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Self-assembled opal crystals (bulk silica opals and PMMA thin opal films)have been studied by atomic force microscopy (AFM) and optical spec-troscopy. Reflectance and transmittance spectra (R(λ) and T (λ), respectively)as well as spectra of ellipsometric parameters Ψ(λ) and Δ(λ)demonstratepronounced changes with changing the angle of light incidence. Diameters ofspheres obtained from AFM-images correspond to those obtained from Braggfit to the diffraction resonance dispersions. The band of light losses detected byellipsometry at the spectral range of avoided band crossing of opal eigenmodeswas assigned to the energy exchange between these modes

Using wide-band (0.5-6.5 eV) spectroscopic ellipsometry we study ultrathin [Bi(0.6-2.5 nm)-FeNi(0.8,1.2 nm)]N multilayer films grown by rf sputtering deposition, where the FeNi layer has a nanoisland structure and its morphology and magnetic properties change with decreasing the nominal layer thickness. From the multilayer model simulations of the ellipsometric angles, Psi(omega) and Delta(omega), the complex (pseudo)dielectric function spectra of the Bi layer were extracted. The obtained results demonstrate that the Bi layer can possess the surface metallic conductivity, which is strongly affected by the morphology and magnetic properties of the nanoisland FeNi layer in the GMR-type Bi-FeNi multilayer structures., 6 pages, 4 figures

This paper reviews the main techniques of optical spectroscopy used for the characterization of sol-gel materials in different forms, including a brief description of instrumentation, followed by a series of selected examples from the literature that illustrate the main methodologies and results which can be obtained and including the main advantages and disadvantages of the different approaches adopted. The review includes separate sections on UV/Vis/NIR spectroscopy, spectroscopic ellipsometry, M-line spectroscopy, infrared and Raman spectroscopies, and photoluminescence spectroscopy.

Understanding the kinetic pathways of self-assembly in block copolymers (BCPs) has been a long-standing challenge, mostly due to limitations of in situ monitoring techniques. Here, we demonstrate an approach that uses optical birefringence, determined by spectroscopic ellipsometry (SE), as a measure of domain formation in cylinder- and lamellae-forming BCP films. The rapid experimental acquisition time in SE (ca. 1 sec) enables monitoring of the assembly/disassembly kinetics of BCP films during solvent-vapor annealing (SVA). We demonstrate that upon SVA, BCP films form ordered domains that are stable in the swollen state, but disorder upon rapid drying. Surprisingly, the disassembly during drying strongly depends on the duration of solvent exposure in the swollen state, explaining previous observations of loss of order in SVA processes. SE thus allows for decoupling of BCP self-assembly and disordering that occurs during solvent annealing and solvent evaporation, which is difficult to probe using other, slower techniques.

Multiple repeated procedure of spin-coating, thermal annealing and midcycle washing of the non-conductive PSS component was developed to fabricate the multilayer PEDOT:PSS films. A 4–5 times enhanc...

We investigated the complex dielectric function of bromide perovskite single crystals (MAPbBr3, FAPbBr3 and CsPbBr3) by spectroscopic ellipsometry from 1 to 5 eV in the 183–423 K temperature range ...

In the present paper, we report a combined experimental and theoretical study of compositionally graded Si1−xGex thin films grown on Si at 550°C. The study has been conducted for two particular val...

The mechanical properties of crystalline materials are crucial knowledge for their screening, design, and exploitation. Density functional theory (DFT), remains one of the most effective computational tools for quantitatively predicting and rationalising the mechanical response of these materials. DFT predictions have been shown to quantitatively correlate to a number of experimental techniques, such as nanoindentation, high-pressure X-ray crystallography, impedance spectroscopy, and spectroscopic ellipsometry. Not only can bulk mechanical properties be derived from DFT calculations, this computational methodology allows for a full understanding of the elastic anisotropy in complex crystalline systems. Here we introduce the concepts behind DFT, and highlight a number of case studies and methodologies for predicting the elastic constants of materials that span ice, biomolecular crystals, polymer crystals, and metal–organic frameworks (MOFs). Key parameters that should be considered for theorists are discussed, including exchange–correlation functionals and dispersion corrections. The broad range of software packages and post-analysis tools are also brought to the attention of current and future DFT users. It is envisioned that the accuracy of DFT predictions of elastic constants will continue to improve with advances in high-performance computing power, as well as the incorporation of many-body interactions with quasi-harmonic approximations to overcome the negative effects of calculations carried out at absolute zero.

