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We present a novel simulation approach combined with pulsed laser experiments, spectroscopic ellipsometry, and Raman spectroscopy to comprehensively analyze phase transformation dynamics in thin films. The simulations apply to any thin film stack and incorporate critical factors, such as thin film interference, heat transfer, and temperature-dependent optical properties during heating and melting. As a case study, we investigate the picosecond laser-induced amorphization of antimony sulfide (Sb2S3) thin films, a promising alternative to traditional phase-change materials in photonic applications to validate the simulation model. The computational efficiency of our simulations enables not only the investigation of the laser-induced phase transformation but also the optimization of key process parameters and parameter fitting. The simulations identified optimal film thickness and laser fluence parameters that maximize energy efficiency, melting effectiveness, and quenching rate while ensuring high reflectivity contrast between the amorphous and crystalline states. By constructing a wide-ranging, high-resolution parameter map of the laser fluence and film thickness dependence of the melting process, we demonstrate how this model guides the understanding of phase transformation dynamics. Raman spectroscopy confirms the polycrystalline to amorphous transition of Sb2S3 and provides a semiquantitative estimate of the amorphous fraction as a function of laser fluence, which is qualitatively consistent with the simulation predictions of the model. The open-source simulation framework, experimentally validated, provides valuable insights into laser-induced amorphization dynamics in Sb2S3 and related phase-change material thin films, enabling rapid optimization of photonic devices. [ABSTRACT FROM AUTHOR]

Photochromic yttrium oxyhydride (YHO) shows a very attractive color-neutral darkening upon photoactivation. However, the exact defect or state responsible for the visible light absorption or the mechanism for its creation is not fully understood. This makes it challenging to optimize and modify the material. In this work, we have investigated the relationship between photon absorption and darkening profile into a YHO film. The extinction coefficient k(λ) is obtained from spectroscopic ellipsometry, and the expected photon absorption profile is calculated. This is then compared to transmittance data during photodarkening by short-wavelength UV (254 nm). Our results show that the darkening is not homogeneous through the film, showing that photon absorption and darkening are positionally correlated, yet we show that the darkening stretches further into the film than the calculated photon absorption. A homogeneously darkened sample cannot always be assumed when assessing optical transmittance, absorbance, and ellipsometry data. [ABSTRACT FROM AUTHOR]

The Hf/Ti ratio was precisely controlled at monolayer thickness using atomic partial layer deposition (APLD). HfxTi1−xO2 films with varying Hf concentrations were deposited by adjusting the pulse time of Hf precursors within a single atomic layer. Characterization using x-ray reflectivity, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry confirmed the presence of Hf, Ti, and O in the films. Increasing the Hf content caused the binding energies of the O 1s peak to shift to higher values, indicating a chemical environment change from TiO2-like to HfO2-like. A higher Hf content also increased the relative atomic percentages of Hf, Ti, and O, altering the film properties. The mass density and optical properties were notably sensitive to changes in the Hf/Ti ratio at monolayer thickness. The potential of APLD to reduce dimensionality through precise control of both thickness and composition renders it especially appropriate for applications requiring highly specific material properties. [ABSTRACT FROM AUTHOR]

The structural relaxation dynamics of conventionally prepared bulk glass of N,N′-bis(3-methylphenyl)-N,N′-diphenyl-benzidine (TPD) was measured by differential scanning calorimetry. The calorimetric data were quantitatively described in terms of the Tool–Narayanaswamy–Moynihan (TNM) model. The TNM parameters were evaluated using a combination of linearization and non-linear optimization methodologies: h*/R = 109.5 kK, ln(A/s) = −321, β = 0.37, x = 0.64. In addition, the TNM phenomenology was used to describe recently reported normalized thickness data of stable and aged thin TPD films measured by ellipsometry. The structural relaxation was found to proceed at a markedly higher rate in these thin films prepared by the physical vapor deposition compared to that of conventional bulk glass. This feature appears to be associated with the significantly narrower distribution of relaxation times (β ≅ 0.8) observed for stable thin film in "as-deposited" form with uniquely dense molecular packing. Interestingly, very similar attributes of the relaxation kinetics were also found in the aged thin film with a previously erased thermal history associated with the deposition. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry and some other optical metrology techniques, such as reflectometry and scatterometry, are model-based optical measurements and, therefore, require appropriate modeling to determine the geometric and material properties of substrates, thin films, and multilayer structures. Parametric sensitivity analysis (SA) provides essential assistance in the model-building process to quantify the relative importance of model parameters for model output and to identify those with high/little influence. SA can be performed in a variety of ways, and this article discusses an application of the Morris or elementary effect (EE) method, a screening type SA procedure, to spectroscopic ellipsometry modeling. The method is a global SA technique and uses a stepping of m parameters along certain so-called "trajectories" or sequences of points in parameter space, randomly constructed in order to maximally fill the volume of the m -dimensional parameter space. However, it was thought that the EE method relies greatly on a sampling strategy or a way of selecting "optimized trajectories" in the parameter space, i.e., a necessary number of trajectories chosen to be well spread over the space to properly cover the entire realistic ranges of all input factors. Here, we use two sampling methods for selecting trajectories with possibly different distributions and investigate their effects on the estimation of various sensitivity measures in spectroscopic ellipsometry data modeling. The SA results indicate that the performance of the sampling strategy should not be judged only by maximizing the trajectory spread but also include some additional convergence criteria for the sensitivity measures. [ABSTRACT FROM AUTHOR]

