Rotating Analyzer Ellipsometer Research Articles

Tuning optical properties of Au thin film using electric field for surface plasmon resonance biosensor application

The effect of electric field application on the optical properties of gold (Au) thin film for spectroscopic ellipsometry-based surface plasmon resonance (SPR) biosensor applications has been successfully studied. The optical properties, such as the complex refractive index, complex dielectric constant, real optical conductivity, and absorption coefficient, were determined by fitting data from the ψ and Δ functions obtained through measurements using a homemade rotating analyzer ellipsometer. The applied electric fields of 0.8 V/cm, 1.6 V/cm, 2.4 V/cm, and 3.2 V/cm were induced by applying voltages of 1 V, 2 V, 3 V, and 4 V for ellipsometer tests, and 1.6 V/cm to 3.2 V/cm for the SPR test. The Au thin film was deposited onto a glass slide using an evaporator for ellipsometer testing and a BK7 half-cylinder prism was employed for SPR testing. The experimental results show that the real part of the refractive index (n) increases in the spectral range from 1.5 eV to 2.2 eV and from 3 eV to 5 eV and tends to be constant in the range from 2.3 eV to 2.8 eV. Conversely, the imaginary part of the refractive index (k) decreases from 2.8 eV to 3.6 eV and tends to remain consistent from 3.9 eV to 5.0 eV. The dielectric constant (ε1) consistently shows a significant increase within the spectral range of 3 eV–5.0 eV, with a tendency to decrease between 2.1 eV and 2.4 eV. Meanwhile, the imaginary part (ε2) demonstrates an increase in the spectral range of 1.5 eV–2.4 eV and 3.3 eV–5.0 eV while maintaining relatively stable values in the energy spectral range of 2.6 eV–3.0 eV. Moving to the real part of optical conductivity (σ1), it increases within the spectral range from 1.5 eV to 2.4 eV and from 3.5 eV to 5 eV, with relatively constant values between 2.6 eV and 3.1 eV. The absorption coefficient (α) exhibits a decrease in the spectrum between 2.8 eV and 3.6 eV, but the values remain stable within the range of 3.9 eV–5.0 eV. The α slightly decreases in the energy range of 1.8 eV–2.6 eV. The outcomes obtained from these experiments are directly linked to the SPR results, revealing a noticeable shift in the SPR angle (θSPR) of 45.51°, 45.61°, and 45.73° and an increase in the minimum reflectance (Rmin) of 0.05, 0.09, and 0.13 for electric field strengths of 0 V/cm, 1.6 V/cm, and 3.2 V/cm, respectively. These results imply that the application of an external electric field to the surface of the Au thin film disrupts the matching condition between the evanescent wave vector and the surface plasmon wave vector, thereby altering the reflected light under resonance conditions indicated by an increase in the minimum reflectance and SPR angle. This development holds significant promise to further enhance the sensitivity of electro-optic modulation-based biosensors.

Optical measurements on a budget: A 3D-printed ellipsometer

Ellipsometry is an optical analysis technique that is useful for characterizing the physical properties of a thin-film system. Light reflected from a sample surface undergoes a change in polarization due to phase delay and anisotropic reflection. This enables one to perform non-destructive measurements of film thickness, surface roughness, refractive index, and other optical constants. Ellipsometric techniques are particularly convenient for characterizing coatings or films in the semiconductor and optics industries. However, these techniques may be inaccessible to undergraduate students and educators due to the prohibitive cost of ellipsometers and similar instrumentation. In response to this roadblock, we describe the construction of a simple, inexpensive, manually operated, rotating analyzer ellipsometer (RAE). Required materials include a laser pointer, polarizing film, photometric detector, and a 3D-printed opto-mechanical framework, which are all readily accessible at most institutions. The instrument's performance was evaluated by comparing thickness measurements of tetraethyl orthosilicate films to those determined by a commercially available reflectometer. An average film thickness difference of 0.77% was measured using the two instruments.