The implantation of high-density polyethylene (HDPE) has been conducted using Ag+ ions with energy of 60 keV, achieved fluences 1.5 and 10?1015 ions/cm2. Transmission electron microscopy (STEM) and field emission gun - scanning electron microscopy (FEG-SEM) showed the existence of nanoparticle clusters. X ray photoelectron spectroscopy (XPS) revealed the presence of silver in the sample surface region. The surface topography was studied by atomic force microscopy (AFM), while the surface composition uniformity was analyzed using phase imaging AFM. Optical characterization obtained by spectroscopic ellipsometry (SE) showed changes in refractive index, extinction coefficient and the optical band gap with the fluence of implanted ions.

Silver (Ag) films with different nanostructures were prepared by electron beam evaporation and characterized by spectroscopic ellipsometry in combination with X-ray diffraction and field emission s...

The present paper demonstrates the annealing temperature effect on the structural, optical and morphological properties of electrodeposited copper (I) oxide (Cu2O) thin films on ITO-glass substrate...

Hybrid materials (HMs) offer unique properties as they combine inorganic and organic components into a single material. Here, we developed HM coatings for marine antifouling applications using sol-gel chemistry and naturally occurring polysaccharides. The coatings were characterized by spectroscopic ellipsometry, contact angle goniometry, AFM, and ATR-FTIR, and their stability was tested in saline media. Marine antifouling and fouling-release properties were tested in laboratory assays against the settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of the diatom Navicula incerta. Furthermore, laboratory data were confirmed in short-term dynamic field assays in Florida, USA. All hybrid coatings revealed a superior performance in the assays compared to a hydrophobic reference. Within the hybrids, those with the highest degree of hydrophilicity and negative net charge across the surface performed best. Alginate and heparin showed good performance, making these hybrid materials promising building blocks for fouling-resistant coatings.

Background: Al-doped ZnO thin films are considered as a promising alternative to ITO in optoelectronic applications. In this work, Al-doped ZnO thin films were prepared using sol-gel spin coating technique. Experimental: The optical properties of the films such as refractive index, extinction coefficient, dielectric function and the absorption coefficient were examined using spectroscopic ellipsometry method in the wavelength range of 300 to 900 nm. The effect of Al doping on ZnO thin films with different Al concentrations was significant. Tauc relation was used to estimate the optical band gap energy of the films. Results: The calculated values of band gap energy were obtained between 3.10 to 3.25 eV. Also the fraction of voids was calculated using Aspnes theory. Conclusion: The free carrier concentration value was obtained in the order of 1019 cm-3.

Oxidation of metallic glasses has been shown to be different from crystalline alloys due to the disordered atomic structures and far-from-equilibrium state, and quick characterization is required to reveal their early stage oxidation. In this study, we investigated the oxidation behavior of a Zr46Cu46Al7Gd1 bulk metallic glass by measuring the changes of optical constants via spectroscopic ellipsometry. Characterizations with X-ray diffraction, scanning electron microscopy, and thermogravimetric analyzer confirmed that the changes of pseudo-optical constants reflected not only the onset temperature at which the alloys underwent obvious oxidation, but also the subtle oxidation which was tedious to characterize. Our study suggests a more efficient and accurate approach to understand the oxidation of metallic glasses with temperature, time and compositions.

