the film have low absorption.

Applied research on the physical model for calculating optical constant of metal oxide films

In the present paper, two metal oxide films of HfO2 and Ta2 O5 were prepared by ion beam sputtering technology. Through measuring ellipsometric parameters of HfO2 and Ta2O5 films, their optical constants can be inversion-calculated by nonlinear least squares techniques. In the fitting process, eight experiment groups were arranged by the orthogonal table L8 (2(7)). After selecting Cauchy model, the largest influencing factor for fitting optical constant of HfO2 is surface layer model and the largest influencing factor for fitting optical constant of Ta2 O5 is refractive index gradient model. The impact of different physical model on MSE and the order for selecting model in the fitting process are determined. According to the selecting model and the determined fitting order, optical constants of the two metal oxide films were inversion-calculated with adding weak absorption model, and the obtained MSE can descend 79% and 39% according to the initial value. The results indicated that the selecting model possesses definite physical significance in the fitting process. The obtained method can be applied in inversion-calculating many metal oxide films with weak absorption. It has wide application value. At 500 nm, the refractive index gradient of Ta2O5 films is greater than HfO2 films, while the extinction coefficient of HfO2 films is greater than Ta2O5. It was shown that Hf metal is easier to form stable oxide than Ta metal. And the absorption of HfO2 films is larger than Ta2O5 films.

Ellipsometric technique for determining in situ the absorption coefficient of semiconducting nanolayers

An algorithm that makes it possible to solve the inverse problem of ellipsometry aimed at determining the absorption coefficient on the basis of a single-zone ellipsometric experiment during the growth of thin semiconducting films is developed and implemented. The technique is based on analysis of the variation of ellipsometric parameters Ψ and Δ directly during the growth. The algorithm is tested in synthesis of Si/SiO2/Si(100) and Hg1 − xCdxTe structures.

Dielectric multilayer beam splitter with differential phase shift on transmission and reflection for division-of-amplitude photopolarimeter.

Dielectric multilayer beam splitter with differential phase shift on transmission and reflection for division-of-amplitude photopolarimeter (DOAP) was presented for the first time to our knowledge. The optimal parameters for the beam splitter are Tp = 78.9%, Ts = 21.1% and Δr - Δt = π/2 at 532nm at an angle of incidence of 45°. Multilayer anti-reflection coating with low phase shift was applied to reduce the backside reflection. Different design strategies that can achieve all optimal targets at the wavelength were tested. Two design methods were presented to optimize the differential phase shift. The samples were prepared by ion beam sputtering (IBS). The experimental results show good agreement with those of the design. The ellipsometric parameters of samples were measured in reflection (ψr, Δr) = (26.5°, 135.1°) and (28.2°, 133.5°), as well as in transmission (ψt, Δt) = (62.5°, 46.1°) and (63.5°, 46°) at 532.6nm. The normalized determinant of instrument matrix to evaluate the performance of samples is respectively 0.998 and 0.991 at 532.6nm.

Multiple oscillator models for the optical constants of polycrystalline zinc oxide thin films over a wide wavelength range

Zinc oxide (ZnO) films were prepared on Si(1 1 1) and quartz substrates using RF-magnetron sputtering in N2 plasma at room temperature. From the X-ray diffraction observations, it was found that all films are polycrystalline with a preferred orientation of (1 0 1). X ray photoelectron spectroscopy was used to analyze the chemical composition of the films by observing the behavior of the Zn2p3, O1s, N1s, and C1s lines. The thicknesses and optical constants of the ZnO thin films were determined using variable angle spectroscopic ellipsometry through the Genosc™ Herzinger–Johs parameterized semiconductor oscillator functions and multiple Gaussian oscillator models. Combining multiple oscillator types provided a very flexible approach to fitting optical constants over a wavelength range 190–1400 nm while simultaneously enforcing Kramers–Kronig consistency in the fitted ellipsometric parameters. Refractive indices of the films were determined to be in the range 1.68–1.93 and extinction coefficients in the range 4.56 × 10−6–0.23. A direct bandgap of 3.38 ± 0.03 eV was calculated from the extinction coefficient. Low temperature photoluminescence studies of the films exhibited one prominent peak at 3.41 eV. The equality of the ZnO thin films was obtained through the depolarization measurements.