The molecular self‐organization and reorganization and thus volumetric and density changes during structural relaxation and melting of modern organic semi‐conducting materials remains largely unknown, particularly in the device relevant thin film geometry where the initial state may be structurally quenched away from equilibrium. Here, the apparent mass‐thickness of a range of semi‐conducting polymeric or molecular model materials systems is measured through in situ ellipsometry. Surprisingly, the volume changes upon melting correlate inversely, with a few exceptions, to the quality of crystallinity found via x‐ray methods (i.e., directly correlate with the paracrystalline g‐parameter) rather than the melting enthalpy that is possibly a proxy for the degree of crystallinity. This study also observes changes in orientation and/or density due to segmental relaxation during the first heat, thus complementing other characterization methods that measure relaxation or reorganization transitions. Semiconducting materials exhibit very large melt expansion and a richer phase‐behavior compared to commodity polymers, presumably due to their complex chemical structure. The results delineate an important and novel structure‐function relation that, together with simulations constrained by these results, will lead to better rational design of semi‐conducting materials. [ABSTRACT FROM AUTHOR]

Semiconductor evaluation methods frequently require sample processing and carry the risk of defects and property changes. Therefore, nondestructive and noncontact electrical property measurement techniques are necessary. Terahertz time‐domain spectroscopic ellipsometry (THz‐TDSE) can simultaneously estimate the electrical properties and film thickness of a sample. However, whether this method can simultaneously determine electrical properties and film thickness for semiconductor thin films of 1 μm or less remains unclear. This study uses THz‐TDSE to evaluate the electrical properties and film thickness of a GaN thin film (≈0.8 μm thick) on a ScAlMgO4 substrate. Using the conventional analysis based on Fresnel's formula (FR model), which is used in the field of optics, uniquely determining the electrical properties and film thickness is not possible owing to multiple optimal solutions. Therefore, a model combining the characteristic impedance model used in the radio‐wave region with the FR model is employed in the analysis. The obtained values of electrical properties of the GaN thin film evaluated using THz‐TDSE are consistent with those using Hall effect measurement. Moreover, the film thickness is consistent with that measured from the cross‐sectional transmission electron microscopy observation. [ABSTRACT FROM AUTHOR]

We present the study of millisecond-resolved polymer brush swelling dynamics using infrared spectroscopy with a home-built quantum cascade laser-based infrared spectrometer at a 1 kHz sampling rate after averaging. By cycling the humidity of the environment of the polymer brush, we are able to measure the swelling dynamics sequentially at different wavenumbers. The high sampling rate provides us with information on the reconformation of the brush at a higher temporal resolution than previously reported. Using spectroscopic ellipsometry, we study the brush swelling dynamics as a reference experiment and to correct artefacts of the infrared measurement approach. This technique informs on the changes in the brush thickness and refractive index. Our results indicate that the swelling dynamics of the polymer brush are poorly described by Fickian diffusion, pointing toward more complicated underlying transport. [ABSTRACT FROM AUTHOR]

The understanding of the optical characteristics and the influence of thermally induced crystallization is vital to evaluate newly synthesized organic semiconductors for their potential applications. Variable‐angle spectroscopic ellipsometry (VASE) is employed to determine the complex dielectric function of two recently developed discrete oligomers based on naphthalene diimide (NDI) and bithiophene (T2), applying an anisotropic optical model. It is shown that the as‐cast films are optically near‐isotropic, while the annealed films exhibit pronounced anisotropies with respect to the orientation of the π−π* transition. Differences between the two distinct molecules are observed and discussed. The degree of optical anisotropy is quantified using the average molecular orientation angle φ, associated with the orientation of the π−π* transition dipole, and the related orientation order parameter S. The molecules are shown to form crystallites of several microns in size upon annealing. Imaging ellipsometry is thus additionally employed to study their optical anisotropy on a microscopic scale, and the agreement with results from macroscopic measurements is evaluated. [ABSTRACT FROM AUTHOR]