In this study, we proposed label-free saxitoxin (STX) sensor using STX specific aptamer in combination with spectroscopic ellipsometry (SE) and attenuated internal reflection (AIR) spectroscopic ellipsometry method which is operated under surface plasmon resonance (SPR) conditions. Besides the other surface plasmon resonance-based applications, AIR-SE applications have unique advantages in terms of sensitivity and it was used herein for real-time detection of STX in real samples. Another method, SE, was also used and compared with AIR-SE. Analytical performances were satisfactory with low detection limits and a wide detection range. Limit of detection was 0.01 ng/mL for AIR-SE and 0.11 ng/mL for SE. Both proposed sensors were operable in 0.01 nM–1000 nM STX range. These methods were also used for the accurate, selective, and sensitive detection of STX from fish and shrimp samples.

A quantitative analysis of the thermally induced degradation of various device relevant multi cation hybrid perovskite films is performed using spectroscopic ellipsometry, for temperatures between 80 and 120 C. The studied compositions are a triple cation perovskite Cs0.05 MA0.17FA0.83 0.95Pb Br0.17I0.83 3, a Rb containing variant Rb0.05Cs0.05 MA0.17FA0.83 0.90Pb Br0.17I0.83 3, and a methylammonium free Rb0.05Cs0.10FA0.85PbI3 composition. A very wide combined spectral range of 200 nm to 25 amp; 956;m is covered by combining the data from two separate instruments. The relative changes in organic cation concentrations are quantified from the middle infrared molecular absorption bands, leveraging the use of point by point fitting for increased sensitivity. Additionally, the formation of PbI2 and non perovskite amp; 948; CsPbI3 phases is evidenced from Bruggemann effective medium fits to the visible and ultraviolet complex refractive indices. Methylammonium is almost completely depleted from the relevant compositions within 100 to 285 min of thermal annealing. The MA free perovskite degrades faster at intermediate temperatures, which is attributed to phase instability due to the formation of amp; 948; CsPbI3 in addition to PbI2

International audience; Indium-tin-oxide (ITO) is a widely employed transparent conducting oxide (TCO), but the indium scarcity and price encourage developing some alternatives. The correlated metals CaVO3 and SrVO3 have been recently identified as new TCOs with functional properties being comparable to ITO. However, their technological potential is limited by the critical requirement of a perovskite structure of the film, impossible to achieve via direct growth on substrates commonly used for applications. In this article, the authors tackle this limitation by demonstrating the crystalline growth of vanadate TCOs on glass at temperatures below 600 °C, with the help of 2D nanosheets as transparent seed layers. The functional properties do not suffer from the textured structure of the films, as confirmed by an in-depth spectroscopic ellipsometry study, allowing for an industrially viable approach to integrate vanadate TCOs on virtually any surface and to exploit their promising performances as a new generation TCO

