Spectroscopic Ellipsometry Method Research Articles

Investigation of optical and electrical properties of TiO2, SiO2, and Ag single and multilayer thin films using spectroscopic ellipsometry and spectrophotometry methods: prepared by spin coating and DC magnetron sputtering

In this work, spectroscopic ellipsometry was used to study the optical and electrical properties of TiO2 and SiO2 thin films deposited by spin-coating at different coating rotation speeds and annealed at various temperatures. In addition, Ag thin films of different thicknesses were deposited by DC magnetron sputtering at ambient temperature. In this method, the optical band gap for TiO2 thin films is between 3.15–3.85 eV, and for SiO2 thin films, it is between 3.2–3.8 eV. The optical properties, including reflectance, transmittance, and absorbance, of TiO2, SiO2, and Ag thin films in the form of single and multilayer thin films in the wavelength range of 200–2500 nm, were investigated using an ultraviolet-visible-near infrared (UV–vis-NIR) dual-beam spectrophotometer. In the TiO2/Ag/SiO2 multilayer thin film, the rejection was 58.6% −73.6% in the NIR wavelength range (800–2500 nm), and a transmittance of 40%–45% was achieved in the visible light range (400–700 nm).

The Optical and Structural Properties of Cu Nanoparticles: Graphene Prepared by Pulsed Laser Ablation in Deionized Water

Background: In this paper, graphene and copper oxide nanoparticles and graphene-based copper oxide nanoparticles have been produced by means of a pulsed laser ablation process (PLA) in a deionized water solution. Methods: The composition ratio of materials has been investigated in the structure of the prepared materials and their optical properties. The absorbance of the samples was obtained by the UV-VIS single beam spectrophotometer in the wavelength range of 290 to 800 nm. Spectroscopic ellipsometry method was used to investigate the linear optical properties of the samples including the real and imaginary parts of refractive index and dielectric function of the samples. The preferred model in the dielectric function modeling was Tauc-Lorentz. Also, the energy band gap of the samples has been calculated using Tauc relation. In addition, the nonlinear optical properties of graphene based copper oxide have been studied by Z-scan technique. Structure of the samples was studied using TEM image. Results: The most and the least absorbance at 532 nm wavelength, and also band gap energy belong to 1.4 ml Gr-0.6 ml Cu and copper oxide, respectively. Conclusion: The band gap energies of the samples were calculated between 3.30 eV and 3.43 eV. The real and imaginary parts of the complex refractive index were obtained in the order of 10-8cm2/W and 10-5cm/W. The results for nonlinear properties show that these samples are suitable for all-optical switching devices.

Low cost sol gel derived silica-titania waveguide films – Characterization

This work reports a study on low-loss waveguide layers for planar evanescent wave sensor applications. Crack-free SiOx:TiOy composite layers with refractive indices of ∼1.65, in the visible spectra range, were fabricated using a sol-gel method and a dip-coating technique. Layers of thickness in the 220–360 nm range were produced in a single coating process. By multiple coatings, SiOx:TiOy composite layers of thickness up to 1000 nm were produced. Fabricated layers demonstrated good waveguide properties in the Vis spectral range. The dispersion characteristics of the developed layers refractive index were determined using the spectroscopic ellipsometry method. Spectrophotometric tests validated their optical homogeneity. Using the Tauc method, the widths of optical band gaps were determined, and their high values (Eg > 3.7 eV) attest to the amorphous nature of the layer material. The FT-IR studies testified to Si-O-Ti bonds, an attribute of amorphous SiOx:TiOy composites. The tests of surface morphology of the SiOx:TiOy layers, using atomic force microscopy, scanning electron microscopy, and optical profilometry, confirmed their high smoothness. Using the m-line method, waveguide properties and optical losses were examined. To facilitate the interpretation of the experimental results, the mode characteristics and the calculated impact of surface morphology of the waveguide layer.

