Ellipsometry Data Research Articles

Systematic Assessment of Phonon and Optical Characteristics for Gas-Source Molecular Beam Epitaxy-Grown InP1−xSbx/n-InAs Epifilms

Experimental and theoretical assessments of phonon and optical characteristics are methodically accomplished for comprehending the vibrational, structural, and electronic behavior of InP1−xSbx/n-InAs samples grown by Gas-Source Molecular Beam Epitaxy. While the polarization-dependent Raman scattering measurements revealed InP-like doublet covering optical modes (ωLOInP~350 cm−1, ωTOInP~304 cm−1) and phonons activated by disorders and impurities, a single unresolved InSb-like broadband is detected near ~195 cm−1. In InP1−xSbx, although no local vibrational (InSb:P; x → 1) and gap modes (InP:Sb; x → 0) are observed, the Raman line shapes exhibited large separation between the optical phonons of its binary counterparts, showing features similar to the phonon density of states, confirming “two-mode-behavior”. Despite the earlier suggestions of large miscibility gaps in InP1−xSbx epilayers for x between 0.02 and 0.97, our photoluminescence (PL) results of energy gaps insinuated achieving high-quality single-phase epilayers with x ~ 0.3 in the miscibility gap. Complete sets of model dielectric functions (MDFs) are obtained for simulating the optical constants of binary InP, InSb, and ternary InP1−xSbx alloys in the photon energy (0 ≤ E ≤ 6 eV) region. Detailed MDF analyses of refractive indices, extinction coefficients, absorption and reflectance spectra have exhibited results in good agreement with the spectroscopic ellipsometry data. For InP0.67Sb0.33 alloy, our calculated lowest energy bandgap E0 ~ 0.46 eV has validated the existing first-principles calculation and PL data. We feel that our results on Raman scattering, PL measurements, and simulations of optical constants provide valuable information for the vibrational and optical traits of InP1−xSbx/n-InAs epilayers and can be extended to many other technologically important materials.

Optical Properties of Ferroelectric Films HfxZryO2 and La:HfxZryO2 according to Ellipsometry Data

Optical Properties of Ferroelectric Films HfxZryO2 and La:HfxZryO2 according to Ellipsometry Data

Dielectric function and band gap determination of single crystal CuFeS2 using FTIR-VIS-UV spectroscopic ellipsometry

Spectroscopic ellipsometry measurements were performed on antiferromagnetic semiconductor CuFeS2 grown via molecular beam epitaxy. UV/Visible and IR ellipsometry data was merged and modeled to derive the dielectric function of CuFeS2 from 30 meV to 4.5 eV. The CuFeS2 samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and cross-section scanning electron microscopy (SEM) which gave the crystal quality, surface roughness and sample film thickness. A critical point analysis revealed a direct band gap of 0.76 eV, while modeling gives a carrier concentration of 8 ± 2 × 1019~cm−3 and an estimate of the indirect band gap of 0.5 eV. Optically active infrared phonons were observed at 319 cm−1 and 350 cm−1 with significant Raman active modes at 85.8 cm−1, 265 cm−1, 288 cm−1, 318 cm−1 and 377 cm−1. The fitted optical constants were then used to characterize the crystal quality and spatial uniformity.

Synthesis of PEDOT: PSS thin film doped with silver nanoparticles via green approach and study their refractive indices and dispersive parameters using Wemple–DiDomenico (WDD) single oscillator model

Silver nanoparticles (AgNPs) synthesised via green synthesis using clove extract were incorporated into PEDOT:PSS polymers using the chemical solution deposition technique (CSD), and the effect of surface plasmon resonance in the nanocomposites was investigated. To assess the effect of Silver nanoparticles (AgNPs) (and surface plasmon resonance) on the polymer, TEM, UV–Visible spectroscopy, FTIR, Ellipsometry, and Photoluminescence are used. The surface plasmon peak of the curves in UV–Vis spectroscopy study of these films has shifted towards the infrared region, which may be useful in increasing the efficiency of optical devices. The optical band gap calculated using UV–Vis results reduced from 1.77eV for pure PEDOT: PSS to 1.53eV for the nanocomposite. Ellipsometry data is used to calculate Ψ, Δ values and thickness of films. The Wemple-DiDomenico (WDD) single oscillator model was used to analyse and estimate the dispersion parameters of these films. Refractive indices the films were calculated in the range 1.256–1.643 using the Ellipsometry data.