A compact, modular, multi-wavelength (200–850nm) rotating-analyzer ellipsometer for optical constant characterization of nanostructured materials

We have developed a compact modular rotating-analyzer ellipsometer (RAE) with a spectrum range of 200–850 nm. Spectroscopic ellipsometry is a non-destructive characterization based on an optical method. It is used widely to obtain the dielectric constant, thickness, and surface roughness of thin films. Our homemade RAE comprises standard modular components that are available on the market, such as (i) a deuterium–halogen DH-2000-BAL light source made by Ocean Optics, (ii) a Rochon prism with an α-BBO substrate from Edmund optics for the polarizer and analyzer, and (iii) a Red Tide USB650UV mini detector from Ocean Optics and a compact ellipsometer arm design to ensure its ease-of-use and future development. Data acquisition is automated and can be controlled using a computer program, and all the moving parts are motorized. The dielectric constant of Au film with a thickness of 300 nm has been measured for calibration of the apparatus. The result was compared with reference measurements that used a commercial ellipsometer, and showed considerable accuracy with a similarity of ∼95%.

Simple and Low-Cost Rotating Analyzer Ellipsometer (RAE) for Wavelength Dependent Optical Constant Characterization of Novel Materials

Simple and low-cost homemade Rotating Analyzer Ellipsometer (RAE) configuration has been developed. Ellipsometer measures the changes of the reflected light polarization of the sample, yielding to the ratio of amplitude (ψ) and phase difference (Δ) between p- and s-polarization. Based on the ψ and Δ values, the dielectric constant of the sample can be extracted. However, the available manufacturer-made ellipsometer is quite expensive and is not a good choice for the student to learn the optical concept since the complexity of its structure could hide the simple optical concept during the measurement. In this work, we have built RAE that constituted of relatively simple components and low-cost as well as simple configuration. Here, we also show the principle of measurement and the ellipsometry data analysis using the optical model related to the system under study Drude-Lorentz model. The calibration of our SE has been done by measuring standard materials in the energy range of 1.5 to 3.3 eV and it was compared to the reference measurement using standard ellipsometer. The result is surprisingly accurate within the error of 5%. This research can be used for studying the several important optical concepts as well as for investigating nanostructured materials.

Spectroscopic Ellipsometry Based Biosensor on Gold Thin Film for Detection of Microalgae

The study of spectroscopic ellipsometry on gold thin film with different thicknesses (30, 50, and 70 nm) for biosensor application has been done. In this work, a rotating analyzer ellipsometer (RAE) has been used to characterize gold thin film and detect microalgae. The measurement was performed at different incidence angles (60°, 65°, 70°, and 75°) assuming the gold film as an isotropic material. The light absorptions of electron represented by the ellipsometer parameter (Δ) and the extinction coefficient (k) are due to the intraband transition of free electrons in the lower photon energy and interband transition of bounded electrons from 5d to 6sp in the higher photon energy. The light absorption increases with the decrease in the thickness of Au thin film. However, for the detection of microalgae, the light absorption of the electron increases with the increase in the thickness of Au thin film due to the dominant absorption by microalgae and PVA. We report that the use of Au thin film with the thickness of 70 nm provides the most sensitive detection of microalgae which is confirmed by the change in Δ (63.1°), at the photon energy of 2.11 eV and the incidence angle of 75°.

Advanced Terahertz Frequency-Domain Ellipsometry Instrumentation for In Situ and Ex Situ Applications

We present a terahertz (THz) frequency-domain spectroscopic ellipsometer design that suppresses formation of standing waves by use of stealth technology approaches. The strategy to suppress standing waves consists of three elements geometry , coating , and modulation . The instrument is based on the rotating analyzer ellipsometer principle and can incorporate various sample compartments, such as a superconducting magnet, in situ gas cells, or resonant sample cavities, for example. A backward wave oscillator and three detectors are employed, which permit operation in the spectral range of 0.1–1 THz (3.3–33 cm $^{-1}$ or 0.4–4 meV). The THz frequency-domain ellipsometer allows for standard and generalized ellipsometry at variable angles of incidence in both reflection and transmission configurations. The methods used to suppress standing waves and strategies for an accurate frequency calibration are presented. Experimental results from dielectric constant determination in anisotropic materials, and free charge carrier determination in optical Hall effect (OHE), resonant-cavity enhanced OHE, and in situ OHE experiments are discussed. Examples include silicon and sapphire optical constants, free charge carrier properties of two-dimensional electron gas in a group III nitride high electron mobility transistor structure, and ambient effects on free electron mobility and density in epitaxial graphene.