The series of three diamond-like carbon films was fabricated using Plasma – Enhanced Chemical Vapor Deposition setup designed for deposition of amorphous silicon films. The deposited films were analyzed by Spectroscopic ellipsometer Semilab SE-2000 in terms of optical properties. All the measurements were analyzed and modeled by the Fresnel equations. Three parameters were identified: refractive index, extinction index, and thickness. The range of these values indicates that the films can be used as antireflection coatings. The obtained values for n, k, and d are located in ranges: for n - 1.484 and 1621, for k - 0.345 and 0.062, and for d- 136.20 and 74.66. Плівки аморфного гідрогенізованого вуглецю а-С:Н завдяки таким властивостям, як хімічна інертність, інфрачервнева прозорість, твердість, зносостійкість, низький коефіцієнт тертя та біосумісність знаходять застосування в оптиці і електроніці, машинобудуванні та медицині. В представленій роботі плівки аморфного вуглецю досліджуються з метою подальшого їх застосування в якості антивідбиваючого покриття на інфрачервневих вікнах з германію, а також для орієнтування рідких кристалічних шарів в рідкокристалічних модуляторах світла. В роботі наведено технологічні чинники плазмохімічного осадження плівок з газової фази як одного з найпоширеніших та результативних технологічних методів. Серія з трьох алмазоподібних вуглецевих плівок була виготовлена за допомогою плазмохімічної установки для осадження a-C:H плівок. Осаджені плівки аналізували спектроскопічним еліпсометром Semilab SE-2000, що являє собою унікальну модульну оптичну платформу, що включає спектроскопічний еліпсометр з обертовим компенсатором. Спектральний еліпсометр дозволяє проводити безконтактний, неруйнівний оптичний аналіз одно- і багатошарових структур на кремнії, склі, плівковому носії, а також визначати товщину тонкоплівкових зразків і їх оптичні властивості такі як: коефіцієнт заломлення, показник поглинання, оптична ширина забороненої зони. В роботі наведено залежності отриманих еліпсометричних коефіцієнтів. На основі отриманих залежностей було виконано розрахунки з використанням матриць та рівнянь Френеля. На основі вимірювань залежності коефіцієнта відбиття від кута падіння монохроматичного випромінювання реалізовані можливості багатопараметричного, локального, експрес-неруйнівного визначення товщини, показників заломлення та поглинання шарів від кількох нанометрів до десятих мікрометра. Отримані значення для n, k і d знаходяться в діапазонах: для n - 1,448 - 1,621, для k - 0,345 - 0,062, а для d від 136,20 нм до 74,66 нм. Для використання вуглецевих плівок в якості антивідбивних покриттів необхідно, щоб його показник заломлення мав значення близько 2,0. Отримані значення показника заломлення є меншими, що не відповідає вимогам для антивідбивних покриттів. Але значення n - 1,448 - 1,621 задовольняє вимогам використання плівок для формування однорідної орієнтації рідких кристалів в пристроях на їх основі.

Electrically tunable optical properties in materials are desirable for many applications ranging from displays to lasing and optical communication. In most two-dimensional thin films and other quan...

We propose a novel spectroscopic ellipsometry capable of measuring line profile of the film thicknesses with a single image at once. By adopting a polarization-pixelated CMOS camera and an imaging spectrometer, spatial, spectral and polarization information of the film structure can be acquired at the frame rate of the camera without any mechanical or electrical adjustments of polarizing optical components. The proposed system is beneficial not only to provide film thickness of the specimen with a single image acquisition, but also to analyze the spatial features of the film layers.

Hypothesis: Surfactants are widely used in agri-sprays to improve pesticide efficiency, but the mechanism underlying their interactions with the surface wax film on plants remains poorly understood. To facilitate physical characterisations, we have reconstituted wheat cuticular wax films onto an optically flat silicon substrate with and without octadecyltrimethoxysilane modification to control surface hydrophobicity. Experiments: Imaging techniques including scanning electron microscopy (SEM) unravelled morphological features of the reconstituted wax films similar to those on leaves, showing little impact from the different substrates used. Neutron reflection (NR) established that reconstituted wax films were comprised of an underlying wax film decorated with top surface wax protrusions, a common feature irrespective of substrate hydrophobicity and highly consistent with what was observed from natural wax films. NR measurements, with the help of isotopic H/D substitutions to modify the scattering contributions of the wax and solvent, revealed different wax regimes within the wax films, illustrating the impact of surface hydrophilicity on the nanostructures within the wax films. Findings: It was observed from both spectroscopic ellipsometry and NR measurements that wax films formed on the hydrophobic substrate were more robust and durable against attack by nonionic surfactant C 12E 6 solubilised with pesticide Cyprodinil (CP) than films coated on the bare hydrophilic silica. Thus, the former could be a more feasible model for studying the wax-surfactant-pesticide interactions.

Spectroscopic ellipsometry was used to check plasmonic properties of thin annealed gold films depending on the thickness of the annealed films and parameters of the annealing. It is demonstrated that the position of the plasmonic resonance is defined by the size of produced nanoparticles together with the strength of interparticle interactions. It is shown that the account of interparticle interactions is necessary for the correct description of optical properties of layers of plasmonic nanoparticles.

