Ellipsometry Method Research Articles

Tuning of the plasmon resonance location in Au nanostructures coated with a ultrathin film of Al2O3 – Optical measurements and FDTD simulations

The Au nanostructures have been coated with an ultra-thin films of amorphous aluminium oxide. Optical absorption spectra show the influence of the thickness of Al2O3 on plasmon resonance wavelength. The observed red-shift of the resonance location with the increase of the thickness of the Al2O3 film, can be explained by the change in the dielectric function of this film. It allows control of the optical spectra of the coated particles. In this paper we present a two ways for determinaton of optical paramaters of aluminium oxide ultra-thin films. The first one is based on a ellipsometry method, while in second approach a shift of plasmon resonance is used for computer simulations of films. The experimental data are in agreement with the results of the FDTD calculations, showing the possibility of both determining such a function for ultra-thin layers by the computer simulation method, as well as predicting the value of the dielectric constant depending on the thickness of the layer. The experimental data needed for the simulation was obtained in studies such as XRD, XPS, SEM and HR TEM. The proposed models can help to adjust the coating thickness to the desired plasmon resonance position.

Preparation and evaluation of high-transparent scratch-resistant thin films on plasma treated polycarbonate substrate

New simple aqueous sol–gel procedure has been used for producing hard transparent organic–inorganic coatings on polycarbonate (PC). Sol-gel thins films were prepared by mixing Si and Al aqueous alkoxides and applied on the plasma treated PC. Tetraethyl orthosilicate (TEOS), 3-glycidoxypropyltrimethoxysilane (GPTMS) and aluminum tri sec-butoxide were used as main precursors. Before applying coatings PC were treated by Dielectric Barrier Discharge (DBD) system being conducted at atmosphere pressure. The effects of temperature, sols volume ratios and aging time on the coatings properties were scrutinized. Chemical, structural, morphological, optical and mechanical analyses of the samples were done by ATR-FTIR, EDS, XRD, FE-SEM, TEM, UV/vis spectroscopy, ellipsometry, pencil hardness and eraser scratch methods. TEM results showed well-dispersed nano-particles in the liquid sol. All of the films showed higher average transmittance (89 %) than the raw PC (86 %) that was stemmed from the lower refractive index (1.481) than raw PC (1.58). Films indicated good adhesion onto the plasma treated substrates (5B). The pencil hardness of the PC substrate (4B) improved to 3H (8 pencil grade increment) with just a single layer coating (775 nm thickness) due to the preparation of new hard structures of interlocked Si and Al atoms.

Investigation of upward speed and thickness effects on optical and mechanical properties of hard transparent thin films deposited on polycarbonate substrate

In the present work, nanomechanical behaviors and optical properties of the nanohybrid thin films coated on the polycarbonate (PC) substrates were investigated. Tetraethyl orthosilicate (TEOS), 3-glycidoxypropyl-trimethoxysilane (GPTMS) and aluminum tri sec-butoxide were used as main precursors through very simple and repeatable sol-gel process. Optical, chemical, structural, morphological and mechanical characteristics of the samples were studied by ellipsometry, UV/vis spectroscopy, ATR-FTIR, EDS, XRD, FE-SEM, TEM and nanoindentation-nanoscratch methods. It was found that upward speed had an important effect on the nanomechanical properties while optical properties remained constant. The obtained results indicated that the refractive index of the prepared thin films were significantly lower (1.483) than PC substrate (1.58) led to increase the transmittance that was measured 89 % compared to pristine PC (86 %). Nanohybrid thin films increased PC hardness and elastic modulus to 0.45 and 7.4 GPa respectively at upward speed 5 mm/s. The friction coefficient was decreased to 0.23 and the pencil hardness was 5H at 1887 nm thickness coating at 9 mm/s upward speed.