Polymerization of aromatic dinitroso derivatives initiated by nitroso-terminated monolayer on Au(111) surface: Insights from ellipsometry, AFM and nano-FTIR spectroscopy

The possibility of on-surface intermolecular interactions of aromatic C-nitroso derivatives and the formation of azodioxy polymer thin films were studied by ellipsometry, atomic force microscopy (AFM) and nanoscale Fourier transform infrared (nano-FTIR) spectroscopy. The nitroso terminal groups of monolayers of 3-thiocyanatopropyl-4-nitrosobenzoate on Au(111) surface were used as initiation sites for formation of azodioxy linkages by interactions with the six structurally different aromatic dinitroso derivatives prone to polymerization. Ellipsometry showed increased thicknesses of films formed by interactions of nitroso groups at the monolayer interface and aromatic dinitroso derivatives in solution suggesting the formation of azodioxy oligomer films. The obtained thickness values indicated that the films are composed of only a few monomeric subunits or that poorly organized surface structures are formed with possibly tilted and intertwined chains. Ellipsometry data were corroborated with AFM topography images which revealed the appearance of a high number of islands, attributed to domains of azodioxy oligomers, and increased local RMS roughness values. Both ellipsometry and AFM indicated a greater tendency towards the azodioxy oligomers on the Au(111) surface at longer adsorption times. Nano-FTIR spectroscopy enabled chemical identification of the films at the nanoscale. Bands attributed to the E-azodioxy groups were detected in nano-FTIR spectra, which strongly supported the conclusion that the islands in the AFM images represent azodioxy oligomers, the formation of which was initiated by interactions of nitroso groups at the monolayer interface with dinitroso derivatives in solution.

Mapping the changes in the optical properties of azobenzene films due to photoisomerization

We used spectroscopic ellipsometry to study the dielectric function of an azobenzene polymer called Poly(disperse Red 1 methacrylate) (PDRM) as it underwent a photoisomerization process. The polymer films were fabricated by dissolving PDRM in tetrahydrofuran, and by spin coating films on silicon substrates. After fabricating the films, we used UV-VIS spectroscopic ellipsometry to determine the index of refraction, extinction coefficient and the thickness of each film. Using a heating cell coupled to the ellipsometer, we obtained temperature dependent ellipsometry data from 34 ℃ to 180 ℃, spanning a spectral region between 300 nm and 1500 nm. Using the raw data, we determined that the glass transition temperature of PDRM was 85 ℃ ± 3 ℃. Employing a three-oscillator model, we deduced the temperature dependent dielectric functions of PDRM films. Subsequently, the films were photoisomerized at two polarizations using a visible laser. For the horizontal polarization, there is nearly a 15% a change in the extinction coefficient as the PDRM films undergo a photoisomerization process.

Enhancing Titania-Tantala Amorphous Materials as High-Index Layers in Bragg Reflectors of Gravitational-Wave Detectors