Kinetic dependences have been determined for the surface tension, dilatational dynamic surface elasticity, and ellipsometric angles of solutions of styrene copolymers with 4-vinylbenzyl chloride modified with N,N-dimethyldodecylamine. The micromorphology of the adsorbed and spread layers of these polyelectrolytes has also been studied. All kinetic dependences of the dynamic surface elasticity have turned out to be monotonic in contrast to those observed for previously studied solutions of polyelectrolytes free of polystyrene fragments. The peculiarities of the surface properties of the studied solutions may be related to the formation of microaggregates in the surface layers, because these microaggregates suppress the formation of loops and tails of polymer chains at the interfaces, and, consequently, decrease the surface elasticity after the local maximum. Atomic force microscopy data also indicate the formation of aggregates with sizes in the Z direction of 1–4 nm in the surface layers. The obtained results confirm the conclusions previously made about the formation of aggregates in the surface layers of solutions of polyelectrolytes containing fragments of sodium poly(styrene sulfonate). A 2D phase transition to a denser surface phase and the formation of aggregates with a size of 40 nm in the Z direction have been observed at surface pressures of 25–30 mN/m for the layers of the studied styrene-free polyelectrolyte spread over an aqueous substrate. [ABSTRACT FROM AUTHOR]

Determining the optical and electronic properties of strongly anisotropic materials with symmetries below orthorhombic remains challenging; generalized ellipsometry is a powerful technique in this regard. Here, we employ Mueller matrix spectroscopic and temperature-dependent ellipsometry to determine the frequency dependence of six components of the dielectric-function tensor of the two-dimensional charge-transfer salt α -(BEDT-TTF)2I3 across its metal–insulator transition. Our results offer valuable insights into temperature-dependent changes of the components of the spectroscopic dielectric-function tensor across the metal–insulator transition. This advanced method allows extension to other electronic transitions. [ABSTRACT FROM AUTHOR]

In this paper, we present spectroscopic ellipsometry measurements of five selected bulk chalcogenide glasses (Ge 28 Sb 6 Se 66 , Ge 19 Sb 17 Se 64 , Ge 12 Sb 25 Se 63 , Ge 28 Sb 12 Se 60 and As 40 Se 60) for broad wavelength range (0.3–15 μm) at the temperatures from room temperature up to glass transition temperature (with reserve). Temperature dependence of bandgap energy obtained from Tauc-Lorentz oscillator together with temperature dependence of refractive index for selected wavelengths (1.55, 3.4, 7.0 and 10.6 μm) where the studied materials are transparent are presented together with thermo-optic coefficients d E g /d T and d n /d T for these wavelengths. [ABSTRACT FROM AUTHOR]

Thin films of pure polyvinylidene fluoride (PVDF) and PVDF/SnO2 nanocomposites were fabricated by sol gel spin coating method. The weight percentage of SnO2 in PVDF matrix was varied from 0.25%, 0.5%, and 1%. X-ray diffraction graphs exhibited the rutile structure of SnO2. Scanning electron microscope confirmed densely packed morphology of pure PVDF and dispersion of SnO2 agglomerated spherical particles in PVDF matrix. The presence of all constituent elements in a specific ratio was confirmed from energydispersive X-ray spectroscopy. Furthermore, optical properties were taken by ellipsometry in terms of (Psi) and (Delta) values which were acquired through the specific fitting model, and these modeled values were fitted with the experimental values. The real part of the dielectric function showed a high refractive index at minimum energy for pure PVDF as compared to PVDF/SnO2 nanocomposite films whereas the imaginary part exhibited significantly high absorption spectra at minimum energy for pure PVDF and vice versa for PVDF/SnO2 films. Furthermore, pure PVDF film showed high absorption which increased with the increase of energy of interacting light but decreased with the incorporation of SnO2 nanoparticles. The entire observation exhibited that PVDF/SnO2 nanocomposite thin films can be utilized for optical devices like transpicuous conductors and chemical sensors etc. [ABSTRACT FROM AUTHOR]

The compound NaBi(MoO4)2 has garnered significant interest in optoelectronic fields. This study employs spectroscopic ellipsometry to thoroughly examine the linear and nonlinear optical characteristics of NaBi(MoO4)2 crystals, offering detailed insights into their optical behavior. Our investigation presents a precise method for discerning the crystal's spectral features, revealing the spectral variations of key optical parameters such as refractive index, extinction coefficient, dielectric function, and absorption coefficient within the 1.2-5.0 eV range. Through analysis, we determined optical attributes including bandgap energy, critical point energy, and single oscillator parameters. Additionally, we explored the nonlinear optical properties of NaBi(MoO4)2, unveiling potential applications such as optoelectronic devices, frequency conversion, and optical sensors. This study enhances comprehension of optical properties of NaBi(MoO4)2, underscoring its significance in future optical and electronic advancements. [ABSTRACT FROM AUTHOR]