Measurement of stress-optic coefficients for metals in the visible to near-infrared spectrum with spectroscopic ellipsometry

• A feasible method is proposed to get stress-optic coefficients of metals with ellipsometry. • The stress-optic coefficients of Cu film from 380 to 1000 nm are measured with spectroscopic ellipsometry. • The relation between stress-optic coefficients and wavelengths of Cu are apparently nonlinear. The measurement of stress-optic coefficients is of great importance in photoelasticity which can be used in many fields, such as stress measuring and nondestructive testing. In this paper, the stress-optic coefficients of Cu film were measured in the visible to near-infrared spectral range by spectroscopic ellipsometry. In order to determine the stress-optic coefficients, a measuring principle is proposed by the combination of the classic 4 × 4 Matrix method of ellipsometry and the stress-optic law. According to this principle, we establish a quantitative relation between the ellipsometric parameters (Ψ, Δ) and stress, which is related to stress-optic coefficients. The ellipsometric parameters of a thin film/substrate assembly by sputtering Cu on polyimide (PI) were experimentally measured under various stress conditions. Fitting the proposed measuring principle to experimental data, the stress-optic coefficients of Cu film in the visible to near-infrared spectral range were obtained. This research provides insights into stress measuring of metal films, which is widely needed in many application fields such as chip processing.

Spectral Ellipsometry as a Method of Investigation of Influence of Rapid Thermal Processing of Silicon Wafers on their Optical Characteristics

One of the possible ways of improvement of the surface properties of silicon is the solid phase recrystallization of the surface silicon layer after the chemical-mechanical polishing with application of the rapid thermal treatment with the pulses of second duration. The purpose of the given paper is investigation of influence of the rapid thermal treatment of the initial silicon wafers of the various doping level and reticular density on their optical characteristics by means of the spectral ellipsometry method.The investigation results are presented by means of the spectral ellipsometry method of the rapid thermal processing influence on the initial silicon wafers (KDB12 orientation <100>, KDB10 orientation <111> and KDB0.005 orientation <100>) of the various level of doping and reticular density influence on their optical characteristics: refraction and absorption ratios. Influence was confirmed of the silicon reticular density on its optical characteristics before and after the rapid thermal processing. It was shown, that reduction of the refraction and absorption ratios in the center of the Brillouin zone for the silicon samples with the high Boron concentration after the rapid thermal processing as compared with the low doped silicon. In the area of the maximum absorption peak, corresponding to the energy of the electron exit from the silicon surface (4.34 eV) the refraction indicator of the high doped silicon becomes higher, than of the low doped silicon, which is determined by the high concentration of the vacant charge carriers on the silicon surface in this spectral range.It was established, that the spectral area 3.59–4.67 eV, corresponding to the work of the electrons, exiting the silicon surface, the most informative way shows the difference of the 3 optical parameters of silicon of the different orientation, and for evaluation of influence of the silicon doping level on its optical characteristics the most informative is the spectral range of 3.32–4.34 eV.

V1−xWxO2 thermochromic films for device applications

V1−xWxO2 is known to be a reliable thermochromic material for multiple practical applications due to its insulator to metal transition temperature controlled by W dopping. In this paper, we present electrical and optical properties of V1−xWxO2 thin films synthesized by PLD technique. In this respect, the electrical resistance, the refractive index (n), and extinction coefficient (k) as a function of temperature from 25 to 80 °C and wavelength ranging from 500 to 3000 nm were obtained using conventional 4-probe resistance and ellipsometry methods. The direct and indirect bandgap values at different doping levels and temperatures have been calculated using n and k versus energy data and compared with thermally activated bandgap from electrical resistance. A decrease in direct and indirect bandgaps with temperature and wavelength was observed with doping and temperature. Comparison between thermal and optical bandgap demonstrates that activated thermal bandgap is only comparable with the lowest optical indirect bandgap.Graphical abstract

Highly Sensitive Plasmonic Structures Utilizing a Silicon Dioxide Overlayer.

