Phase-modulated Ellipsometry Research Articles

Enhanced optical absorption of graphene-based heat mirror with tunable spectral selectivity

Graphene based heat mirror (i.e., graphene/Cu/graphene multilayer coating) was designed and developed to achieve enhanced optical absorption with tunable spectral selectivity. The concept of a heat mirror and a high/low/high refractive index stack was used to develop the graphene/Cu/graphene absorber and the transition from high transmittance to high absorptance was realized on quartz substrates. The thickness of the Cu layer has an important role in creating the destructive interference, for achieving high absorptance and low emittance. The refractive index of the multilayer graphene transferred on Si substrate was studied using phase-modulated spectroscopic ellipsometry. An absorptance of 0.91 and emittance of 0.22 was achieved for the SiO2/graphene/Cu/graphene multilayer coating. For the first time, the feasibility of graphene/Cu/graphene multilayer coating for photothermal applications have been demonstrated.

Optical properties of TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber coatings by phase-modulated spectroscopic ellipsometry

TiAlC, TiAlCN, TiAlSiCN, TiAlSiCO, and TiAlSiO layers of thicknesses ~2.2 μm, 755, 491, 393, and 431 nm, respectively, were deposited on stainless steel, silicon, and glass substrates to study their refractive indices and extinction coefficients using the phase-modulated spectroscopic ellipsometry in the wavelength range of 300–1200 nm. Absorption coefficient of each layer was calculated from the extinction coefficient of the layer. The results indicate that the first three layers (i.e., TiAlC, TiAlCN, and TiAlSiCN) are absorbing in nature, while TiAlSiCO and TiAlSiO act as intermediate and antireflection layers. Subsequently, a tandem absorber of TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO with layer thicknesses of 62, 20, 18, 16, and 27 nm, respectively, was deposited on stainless steel substrates to fabricate a spectrally selective coating with absorptance of 0.961 and emittance of 0.15 at 82 °C. The obtained refractive indices and extinction coefficients of the tandem absorber were used to simulate the reflectance of the deposited tandem absorber using SCOUT software. Simulated reflectance data of the tandem absorber showed a good agreement with the experimental data measured by UV–Vis–NIR and FTIR spectrophotometry. The angular dependence of the selective properties of the tandem absorber was studied by measuring the reflectance spectra of the tandem absorber at different incident angles.

Microstructure and Optical Properties of SS/Mo/Al2O3 Spectrally Selective Solar Absorber Coating

Surface-textured Mo thin film is fabricated by magnetron sputtering through the adjustment of deposition parameters, which exhibits a high absorptance of 0.80 and a low emittance of 0.09. The single-layer Mo deposited on stainless steel (SS) is characterized by x-ray diffraction (XRD), ultra-high resolution scanning electron microscope, atomic force microscope and optical measurement. The controlled surface roughness combined with larger aspect ratio contributes much to the high absorptance and low emittance. Based on the SS/Mo coating, a spectrally selective coating (SS/Mo/Al2O3) is designed and fabricated. The coating shows an amorphous structure and exhibits an absorptance of 0.90 and an emittance of 0.08. Tauc-Lorentz and Drude free-electron models are used to modeling the optical properties of Al2O3 and Mo layers by phase-modulated spectroscopic ellipsometry.

弹光和电光级联的组合相位调制型椭偏测量术

弹光和电光级联的组合相位调制型椭偏测量术

Demonstration of glass transition temperature shift in thin supported polystyrene films by internal reference method

An internal reference method is used for the first time to clearly demonstrate the glass transition temperature (Tg) depression effect in 5 nm thick polystyrene films spin-cast on silicon wafers. Initially flat films exhibit depressed Tg at approximately 85 °C. Temperature-induced dewetting on hexamethyldisilazane-treated silicon substrates leads to formation of discontinuous films with average effective thickness of 15-30 nm. Dewetted films demonstrate Tg close to the bulk value (≈ 100 °C) and are used as internal references. Data both for continuous and discontinuous films are obtained in the same experimental run for the same sample, which allows direct comparison between datasets. Phase-modulated ellipsometry in vacuum is used to monitor glass transition. Both traditional linear temperature scan method and a novel temperature modulated technique have been employed in the measurements.

