Analyzer Ellipsometry Research Articles

Vacuum ultraviolet optical properties of GaSb determined by synchrotron rotating analyzer ellipsometry: applications in nanopillars and plasmonics

The vacuum ultraviolet (VUV) optical properties in the range 4 eV to 15 eV of GaSb have been determined by rotating analyzer ellipsometry (RAE) using synchrotron light. The localized surface plasmon resonances (LSPRs) and surface plasmon polaritons (SPPs) are studied as a means to understand the plasmonic behavior of GaSb. The large imaginary part of the dielectric function causes poor confinement of the SPP. Self-assembled GaSb nanopillars of 35 nm height are studied experimentally by RAE at different angles of incidence. The pillars are simulated numerically using an effective medium approach and the finite element method (FEM), where clear similarities between the simulations and experiment are observed. Additional dips in the reflectivity accompanied by increased nanopillar absorption and local field enhancement were observed near the surface of the pillars. These results demonstrate GaSb nanopillars to be promising candidates for photocathodes.

Element-selective magnetization states in a Gd23Fe67Co10 alloy, probed by soft X-ray resonant magneto-optical Kerr effect

The core-level resonant magneto-optical Kerr effect of a ferrimagnetic metal alloy, Gd23Fe67Co10, was measured at the Fe M-shell and Gd N-shell absorption edges using rotating analyzer ellipsometry. A large Kerr rotation angle of several degrees was detected at room temperature. The signal was found to be strong enough for element-selective magneto-optical experiments to trace various magnetic events, such as all-optical magnetization switching.

Shadow-casted ultrathin surface coatings of titanium and titanium/silicon oxide sol particles via ultrasound-assisted deposition

Ultrasound-assisted deposition (USAD) of sol nanoparticles enables the formation of uniform and inherently stable thin films. However, the technique still suffers in coating hard substrates and the use of fast-reacting sol–gel precursors still remains challenging. Here, we report on the deposition of ultrathin titanium and titanium/silicon hybrid oxide coatings using hydroxylated silicon wafers as a model hard substrate. We use acetic acid as the catalyst which also suppresses the reactivity of titanium tetraisopropoxide while increasing the reactivity of tetraethyl orthosilicate through chemical modifications. Taking the advantage of this peculiar behavior, we successfully prepared titanium and titanium/silicon hybrid oxide coatings by USAD. Varying the amount of acetic acid in the reaction media, we managed to modulate thickness and surface roughness of the coatings in nanoscale. Field-emission scanning electron microscopy and atomic force microscopy studies showed the formation of conformal coatings having nanoroughness. Quantitative chemical state maps obtained by x-ray photoelectron spectroscopy (XPS) suggested the formation of ultrathin (<10nm) coatings and thickness measurements by rotating analyzer ellipsometry supported this observation. For the first time, XPS chemical maps revealed the transport effect of ultrasonic waves since coatings were directly cast on rectangular substrates as circular shadows of the horn with clear thickness gradient from the center to the edges. In addition to the progress made in coating hard substrates, employing fast-reacting precursors and achieving hybrid coatings; this report provides the first visual evidence on previously suggested “acceleration and smashing” mechanism as the main driving force of USAD.

Optical properties, lattice dynamics, and structural phase transition in hexagonal2H−BaMnO3single crystals

Optical properties and lattice dynamics of hexagonal $2H\ensuremath{-}\mathrm{BaMn}{\mathrm{O}}_{3}$ single crystals are studied experimentally in a wide temperature range by means of rotating analyzer ellipsometry and Raman scattering. The magnitude of the direct electronic band gap is found to be ${E}_{g}=3.2\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. At room temperature the far-infrared (IR) ellipsometry spectra reveal six IR-active phonons; two of them are polarized along the $c$ axis and four are polarized within the a-b plane. Seven phonon modes are identified in the Raman scattering experiments. Group theoretical mode analysis and complementary density functional theory lattice dynamics calculations are consistent with the $2H\ensuremath{-}\mathrm{BaMn}{\mathrm{O}}_{3}$ structure belonging to the polar $P{6}_{3}mc$ space group at room temperature. All observed vibrational modes are assigned to specific eigenmodes of the lattice. The neutron diffraction measurements reveal a structural phase transition upon cooling below ${T}_{C}=130\ifmmode\pm\else\textpm\fi{}5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is accompanied by a lattice symmetry change from $P{6}_{3}mc$ to $P{6}_{3}cm$. Simultaneously, at temperatures below ${T}_{C}$ several additional IR- and Raman-active modes are detected in experimental spectra. This confirms the occurrence of a structural transition, which is possibly associated with the appearance of electrical polarization along the $c$ axis and a previously known tripling of the primitive cell volume at low temperatures.