In this paper, simple and highly sensitive plasmonic structures are analyzed theoretically and experimentally. A structure comprising a glass substrate with a gold layer, two adhesion layers of chromium, and a silicon dioxide overlayer is employed in liquid analyte sensing. The sensing properties of two structures with distinct protective layer thicknesses are derived based on a wavelength interrogation method. Spectral reflectance responses in the Kretschmann configuration with a coupling BK7 prism are presented, using the thicknesses of individual layers obtained by a method of spectral ellipsometry. In the measured spectral reflectance, a pronounced dip is resolved, which is strongly red-shifted as the refractive index (RI) of the analyte increases. Consequently, a sensitivity of 15,785 nm per RI unit (RIU) and a figure of merit (FOM) of 37.9 RIU are reached for the silicon dioxide overlayer thickness of 147.5 nm. These results are in agreement with the theoretical ones, confirming that both the sensitivity and FOM can be enhanced using a thicker silicon dioxide overlayer. The designed structures prove to be advantageous as their durable design ensures the repeatability of measurement and extends their employment compared to regularly used structures for aqueous analyte sensing.

Interferometric Imaging Ellipsometer for Characterizing the Physical Parameters of a Grown Oxide Layer

Interferometric and ellipsometric techniques are widely used in object characterization, investigation and testing. Both techniques are crucial for industrial sectors in manufacturing and production. In this work, an interferometric imaging ellipsometry method has been developed to measure the ellipsometric parameters Ψ, Δ and thickness t of native oxide layer formed on a copper thin film at wide angle of incidence 57.8–80.2º instantaneously. In this system, Michelson interferometer is illuminated with 45° polarized laser beam of 30 mm diameter. The produced fringes are split by a polarizing beam splitter (PBS) into p- and s- polarization fringes. The interferograms are captured separately by two CCD sensors at the reference and the measurement states without moving any parts in the optical system for each state. The detected p- and s- interferograms are analyzed using ImageJ software for mathematically calculating the values of Ψ, Δ and t of the oxide layer grown on copper thin film surface. The proposed method avoids the offset errors and the probable misalignment resulting from the beam and the optical components. In addition, it gathers the information of the interference pattern with the state of polarization of light for accurate, precise and real time contrast images. The oxide layer thickness is determined under controlled environment with high accuracy and low uncertainty. The results obtained by the proposed technique are consistent with the spectroscopic ellipsometer measurements.

Ellipsometry-transmission measurement of the complex refractive indices for a series of organic solvents in the 200–1700 nm spectral range

Organic solvents are fluids commonly used in different branches of materials science. The determination of the wavelength-dependent complex refractive index of organic solvents is essential in physical, chemical, biological, and optical applications. The existing databases for the complex refractive index of many organic solvents are insufficient and have low accuracy, particularly in the ultraviolet (UV), visible (Vis), and near-infrared (NIR) spectral ranges. In this work, using spectroscopic ellipsometry combined with the transmission method, the complex refractive indices of isopropyl acetate (IPAC), dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N-dimethylaniline (DMA), dichloromethane (DCM), tetrahydrofuran (THF), P-Xylene (PX), and ethyl acetate (EA) were measured in the spectral range 200–1700 nm at room temperature and ambient pressure. The refractive index and absorption index were measured by the ellipsometry and transmission method, respectively, allowing accurate measurement of the complex refractive index of materials with weak optical absorption. Based on these experimental data, the refractive indices in the weak absorption waveband were fitted using Cauchy’s dispersion formula. According to the dispersion relationships and molecular structure of each solvent, it is known that the addition of benzene rings, sulfur atoms, chlorine atoms, nitrogen atoms, and epoxides can increase the refractive index of a material. The results obtained in our laboratory for organic solvents provide evidence that the ellipsometry-transmission method is a promising technique for characterizing the optical constants of different types of materials. The experimental data of the complex refractive indices and their dispersion of organic solvents can provide a reference for its practical applications.