Volume polarization holographic recording in thick phenanthrenequinone-doped poly(methyl methacrylate) photopolymer

Volume polarization holographic recording in phenanthrenequinone-doped poly (methyl methacrylate) photopolymer is obtained. Photoinduced birefringence in a 2 mm thick sample is measured by a phase-modulated ellipsometry. The birefringence induced in this material by linearly polarized beam at 514 nm reaches 1.2×10(-5). In addition, ability for recording volume polarization grating using two different polarization configurations is demonstrated and compared. The experimental results show that the diffraction efficiency of the hologram reaches to ∼40% by using two orthogonal circularly polarized beams.

Variable-angle spectroscopic ellipsometry of considerably non-uniform thin films

A theoretical approach for including considerable thickness non-uniformity of thin filmsinto the formulae employed within variable-angle spectroscopic ellipsometry is presented. Itis based on a combination of the efficient formulae derived for the thickness distributiondensity corresponding to a wedge-shaped non-uniformity with dependences of the meanthickness and root mean square (rms) of thickness differences on the angle of incidence thattake into account the real non-uniformity of the shape. These dependences are derivedusing momentum expansion of the thickness distribution density. The derived formulaeare tested by means of numerical analysis. An application of this approach isillustrated using the optical characterization of a selected sample of non-uniformSiOxCyHz thin films using phase-modulated ellipsometry.

Phase-modulated ellipsometry for probing the temperature-induced phase transition in ruthenium-doped lead zinc niobate–lead titanate single crystal

Phase-modulated ellipsometry was applied to measure changes in the refractive index of pure and ruthenium (Ru)-doped 0.9Pb (Zn1/3Nb2/3)O3 (PZN)–0.1PbTiO3 (PT) during the heating process in real time. Both samples were heated from room temperature to 200°C in a thermally insulated chamber. In both samples, the phase transitions were observed to change from tetragonal to cubic. The temperature region at which the phase transition (Curie region) of Ru-doped 0.9PZN–0.1PT occurred not only broadened but also shifted to a lower temperature. The refractive indices were extremely stable in this region, meaning that Ru-doped 0.9PZN–0.1PT is a more favorable medium for the fabrication of optical memories.

Dependence of Optical Anisotropy of ZnO Thin Filmson the Structural Properties

The structural properties and optical anisotropy of strained ZnO films prepared by rf magnetron sputtering were investigated. Anisotropic complex refractive index spectra of the films were determined by using the Adachi-New Forouhi dispersion model with phase-modulated spectroscopic ellipsometry in the range of 1.0 4.0 eV. A negative strain was induced by the mismatch between the ZnO film and the Al2O3 substrate and decreased with improving crystallinity of the film. The size of the grains formed in the films showed a linear dependence on the strain. The optical anisotropy of the ZnO films was enhanced with improving crystallinity of the films. A shifting of the critical points of the anisotropic complex refractive index spectra was observed due to variations in the strain. The anisotropic complex refractive index spectra showed a strong dependence on structural changes in the ZnO films.

Real-time measurement of photo-induced effects in 9,10-phenanthrenequinone-doped poly(methyl methacrylate) photopolymer by phase-modulated ellipsometry

The photo-induced effects in 9,10-phenanthrenequinone-doped (PQ-doped) poly(methyl methacrylate) (PMMA) photopolymer were studied by phase-modulated ellipsometry and polarimetry in real time. The PQ-doped PMMA was exposed to an Ar/Kr tunable laser at the wavelength of 488 nm and measured by a HeNe laser (632.8 nm). We measured the induced birefringence and the variation of the refractive index separately during exposure; there was a difference of three orders of magnitude between these two effects. This suggested that the physical mechanism of holographic recording in PQ-doped PMMA is mainly due to the photo-induced variation in the refractive index.