Vacuum ultraviolet ellipsometer using inclined detector as analyzer to measure stokes parameters and optical constants — With results for AlN optical constants

Principle and analysis for ellipsometers usable in the vacuum ultraviolet (VUV) region up to about 25eV, which are consisting of a sample mirror and an inclined photodiode, are described. Our ellipsometer has two degrees of freedom in rotation; the main chamber can rotate around the axis of incidence and, the analyzer unit can also rotate around the axis of reflection. All the unknown parameters (Stokes parameters of the source, ellipsometric parameters of the sample and the polarization sensitivity of the inclined detector) are obtained by rotating the main chamber and analyzer independently and solving the simultaneous equations with the measurands. Measurement results on polarization characteristics of photodiodes, Stokes parameters of the beam emerging from a synchrotron radiation beamline, and optical constants of AlN film are given. It is concluded that the ellipsometer is advantageous in the simplicity and worked as intended.

Correction of large birefringent effect of windows for in situ ellipsometry measurements

To extract true optical properties of samples in a chamber with entrance and exit optical windows, oftentimes the windows were approximated as simple retarders where the retardation was small and premeasured under a given condition. The proposed method allows to cope with large birefringent effect of chamber windows thanks to its capability of extracting ellipsometric parameters (Δ, Ψ) of isotropic samples as well as measuring birefringent parameters (δ, θ) of each window separately and simultaneously. This method is, however, not valid for anisotropic samples. Ex situ results and extracted ellipsometric parameters results from in situ measurements of a silicon substrate and a SiO2 film thermally grown on the silicon substrate exhibited excellent agreement and provided significance of this method.

In situ observation of Pt deposition process by using spectroscopic ellipsometry

Supercritical fluid chemical deposition is a technique for depositing films and particles in a supercritical medium. In this article, Pt thin films were grown from the supercritical CO2 that dissolves Pt(hfac)2 and H2, and the temperature dependence was studied using in situ ellipsometry. The temperature needed to form a continuous film was determined from the change of ellipsometric parameters. The determined temperature, about 70°C, was lower than the reported values.

Nonlinear magneto-optic ellipsometry

The ellipsometric parameters for light reflection from a dielectric film with Kerr optical nonlinearity on a bigyrotropic magneto-electric film are theoretically investigated. The combined contributions of cubic optical nonlinearity and magneto-electric coupling allow us to control the ellipsometric parameters and thus, for example, the Kerr rotation with the incoming light intensity, in particular at incidence angles close to the pseudo-Brewster angle.

Optical properties of aluminum-doped zinc oxide films deposited by direct-current pulse magnetron reactive sputtering

A series of 〈103〉-oriented aluminum-doped zinc oxide (AZO) films were deposited on glass substrates via direct-current pulse magnetron reactive sputtering at different O2-to-Ar gas flow ratios (GFRs). The optical properties of the films were characterized using the fitted optical constants in the general oscillator model (which contains two Psemi-Tri oscillators) through the use of measured ellipsometric parameters. The refractive index dispersion data below the interband absorption edge were analyzed using a single-oscillator model. The fitted optical energy gap obtained using the single-oscillator model clearly shows a blue shift, followed by a red shift, as the GFR increases from 0.9/18 to 2.1/18. This shift can be attributed to the change in the free electron concentration of the film, which is closely related to the film stress. In addition, the fitted β value indicates that the AZO film falls under the ionic class. The photoluminescence spectrum indicates a photoluminescence mechanism of the direct and wide energy gap semiconductor.