Enhancing analysis efficiency: Automation of spectroscopic ellipsometry for crystalline semiconductors and transparent conductive oxides

One significant drawback of a spectroscopic ellipsometry (SE) technique is its time-consuming and often complicated analysis procedure necessary to assess the optical functions of thin-film and bulk samples. Here, to solve this inherent problem of a traditional SE method, we present a general way that allows complete automation of SE analyses for crystalline-phase semiconductors and transparent conductive oxides (TCOs), exhibiting complex absorption features. In particular, we have modified a scheme established in our previous study, which performs a non-linear SE fitting analysis only in a low energy region at the beginning, while the analyzed energy region is gradually expanded toward higher energy by incorporating additional optical transition peaks. In this study, we have further developed a unique analyzing-energy search algorithm, in which a proper analyzing-energy region is determined to incorporate the feature of a new transition peak. The proposed method (ΔM method) has been applied to analyze perovskite-based crystalline samples, including hybrid perovskite (CH3NH3PbI3), chalcogenide perovskites (SrHfS3 and BaZrS3), and TCOs (In2O3:W, In2O3:Sn, and ZnO:Ga). In the automated analyses of the crystalline semiconductors, 7 ∼ 8 transition peaks are introduced automatically to describe sample dielectric functions, while structural parameters, such as thin-film and roughness thicknesses, are also determined simultaneously. It is, however, found that, in the crystalline semiconductor analyses, the slight correction for the surface roughness layer thickness is necessary to remove the artifact generated in the automated analyses. We have further confirmed that the developed method is superior to a B-spline semiautomatic-analysis method, which has been adopted in earlier studies. The established method can drastically reduce an analysis time and expands the application area of spectroscopic ellipsometry considerably.

Effect of benzene-based dyes on optothermal properties of active layers for ternary organic solar cells

This publication focuses on the fabrication and thermo-optical examination of donor–acceptor layers doped with small molecules for ternary photovoltaic cell applications. The main focus of this research is the investigation of a two-component system, consisting of regioregular poly (3-hexylthiophene-2,5-diyl) as the donor material, combined with two different types of fullerene acceptors. Moreover, the article explores the characteristics of thin films composed of a combination of donor materials and acceptor materials, along with the inclusion of a specific additive. The research provides insights into the ternary systems within a temperature range of 10–120 °C. Changes in the absorption spectrum in UV–Vis region for the studied layers before and after thermal treatment was demonstrated. Variations in the crystallinity and roughness of the layers were demonstrated using atomic force microscopy. The process and changes in layer thickness were recorded using a spectroscopic ellipsometry method. The influence of temperature on the dispersion dependence of the refractive index and extinction coefficient for the layers under consideration was also investigated.

Structural and Optical Properties of PEDOT: PSS

In recent years, films fabricated from poly (3, 4-ethylenedioxythiophene): poly (4-styrenesulfonate) (PEDOT: PSS) aqueous dispersions have attracted lot of attention due to their exceptional advantages of high transparency in the visible range, excellent thermal stability and aqueous solution processibility. The effect of annealing on the structural, and optical properties of films obtained by the spin coating method on glass substrates has been investigated. This work investigated the impact of second annealing on the structural, and optical properties of poly (3, 4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) thin films. Thin films PEDOT: PSS of about 150 nm thicknesses were deposited by sol-gel method spin coating technique at room temperature. The obtained films were annealed twice: by annealing at 110 °C temperature for 15 min, and at 170 °C within one hour. The films were characterized by X-ray diffraction (XRD), spectroscopic ellipsometry (SE), photoluminescence spectroscopy, and atomic force microscopy (AFM) methods. Studies have shown that second annealing has reduced defects, efficiently.

The influence of annealing (900◦C) of ultra-thin PECVD silicon oxynitride layers

This work reports on changes in the properties of ultra-thin PECVD silicon oxynitride layers after high- temperature treatment. Possible changes in the structure, composition and electrophysical properties were investigated by means of spectroscopic ellipsometry, XPS, SIMS and electrical characterization methods (C-V, I-V and charge- pumping). The XPS measurements show that SiOxNy is the dominant phase in the ultra-thin layer and high-temperature annealing results in further increase of the oxynitride phase up to 70% of the whole layer. Despite comparable thickness, SIMS measurement indicates a densification of the annealed layer, because sputtering time is increased. It suggests complex changes of physical and chemical properties of the investigated layers taking place during high-temperature annealing. The C-V curves of annealed layers exhibit less frequency dispersion, their leakage and charge-pumping currents are lower when compared to those of as-deposited layers, proving improvement in the gate structure trapping properties due to the annealing process.