PECULIAR OPTICAL PROPERTIES OF Co2MnGa ALLOYS

Co2MnGa alloy was prepared by the conventional arc-melting method. The optical conductivity (OC) spectrum of the alloy was measured by a rotating-analyzer spectroscopic ellipsometer. The OC spectrum was also calculated based on the electronic structure by using the full-potential linearized-augmented-plane-wave method within the local-spin-density approximation to the density-functional theory. The calculated OC spectrum does not agree well with the experimental one. Since the Co2MnGa alloy could be a strongly-correlated material, the so-called 'LDA+U' method was applied with U = 5.4 eV. The calculated OC spectrum using the 'LDA+U' method agrees very well with the experimental one. The inclusion of the onsite Coulombpotential during the self-consistent calculation significantly modifies the minorityspin Co and Mn 3d bands, resulting in a contraction of the energy gaps between states which are strongly involved in interband absorption peaks.

Inexpensive Home-Made Single Wavelength Ellipsometer (λ = 633 nm) for Measuring the Optical Constant of Nanostructured Materials

Inexpensive home-made Single wavelength Ellipsometry with RAE (Rotating Analyser Ellipsometer) configuration has been developed. Spectroscopic ellipsometry (SE) is an optical measurement technique which is based on the measurement of the change of the phase difference (Δ) and the amplitude ratio (ψ) between p and s linear polarized of reflected (or transmitted) light. Our RAE configuration system composed of polarizer, sample, analyzer, detector, and He-Ne laser (λ = 633 nm) that acted as the monochromatic light source. To test the reliability of our SE system, we measure the optical constant of Au bulk and Cr (30 nm thick) film. The optical constant and the thickness were extracted by employing the pseudo-dielectric function and numerical inversion which is based on the secant method, the ψ and Δ of our SE data which is modelled by Fresnel equation. From the extraction using the secant method we obtain the optical constant of the Au bulk sample with n = 0.11 to 0.22 and k = 3.26 to 3.37 which is close to that of using pseudo-dielectric method. We obtain the same result for Cr film with n = 3.66 to 3.81 and k = 5.32 to 5.38 which is close to the result from reference. These results show that our inexpensive home-made Single wavelength Ellipsometry instrument and the extraction method are reliable for determining the optical constant of nanostructured materials.

Fast IR laser mapping ellipsometry for the study of functional organic thin films.

Fast infrared mapping with sub-millimeter lateral resolution as well as time-resolved infrared studies of kinetic processes of functional organic thin films require a new generation of infrared ellipsometers. We present a novel laboratory-based infrared (IR) laser mapping ellipsometer, in which a laser is coupled to a variable-angle rotating analyzer ellipsometer. Compared to conventional Fourier-transform infrared (FT-IR) ellipsometers, the IR laser ellipsometer provides ten- to hundredfold shorter measurement times down to 80 ms per measured spot, as well as about tenfold increased lateral resolution of 120 μm, thus enabling mapping of small sample areas with thin-film sensitivity. The ellipsometer, equipped with a HeNe laser emitting at about 2949 cm(-1), was applied for the optical characterization of inhomogeneous poly(3-hexylthiophene) [P3HT] and poly(N-isopropylacrylamide) [PNIPAAm] organic thin films used for opto-electronics and bioapplications. With the constant development of tunable IR laser sources, laser-based infrared ellipsometry is a promising technique for fast in-depth mapping characterization of thin films and blends.

Optical properties of thin films of mixed Ni–W oxide made by reactive DC magnetron sputtering

Thin films of NixW1−x oxides with x=0.05, 0.19, 0.43 and 0.90 were studied. Films with thicknesses in the range 125–250nm were deposited on silicon wafers at room temperature by reactive DC magnetron co-sputtering from targets of Ni and W. The films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopic ellipsometry (SE). XRD spectra and SEM micrographs showed that all films were amorphous and possessed a columnar structure. The ellipsometric angles Ψ and Δ of as-deposited films were measured by a rotating analyzer ellipsometer in the UV–visible-near infrared range (0.63–6.18eV) and by an infrared Fourier transform rotating compensator ellipsometer in the 500–5200cm−1 wavenumber range. SE measurements were performed at angles of incidence of from 50° to 70°. Parametric models were used to extract thicknesses of the thin films and overlayers of NixW1−x oxide at different compositions, band gaps and optical constants. Features in the optical spectra of the NixW1−x oxides were compared with previous data on tungsten oxide, nickel oxide and nickel tungstate.