In this work, the integration of graphene nanoplatelets (GNPs) with amorphous germanium (Ge) substrates is explored. The optical properties were characterized using Variable-Angle Spectroscopic Ellipsometry (VASE). The findings of this study reveal a strong interaction between GNPs and amorphous germanium, indicated by a significant optical absorption. This interaction suggests a change in the electronic structure of the GNPs, implying that amorphous germanium could enhance their effectiveness in devices such as optical sensors, photodetectors, and solar cells. Herein, the use of amorphous germanium as a substrate for GNPs, which notably increases their refractive index and extinction coefficient, is introduced for the first time. By exploring this unique material combination, this study provides new insights into the interaction between GNPs and amorphous substrates, paving the way for the develop of high-performance, scalable optoelectronic devices with enhanced efficiency. [ABSTRACT FROM AUTHOR]

Tetrachlorodiethyl Benzimidazo Carbocyanine (TDBC) layers are very interesting for photonics applications due to their huge oscillator strength, narrow absorption and low-cost fabrication. They are mainly used in strong coupling studies but also for wavelength selective grating fabrication, light concentration, absorption enhancement and so on. However, these intrinsic properties, particularly the refractive index, require further investigation. In this work, we first reviewed the values of the refractive index of TDBC layers reported in the literature. Using fitting with the Drude–Lorentz model, differences are highlighted. We then fabricated pure TDBC layers and measured their properties using ellipsometry and absorption spectroscopy. Finally, we also evaluated the refractive index as a function of the layer bleaching. This work shows that although the precise refractive index evaluation of pure TDBC layers is dependent on the measurement method, their oscillator strength force still remains very high without bleaching. [ABSTRACT FROM AUTHOR]

Ti-Nb alloys are gaining more prominence in the industrial and scientific environment due to their high biocompatibility, mechanical strength/weight ratio, and exceptional corrosion resistance compared to other metallic materials. Metals exhibiting this passivation characteristic are known as metal valves and may exhibit semiconductive or insulating oxides. Controlling the growth of distinct thickness layer films is possible through tunning anodization conditions. In this work, a Ti-Nb binary system is anodized, and the grown oxide layer is comprehensively characterized using ellipsometry based on its optical properties and thickness at different applied potentials. Confocal Microscopy assessed their surface roughness, and SEM/EDS probed the surface material's elemental composition. CF-LIBS successfully confirmed the 70/30 composition of the Ti-Nb alloy. Raman spectra have detected the presence of amorphous TiO2 and Nb2O5 at potentials 80 V, 100 V, and 120 V. Finally, a linear dependence of the oxide thickness with the applied potential was observed.

An ultra-fast change of the absorption onset for zincblende gallium-nitride (zb-GaN) (fundamental bandgap: 3.23 eV) is observed by investigating the imaginary part of the dielectric function using time-dependent femtosecond pump–probe spectroscopic ellipsometry between 2.9 and 3.7 eV. The 266 nm (4.66 eV) pump pulses induce a large electron–hole pair concentration up to 4 × 10 20 cm − 3 , which shift the transition energy between conduction and valence bands due to many-body effects up to ≈ 500 meV. Here, the absorption onset increases due to band filling while the bandgap renormalization at the same time decreases the bandgap. Additionally, the absorption of the pump-beam creates a free-carrier profile within the 605 nm zb-GaN layer with high free-carrier concentrations at the surface, and low concentrations at the interface to the substrate. This leads to varying optical properties from the sample surface (high transition energy) to substrate (low transition energy), which are taken into account by grading analysis for an accurate description of the experimental data. For this, a model describing the time- and position-dependent free-carrier concentration is formulated by considering the relaxation, recombination, and diffusion of those carriers. We provide a quantitative analysis of optical experimental data (ellipsometric angles Ψ and Δ) as well as a plot for the time-dependent change of the imaginary part of the dielectric function. [ABSTRACT FROM AUTHOR]