The resistivities of P+-implanted 4H-SiC samples, each prepared at different implantation and annealing temperatures, were measured using terahertz time-domain spectroscopic ellipsometry and compared with the results of the previously reported Raman spectra. The 4H-SiC samples of one group were implanted with P+ at 30 °C, 150 °C, 300 °C, and 500 °C, respectively, and annealed at 1600 °C. The resistivity was found to be approximately 8 mΩ·cm for the samples implanted at 30 and 150 °C and approximately 2 mΩ·cm for the remaining two samples. The 4H-SiC samples of the other group were implanted at 500 °C followed by annealing at 1200 °C, 1400 °C, 1600 °C, and 1800 °C, respectively. The resistivity was measured as 10 mΩ·cm for the sample annealed at 1200 °C and 3.0−1.8 mΩ·cm for the remaining three samples. These resistivity values are correlated with the Raman peak widths that reflect the lattice disorder.

Hybrid organic-inorganic perovskites (HOIPs) have emerged to the forefront of optoelectronic material advancements for the past few years. However, our understanding on electronic structure and correlations are still lacking. Herewith, by simultaneously analyzing complex dielectric function, loss functions, and reflectivity directly obtained from spectroscopic ellipsometry and supported with theoretical calculations, we report new spin correlated-plasmons with low loss in (MA)2CuCl4. Photoluminescence and time-resolved photoluminescence measurements show a broadband emission band originating from the self-trapped emission excitons. Through X-ray absorption spectroscopy and resonant photoemission spectroscopy measurements at the C K-edge, a resonance enhancement peak is observed and unravels a charge transfer event due to the opening of an extra autoionization channel. Our result shows the importance of coupling between spin correlated-plasmons and electron-hole pairs together with spin-dependent exchange interaction in determining electronic structure and optical properties of HOIPS. Ministry of Education (MOE) National Research Foundation (NRF) This work is supported by the Singapore Ministry of Education (MOE) AcRF Tier-2 (MOE2017 T2-1-135, MOE2018-T2-1- 088, MOE2018-T2-2-117, and MOE2019-T2-1-163), MOE AcRF Tier-3 (MOE2014-T3-1-004), MOE-AcRF Tier-1 (R144-000-423-114, R-144-000-398-114, R-144-000-379-114 and R-144-000-368-112), the Singapore National Research Foundation under its Competitive Research Funding (No. R-398-000- 087-281) and under its Medium Sized Centre Program (Centre for Advanced 2D Materials and Graphene Research Centre), NUS YIA, and the 2015 PHC Merlion Project. NTU authors acknowledge the MOE-AcRF Tier-2 (MOE2016-T2-1-052). The authors acknowledge the Singapore Synchrotron Light Source (SSLS) for providing the facility necessary for conducting the research. The Laboratory is a National Research Infrastructure under the National Research Foundation Singapore.

The spectroscopic ellipsometry method is used to investigate the optical properties of PbSe nanostructured thin films formed by the chemical deposition method. Function d2e/dω2 formed by numerical differentiation of experimental data of the dielectric function e/ω is used for better structural resolution of the interband transitions and the determination of critical points. Theoretical fitting is performed using the “Graphical Analysis” program. The best fit is found for the two-dimensional (2D) shape of the critical point (m = 0) for the energy region E = 2–3 eV, and one critical point corresponding to Eg = 2.5 eV is determined. This value is attributed to the L4 → L6 transition of the Brillouin zone.

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 5dto 6spin 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°.

We investigated the temperature-dependent optical response of ordered lattices of noninteracting gold-core/poly(N-isopropylacrylamide)-shell nanoparticles (NPs), a system with proven photothermal a...

Ultrathin Bi2O3 films were grown by thermal- and plasma-enhanced ALD by using [Bi(tmhd)3] as bismuth precursor. The use of an O2 plasma instead of H2O as oxidant increases the growth per cycle (GPC...