Optimization of Bulk Heterojunction Photovoltaic Structures with Heterocyclic Derivatives

Photovoltaic structures of the bulk heterojunction type were fabricated, in which derivatives of N,N-diethylamine-3-Methyl-1-Phenyl-1H-pyrazolo[3,4-b]quinoxalines were used as the active layer. The compounds differed in the position of the electron-donating substituent in the carbocyclic ring. Four isomers were subjected to UV-Vis spectrophotometric measurements in solvents of different polarities. The absorption characteristics were experimentally determined for the tested derivatives. The values of HOMO-LUMO levels were determined by means of quantum chemical calculations using the HyperChem software. The current–voltage and dispersion characteristics of the produced OPV were determined. The spectral characteristics of the refractive indices and extinction coefficients of the active layers were determined using the spectroscopic ellipsometry method. These results were used in the analysis and optimization of photovoltaic structures. It was shown that the location of the N,N-diethylamine substituent affects the photophysical properties of the structure and the photovoltaic properties. The optimization of the OPV_2 photovoltaic structure using the coherent model and the 2 × 2 matrix method can be successfully used in modeling optical multilayer structures, including photovoltaic structures.

Disorder and cavity evolution in single-crystalline Ge during implantation of Sb ions monitored in-situ by spectroscopic ellipsometry

Ion implantation has been a key technology for the controlled surface modification of materials in microelectronics and generally, for tribology, biocompatibility, corrosion resistance and many more. To form shallow junctions in Ge is a challenging task. In this work the formation and accumulation of shallow damage profiles was studied by in-situ spectroscopic ellipsometry (SE) for the accurate tracking and evaluation of void and damage fractions in crystalline Ge during implantation of 200-keV Sb + ions with a total fluence up to 1016 cm−2 and an ion flux of 2.1 × 1012 cm−2s−1. The consecutive stages of damage accumulation were identified using optical multi-layer models with quantitative parameters of the thickness of modified layers as well as the volume fractions of amorphized material and voids. The effective size of damaged zones formed from ion tracks initiated by individual bombarding ions can be estimated by numerical simulation compared with the dynamics of damage profiles measured by ion beam analysis and ellipsometry. According to our observations, the formation of initial partial disorder was followed by complete amorphization and void formation occurring at the fluence of about 1 × 1015 cm−2, leading to a high volume fraction of voids and a modified layer thickness of ≈200 nm by the end of the irradiation process. This agrees with the results of numerical simulations and complementary scanning electron microscopy (SEM) measurements. In addition, we found a quasi-periodic time dependent behavior of amorphization and void formation represented by alternating accelerations and decelerations of different reorganization processes, respectively. For the understanding and prevention of adverse void formation and for controlled evolution of subsurface nanocavities or cellular surface texture the in-situ monitoring of the dynamics of structural damage accumulation by the developed SE method is essential.

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.

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.

Variation of TiO2/SiO2 mixed layers induced by Xe+ ion irradiation with energies from 100 to 250 keV

The broadening and changes in optical parameters of TiO2/SiO2 transition layers irradiated with Xe+ ions of energies 100, 150, 200, and 250 keV have been investigated using the Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE) methods. We observed that a rise in atomic mixing at the TiO2/SiO2 interface increases its transition layer thickness with increasing ion energy. The discrepancies in transition layers are interpreted by employing the defect profiles and ion energy loss obtained from Stopping and Range of Ions in Matter (SRIM) calculations. The refractive index and the extinction coefficient of irradiated TiO2/SiO2 samples were found to be higher than those of virgin ones with irradiating ion energies below 250 keV. Their disparity heightens with increasing ion energy up to 200 keV and then decreases at 250 keV.

Application of Tamm Plasmon Polaritons and Cavity Modes for Biosensing in the Combined Spectroscopic Ellipsometry and Quartz Crystal Microbalance Method.

Low-cost 1D plasmonic photonic structures supporting Tamm plasmon polaritons and cavity modes were employed for optical signal enhancement, modifying the commercially available quartz crystal microbalance with dissipation (QCM-D) sensor chip in a combinatorial spectroscopic ellipsometry and quartz microbalance method. The Tamm plasmon optical state and cavity mode (CM) for the modified mQCM-D sample obtained sensitivity of ellipsometric parameters to RIU of ΨTPP = 126.78 RIU−1 and ΔTPP = 325 RIU−1, and ΨCM = 264 RIU−1 and ΔCM = 645 RIU−1, respectively. This study shows that Tamm plasmon and cavity modes exhibit about 23 and 49 times better performance of ellipsometric parameters, respectively, for refractive index sensing than standard spectroscopic ellipsometry on a QCM-D sensor chip. It should be noted that for the optical biosensing signal readout, the sensitivity of Tamm plasmon polaritons and cavity modes are comparable with and higher than the standard QCM-D sensor chip. The different origin of Tamm plasmon polaritons (TPP) and cavity mode (CM) provides further advances and can determine whether the surface (TPP) or bulk process (CM) is dominating. The dispersion relation feature of TPP, namely the direct excitation without an additional coupler, allows the possibility to enhance the optical signal on the sensing surface. To the best of our knowledge, this is the first study and application of the TPP and CM in the combinatorial SE-QCM-D method for the enhanced readout of ellipsometric parameters.