The optical constants of single-crystal AlxGa1−xP and AlxGa1−xAs have been widely studied at various Al compositions but have not yet been thoroughly investigated as polycrystalline materials. Using variable-angle spectroscopic ellipsometry, we estimate and analyze the optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As that were non-epitaxially deposited at deposition temperatures of either 250 or 420 °C, and with various dopant species, dopant concentrations, and V/III flux ratios. For wavelengths of 350–400 nm, decreasing the V/III ratio increases the refractive index of Be-doped polycrystalline Al0.25Ga0.75P. For wavelengths >500 nm, as the targeted Be dopant concentration increases for polycrystalline Al0.25Ga0.75P, the amount the extinction coefficient increases and the indirect bandgap decreases depends on the V/III ratio. Furthermore, Si-doped polycrystalline Al0.25Ga0.75P has significantly smaller extinction coefficient values than when it is Be-doped, for the same V/III ratio and targeted doping concentration, at wavelengths >500 nm. Based on our findings, we hypothesize that the dopant species, dopant concentration, and the V/III ratio dictate various types of defect concentrations, which then affect the optical constants and indirect bandgap of polycrystalline Al0.25Ga0.75P. Additionally, for wavelengths >500 nm, we find that polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As have the lowest extinction coefficient values when deposited at 420 °C, as opposed to 250 °C. Thus, we hypothesize that the deposition temperature is the most significant factor in dictating the optical constants of these polycrystalline III-Vs. Ultimately, this work demonstrates alternative methods to tune the optical constants of polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As, as opposed to tuning the Al composition. [ABSTRACT FROM AUTHOR]

We recently published a study concerning femtosecond pump–probe absorption edge spectroscopy of cubic GaN (fundamental bandgap: 3.23 eV), resulting in the transient dielectric function. In the present study, we continue our investigations of those pump–probe measurements by determining the time-dependent transition energy at the Fermi-vector between the conduction and valence bands. The generation of electron–hole pairs by the 266 nm pump-beam (4.66 eV) shifts the absorption edge by ≈ 500 meV within 1 ps due to many-body effects like band-filling and bandgap renormalization. Modeling this ultra-fast change is achieved by converting the transition energies into free-carrier concentrations, assuming the electron contributions to be dominant. We consider the relaxation, recombination, and diffusion of those free-carriers as well as either an additional gain-recombination or temperature effects. This allows for describing the transition energies on short time scales. Both models yield similar values for the characteristic relaxation time (≈ 0.21 ps), recombination time (≈ 25 ps), and diffusion coefficient (≈ 1 cm 2 /s). [ABSTRACT FROM AUTHOR]

Material characterization in the terahertz range is an interesting topic of research due to its great applications in material science, health monitoring, and security applications. Advances in terahertz generation, detection, and data acquisition have contributed to improved bandwidth, signal power, and signal-to-noise ratio. This enables advanced material characterization methods such as ellipsometry, which has been little explored in the terahertz frequency range, yet. Here, we introduce a comparison between material characterization with terahertz time-domain spectroscopy in transmission geometry and ellipsometry reflection geometry. Terahertz ellipsometry images were taken, showing spatially resolved refractive index estimation in the far field and higher image quality compared to single-polarization imaging. [ABSTRACT FROM AUTHOR]

We present two ideas to simplify the measurement and analysis of terahertz time-domain spectroscopic ellipsometry data of ultrathin films. The measurement is simplified by using a specially designed sample holder with mirrors, which can be mounted on a cryostat. It allows us to perform spectroscopic ellipsometry by simply inserting the holder into a conventional terahertz spectroscopy system for measurements in transmission geometry. The analysis of the obtained data is simplified by considering a single interface with a certain sheet conductivity σ s (since the film thickness is significantly smaller than the wavelength of the terahertz light). We demonstrate the application of these ideas by evaluating the sheet conductivities of two perovskite rare-earth nickelate thin films in the temperature range 78–478 K. The use of this particular analytical method and the sample holder design will help to establish terahertz time-domain spectroscopic ellipsometry as a characterization technique for ultrathin films. [ABSTRACT FROM AUTHOR]

Cryogenic etching of a-Si, SiO2, and Si3N4 materials by CHF3/Ar inductively coupled plasma is investigated in a range of temperature from −140 to +20 °C. Samples of the three different materials are placed together on the same silicon carrier wafer. Depending on the experimental conditions, etching or deposition regimes were obtained on the samples. The thickness variation was measured by spectroscopic ellipsometry. A process window between −120 and −80 °C was found in which the Si3N4 surface is etched while CFx deposition is obtained on a-Si and SiO2 surfaces, resulting in the infinite etching selectivity of Si3N4 to the other materials. At high enough self-bias (−120 V) and very low temperature (<−130 °C), Si3N4 etch is reduced down to a very low value, while a-Si and SiO2 are still being etched, which inverses the selectivity between Si3N4 and the two other materials. EDX analyses of a Si3N4/a-Si/SiO2 layer stack after the same etching process carried out at 20 and −100 °C confirm the presence of carbon and fluorine on a-Si at low temperature, showing the effect of the low temperature to switch from the etching to deposition regime on this material. [ABSTRACT FROM AUTHOR]