Amorphous mixed titania-tantala coatings are key components of Bragg reflectors in gravitational-wave detectors (GWDs). Attaining the lowest possible values of optical absorption and mechanical losses in coatings is of paramount importance for GWDs, and this requires a complex optimization of the coating deposition and postdeposition annealing. We present here a systematic investigation of the optical properties and internal friction of amorphous mixed titania-tantala coatings grown by ion beam sputtering. We consider coatings with six different cation mixing ratios─defined as Ti/(Ti + Ta)─and we study them both in the as-deposited and annealed states. All coatings have been subject to the same annealing of 500 °C for 10 h in air, which is the postdeposition treatment adopted so far for Bragg reflectors in GWD applications. By exploiting spectroscopic ellipsometry data and modeling, along with ancillary techniques, we retrieved the dielectric function of the coatings in a wide spectral range. When varying the mixing ratio and performing the annealing, we find monotonic─in some cases, almost linear─trends for most of the aforementioned properties. Remakably, the postannealing Urbach energy displays a definite minimum for a mixing ratio around 20%, very close to the composition of the coatings showing the lowest optical absorption for GWD applications. We suggest that the observed minimum in the Urbach energy depends not only on the mixing ratio but also on the annealing parameters. On the other hand, the minimum coating loss angle was found to be weakly dependent on the considered measurement frequency and to lie within a rather broad range of Ti content (cation ratios of 21 and 44%), suggesting that the search for an absolute minimum following postdeposition annealing should be rather sought in the study of the best annealing parameters for each specific cation ratio considered. This work constitutes a reference for the optical properties of the amorphous mixed titania-tantala coatings and highlights the relevance of the Urbach energy as an additional parameter to guide the optimization process of materials for high-performing Bragg reflectors.

Investigation of porous ZnSe thin films prepared by thermal evaporation

ZnSe films with thickness of 50, 70 and 100 nm were prepared on Corning 7059 glass substrates at room temperature by applying continuous or periodically interrupted physical vapour deposition at very low deposition rates (0.2 and 0.5 nm s−1). Part of the films was annealed at 200 °C after deposition. Optical absorption spectra determined from spectroscopic ellipsometry data show direct allowed transitions, which indicate that the films have microcrystalline structure. This is in agreement with scanning electron microscopy and atomic force microscopy results. The spectroscopic ellipsometry results also show that the porosity of the films is strongly affected by both manner of deposition and deposition rate; the annealing causes some porosity decrease. Optical transmission spectra reveal that the transmittance of as-deposited films, obtained by periodically interrupted manner is significantly influenced by their porosity.

The role of small molecules and quantum dots doping on the morphology of layers for potential applications in ternary solar cells

The publication presents the effect of different types of the third component on the morphologies and layer arrangement in three-component mixtures. The three-component layers are being studied for implementation as an active layer for a three-component organic cell. Thin films were studied using optical methods. The gradient model for the individual layers and the dispersion relations of the refractive indices and extinction coefficients were obtained. Layer modeling was carried out using spectroscopic ellipsometry data. The morphology of the layers was demonstrated using atomic force microscopy. Images of the ternary layers were also obtained using the scanning electron microscopy method.

Evaluation of the surface and subsurface evolution of single-crystal yttrium aluminum garnet during polishing

Yttrium aluminum garnet (Y3Al5O12/YAG) has attracted extensive research and application interest in the field of optoelectronics. However, the evolution mechanism of the surface and subsurface of YAG single crystals during polishing have not been elucidated, thus hindering the in-depth understanding of the processing mechanism of brittle solids. Herein, rough and fine polished YAG crystals were obtained by designing a processing scheme, and the surface and subsurface were expeditiously evaluated simultaneously by angle-resolved ellipsometry. The dependence between the ellipsometric parameter near the Brewster angle and the surface and subsurface quality was determined by modeling the polished surface and subsurface damage optics. The monotonicity of the quasi-Brewster angle shift (qBAS) reveals the diminishing feature of subsurface damage, and the oscillation of the slope unveils the atomic-level topography evolution of the polished planes. The results were validated using data from surface and subsurface damage tests, thereby proving the feasibility and reliability of the method. Furthermore, the refractive indices (210–1690 nm) of YAG were identified based on the spectroscopic ellipsometry data of the fine polished crystal. These findings provide a promising paradigm for predicting and evaluating the surface and subsurface microstructures and optical properties of brittle solids in material-removal-based surface engineering.