Improved full-field rotating analyzer ellipsometry method for ultrathin film characterization

We describe an improved approach for accurately characterizing the thickness distribution of ultrathin films by using full-field rotating analyzer ellipsometry. The significant improvements originate from the combination of angle optimization and error compensation. Angle optimization is achieved by fixing the polarizer and the quarter wave plate (QWP) at the averaged values of a series of optimal angles, which correspond to a certain thickness range of the sample. At the same time, error compensation further improves the accuracy by determining and removing the nonuniform impact of the QWP. To verify the applicability of the proposed method, experiments based on varied ultrathin films are implemented and compared with the results of two conventional methods. The results from the proposed method are in accord with those obtained using commercial instrument and the design value in thermal evaporation system. Further investigation shows that the uncertainties of the ellipsometric angles, both Ψ and Δ, are less than 0.045 deg, with a lateral resolution of 4.65 μm. Because of its improved accuracy, this method offers a feasible route for characterizing film thickness, especially in the case of monitoring the growth of thin layers from a bare substrate or following changes in the sample parameters during a kinetic process.

Ultrafast spin-switching of a ferrimagnetic alloy at room temperature traced by resonant magneto-optical Kerr effect using a seeded free electron laser.

Ultrafast magnetization reversal of a ferrimagnetic metallic alloy GdFeCo was investigated by time-resolved resonant magneto-optical Kerr effect measurements using a seeded free electron laser. The GdFeCo alloy was pumped by a linearly polarized optical laser pulse, and the following temporal evolution of the magnetization of Fe in GdFeCo was element-selectively traced by a probe free electron laser pulse with a photon energy tuned to the Fe M-edge. The results have been measured using rotating analyzer ellipsometry method and confirmed magnetization switching caused by ultrafast heating.

Asymmetric information hiding and noise-free recovery based on rotating analyzer ellipsometry and quick-response code.

We report an asymmetric optical information hiding method based on a rotating analyzer ellipsometry technique. This asymmetric hiding architecture not only avoids the interception of keys during transmission or distribution but also makes the cyphertext more inconspicuous for attackers. A new kind of one-way optical trapdoor function is constructed based on the fact that the state of polarization (SOP) of elliptical polarized light cannot be recovered with only the knowledge of intensity captured after passing through a linear polarizer. Meanwhile, the SOP of a polarization ellipse could be calculated by rotating the polarizer to record two scenes of intensity after it. Introduction of a quick response code as a container leads to noise-free recovery for original information and enhances practicality of the proposed cryptosystem with versatile key sensitivity and fault tolerance capability. Numerical simulation results that support theoretical analysis are presented. Analysis on the relationship between hiding effect or quality of decryption and parameters of the algorithm also is provided.

Infrared-active optical phonons and magnetic excitations in the hexagonal manganites RMnO3 ( R=Ho , Er, Tm, Yb, and Lu)

Optical properties of hexagonal multiferroic oxides $R\mathrm{Mn}{\mathrm{O}}_{3}$, where $R=\mathrm{Ho}$, Er, Tm, Yb, and Lu, have been studied in the far-infrared spectral range between 100 and 2000 cm${}^{\ensuremath{-}1}$ and temperatures between 1.5 and 300 K by means of several experimental techniques: Mueller matrix spectroscopic ellipsometry, rotating analyzer ellipsometry, and optical transmission spectroscopy. Spectra of the optical phonons are described in terms of the temperature dependencies of their frequency, damping, and oscillator strength. For all studies, oxide materials' clear signatures of the spin-phonon interaction have been found below the temperature of the antiferromagnetic phase transition ${T}_{N}$ due to magnetic ordering of ${\mathrm{Mn}}^{3+}$ spins. A decrease of the ionic radius for ${R}^{3+}$ ions between ${\mathrm{Ho}}^{3+}$ and ${\mathrm{Lu}}^{3+}$ in the corresponding $R\mathrm{Mn}{\mathrm{O}}_{3}$ compounds resulted in systematic variation of the frequency for several optical phonons. A magnetic excitation at \ensuremath{\sim}190 cm${}^{\ensuremath{-}1}$ was observed at low temperatures below ${T}_{N}$ and interpreted as resulting from two-magnon absorption.

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.

결맞음길이보다 두꺼운 두 개의 막에 덮여있는 시료의 타원식

회전검광자 방식의 타원계 구조에 기초하여 두꺼운 막들 내부에서 일어나는 다중반사에 인한 빛의 세기를 결맞지 않도록 중첩함으로써 결맞음길이보다 두꺼운 막 두 개가 다층박막시료 위에 있을 때 적용되는 타원상수 표현들을 유도하였다. 유도된 표현들을 커버유리와 공기층 아래에 있는 산화규소 박막이 코팅되어 있는 시료의 타원법 분석에 적용하여 그 유용성을 확인하였다. The expressions for ellipsometric constants of a sample covered with two thick films are derived, where incoherent superposition of multiply reflected lights inside thick films is properly considered in the frame of the rotating analyzer ellipsometry. The derived expressions are successfully applied to the analysis of a silicon wafer with a thin silicon dioxide film on it, which is placed beneath a cover glass and an air gap.