Abstract In recent years, handheld and portable terahertz instruments have been in rapid development for various applications ranging from non-destructive testing to biomedical imaging and sensing. For instance, we have deployed our Portable Handheld Spectral Reflection (PHASR) Scanners for in vivo full-spectroscopic imaging of skin burns in large animal models in operating room settings. In this paper, we debut the polarimetric version of the PHASR Scanner, and describe a generalized calibration technique to map the spatial and spectral dependence of the Jones matrix of an imaging scanner across its field of view. Our design is based on placement of two orthogonal photoconductive antenna (PCA) detectors separated by a polarizing beam splitter in the PHASR Scanner housing. We show that as few as three independent measurements of a well-characterized polarimetric calibration target are sufficient to determine the polarization state of the incident beam at the sample location, as well as to extract the Jones propagation matrix from the sample location to the detectors. We have tested the accuracy of our scanner by validating polarimetric measurements obtained from a birefringent crystal rotated to various angles, as compared to the theoretically predicted response of the sample. This new version of our PHASR scanner can be used for high-speed imaging and investigation of heterogeneity of polarization-sensitive samples in the field.

The results of a study of the optical properties of thin films based on indium tin oxides (ITO) with single-walled carbon nanotubes are presented. ITO thin films were deposited onto K8 crown glass substrates using laser-oriented deposition. Using the same method, single-walled carbon nanotubes were deposited onto the ITO surface. To vary the parameters of the interface, the average electric field strength in the range of 100–600 V/cm was adjusted during the deposition process. Identification of the structures was carried out by ellipsometry in the spectral range of 200–800 nm. To interpret the ellipsometry results of ITO thin films on K8 crown glass substrates, the Cauchy (for substrates) and Lorentz (for ITO) models were used together. The ITO–carbon nanotubes interface analysis was carried out by effective medium approximation and the Lorentz model using several oscillators. It has been shown, that in laser-oriented deposition of carbon nanotubes onto the surface of ITO thin films, according to the effective medium approximation, the thickness of the carbon nanotubes-ITO interface varies in the range of 23–36 nm with the percentage of carbon nanotubes in the range of 30–64 % at the interface. The increase in these parameters correlates with an increase in the average electric field strength during the deposition of carbon nanotubes. In accordance with the Lorentz model, a long-wavelength shift of the extinction coefficient peaks and a decrease in the refractive index of the interface in the visible region are observed. This phenomenon is caused by the implantation of carbon nanotubes into ITO. As the electric field strength increases, the contribution of laser-deposited carbon nanotubes to the ITO–carbon nanotubes interface increases, which is accompanied by a decrease in the refractive index in the visible region and a long-wavelength shift of the extinction coefficient peaks. The data obtained indicate the formation of a composite structure based on ITO with carbon nanotubes, the optical properties of which can be controlled by the average electric field strength during the laser-oriented deposition. These structures can be used in the design of optical electronics elements problems in cases where optical matching with adjacent functional layers is necessary.

The tailoring of the surface properties of cellulose nanocrystals (CNCs) to meet various requirements in environmental, food, and material areas has always been of great interest. In this study, the surface chemistry of CNCs was noncovalently modified by cetyltrimethylammonium bromide (CTAB), followed by characterizations and an investigation into its application as a coating material for interfacial interaction over various substrates. Due to the CTAB modification, the surface charge of the CNCs was neutralized, resulting in an increased size of each nanocrystal at the aqueous status and the aggregated microfibers when dried up. The CTAB modification not only decreased the crystallinity of the samples from 48.57% to 9.12%, but also reasonably hydrophobized the CNCs and decreased their total surface energy. Finally, the adsorption behavior of the CNCs and CTAB-CNCs over nonionic, anionic, and cationic polymers was investigated by ellipsometry. Based on the thickness of the CNC and CTAB-CNC layers over 2-Hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), and polyethyleneimine (PEI), we proposed that the adsorption behavior was overall influenced by electrostatic interaction, hydrogen bonding, and van der Waals forces, and the thickness of the adsorbed layers could be impacted by both the surface charge and the size of the crystals.

Abstract Monolayer materials typically display intriguing temperature-dependent dielectric and optical properties, which are crucial for improving the structure and functionality of associated devices. Due to its unique photoelectric capabilities, monolayer WSe2 has recently received a lot of attention in the fields of atomically thin electronics and optoelectronics. In this work, we focus on the evolution of the temperature-dependent dielectric function (ε = ε1 + i ε2) of monolayer WSe2 over energies from 0.74 to 6.40 eV and temperatures from 40 to 350 K. We analyze the second derivatives of ε with respect to energy to accurately locate the critical points (CP). The dependence of the observed CP energies on temperature is consistent with the alternative domination of the declining exciton binding energy as the temperature increases.