Spectroscopic ellipsometry study of the Zn3N2 films prepared by radio-frequency sputtering

Zinc nitride (Zn3N2) thin films were deposited on glass substrates by reactive radio-frequency magnetron sputtering from a pure Zn target in nitrogen-argon ambient. X-ray diffraction analysis indicates that the films just after the deposition are polycrystalline with a preferred orientation of (400). With increasing substrate temperature, the grain size in zinc nitride film increases from 26.5 nm (100 ℃) to 33.6 nm (200 ℃), and then decreases to 17.8 nm (300℃). Atomic force microscopy reveals that the film surface morphology is dependent on the substrate temperature. With reflective spectroscopic ellipsometry, the ellipsometric parameters ψ and Δ of Zn3N2 films are measured. Then, a new model for Zn3N2 films is built. With the Tauc-Lorentz dispersion formula, the ellipsometric data are fitted, and both the thickness and optical constants (refractive index and extinction coefficient) of the films are obtained at a wavelength of 430–850 nm. The optical band gap is calculated from the extinction coefficient by using the Tauc formula, and a direct band gap of 1.73–1.79 eV is obtained.

Ellipsometry data analysis and ellipsometric spectra of complex materials

Optical and structural properties of materials can be characterized by spectroscopic ellipsometry which represents an experimental technique that measures polarized light reflected from a material surface. Since the most complicated part of this method is data analysis and modeling, we present the calculation of the ellipsometric parameters for bi-isotropic materials. We consider the ellipsometric model for these materials which require not just permittivity like in conventional model, but also magnetic permeability and magneto electric coupling.

Surface plasmon resonance combined with spectroscopic ellipsometry read-out for probing surface–biomolecule interaction

Spectroscopic ellipsometry combined with localized surface plasmon resonance (LSPR) of gold nanoparticles (Au NPs) is exploited to design label-free bionsensors. We demonstrate that the size of Au NPs significantly affects the sensitivity of the ellipsometry analysis. Additionally, functionalizing Au NPs of different sizes with molecules/proteins of different sizes and shapes, such as dodecanethiol, hemin, human albumin and its antibody, we show that the size of nanoparticles can strongly influence the binding activity of adsorbed proteins and, consequently, the sensor functioning. Specifically, Au NPs with a diameter in the range 30–50nm exhibit higher sensitivity to the change in the optical properties, and the variations of the ellipsometric parameter Ψ allow discerning phenomena of aggregation of Au NPs of the sensor, of detachment of Au NPs and of protein chemisorption on Au NPs. The data are discussed in terms of two main factors affecting the ellipsometry sensitivity, i.e., the dependence of the LSPR electromagnetic enhancement on the Au NP size, and the strength of the interaction of the functionalizing molecule with Au NPs.

Anisotropic plasmonic Cu nanoparticles in sol-gel oxide nanopillars studied by spectroscopic Mueller matrix ellipsometry

Broadened plasmon resonances of Cu nanoparticles in nanopatterned mixed oxide sol-gel nanopillars are shown to be readily detected by spectroscopic Mueller matrix ellipsometry. The plasmonic nanomaterials are obtained by low energy ion sputtering of a CuO sol-gel film. Both s- and p-polarized plasmon resonances are observed in the off-block-diagonal and the block-diagonal Mueller matrix elements as well as in the generalized ellipsometric parameters. The resonant features in all elements correlate with both maximum depolarization and a minimum in the reflected intensity. The spectral position and the polarization character of the plasmon resonances are discussed phenomenologically through effective medium theory.

Rotating polarizer, compensator, and analyzer ellipsometry

In this paper we propose theoretically a set of ellipsometric configurations using a rotating polarizer, compensator, and analyzer at a speed ratio of N1ω:N2ω:N3ω. Different ellipsometric configurations can be obtained by giving different integral values to N1, N2, and N3. All configurations are applied to bulk c-Si and GaAs to calculate the real and imaginary parts of the refractive index of the samples. The accuracies of all ellipsometric configurations are investigated in the presence of a hypothetical noise and with small misalignments of the optical elements. Moreover, the uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients are studied. The comparison among different configurations reveals that the rotating compensator—analyzer configuration corresponds to the minimum error in the calculated optical parameters.