Pseudo-dielectric function spectra of the near surface layer of GaAs implanted with various fluence of Xe+ ions

Monocrystalline (100) semi-insulating gallium arsenide (GaAs) samples were irradiated with a 250-keV Xe+ ion beam at room temperature. To investigate the effect of ion irradiation on GaAs samples, the ion fluence was varied from 1 × 1012 to 3 × 1016 ions/cm2. The spectroscopic ellipsometry (SE) method and the Rutherford backscattering spectrometry (RBS) with nuclear reaction (NR) method were used to determine the properties of the virgin and implanted samples. The SE approach reveals that the pseudo-dielectric function of implanted GaAs samples varies with ion fluence. The RBS approach, which exposes the depth-profile of As, Ga, and Xe in the implanted samples, allows us to correlate changes in the pseudo-dielectric function with structural modifications caused by the ion irradiation. The NR approach points out the existence of an oxygen-enriched layer on the surface of implanted GaAs samples. Lastly, the optical study involving the Cauchy and Urbach dispersion model measures the refractive index n and extinction coefficient k of the native oxide layer on the surface of GaAs samples.

Visualizing dynamic evolution of electrode/electrolyte interface via model-free analysis of in-situ spectroscopic ellipsometry

Spectroscopic ellipsometry is a promising technique for realizing in-situ study of electrode/electrolyte interface (EEI) owing to its high-sensitive and non-destructive advantages. However, difficulties in modelling complex systems and analysing massive data of in-situ tests hinder its widespread applications. Herein, a model-free method was established and a featured parameter named interfacial evolution rate (IER) was proposed to qualitatively and quantitatively probe the dynamic evolution rate of EEI. The in-situ electrochemistry-spectroscopic ellipsometry measurement of pure magnesium corrosion in 5 wt.% NaCl solution before and after adding Na2SiO3·9H2O inhibitor (0.001 mol L−1) was conducted to verify the utility of the established method. Without the inhibitor, IER exponentially decreases from 12 to 3 and lasts for about 60 min, indicating the gradual stabilization of the interface. The subsequent increase of IER suggests the accelerated dynamic evolution of EEI. In the presence of the inhibitor, IER decreases from 0.5 to 0.3 and remains stable for 230 min, corresponding to the significant corrosion inhibition of sodium silicate. Ex-situ SEM, EDS, Raman and XPS characterizations of the corrosion products were also performed to support the analysis. The model-free analysis method of spectroscopic ellipsometry established in this work shows potential applications in the in-situ investigations of various complex systems.

CONTROL OF THE OPTICAL SURFACE PURITY OF THE ELEMENTS BY THE ELLIPSOMETRIC METHOD

The possibility of controlling the chemical purity of the surface of optical elements by the ellipsometric method has been analyzed. The rationale of the possibility of measuring the parameters of contaminating films on the optical surface of elements by the ellipsometric method has been given simplification has been
 shown of the process of determining the thickness of the contaminating film while expanding the possibility of its measurement on an optical element made of different materials. Ellipsometric studies of freshly polished and used metal mirrors made of copper and copper alloy (zirconium bronze), aluminum and its alloys AMG-6, AL-9, AL-24 have been carried out. Research has also been conducted on elements made of K-8 and
 K-108 (State Standard 3514-94) optical glasses, which are the most typical materials used for manufacture of optical parts for laser technique of visible and near IR-range, from single crystals of NaCl, BaF2 and sapphire (Al2O3). Parameters of contaminating films on the surface of these elements have been measured.
 It has been concluded that it is advisable to use the ellipsometry method during the input (before carrying out physicochemical cleaning) and during the output (after cleaning) control of the optical element to assess the contamination of the optical surface and also for the quantitative analysis of the concentration of contaminants on the optical surface of the elements while working off the technology of their physicochemical cleaning.

Investigation and Comparison of Specific Antibodies' Affinity Interaction with SARS-CoV-2 Wild-Type, B.1.1.7, and B.1.351 Spike Protein by Total Internal Reflection Ellipsometry.