Hydrogen-Bonded Hybrid Multilayers: Film Architecture Controls Release of Macromolecules

We report on the construction of purely hydrogen-bonded hybrid polymer multilayers, which are composed of polymer pairs with low- and high- pH stability, and show that the critical pH value of film deconstruction, fraction of components released, and the rate of film dissolution can be tuned in a wide pH range from 3 to 9.5 by varying film composition and architecture. The film building blocks were poly(N-vinylcaprolactam) (PVCL)/poly(l-aspartic acid) (PLAA) bilayers as pairs of hydrogen-bonded polymers with low pH stability (critical disintegration pH of ∼ 3.3), and poly(N-vinylcaprolactam) (PVCL)/tannic acid (TA) bilayers as hydrogen-bonded polymers with a higher critical disintegration pH of ∼9.5. Hybrid TA/PVCL/PLAA multilayers were prepared at low pH using a layer-by-layer technique. Film deposition and pH-induced deconstruction were followed by in situ Fourier transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR) and phase-modulated ellipsometry. PVCL/TA and PVCL/PLAA pairs ...

Temperature-dependent and pump-probe ellipsometric studies of TlInSe 2

Temperature-dependent phase-modulated spectroscopic ellipsometry over the photon energies 1.5–5.5 eV and temperatures 300–400 K, as well as pump-probe single wavelength rotating-analyzer laser ellipsometry at photon energy 1.61 eV and pumping power-density up to 160 W/cm 2 has been carried out on TlInSe 2 that has a quasi one-dimensional crystalline structure and apparently undergoes an incommensurate phase transition with temperature. Refractive indices and extinction coefficients, as well as their variation with temperature and pumping power-density have been determined. The change of the surface profile under pumping has been disclosed. The reversibility of the effect has been confirmed by the dynamic reflectance examination. Obtained results are discussed in terms of thermal effects and incommensurate phase transition in TlInSe 2. It is proposed that a giant thermo-elastic effect and a soliton wave formation are behind the observed reversible change of the surface profile.

Characterization of non-uniform diamond-like carbon films by spectroscopic ellipsometry

Optical characterization of diamond-like carbon (DLC) films non-uniform in thickness is performed using spectroscopic phase-modulated ellipsometry. This characterization is based on new formulas for the associated ellipsometric parameters of thin films exhibiting a wedge-shaped thickness non-uniformity. These formulas express the associated ellipsometric parameters by means of the density of distribution of local film thickness. The spectral dependences of the optical constants of these non-uniform DLC films are expressed using the dispersion model based on parametrization of density of electronic states. It is shown that this model of the thickness non-uniformity provides a relatively good agreement between the experimental and theoretical data, indicating that the results of the optical characterization of the non-uniform DLC films are close to the correct results. Moreover, it is shown that the model of uniform thin films is unsuitable for the optical characterization of the non-uniform DLC films studied.

Silane injection in a high-density low-pressure plasma system and its influence on the deposition kinetics and material properties of SiO2

High-rate, low temperature deposition is an essential requirement for industrial fabrication technology to be suitable for the deposition of optical and protective coatings. High-density, low-pressure plasmas have received significant attention for such applications due to their ability to create large and controllable ion fluxes onto the substrate. In this study, the high-rate deposition of silica films from a silane and oxygen gas mixture in a high-density plasma system based on a matrix distributed electron cyclotron resonance (MDECR) plasma source is investigated using directional jet injection of undiluted silane. The influence of process parameters such as the microwave power, radio frequency biasing of the substrate holder, and gas flows on the OH content of the oxide films is studied using phase-modulated spectroscopic ellipsometry (SE), Fourier transform infrared (FTIR) spectroscopy, and transmission measurements. The results of the measurements, taken at various points across the wafer, show a decrease in the thickness-normalized OH concentration in the areas of higher deposition rates. The corresponding gas phase composition is investigated using optical emission spectroscopy and compared to the FTIR, transmission and SE measurement results in order to validate our findings and ultimately optimize the deposition process. It is found that the primary silane flux onto the surface, which depends on the positioning of the jet injection point and gas flow rate, plays an important role not only on the deposition rate but also on the OH content of the films. The authors conclude that high-density plasma deposition systems such as the MDECR plasma enhanced chemical vapor deposition system cannot be considered as well mixed for gases with dissociation products that have high sticking coefficients, contrary to the accepted paradigm.