In situ spectroscopic ellipsometry and rigorous coupled wave analysis for real time profile evolution of atomic layer deposited films inside SiO2 nanotrenches

Rigorous coupled wave analysis (RCWA) is conducted on in situ spectroscopic ellipsometry data to understand profile evolution during film deposition inside nanotrenches. Lithographically patterned SiO2 nanotrenches are used as test structures. The nanotrenches are 170 nm wide at the top with a taper angle of 4.5° and are 300 nm in depth. Atomic layer deposition of ZnO is used as a model process where the thickness (cycles) of the film is varied from 0 (0 cycles) to 46 nm (300 cycles). The analysis predicts transient behavior in deposition affecting film conformality and changes to the trench taper angle. In the process, the aspect ratio varies from 2.05 at the start of the process to 6.67 at the end. The model predicts changes in the refractive index of the ZnO film as a function of thickness. The real and imaginary parts of the refractive index at a wavelength of 350 nm change from 1.81 to 2.37 and 0.25 to 0.87, respectively. Scanning electron microscopy cross sections confirm thickness at the top and bottom of the trench to within 13% of those predicted by RCWA. The experimentally measured conformality degrades as film deposition proceeds from 97.3% at 100 cycles to 91.1% at 300 cycles. These results demonstrate the potential of using RCWA for continuous and in situ monitoring of growth inside 3D nanostructures.

Investigating the optical response of titanium-nitride thin films after silver ion implantation and post-thermal annealing

The paper reports the study on dielectric functions of TiN films implanted with Ag ions and after annealing at 400 °C and 700 °C, employing spectroscopic ellipsometry technique. By using Drude-Lorentz modelling we have analysed and discussed in detail the evolution of screened and unscreened plasma frequency as well as Drude parameter. In comparison to as deposited film the real part of dielectric constant for Ag-implanted layers exhibits less negative values with increasing ion fluence implying the films possess less metallicity, whereas after annealing TiN becomes more metallic. Simultaneously, after implantation, the imaginary part is more than an order of magnitude lower than for the as deposited TiN and several times lower than that of Au and Ag. The magnitude of imaginary contribution of Ag-implanted TiN films decreases further after subsequent heat treatment at both 400 °C and 700 °C annealing temperatures. Although the differences in stoichiometry and microstructural changes, such as crystallite size, concentration of grain boundaries and defect density were assumed to be the major reason for the variation in optical properties of TiN, spectroscopic ellipsometry data exhibited much stronger effects than expected and indicated some other mechanisms could also be responsible for such behaviour.

A model for spectroscopic ellipsometry analysis of plasma-activated Si surfaces for direct wafer bonding

In this work, the impact of plasma treatment on Si wafers with native oxide on top was systematically investigated using spectroscopic ellipsometry. A general applicable three-layer optical model structure for ellipsometry data fitting was developed and employed on samples treated with the N2, O2, and N2/O2 mixture plasma. Oxide-growth, amorphization of crystalline Si, and the formation of a transition layer between the SiO2 and the amorphous Si were detected. The estimated thicknesses of produced layers were confirmed by complementary methods, which allow precise ultra-thin layers thicknesses detection, namely, angle-resolved x-ray photoelectron spectroscopy and transmission electron microscopy. The depth-resolved chemical composition and the direct thickness measurements of the produced amorphous structure revealed pronounced elemental gradients and the absence of sharp interfaces. Nitrogen gas used in the plasma process was found to be implanted mainly at the interface of the SiO2/transition layer in the form of Si3N4. However, it was verified that it is feasible to employ one general ellipsometry model consisting of SiO2/transition layer/amorphous Si on crystalline Si for all plasma species due to comparably low Si3N4 concentrations as well as its refractive index n and absorption k similarity to SiO2. Spectroscopic ellipsometry is nondestructive and can be efficiently applied to analyze whole wafers without any sample preparation. It can be concluded that the present approach to ellipsometry model development and verification is well suited for plasma-activated direct wafer bonding processes.

Carbon Nanoparticle-Induced Changes to Lipid Monolayer Structure at Water-Air Interfaces.