SARS-CoV-2 vaccines provide strong protection against COVID-19. However, the emergence of SARS-CoV-2 variants has raised concerns about the efficacy of vaccines. In this study, we investigated the interactions of specific polyclonal human antibodies (pAb-SCoV2-S) produced after vaccination with the Vaxzevria vaccine with the spike proteins of three SARS-CoV-2 variants of concern: wild-type, B.1.1.7, and B.1.351. Highly sensitive, label-free, and real-time monitoring of these interactions was accomplished using the total internal reflection ellipsometry method. Thermodynamic parameters such as association and dissociation rate constants, the stable immune complex formation rate constant (kr), the equilibrium association and dissociation (KD) constants and steric factors (Ps) were calculated using a two-step irreversible binding mathematical model. The results obtained show that the KD values for the specific antibody interactions with all three types of spike protein are in the same nanomolar range. The KD values for B.1.1.7 and B.1.351 suggest that the antibody produced after vaccination can successfully protect the population from the alpha (B.1.1.7) and beta (B.1.351) SARS-CoV-2 mutations. The steric factors (Ps) obtained for all three types of spike proteins showed a 100-fold lower requirement for the formation of an immune complex when compared with nucleocapsid protein.

Spectroscopic Ellipsometry and Optical Modelling of Structurally Colored Opaline Thin-Films

The method of spectroscopic ellipsometry is applied to complex periodic nanomaterials, consisting of shear-ordered polymeric nanosphere composites, with intense resonant structural color. A corresponding multilayer optical quasi-model of the system, parametrizing the inherent degree of sample disorder and encompassing key properties of effective refractive-index and index-contrast, is developed to elucidate the correlation between the ∆ and Ψ ellipsometric parameters and the shear-induced opaline crystallinity. These approaches offer reliable means of in-line tracking of the sample quality of such “polymer opals” in large scale processing and applications.

Development of rigid amorphous fraction in cold‐crystallized syndiotactic polystyrene films confined near the nanoscale: Novel analysis via ellipsometry

AbstractRigid amorphous fraction (RAF) in syndiotactic polystyrene (sPS) thin films was studied as a function of crystalline fraction (CF). In contrast to bulk sPS, confined films yield close‐to‐amorphous sPS, thus allowing for a complete description of RAF development. To study thin‐film samples, we developed an ellipsometry‐based method to quantify CF and RAF. Maximum crystallinity was thickness dependent, indicating a strong effect of near‐nanoscale confinement on CF. ~360‐nm‐thick spin‐coated films were isothermally cold crystallized to tune CF from 1% to a maximum of 12%. Combining RAF characterized at low CF here by ellipsometry with results from an earlier differential scanning calorimetry (DSC)‐based study on bulk sPS with higher CF, a complete picture was obtained of RAF development as a function of CF in cold‐crystallized sPS. RAF increases from ~4% at 1% CF to ~16% for 10% < CF < 25%; above 25% CF, RAF decreases monotonically with increasing CF, reaching ~7% at a maximum 50% CF. Specific RAF (=RAF/CF) decreases with increasing CF, consistent with increasing crystal perfection with isothermal cold crystallization. This ellipsometry method can be an important tool for evaluating RAF, mobile amorphous fraction (MAF), and CF in semi‐crystalline polymer films and for studying confinement effects on RAF, MAF, and CF.

The Influence of Argon Cluster Ion Bombardment on the Characteristics of AlN Films on Glass-Ceramics and Si Substrates.

In this paper, the influence of surface modification on the characteristics and properties of AlN thin films on Si and glass-ceramics substrates is investigated. The surface modification was made at various parameters of argon cluster ions. By using XRD and Raman spectroscopy, it was shown that the obtained AlN films have a hexagonal structure with a characteristic direction of texturing along the c axis and slight deviations from it. A comparison of the AlN surface morphology obtained by atomic force microscopy before and after cluster processing was demonstrated. This demonstrated that the cluster ions with low energy per atom (E/N = 10 eV/atom) have a high efficiency of surface smoothing. A decrease in the intensity of the Raman peaks and an increase in their full-width after bombardment with cluster ions were found, which may be caused by a change in the physicochemical state of the surface. The optical properties, the quality of the boundaries, and the distribution map of the thickness of the functional layer of AlN were investigated by the methods of spectral and spatial resolution ellipsometry. By using the cross-sectional SEM, the direction of crystallite texturing was demonstrated. The influence of argon cluster ion bombardment on the stoichiometry of samples was analyzed by EDX spectroscopy. The results obtained demonstrate the efficiency of the cluster ion smoothing of polycrystalline thin films for microelectronics, particularly when creating surface acoustic wave resonators.