This work investigates the influence of hydrocarbon pollution on the performance of desalination membranes with a polysulfone support. Toluene was chosen as the model hydrocarbon compound and permeation measurements were performed on two commercial membranes with a polysulfone support in water saturated with toluene. Over time, the TriSep TS80 membrane under analysis broke down and the delamination of the separation layer was observed. The influence of the polysulfone layer on the membrane deterioration was studied in detail by the use of a model system of a thin polysulfone film on top of a silicon wafer. In situ spectroscopic ellipsometry, and in situ optical microscopy revealed that the non-ideality of the hydrocarbon in water system initiates a dewetting of the polysulfone layer which is the root cause of the membrane failure.

We present a comprehensive analysis on how the electronic structure and the optical properties of an organic polymer can be modulated, based on the example of the dinitrosobenzene polymer (1). Using a combination of computational and experimental tools, we explore the effects of solid-state packing, backbone torsion, surface adsorption, the conjugation in the aromatic core, and substituents. The band gap (Eg) and optical spectrum of 1 are calculated using both GW-BSE with zero-gap renormalization (ZGR) and hybrid TD-DFT, with the former method predicting a value (2.41 eV) in excellent agreement with our diffuse reflectance spectroscopy measurements (2.39 eV). Using GW-BSE-ZGR, changes occurring upon solidstate packing are separated into a contribution arising from (i) the change in the torsional angle and (ii) the change in the screened Coulombic interaction, which strongly effects the exciton binding energies. Comprehensive hybrid TD-DFT calculations find that the effects of substituents on Eg and on transport properties can mostly be explained through changes in the torsional angle, and predict a linear dependence between it and Eg. Extending the conjugation in the aromatic core is found to enhance transport properties and narrow Eg, identifying future synthetic targets. Atomic force microscopy and spectroscopic ellipsometry are used to study 1 adsorbed to a (111) gold surface (1@Au), with the latter method showing a significant narrowing of the band gap to 0.68 eV, in good agreement with TD-DFT predictions.

The datasets in this work contain the experimentally measured (real) refractive indices, optical transmission intensity, and optical absorption spectra of bifunctional urethane methacrylate perfluoropolyether (PFPE; Fluorolink® MD700) substrate of (0.98 ± 0.13) mm thickness and polyvinylidene fluoride (PVDF; Kynar® 705) thin-film of (4.47 ± 0.29) µm thickness over a spectral range from 300 nm to 1000 nm, as measured via variable angle spectroscopic ellipsometry. The refractive indices data were determined by employing a single Cauchy optical constants function based layer using a Levenberg-Marquardt multi-iterative regression algorithm for all model minimizations. The mean-squared error (MSE) was used as the maximum likelihood estimator, with a convergence of the Levenberg-Marquardt algorithm reached when successive iterations were unable to improve the MSE. The resulting best-fit parameter values were evaluated for sensitivity (expressed as a confidence limit), and possible correlations. Furthermore, the experimentally measured optical transmission intensity and determined optical absorption of PFPE and PVDF, over a spectral range from 300 nm to 1000 nm, is also presented, as measured via ellipsometry and corrected using Fresnel equations to accommodate surface interference. Given the high transmission of (88.4 ± 0.5)% for PFPE and (95.6 ± 0.6) % for PVDF found, and the low refractive index 1.27 (λ = 589.3 nm) found for PFPE; it is thought that these datasets may be useful for optical applications, such as for photo-curable synthesis processes, or being used as a host-matrix material for photoluminescent compounds.

Noble transition metal dichalcogenides (TMDCs) such as PtS2 and PtSe2 show significant potential in a wide range of optoelectronic and photonic applications. Noble TMDCs, unlike standard TMDCs such as MoS2 and WS2, operate in the ultrawide spectral range from ultraviolet to mid-infrared wavelengths; however, their properties remain largely unexplored. Here, we measured the broadband (245–3300 nm) optical constants of ultrathin PtS2 and PtSe2 films to eliminate this gap and provide a foundation for optoelectronic device simulation. We discovered their broadband absorption and high refractive index both theoretically and experimentally. Based on first-principle calculations, we also predicted their giant out-of-plane optical anisotropy for monocrystals. As a practical illustration of the obtained optical properties, we demonstrated surface plasmon resonance biosensors with PtS2 or PtSe2 functional layers, which dramatically improves sensor sensitivity by 60 and 30%, respectively.