Optical properties of bismuth niobate thin films studied by spectroscopic ellipsometry

We performed optical analysis of bismuth niobate thin films using spectroscopic ellipsometry (SE). The films were grown on Pt/Ti/SiO 2/Si substrates with pulsed laser deposition. Six films were prepared using various deposition temperatures and thermal-annealing times. The room-temperature SE spectra of these films were measured by a rotating-analyzer ellipsometer from 1.12 to 6.52 eV at incidence angles of 50, 55, 60, 65, and 70°. The resulting refractive indices and extinction coefficients show significant changes with deposition temperature and thermal annealing.

Determination of the molecular tilt profile of a liquid crystal under applied electric field by generalized transmission ellipsometry

It has been demonstrated that, with the use of a standard rotating analyzer ellipsometer, generalized transmission ellipsometry (GTE) is able to uniquely determine the molecular tilt profile of a commercial nematic liquid crystal variable retarder (LCVR) with applied voltage. Also, the presence of the tilted anisotropic layer permits us to determine, solely with GTE measurements, both the ordinary and extraordinary indices of refraction of the liquid crystal. The isotropic layers of the LCVR, which are of no interest in this kind of measurement, can be completely omitted during modeling. The sensitivities of the technique to the determination of the ordinary index of refraction, the difference between ordinary and extraordinary indices of refraction, and tilt profile are discussed with strategies to improve the three. Previous measurements using guided modes that require special LCVR cells, or the complete modelling of the device due to the use of transmission and reflection data, are in agreement with the results obtained in this paper.

In Situ Ellipsometry Analysis on Formation Process of Al2O3-Ta2O5 Films in Ion Beam Sputter Deposition

thin films are known as highly corrosion-resistant materials for coatings. Here the formation process of films was analyzed by in situ ellipsometry during deposition by ion beam sputtering. Composite targets composed of and plates were used for sputter deposition. During deposition, the formation process of thin films was monitored by a single-wavelength rotating analyzer ellipsometer attached to the sputtering system. The composition, the chemical binding states of constituent elements, and the depth profile of the elements of the films were analyzed by inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy (XPS), and auger-electron spectroscopy (AES), respectively. Ellipsometric analysis showed that the thickness of the film increased linearly with time after short induction periods. The refractive index of the films increases with increasing tantalum cationic fraction. The extinction coefficient of the films was larger than those of single and films. The XPS analysis showed that the preferential deposition of the component occurred in the induction period and the codeposition of and in the linear growth stage. The AES analysis showed that the content of constituent elements was homogeneous from the top to the bottom of the films in the linear growth stage.

편광법을 이용한 LCD 편광판과 보상판의 광축 정렬오차 측정

회전검광자방식 편광분석방법을 이용하여 LCD (liquid crystal display) 편광판에 부착되어 있는 보상판의 느린축이 편광판의 투과축 대비 틀어진 각도를 0.1도 이내로 정밀하게 측정할 수 있는 방법을 제안하였다. 본 방법을 이용하면 보상판을 LCD 편광판과 접합하는 공정에서 발생하는 광축정렬의 오차를 줄일 수 있고 궁극적으로 LCD의 화질을 일정하게 유지, 관리하는데 기여할 수 있을 것으로 기대된다. Using a polarimetry based on the rotating analyzer ellipsometer, a technique of measuring off-alignment angle between the slow-axis of the LCD (Liquid Crystal Display) polarizing plate and the transmission axis of the compensating plate attached to the polarizing plate is proposed. It is anticipated that this technique will reduce the optic axis off-alignment error coming from the process of attaching the compensating plate to the LCD polarizing plate markedly, and therefore will help maintain the quality of LCD display image uniformly.

Mueller matrix ellipsometry study of uniaxial deuterated potassium dihydrogen phosphate (DKDP)

Deuterated potassium dihydrogen phosphate (DKDP) is used for third harmonic generation (frequency tripling) in high power laser applications [Ferroelectrics, 72, 1987, 397–441; Int. Mater. Rev. 47, 2002, 113–152]. DKDP is a uniaxial anisotropic crystal, which is highly transparent in the visible and infrared spectral ranges. This makes DKDP challenging but well suited for study by both transmission ellipsometry and more conventional reflection-mode ellipsometry. Mueller matrix ellipsometry measurements were required because the data included both anisotropic and depolarizing effects. A rotating analyzer ellipsometer, with computer-controlled Berek compensator after the input polarizer and before the sample, allowed measurement of 11 Mueller matrix elements in transmission mode. Spectroscopic transmission Mueller matrix measurements allow the index difference Δ n= n o− n e to be determined throughout the transparent spectral range along with the orientation of the optic axis. Reflection mode ellipsometry is used to extract the absolute index of the ordinary component over the spectral range 0.73 to 9 eV (138–1700 nm). Determination of one index component allows calculation of the other component since the difference n o− n e is known from the transmission Mueller matrix measurements.