On the Mechano‐Chiral Effect of Vortical Flows on the Dichroic Spectra of 5‐Phenyl‐10,15,20‐tris(4‐sulfonatophenyl)porphyrin J‐Aggregates

Phase-modulated ellipsometry of the J-aggregates of the title porphyrin shows that the material gives a true CD signal. This confirms that there is a real chiral transfer by mechanical forces, mediated by shear gradient flows, from the macroscopic to the electronic transition level. Dislocations in the structure of the aggregate could justify the formation of chirality at the level of the electronic transitions once the mesophases can be sculptured by hydrodynamic gradient flows.

Hydrogen-Bonded Multilayers of a Neutral Polymer and a Polyphenol

We report on association of tannic acid (TA) with neutral or charged polymers in solution and at surfaces and contrast hydrogen-bonded and electrostatically associated polymer/TA complexes and TA/polymer layer-by-layer (LbL) films as per their stability in the pH scale. The neutral polymers used for hydrogen bonding with TA were poly(N-vinylcaprolactam) (PVCL), poly(N-vinylpyrrolidone) (PVPON), poly(ethylene oxide) (PEO), or poly(N-isopropylacrylamide) (PNIPAM), and the polymer used to explore electrostatic binding with TA was 90% quaternized poly(4-vinylpyridine) (Q90). Association of TA with polymers in solution was explored by measuring the turbidity of solutions. At surfaces, LbL film deposition and pH stability were followed by phase-modulated ellipsometry and in-situ Fourier transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR). While electrostatically stabilized films of TA with Q90 could not be deposited at low pH values (pH = 2), hydrogen-bonded films of TA with PVCL, PVP...

Spectrally selective NbAlN/NbAlON/Si 3N 4 tandem absorber for high-temperature solar applications

A new spectrally selective NbAlN/NbAlON/Si 3N 4 tandem absorber was deposited on copper substrates using a reactive direct current magnetron sputtering system. A high solar absorptance (0.956) and a low emittance (0.07) were achieved by gradually decreasing the refractive index from the substrate to the surface. The tandem absorber was characterized using solar spectrum reflectometer and emissometer, X-ray photoelectron spectroscopy, phase-modulated spectroscopic ellipsometry, atomic force microscopy and micro-Raman spectroscopy techniques. In order to study the thermal stability of the tandem absorbers, they were subjected to heat treatment (in air and vacuum) at different durations and temperatures. The tandem absorber deposited on copper substrate exhibited high solar selectivity in the order of 13–15 even after heat treatment in air up to 500 °C for 2 h. These tandem absorbers also exhibited high thermal stability (450 °C) in air for longer durations (116 h). The onset of oxidation for the tandem absorber deposited on silicon substrates was 650 °C, indicating a high oxidation resistance. The results of the present study indicate the importance of NbAlN/NbAlON/Si 3N 4 tandem absorber for high-temperature solar selective applications.