Many species of beetles from the family Scarabaeidae reflect light with near-circular polarization. In some cases, spectral narrow-band polarization phenomena result in a distinct color with a metallic shine. In other cases, broad-band features are seen, and these beetles have a silvery or goldish appearance. These features in the cuticles originate from helicoidal structures, so-called circular Bragg structures and also referred to as Bouligand structures. In this communication, Protaetia mirifica, exhibiting near-circular polarization properties in dual spectral regions, centered approximately at the wavelengths of 474 and 770 nm, is investigated in considerable detail using Mueller matrix spectroscopic ellipsometry (MMSE). From interference oscillations in the MMSE spectra, the pitch profile of the helicoidal structures in the beetle cuticle is extracted and further used in electromagnetic modeling of the cuticle structure, including the determination of epicuticle and exocuticle thicknesses (280 nm and 8.1 µm, respectively) and anisotropic optical properties. These findings are confirmed by scanning electron microscopy. The analysis shows that the uppermost 4 µm of the cuticle has a nearly constant pitch of 310 nm, which abruptly jumps to 440 nm and then gradually increases up to 575 nm. Sum decompositions of MMSE spectra reveal that the beetle cuticle reflects like a circular polarizer or like a dielectric mirror, depending on the spectral region. [ABSTRACT FROM AUTHOR]

Plasmon nanostructures are synthesized for the first time as a result of Cu diffusion into an As2Se3 film during the formation of a Cu/As Se film structure by the successive deposition of Cu and As2Se3 in vacuum. Using spectroscopic ellipsometry, the spectra of the extinction coefficients and refractive index, as well as the real and imaginary parts of the permittivity of the synthesized structures in the wavelength range of 240–2500 nm, that indicate the presence of localized surface plasmon resonances are obtained. It is shown that the frequency position of plasmon resonances in the wavelength range from 470 to 660 nm can be controlled by changing the thickness of the copper film and annealing. [ABSTRACT FROM AUTHOR]

Thermoset resins are singular materials in the field of microelectronics. Because they exhibit a high contrast of thermomechanical properties with other integrated materials like oxides, metals or silicon, polymers can threaten the mechanical integrity of stacks. Knowing polymer properties allows manufacturers to foresee the compatibility between materials and improve chipsets reliability. At a bilayer scale, the properties mismatch between the polymer film and the silicon substrate causes an overall curvature of the wafer which evolves with temperature. By comparing the thermally induced curvature of two distinct substrates with the same film, the biaxial modulus and the coefficient of thermal expansion of the film can be determined. This method can not only check the achievement of the polymer cross-linking, but also estimates their relaxation temperatures. In this article, we present the ability of this method to, not only, measure those properties in the glassy state, but also, for the first time, in the rubbery state. We also illustrate the proficiency of this approach in detecting and characterizing two successive glassy states. [ABSTRACT FROM AUTHOR]

A preliminary investigation of the optical properties of complex Cr-based hard coatings and their connection with the compound structure of the coatings is presented. Cr/CrN, Cr/CrN/CrAlN, Cr/CrN/CrTiAlN, and Cr/CrN/CrAlTiN coating structures were deposited through unbalanced magnetron sputtering. Their mechanical properties, especially nanohardness, coefficient of friction, and adhesion, were measured. The structure and composition of the coatings were characterised through SEM, FIB, XPS, and TEM. Their optical properties were investigated by UV-VIS ellipsometry. The optical parameters' phase difference Δ, the amplitude ratio Ψ, the frequency-dependent real (ε1(ω)) and imaginary (ε2(ω)) part of the dielectric function, and the corresponding refractive and extinction indexes n(ω) and k(ω) were measured and modelled via regression analysis implemented using the WVASE© software version 3.686. Satisfactory coincidence was achieved between the measured optical data and the corresponding fitting models. The physical polycrystalline optical constants of the industrial samples were extracted from modelling data with roughness. The analysis of the data showed that ellipsometric characterisation can be used in order to determine the physical properties of Cr-based hard coatings with complex structure and composition, as well as for repeatability control of the deposition process. However, more detailed research is needed to predict the composition based on measured optical properties. [ABSTRACT FROM AUTHOR]

In recent years, handheld and portable terahertz instruments have been in rapid development for various applications ranging from non-destructive testing to biomedical imaging and sensing. For instance, we have deployed our Portable Handheld Spectral Reflection (PHASR) Scanners for in vivo full-spectroscopic imaging of skin burns in large animal models in operating room settings. In this paper, we debut the polarimetric version of the PHASR Scanner, and describe a generalized calibration technique to map the spatial and spectral dependence of the Jones matrix of an imaging scanner across its field of view. Our design is based on placement of two orthogonal photoconductive antenna (PCA) detectors separated by a polarizing beam splitter in the PHASR Scanner housing. We show that as few as three independent measurements of a well-characterized polarimetric calibration target are sufficient to determine the polarization state of the incident beam at the sample location, as well as to extract the Jones propagation matrix from the sample location to the detectors. We have tested the accuracy of our scanner by validating polarimetric measurements obtained from a birefringent crystal rotated to various angles, as compared to the theoretically predicted response of the sample. This new version of our PHASR scanner can be used for high-speed imaging and investigation of heterogeneity of polarization-sensitive samples in the field. [ABSTRACT FROM AUTHOR]