Separating Non-linear Optical Signals of a Sample from High Harmonic Radiation in a Soft X-ray Free Electron Laser

Second harmonic generation (SHG) is a unique non-linear optical effect that can be used to investigate chemical states of molecules at surfaces/interfaces. By the use of soft X-rays, SHG gains element selectivity through the inner-core excitation resonance. However, it is challenging to observe SHG signals separately from the second-order light generated from the undulator. Here, we report a new ellipsometry method for soft X-ray SHG to suppress the contribution of second-harmonic radiation from the light source. Through measurements of a GaAs(100) crystal, we demonstrate that pure SHG signals can be obtained for the horizontally polarized component. The present method is generally applicable regardless of the incident photon energy and hence the absorption edge of the targeted materials. If combined with optical filters blocking the second-harmonic radiation and equipped with soft X-ray phase shifters, the method allows one to obtain further information from SHG signals such as tensor components of second-order non-linear susceptibility.

Preparation of nickel-coated graphene and evaluation of infrared interference performance

In this paper, reduced graphene oxide (RGO) was prepared by oxidation-reduction method, and then RGO/Ni composite was prepared by chemical plating method. The RGO and RGO/Ni samples were characterized by the methods of SEM, TEM, XPS, EDS, XRD, etc. The complex refractive index of the samples in 2~14μm infrared wavebands was measured by ellipsometry method, and the infrared absorption characteristic was calculated by DDA method. Then, the infrared interference performance was tested by the method of Fourier transform spectrometer connected with smaller smoke box, and the dispersivity was also comprehensively evaluated by Carr index method. It is found that electroless nickel plating not only can ease the secondary agglomeration between the RGO layers, improve its dispersivity, but also change the electromagnetic properties of graphene surface and significantly improve its infrared absorption. From the infrared interference performance test, it can be seen that the average extinction coefficients of RGO smoke to 3~5 μm and 8~14 μm infrared is 2.56m2/g and 1.8m2/g, respectively. While the average infrared extinction coefficients of RGO/Ni in the corresponding wavebands is 2.9m2/g and 2.55m2/g, respectively. It further indicates that the surface modification of electroless nickel plating can greatly promote the infrared interference performance of RGO. In particular, the far-infrared extinction performance has been obviously improved.

Ab initio calculations and experimental study of the electronic properties of CdGa-=SUB=-2-=/SUB=-S-=SUB=-4-=/SUB=- single crystals by spectral ellipsometry

The electronic properties of CdGa2S4 single crystals have been studied experimentally using spectral ellipsometry and theoretically from first principles using density functional theory (DFT). Using ellipsometric studies in the energy range of 0.7-6.5 eV, the imaginary and real parts of the dielectric function along and perpendicular to the optical axis, the dispersion of the refractive, extinction, and absorption coefficients are determined. The width of the direct band gap is estimated. The band structure, the origin of the energy states, the optical functions, and the partial densities of states (PDOS) projected onto the atoms are determined by ab initio calculations. The theoretically calculated results are compared with the experimental data of the present work obtained by the method of spectral ellipsometry and with the experimental results available in the literature. Keywords: spectral ellipsometry, ellipsometric angles, dielectric function, refractive index, extinction coefficient, Brillouin zone, band structure.

Phase-spectral ellipsometry method for non-destructive control of the chemical composition of thin metal-oxide heterostructures

Phase-spectral ellipsometry method for non-destructive control of the chemical composition of thin metal-oxide heterostructures