Synchrotron radiation-based far-infrared spectroscopic ellipsometer with full Mueller-matrix capability

We developed far-IR spectroscopic ellipsometer at the U4IR beamline of the National Synchrotron Light Source in Brookhaven National Laboratory. This ellipsometer is able to measure both, rotating analyzer and full-Mueller matrix spectra using rotating retarders, and wire-grid linear polarizers. We utilize exceptional brightness of synchrotron radiation in the broad spectral range between about 20 and 4000 cm(-1). Fourier-transform infrared (FT-IR) spectrometer is used for multi-wavelength data acquisition. The sample stage has temperature variation between 4.2 and 450 K, wide range of θ-2θ angular rotation, χ tilt angle adjustment, and X-Y-Z translation. A LabVIEW-based software controls the motors, sample temperature, and FT-IR spectrometer and also allows to run fully automated experiments with pre-programmed measurement schedules. Data analysis is based on Berreman's 4 × 4 propagation matrix formalism to calculate the Mueller matrix parameters of anisotropic samples with magnetic permeability μ ≠ 1. A nonlinear regression of the rotating analyzer ellipsometry and∕or Mueller matrix (MM) spectra, which are usually acquired at variable angles of incidence and sample crystallographic orientations, allows extraction of dielectric constant and magnetic permeability tensors for bulk and thin-film samples. Applications of this ellipsometer setup for multiferroic and ferrimagnetic materials with μ ≠ 1 are illustrated with experimental results and simulations for TbMnO3 and Dy3Fe5O12 single crystals. We demonstrate how magnetic and electric dipoles, such as magnons and phonons, can be distinguished from a single MM measurement without adducing any modeling arguments. The parameters of magnetoelectric components of electromagnon excitations are determined using MM spectra of TbMnO3.

Measurement of the polarization for soft X-ray magnetic circular dichroism at the BSRF beamline 4B7B

Three ultra-short-period W/B4C multilayers (1.244 nm, 1.235 nm and 1.034 nm) have been fabricated and used for polarization measurement at the 4B7B Beamline at the Beijing Synchrotron Radiation Facility (BSRF). By using the rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700–860 eV. The first soft X-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.

Far-infrared spectra of the magnetic exchange resonances and optical phonons and their connection to magnetic and dielectric properties of Dy3Fe5O12garnet

Far-infrared spectra of ferrimagnetic Dy${}_{3}$Fe${}_{5}$O${}_{12}$ single crystals have been studied in the spectral range between 12 and 700 cm${}^{\ensuremath{-}1}$ and in a wide temperature range between 5 K and 300 K using transmission spectroscopy and rotating analyzer ellipsometry. In the temperature range below ${T}_{C}$ = 16 K for the magnetic ordering of Dy${}^{3+}$ spins, a number of ligand field and Kaplan-Kittel (KK) exchange resonance modes have been found. Temperature dependencies of their frequencies allowed us to estimate the ratio between the Fe-Dy and Dy-Dy exchange constants. We found that variation of the oscillator strength of the KK modes correlates with the magnetic-field-induced changes of magnetic permeability. The low-temperature peak in the static value of the dielectric function at ${T}_{C}$ = 16 K may be related to the observed temperature-induced variation of the oscillator strength of the optical phonons.

Adjusted oscillator strength matching for hybrid magnetic and electric excitations in Dy3Fe5O12garnet

Far-infrared spectra of magneto-dielectric Dy3Fe5O12 garnet were studied between 13 and 100 cm-1 and at low temperatures between 5 and 80 K. A combination of transmission, reflectivity, and rotating analyzer ellipsometry was used to unambiguously identify the type of the dipole activity of the infrared modes. In addition to purely dielectric and magnetic modes, we observed several hybrid modes with a mixed magnetic and electric dipole activity. These modes originate from the superexchange between magnetic moments of Fe and Dy ions. Using 4x4 matrix formalism for materials with Mu=/=1, we modeled the experimental optical spectra and determined the far-infrared dielectric and magnetic permeability functions. The matching condition Mu(Wh)*Se=Eps(Wh)*Sm for the oscillator strengths Se(m) explains the observed vanishing of certain hybrid modes at Wh in reflectivity.

3-dimensional local field polarization vector mapping of a focused radially polarized beam using gold nanoparticle functionalized tips

We have measured local electric field polarization vectors in 3-dimensional space on the nanoscale. A radial polarized light is generated by using a radial polarization converter and focused by an objective lens. Gold nanoparticle functionalized tips are used to scatter the focused field into the far-field region. Two different methods, rotational analyzer ellipsometry and Stokes parameters, are used in determining the polarization state of the scattered light. Two methods give consistent results with each other. Three dimensional local polarization vectors could be reconstructed by applying back transformation of the fully characterized polarizability tensor of the tip.