Spectroscopic ellipsometry methods for brevetoxin detection

The spectroscopic ellipsometry (SE), and attenuated internal reflection spectroscopic ellipsometry (TIRE) are promising methods in label-free biosensing applications. An ellipsometer running under surface plasmon resonance (SPR) conditions has unique advantages over other SPR-based methods in terms of sensitivity and real-time/label-free measurement capability. In this study, both SE and TIRE-based brevetoxin B (BTX) sensors were developed using two anti-BTX aptamers reported before. A new aptamer sequence was also derived from these two antiBTX aptamers using predictive modeling tools and an exclusion method. All three antiBTX aptamers' analytical performances were quite competitive in terms of both detecting range and detection limits. However, the selectivity of the previously reported aptamers against analogs of BTX was poor at low detection ranges, especially for okadaic acid. Furthermore, the selectivity of the derived aptamer was lower than its predecessors. The sensors were capable of detecting BTX in the range of 0.05 nM–1600 nM in the TIRE and 0.5 nM–2000 nM in the SE configuration. The detection limits of the sensors were 1.48 nM (1.32 ng/mL) and 0.80 nM (0.72 ng/mL) for SE and TIRE configurations, respectively. Both configurations have been used successfully to detect BTX standards spiked into real fish and shrimp samples.

The new innovative optic complete method of identification of oil and its fraction

Development and demonstration of a new method for highly accurate forecasting of the hydrocarbon composition of oil based on determining the spectrum of its universal material constant–dielectric function, as by direct measurement using the method of spectroscopic ellipsometry, are today accepted as the world standard for determining the optical functions of any substance in a liquid or solid state, and by its quantum-mechanical calculation from first principles to complete coincidence with the measurement results. A methodology will be proposed for the complete description of any oil and the identification of it belonging to a particular oilfield. The methodology is not only universal and highly accurate, but also economical. In this work, we obtained several groups of fractions of crude oilsamples from different oil fields in Azerbaijan, which were accessed by spectroscopic ellipsometry over the 1.5–6.5 eV spectral range at room-temperature. Optical constants and dielectric function were obtained for massive samples of each substance and fractions. The proposed method is a complete dielectric fingerprint of oils for widespread use, including for environmental monitoring of oil-contaminated areas of the sea and land.

Sol-gel Growth of Ni-doped CdS on Glass Substrates: Effect of Spin Coating Speed and Dopant Concentration

Background: In this work, CdS thin films were synthesized by the sol-gel method (spin coating technique) on glass substrates to investigate the optical behavior of the film. Methods: Different substrate spin coating speeds of 2400, 3000, 3600 rpm and different Ni dopant concentrations of 0 wt.%, 2.5 wt.%, and 5 wt.%) were investigated. The optical properties of thin films, such as the refraction index, extinction coefficient, dielectric constant, and optical bandgap energy of the layers were discussed using spectroscopic ellipsometry method in the wavelength range of 300 to 900 nm. Results: It can be deduced that substrate rotation speed and dopant concentration have an influence on the optical properties of thin films by decreasing the rotation speed of the substrate, which results in films with more thicknesses, and more optical interferences were observed in the results. Conclusion: The samples doped with Ni, when compared to pure ones, were found to have more optical bandgap energy.

Investigation of volume fraction of GaP nanowires by SEM characterization and spectroscopic ellipsometry

In this paper we focus on investigation of GaP volume fraction in GaP nanowires (NWs) prepared on GaP substrates by MOVPE using VLS mode. For this purpose, spectroscopic ellipsometry (SE) and scanning electron microscopy (SEM) image processing methods were used showing a good agreement. In ellipsometry, composition of GaP and void was modeled using linear gradient model in combination with Bruggeman Effective Medium Approximation (BEMA). From this model the volume fraction of GaP on the top of the nanowires was determined from 1.5%–6.3%) and in the bottom of the nanowires from 34.8%–39.6%), respectively. The histogram of GaP nanowires SEM image was divided into 10 bins above the plane. The volume fraction of GaP nanowires determined from these bins ranged from 1.4 % to 3.8 % on the top of the nanowires and from 33.5%–46.2% in their bottom. Linearity of the SEM histogram bins gradient was further compared to the linearity of the linear gradient layer model.