CRYSTAL TO AMORPHOUS TRANSITION OF SI AND AR IMPLANTED SILICON USING SINGLE-EFFECTIVE OSCILLATOR MODEL

Complex dielectric function was used to calculate refractive index and optical dispersion parameters for silicon wafers implanted with Si and Ar ions with different fluences. Energies of 200 and 800 keV were used, in order to relate ion implantation parameters with lattice perturbation. Single-effective oscillator energy, average strength of the interband optical transition, zero frequency (static) refractive index, moments of e(E) dispersion spectra, plasma angular frequency, lattice energy, the contribution of the free carriers and Urbach energy were obtained on the basis of the single-effective oscillator model proposed by Wemple and DiDomenico to monitor crystalline-amorphous transformation. Used experimental techniques and damage profiles have been demonstrated elsewhere(1). Real and imaginary parts of the dielectric constant were calculated from the recently measured ellipsometric parameters (phase difference D and amplitude ratio y ) (1,2). Progressive increase in the absorption coefficient magnitude below fundamental edge, oscillator energy E0, and oscillator average strength Ed with increasing ion fluence is primarily a defect formation effect, which produce a perturbation to the periodic potential of the crystal resulting a localized states in the band gap. The suggested mechanism can account for the decrease of both lattice energy (El) and N/m* behavior. Decrease of static refractive index in the low fluencies interpreted as a decrease in the dangling bonds which attributed to restructuring of the bonds. With increase of fluence the dangling bonds increased denoting formation of clusters together and increasing its mean size up to a percolation threshold. Increasing Urbach energy as a function of fluencies was observed and interpreted from the point view of Mott–Anderson transition.

Calibration of a snapshot phase-resolved polarization-sensitive spectral reflectometer

This Letter describes a universal calibration theory by which conventional interferometry can be extended to vibration robust snapshot polarization-sensitive spectral reflectometry without any complicated optical components or active devices. Experiments for verifying the proposed calibration theory have been conducted by using a Michelson-interferometer-based normal incidence spectroellipsometric system, and also some key system design considerations for object 3D pose tolerant measurement capability have been drawn. The proposed solution enables us to extract the spectroscopic ellipsometric parameter Δ(k) of an anisotropic object within 10 ms with high accuracy.

Optical study of Ba(MnxTi(1−x)O3) thin films by spectroscopic ellipsometry

Stoichiometric Ba(MnxTi(1−x)O3) (BMT) thin films with various values of x were deposited on Si(111) substrates by the sol-gel technique. The influence of Mn content on the optical properties was studied by spectroscopic ellipsometry (SE) in the UV—Vis—NIR region. By fitting the measured ellipsometric parameter (Ψ and Δ) with a four-phase model (air/BMT+voids /BMT/Si(111)), the key optical constants of the thin films have been obtained. It was found that the refractive index n and the extinction coefficient k increase with increasing Mn content due to the increase in the packing density. Furthermore, a strong dependence of the optical band gap Eg on Mn/Ti ratios in the deposited films was observed, and it was inferred that the energy level of conduction bands decreases with increasing Mn content.

A spectroscopic ellipsometer using rotating polarizer and analyzer at a speed ratio 1:1 and a compensator

Ellipsometers have been widely used in thin film characterization. They have shown a high degree of accuracy. We here propose theoretically a rotating polarizer and analyzer ellipsometer at a speed ratio 1:1 with a fixed compensator placed just after the rotating polarizer. Our calculations of the optical properties of c-Si and SiO\(_{2}\) reveal a substantial decrease in the percent error due to the fixed compensator. The uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients are presented in details.