Characteristic of Nanoporous SiO&lt;sub&gt;2&lt;/sub&gt; Thin Film Prepared by Sol-Gel Method with Catalyst HF

The characteristic of nanoporous SiO2 thin film prepared by sol-gel method with catalyst HF was studied by scanning electron microscopy, Fourier transform infrared, HP analyzer series and ellipsometry. Results showed the incorporation of HF effectively adjusted the pore size and distribution, and lowered the leakage current density and dielectric constant. This might be related to the weak acidity of HF, which properly controlled the velocity of chemical reaction in solution, and to the introduction of strong Si-F bonds, which had the lower electronegative and the larger volume.

Liquid phase epitaxy growth of bismuth-substituted yttrium iron garnet thin films for magneto-optical applications

The novel Bi-substituted rare-earth iron garnet films were grown by the modified liquid phase epitaxy (LPE) technique for use as a 45° Faraday rotator in optical isolators. First, single crystals of Y 3Fe 5O 12 (YIG), with a lattice constant of 1.2378 nm, were grown by means of the Czochralski method. Using the seed crystal of YIG instead of the conventional non-magnetic garnet of Gd 3Ga 5O 12 as a substrate, a film of BiYbIG was grown by means of the LPE method from Bi 2O 3–B 2O 3 fluxes. The structural, magnetic and magneto-optical properties of BiYbIG LPE film/YIG crystal composite have been investigated using directional X-ray diffraction, electron probe microanalysis, vibrating sample magnetometer and near-infrared transmission spectrometry. The saturation magnetization 4πM s has been estimated to be approximately 1200 G. The Faraday rotation spectrum was measured by the method of rotating analyzer ellipsometry with the wavelength varying from 800 to 1700 nm. The resultant Bi 0.37Yb 2.63Fe 5O 12 LPE film/YIG crystal composite showed an increased Faraday rotation coefficient due to doping Bi 3+ ions on the dodecahedral sites of the magnetic garnet without increasing absorption loss, therefore a good magneto-optic figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved of 21.5 deg/dB and 30.2 deg/dB at 1300 nm and 1550 nm wavelengths, respectively, at room temperature. Since Yb 3+ ions and Y 3+ ions provide the opposite contributes to the wideband and temperature characteristic of Faraday rotation, the values of Faraday rotation wavelength and temperature coefficients were reduced to 0.06%/nm and 0.007 deg/°C at 1550 nm wavelength, respectively.

The optical properties of liquid plutonium at 632.8 nm

The optical properties and normal, spectral emissivity of liquid plutonium at 632.8 nm were measured over a temperature range of 2016–2189 K using rotating analyzer ellipsometry. The purity of the liquid was maintained in a containerless environment using electromagnetic levitation and heating. The material investigated contained 1 wt% Ga that was added during the casting process. The measured values of the optical property results are given as a function of temperature by ϵ λ =5.38×10 −5 T+0.250, n λ =−1.29×10 −4 T+3.82, and k λ =−7.04×10 −4 T+5.77 over the investigated temperature range.

Depolarization and principal Mueller matrix measured by null ellipsometry

Methods for accurately measuring depolarization and principal Mueller matrix by null ellipsometry are devised. The measurement errors obtained with these methods are analyzed, and methods to correct for the errors are devised. The depolarization spectrum measured directly by null ellipsometry for a sapphire slab agrees excellently with the depolarization spectrum reduced indirectly from the retardance spectrum measured by rotating analyzer ellipsometry and the depolarization spectrum simulated for the retardance spread caused by a finite bandwidth of monochromator [J. Opt. Soc. Am. A 17, 2067 (2001)]. The measured cross-polarized depolarization for the sapphire slab is much smaller than the total depolarization.

The optical properties of liquid cerium at 632.8 nm

The normal, spectral emissivity, ε λ (T), and optical constants, n and k, of liquid cerium were measured at 632.8 nm over a temperature range of 1700–2130 K using rotating analyzer ellipsometry. The cerium was electromagnetically levitated to prevent contamination of the liquid metal by contact with a container and purified by vaporization of volatile oxides at high temperature. The emissivity at 0.9 μm and 1900 K was determined from the brightness temperature. The solubility of oxygen in liquid cerium at 1786 K was estimated and the effect of oxygen on the optical properties was demonstrated. Using available thermodynamic data and assumptions of ideal solution behavior, the volatilization of oxygen and nitrogen impurities is discussed. At 1786 K, the solubility of oxygen in liquid cerium is between 3 and 7 atom percent.