Quantitative analysis of stereoscopic molecular orientations in thermally reactive and heterogeneous noncrystalline thin films via variable-temperature infrared pMAIRS and GI-XRD

The quantitative estimation of stereoscopic molecular orientations in semicrystalline polymer thin films with characteristic heterogeneous structures is essential for the development of advanced film materials. Grazing-incidence X-ray diffraction (GI-XRD) is a powerful technique used to evaluate the orientational order of crystalline lattices; however, it provides the orientational order of only ordered regions (crystal and glassy liquid crystal regions). In contrast, infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) can provide the averaged orientational order of overall regions in a film regardless of sample crystallinity. This paper combines variable-temperature (VT) pMAIRS, static GI-XRD and spectroscopic ellipsometry and reports general insight into the molecular orientation mechanism occurring in polymer films revealed through the precise analysis of the structural evolution of linear poly(amic n-alkyl ester), PAE, with different lengths of n-alkyl chains during thermal curing, which involves solvent evaporation and dehydration imidization reactions to form the corresponding polyimide (PI). This combined method clarified that the PAE and PI thin films had a heterogeneous structure consisting of a glassy liquid-crystalline (ordered) region and a nonoriented amorphous region. Furthermore, imidization proceeded faster in the amorphous region than in the ordered (oriented) region. In addition, anomalies of refractive index and birefringence were found by comparing pMAIRS and spectroscopic ellipsometry, although the effect of the side chain length on the molecular orientation of PI was insignificant. The anomalies indicate that an isotropic void structures were generated by the elimination reaction of the side chains and that the volume fraction of voids increased with increasing side chain length. These results demonstrated that the combination of VT-pMAIRS and GI-XRD is a very powerful tool for the in situ structural analyses of noncrystalline (disordered crystal, glassy liquid crystal, and oriented amorphous) thin-film materials ongoing chemical reactions in their components and is inherently applicable to all kinds of interesting polymeric thin-film materials. Thin film aromatic polyimides were quantitatively analyzed by grazing-incidence X-ray diffraction (GI-XRD), variable-temperature infrared p-polarized multiple-angle resolution spectroscopy (VT-pMAIRS), and spectroscopic ellipsometry (SE) methods. Combining VT-pMAIRS and GI-XRD revealed characteristic heterogeneous structures comprising non-oriented amorphous and oriented liquid-crystalline glass regions. Additionally, SE indicated that the film involved anisotropic-shaped void inducing form-birefringence. Such an excess of birefringence can make it difficult to estimate orientational order using birefringence measurement. This methodology presented here will remarkably contribute to general structural analyses of all intriguing thin-film polymers with characteristic heterogeneity.

Copper Nitride Nanowire Arrays-Comparison of Synthetic Approaches.

Copper nitride nanowire arrays were synthesized by an ammonolysis reaction of copper oxide precursors grown on copper surfaces in an ammonia solution. The starting Cu films were deposited on a silicon substrate using two different methods: thermal evaporation (30 nm thickness) and electroplating (2 μm thickness). The grown CuO or CuO/Cu(OH)2 architectures were studied in regard to morphology and size, using electron microscopy methods (SEM, TEM). The final shape and composition of the structures were mostly affected by the concentration of the ammonia solution and time of the immersion. Needle-shaped 2–3 μm long nanostructures were formed from the electrodeposited copper films placed in a 0.033 M NH3 solution for 48 h, whereas for the copper films obtained by physical vapor deposition (PVD), well-aligned nano-needles were obtained after 3 h. The phase composition of the films was studied by X-ray diffraction (XRD) and selected area electron diffraction (SAED) analysis, indicating a presence of CuO and Cu(OH)2, as well as Cu residues. Therefore, in order to obtain a pure oxide film, the samples were thermally treated at 120–180 °C, after which the morphology of the structures remained unchanged. In the final stage of this study, Cu3N nanostructures were obtained by an ammonolysis reaction at 310 °C and studied by SEM, TEM, XRD, and spectroscopic methods. The fabricated PVD-derived coatings were also analyzed using a spectroscopic ellipsometry method, in order to calculate dielectric function, band gap and film thickness.