This paper describes a new approach for large-scale thin film thickness mapping based on dynamic spectroscopic ellipsometry. The proposed system can provide a real time thin film uniformity measurement capability with high precision. We expect the proposed scheme can be applied for various large-scale thin film deposition process applications such as roll to roll manufacturing where real time process uniformity monitoring becomes crucial.

Motivated by their utility in CdTe-based thin film photovoltaics (PV) devices, an investigation of thin films of the magnesium-zinc oxide (MgxZn1−xO or MZO) alloy system was undertaken applying spectroscopic ellipsometry (SE). Dominant wurtzite phase MZO thin films with Mg contents in the range 0 ≤ x ≤ 0.42 were deposited on room temperature soda lime glass (SLG) substrates by magnetron co-sputtering of MgO and ZnO targets followed by annealing. The complex dielectric functions ε of these films were determined and parameterized over the photon energy range from 0.73 to 6.5 eV using an analytical model consisting of two critical point (CP) oscillators. The CP parameters in this model are expressed as polynomial functions of the best fitting lowest CP energy or bandgap E0 = Eg, which in turn is a quadratic function of x. As functions of x, both the lowest energy CP broadening and the Urbach parameter show minima for x ~ 0.3, which corresponds to a bandgap of 3.65 eV. As a result, it is concluded that for this composition and bandgap, the MZO exhibits either a minimum concentration of defects in the bulk of the crystallites or a maximum in the grain size, an observation consistent with measured X-ray diffraction line broadenings. The parametric expression for ε developed here is expected to be useful in future mapping and through-the-glass SE analyses of partial and complete PV device structures incorporating MZO.

In this paper we report the crystal growth conditions and optical anisotropy properties of Tungsten ditelluride (WTe2) single crystals. The chemical vapor transport (CVT) method was used for the synthesis of large WTe2 crystals with high crystallinity and surface quality. These were structurally and morphologically characterized by means of X-ray diffraction, optical profilometry and Raman spectroscopy. Through spectroscopic ellipsometry analysis, based on the Tauc–Lorentz model, we identified a high refractive index value (~4) and distinct tri-axial anisotropic behavior of the optical constants, which opens prospects for surface plasmon activity, revealed by the dielectric function. The anisotropic physical nature of WTe2 shows practical potential for low-loss light modulation at the 2D nanoscale level.

International audience

By reactive DC magnetron sputtering from a pure Ta target onto silicon substrates, Ta(N) films were prepared with different N2 flow rates of 0, 12, 17, 25, 38, and 58 sccm. The effects of N2 flow rate on the electrical properties, crystal structure, elemental composition, and optical properties of Ta(N) were studied. These properties were characterized by the four-probe method, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). Results show that the deposition rate decreases with an increase of N2 flows. Furthermore, as resistivity increases, the crystal size decreases, the crystal structure transitions from β-Ta to TaN(111), and finally becomes the N-rich phase Ta3N5(130, 040). Studying the optical properties, it is found that there are differences in the refractive index (n) and extinction coefficient (k) of Ta(N) with different thicknesses and different N2 flow rates, depending on the crystal size and crystal phase structure.

By reactive DC magnetron sputtering from a pure Ta target onto silicon substrates, Ta(N) films were prepared with a different N2 flow rate of 0, 12, 17, 25, 38, 58 sccm. The effects of N2 flow rate on the electrical properties, crystal structure, elemental composition and optical properties of Ta(N) were studied. These properties were characterized by the four-probe method, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). Results show that the deposition rate decreases with an increase of the N2 flows. On the other hand, the resistivity increases, the crystal size decreases, and the crystal structure transitions from β-Ta to TaN(111), and finally becomes the N-rich phase Ta3N5 (130,040). Studying the optical properties, it is found that there are differences in the refractive index (n) and extinction coefficient (k) of Ta(N) with different thicknesses and different N2 flow rates, and dependent on the crystal size and crystal phase structure.