Optimizing precision of rotating-analyzer and rotating-compensator ellipsometers.

I investigate the dependence of shot-noise-limited uncertainties of the ellipsometric parameters psi, and delta for the rotating-analyzer ellipsometer (RAE) and the rotating-compensator ellipsometer (RCE) of the polarizer-sample-compensator-analyzer type. The development is general and takes into account correlations among the Fourier coefficients of the transmitted intensity, in particular the average intensity, which is necessarily correlated with all other coefficients through normalization. The results are expressed in terms of the traditional uncertainties delta(psi) and delta(delta) of the ellipsometric parameters psi and delta, respectively, although a more appropriate measure of uncertainty is the differential area 2delta(psi) x sin psi(delta)delta on the unit-radius Poincaré sphere. Numerical results for broadband operation from 1.5 to 6.0 eV with a Si sample show that the optimum measurement conditions for both configurations occur when the intensity of light reflected from the sample is approximately balanced between the TE and the TM modes, and, for the RCE, when the analyzer azimuth is essentially equal to that of the polarizer. Under typical broadband operating conditions in which components cannot be optimized on a wavelength-by-wavelength basis, the RCE is better at determining delta, whereas the RAE is better at determining psi. The approach is easily generalized to other configurations and other types of experimental uncertainty, both random and systematic.

Precision in ellipsometrically determined sample parameters: simulation and experiment

A methodology for evaluating the precision of ellipsometrically determined model parameters (such as thickness) as a function of the measured data set (wavelength(s) and angle(s) of incidence) is presented and experimentally validated. This methodology is used to determine acceptable angle of incidence ranges for ellipsometric measurements and to study the merits of including multiple angles in the data set. Simulations and experimental results are presented for rotating analyzer ellipsometer and rotating compensator ellipsometer systems, using examples of thin and thick films on silicon substrates. A rigorous noise model is used to predict the ellipsometric measurement noise and Monte Carlo simulations are used to determine the parameter precision for a given data set.

Visible and infrared ellipsometry applied to the study of metal-containing diamond-like carbon coatings

Metal-containing diamond-like carbon (Me-DLC) films were deposited by combining r.f. plasma-enhanced chemical vapour deposition (PECVD) and pulsed d.c. magnetron sputtering of several target materials (Mo, Nb, Ti and W) at different gas mixtures of methane and argon (relative methane flow ratios varying from 0 to 25%). Spectroscopic ellipsometric measurements from 1.5 to 4.1 eV were performed by a multichannel rotating analyser ellipsometer. It can detect a full spectrum in 20 ms at fixed positions of the analyser. IR ellipsometric spectra of the Me-DLC thin films as well as of the bare substrates were obtained from 900 to 3500 cm −1 with a FTIR phase-modulated ellipsometer that takes advantage of an optimized calibration method. The optical properties (refractive index and absorption) showed a clear dependence on concentration and type of metal on the film. When methane flow ratio increases, the size and concentration of nanocrystalline particles determine the variation from pure metal optical properties to typical DLC values. Optical results are discussed along with X-ray diffraction data and ellipsometry allows for a high sensitive analysis of Me-DLC films.

Optical properties of CdSexTe1−x epitaxial films studied by spectroscopic ellipsometry

We have determined the dielectric constants for a series of CdSexTe1−x thin films grown on Si substrates using a rotating-analyzer spectroscopic ellipsometer. Initially, the alloy concentration and the sample quality were determined using x-ray diffraction. A standard inversion technique was then used to obtain the dielectric constants from the measured ellipsometric spectra. Using these calculated absorption spectra, we were able to estimate the fundamental bandgap for these CdSexTe1−x alloys. In addition, we also determined the dispersion of the indices of refraction as well as the critical points related to the higher-order electronic transitions for this alloy.

Precision auto-alignment for the specimen stage of an ellipsometer

We present a new three-step auto-alignment algorithm for the specimen stage of an ellipsometer with adjustable angle of incidence. Correction of errors in tilt angle and position of the specimen stage can be performed by locating the reflected light spot at the center of the detector at two different angles of incidence. The current method does not need auxiliary focusing equipment. The alignment algorithm works to high precision in both model simulation and practical experiments with a rotating analyzer ellipsometer.