Deposition and characterization of TiAlN/TiAlON/Si 3N 4 tandem absorbers prepared using reactive direct current magnetron sputtering

Spectrally selective TiAlN/TiAlON/Si 3N 4 tandem absorber was deposited on copper, glass, stainless steel, nickel and nimonic substrates using a reactive direct current magnetron sputtering system. In this tandem absorber, TiAlN acts as the main absorber layer, Si 3N 4 acts as an antireflection coating and TiAlON acts as a semi-absorber layer. The tandem absorber was characterized using solar spectrum reflectometer and emissometer, cross-sectional transmission electron microscopy (XTEM), selected area diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and phase-modulated ellipsometry techniques. The compositions and thicknesses of the individual component layers were optimized to achieve high solar absorptance and low thermal emittance. The XPS data indicated that, for the TiAlN and Si 3N 4 layers, nitrogen was attached to Ti, Al and Si, whereas prominent peaks pertaining to TiO 2 were observed in the case of TiAlON. The XTEM data indicated that both the TiAlN and TiAlON layers were nanocrystalline, whereas Si 3N 4 was amorphous in nature. The optimized tandem absorber deposited on copper substrate exhibited an absorptance of 0.958 and an emittance of 0.07. The high solar absorptance of the tandem absorber was achieved by increasing the refractive index from the surface to the substrate. The high thermal stability of the component layers indicates the importance of TiAlN/TiAlON/Si 3N 4 tandem absorber for high temperature solar selective applications.

Friction and adsorption of aqueous polyoxyethylene (Tween) surfactants at hydrophobic surfaces

The nanotribological responses of a series of nonionic polyoxyethylene surfactants (Tween 20, Tween 40, Tween 60, and Tween 80) were investigated after they were adsorbed from aqueous solution onto atomically smooth hydrophobic substrates. The hydrophobic surfaces were composed of a condensed monolayer of octadecyltriethoxysilane (OTE; contact angle θ > 110 ° ). The nanorheological measurements were performed using a modified surface forces apparatus after coating atomically smooth mica with these OTE monolayers, while adsorption measurements were performed using phase-modulated ellipsometry on silicon wafers coated with these same monolayers. The minimum surface–surface separation observed under high load in friction studies agreed quantitatively with the thickness obtained from ellipsometry. For Tweens 20, 40, and 60, the thickness of the adsorbed film increases with increasing alkyl chain length. Systematic investigations of the nanorheological response showed that there is a “solid-like” elastic response from confined surfactant layers, which is the case for the smallest separations to separations up to slightly larger than twice the adsorbed film thickness. In kinetic friction, these confined layers are characterized by a shear stress of approximately 3 MPa with minimal dependence on shear rate. The magnitude of the sliding shear stress is the same as the apparent yield stress at ≈3 MPa; it is independent of alkyl chain length within the Tween family of surfactants and corresponds to a nominal friction coefficient of μ ∼ 1 . A similar friction coefficient is observed for boundary lubrication on the macroscopic scale in a tribometer utilizing hydrophobic surfaces and μ ≈ 1.1 for Tweens 20, 40, and 60. These results suggest that while Tween molecules adsorb onto hydrophobic surfaces to form a robust separating layer, the lubricating properties of these layers are dominated by a highly dissipative slip plane, the same for all alkyl chain lengths.

RETRACTED ARTICLE: Refractive-index tailoring and morphological evolutions in Gd2O3–SiO2 and ZrO2–SiO2 composite thin films

Refractive-index tailoring and morphological evolutions in two different thin film composite systems of gadolinia–silica (Gd2O3:SiO2) and zirconia–silica (ZrO2:SiO2) deposited through reactive electron-beam codeposition processes are discussed in this research paper. For Gd2O3:SiO2 the refractive-index tuning has been achieved from 1.45 to 2.18, whereas in the case of ZrO2:SiO2 the achieved tunable range is from 1.45 to 2.45 in the ultraviolet region. Under certain compositional mixings with lower silica fractions both the systems demonstrated relative microstructural and morphological densifications. Such evolutions were very successfully derived through phase-modulated ellipsometry and atomic force microscopy. The composition-dependent refractive-index tailoring and microstructural densifications have been investigated by adopting Tauc–Lorentz and single-effective-oscillator models. The morphological correlation functions have also very aptly supported such evolutions in these composite films. These experimental results indicate their favourable properties and applicability down to the extreme ultraviolet wavelength region of the electromagnetic spectrum.