Zinc selenide (ZnSe) thin films were deposited by RF magnetron sputtering in specific conditions, onto optical glass substrates, at different RF plasma power. The prepared ZnSe layers were afterwards subjected to a series of structural, morphological, optical and electrical characterizations. The obtained results pointed out the optimal sputtering conditions to obtain ZnSe films of excellent quality, especially in terms of better optical properties, lower superficial roughness, reduced micro-strain and a band gap value closer to the one reported for the ZnSe bulk semiconducting material. Electrical characterization were afterwards carried out by measuring the current–voltage (I-V) characteristics at room temperature, of prepared “sandwich”-like Au/ZnSe/Au structures. The analysis of I-V characteristics have shown that at low injection levels there is an Ohmic conduction, followed at high injection levels, after a well-defined transition voltage, by a Space Charge Limited Current (SCLC) in the presence of an exponential trap distribution in the band gap of the ZnSe thin films. The results obtained from all the characterization techniques presented, demonstrated thus the potential of ZnSe thin films sputtered under optimized RF plasma conditions, to be used as alternative environmentally-friendly Cd-free window layers within photovoltaic cells manufacturing.

Graphene is a promising building block material for developing novel photonic and optoelectronic devices. Here, we report a comprehensive experimental study of chemical-vapor deposited (CVD) monolayer graphene’s optical properties on three different substrates for ultraviolet, visible, and near-infrared spectral ranges (from 240 to 1000 nm). Importantly, our ellipsometric measurements are free from the assumptions of additional nanometer-thick layers of water or other media. This issue is critical for practical applications since otherwise, these additional layers must be included in the design models of various graphene photonic, plasmonic, and optoelectronic devices. We observe a slight difference (not exceeding 5%) in the optical constants of graphene on different substrates. Further, the optical constants reported here are very close to those of graphite, which hints on their applicability to multilayer graphene structures. This work provides reliable data on monolayer graphene’s optical properties, which should be useful for modeling and designing photonic devices with graphene.

Monolayer, few‐layer, and thin‐film MoS2 is synthesized using chemical vapor deposition (CVD) and thermal vapor sulfurization (TVS) methods. The complex refractive index of these samples is assessed using variable angle spectroscopic ellipsometry (VASE) measurements over a broad spectral range between 190 and 1700 nm. The ellipsometry data are sensitive to birefringence effects in the thickest thin‐film sample. These birefringence effects are investigated, and an analysis method is developed to extract the in‐plane and out‐of‐plane optical properties. The complex refractive index is then used to calculate reflectance, transmittance, and absorption of the MoS2 films using the transfer‐matrix method (TMM) and is matched with experimentally measured transmittance of the same samples. The modeled results show that the monolayer, few‐layer, and thin‐film MoS2 absorbs 7.4%, 12.6%, and 32.4% of the incident light, respectively, between 300 and 700 nm. When normalized to per unit‐thickness absorption, they absorb 12.1%, 5.9%, and 1.1% nm−1, respectively, clearly showing superior light–matter interaction in the monolayer and few‐layer films. These new complex refractive index data are further used to design optical coatings for these films to either confine absorption in a narrow bandwidth for photodetector applications or enhance broadband absorption for photovoltaic applications.

The research focused on materials having potential applications in technology of planar evanescent wave sensors. Four samples of binary SiO2:TiO2 thin films having different titania content were manufactured through the sol-gel method and dip-coating technique on polished silicon substrates. The samples were subjected to repeated heating/cooling protocols. Simultaneously, their optical parameters were monitored by spectroscopic ellipsometry as they evolved under varying temperature. Subsequent analysis confirmed linear dependence of refractive index on titania content, at least in vis-NIR wavelengths, as well as a low value of the thermal expansion coefficient. It was shown that the thickness of SiO2:TiO2 films decreased as a result of annealing processes, which may be a consequence of reduced porosity.