Surface specific vibrational spectroscopy experiments together with surface tension measurements and spectroscopic ellipsometry data were used to characterize the effects of soluble carbon particulates on compressed and partially compressed lipid monolayers adsorbed to the water-air interface. The lipid monolayers consisted of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DPPC), and measurements were made for both tightly packed monolayers (40 Å2/molecule) and monolayers in their liquid condensed state (55 Å2/molecule). Langmuir trough data show that very small amounts of PHF (0.0075 mg/mL or 6.4 × 10-6 M) decrease lipid film compressibility. This finding supports a cooperative adsorption mechanism whereby the soluble PHFs are drawn to the surface and associate with the insoluble DPPC monolayer. Excess free energies (ΔGmixE) were positive, consistent with the cooperative adsorption mechanism, and although the excess free energies are small (≤1 kJ/mol), adsorbed PHF has measurable effects on monolayer structure. Further support for the cooperative adsorption mechanism at the water-air interface comes from vibrational sum frequency generation (VSFG) experiments. Low PHF concentrations (≤0.06 mg/mL) increase DPPC acyl chain ordering in liquid condensed lipid films and decrease DPPC acyl chain ordering and film thickness in tightly packed lipid films.

Spectroscopic ellipsometry characterization of PbWO4 single crystals

Optical characterization of PbWO4 single crystals grown by Czochralski method was achieved in virtue of spectroscopic ellipsometry experiments carried out in the energy region of 1.0–5.6 eV at room temperature. Tetragonal scheelite structure with lattice parameters of a = b = 5.4619 Å and c = 12.0490 Å was determined for the bulk crystal utilizing from XRD analysis. Analyses of the ellipsometry data presented the photon energy dependencies of complex dielectric function of the crystal. The real part of the dielectric function exhibited increasing behavior with energy in the below 4.1 eV and then decreased immediately. Zero frequency refractive index and dielectric constant were determined to be 2.02 and 4.08, respectively, using Wemple and DiDomenico oscillator model. High frequency dielectric constant was calculated as 4.30 by Spitzer-Fan model. Optical band gap of PbWO4 was found to be 3.24 eV from the dielectric relaxation time spectrum. Moreover, existence of two critical points with energies of 3.70 and 4.58 eV was revealed from the analyses of extinction coefficient and second derivative of the dielectric function. These levels were considered to be due to creation of cation exciton (Pb2+ 6s2 − Pb2+ 6s6p) and transitions in the [WO4]2− group.

Certain topics in ellipsometric data modeling with splines: a review of recent developments

AbstractDielectric function representation by a variety of polynomial spline functions provides a consistent and efficient method for accurate modeling of the material optical properties in the context of spectroscopic ellipsometry data interpretation. Splines as an elegant and purely mathematical way for such modeling task were introduced about three decades ago. In the following years the use of splines in the area of ellipsometric data analysis became widely utilized. The goal of this review is to provide a self-contained presentation on the current status of the dielectric function modeling by splines for advanced industrial ellipsometry users but, hopefully, it can be useful for some scholarly users as well. It is also intended to promote more extended recognition of the spline-based modeling among optical metrology professionals. Here, a brief description of different ways, – ordinary polynomials, piecewise polynomials (splines), and B(asis)-spline functions, – is presented to parameterize an arbitrary function which can be used as an analytic representation of the dielectric-function curves. A number of particular polynomial-based models for the optical functions of materials and how they may be used in applications are also discussed. Particular attention is paid to different concepts of the efficient and optimal spline construction.

Investigation of optical characteristics of PbMoO4 single crystals by spectroscopic ellipsometry

In this study, we investigated the optical properties of PbMoO4 single crystals grown by Czochralski method. Spectroscopic ellipsometry measurements were carried out in the energy region between 1.0 and 5.5 eV at room temperature. X-ray diffraction measurements were achieved for structural characterization. The resulted pattern exhibited one peak belonging to (200) plane. Spectral variations of complex dielectric function, complex refractive index, absorption coefficient and dissipation function were obtained from the analyses of ellipsometry data. Real part of dielectric function increased up to 4.0 eV and then decreased suddenly at above this value. Zero frequency refractive index and dielectric constant were found to be 2.04 and 4.15, respectively. High frequency dielectric constant was determined to be 4.36. Optical band gap of PbMoO4 crystals was calculated as 3.09 eV. Two critical points with energies of 3.57 and 4.34 eV were estimated from the analyses of second-energy derivative spectra of real and imaginary parts of dielectric function. It was determined that [MoO4]2− complexes and charge transfer from Pb2+ ions into the neighboring Mo groups were responsible for these interband transitions. Dissipation function increased with increasing photon energy.

The spectroscopic ellipsometry measurement of non-polar freestanding GaN: comparison between isotropic and anisotropic models

For anisotropic materials, the pseudo-dielectric function (DF) from isotropic model is often applied in spectroscopic ellipsometry data analysis instead of the DF from anisotropic model because of its simplicity. Whether this approximation is applicable depends on the discrepancy between the pseudo-DF and the DF, which we find to be related to the illumination configuration greatly. For the ellipsometry spectra obtained from a non-polar freestanding GaN in two configurations with the c-axis perpendicular and parallel to the incident plane respectively, both anisotropic model and isotropic model are used to compare the difference between the fitted absorption coefficient and pseudo-absorption coefficient. As a consequence, the discrepancy between the two coefficients is less than 10 even at the absorption edge when electric field is perpendicular to the c-axis, while the discrepancy exceeds 40 at the absorption edge when electric field is parallel to the c-axis. These results indicate that the approximation of using isotropic model instead of anisotropic model is reasonable in the former configuration, while it is not applicable in the latter configuration and will render an overestimation of bandgap. The above two different discrepancies could be explained by the first-order term approximation of pseudodielectric function. We further demonstrate the necessity for anisotropic model by comparing the deviations of the crystal-field splitting obtained from anisotropic and isotropic model with the theoretical value respectively.

Optical properties of Sub-30 nm-thick ZnS films studied by spectroscopic ellipsometry

The sub-30 nm-thick ZnS thin films with different thicknesses were deposited on Si substrates by electron beam evaporation (EBE). The thickness and optical constants of ZnS films were obtained by fitting spectroscopic ellipsometry (SE) data using Tauc-Lorentz Model. The variation of refractive index, extinction coefficient, optical band gap, the complex dielectric function of the samples with film thickness was analyzed. Due to the increase of film density, the refractive index increases with the thickness, and the extinction coefficient has the same trend. Due to the quantum size effect, the optical band gap decreases from 3.56 eV to 3.23 eV with increasing film thickness. Two peaks (E0 and E1) are obtained from the complex dielectric function spectrum, which most likely corresponds to the central energy of the exciton optical transition. Three critical points (CP) energies (EA, EB, and EC) and the types of interband optical transitions were extracted from the standard linear analysis of the second-order derivatives of the dielectric function. The three CPs energies have a significant thickness dependence, which is mainly attributed to quantum size effects. This result is beneficial for the design and application of photonic and optoelectronic devices with sub-30 nm-thick ZnS films.

Optical properties of ferroelectric films Hf-=SUB=-x-=/SUB=-Zr-=SUB=-y-=/SUB=-O-=SUB=-2-=/SUB=- and La : Hf-=SUB=-x-=/SUB=-Zr-=SUB=-y-=/SUB=-O-=SUB=-2-=/SUB=- according to ellipsometry data

Recently ferroelectric properties have been found in hafnia-based nanosized films. Such films are of the utmost interest for development of a universal memory, which combines the advantages of random access memory and flash memory. The paper studies optical properties of hafnia-zirconium oxide films HfxZryO2 and lanthanum-alloyed hafnia-zirconium oxide films La : HfxZryO2. Fluctuations of thickness in HfxZryO2 do not exceed 3.5%, fluctuations of thickness in La : HfxZryO2 films --- 3.2%. Optical properties are analyzed based on effective-medium theory. According to effective-medium theory data, HfxZryO2 films contain 46% HfO2, 54% ZrO2, La : HfxZryO2 films contain 47.5% HfO2, 52.4% ZrO2, 2.5% La2O3. Keywords: ferroelectric, refraction index, spectral ellipsometry, effective-medium theory.