The precise mechanism governing the reversible semiconductor‐to‐metal transition (SMT) in V2O5 remains elusive, yet its investigation is of paramount importance due to the remarkable potential of V2O5 as a versatile "smart" material in advancing optoelectronics, plasmonics, and photonics. In this study, distinctive experimental insights into the SMT occurring in amorphous V2O5 through the application of highly sensitive, temperature‐dependent, in situ analyses on a V2O5 thin film deposited on soda‐lime glass are presented. The ellipsometry measurements reveal that the complete SMT occurs at ≈340 °C. Remarkably, the refractive index and extinction coefficients exhibit reversible characteristics across visible and near‐infrared wavelengths, underscoring the switch‐like behavior inherent to V2O5. The findings obtained from ellipsometry are substantiated by calorimetry and in situ secondary ion mass spectrometry analyses. In situ electron microscopy observations unveil a separation of oxidation states within V2O5 at 320 °C, despite the thin film retaining its amorphous state. The comprehensive experimental investigations effectively demonstrate that alterations in electronic state can trigger the SMT in amorphous V2O5. It is revealed for the first time that the SMT in V2O5 is solely contingent upon electronic state changes, independent of structural transitions, and importantly, it is a reversible transformation within the amorphous state itself. [ABSTRACT FROM AUTHOR]

Hydrogels are usually depicted as a homogenous polymer block with a distinct surface. While defects in the polymer structure are looked into frequently, structural irregularities on the hydrogel surface are often neglected. In this work, thin hydrogel layers of ≈100 nm thickness (nanogels) are synthesized and characterized for their structural irregularities, as they represent the surface of macrogels. The nanogels contain a main‐chain responsiveness (thermo responsive) and a responsiveness in the cross‐linking points (redox responsive). By combining data from ellipsometry using box‐model and two‐segment‐model analysis, as well as atomic force microscopy, a more defined model of the nanogel surface can be developed. Starting with a more densely cross‐linked network at the silica wafer surface, the density of cross‐linking gradually decreases toward the hydrogel–solvent interface. Thermo‐responsive behavior of the main chain affects the entire network equally as all chain segments change solubility. Cross‐linker‐based redox‐responsiveness, on the other hand, is only governed by the inner, more cross‐linked layers of the network. Such dual responsive nanogels hence allow for developing a more detailed model of a hydrogel surface from free radical polymerization. It provides a better understanding of structural defects in hydrogels and how they are affected by responsive functionalities. [ABSTRACT FROM AUTHOR]

We demonstrate the ability of a single magneto-optical reflection experiment to achieve layer-resolved vector magnetometry in multilayer films. For this purpose, we designed, fabricated, and measured a set of epitaxial ferromagnetic/non-magnetic/ferromagnetic heterostructure multilayer samples that exhibit in-plane uniaxial anisotropy and a tunable ferromagnetic interlayer coupling strength through the non-magnetic interlayer. By means of generalized magneto-optical ellipsometry measurements, we obtain the magnetization angles of the two different ferromagnetic layers independently as a function of the applied field. Hereby, we observe that the magnetization switching of one layer can trigger a discontinuous shift of the magnetization angle in the second layer if ferromagnetic interlayer coupling is present. Moreover, we reproduce the obtained behavior using a model of two coupled macrospins, which corroborates even the unexpected aspects of our experimental results and thus reinforces the sensitivity and reliability of our experimental layer-resolved vector magnetometry. [ABSTRACT FROM AUTHOR]

Many optical applications, including free-space optical communications, lidar, and astronomical measurements, are impacted by the presence of light-scattering particles also known as obscurants. Scattering from particles consisting of sand, dust, dirt, and other substances can significantly degrade optical signals. For many obscurants, the index of refraction is dependent on the wavelength of light, and there exists a Christiansen wavelength (λc) at which scattering is at a minimum. At λc the index of refraction of the scattering particles (ns) matches that of the surrounding medium, in this case air (with refractive index na). This condition makes the scattering particulates almost invisible to the propagating light, minimizing scattering and increasing transmission at λc. Previously, the authors showed a technique for measuring the index of refraction n (λ) and the extinction coefficient k (λ) using spectroscopic ellipsometry for various sand samples. Spectroscopic measurements on static sand samples demonstrated good agreement with the predicted spectral properties and highlighted the presence of a Christiansen feature near 8 µm. However, in outdoor environments, the scattering particles are never stationary but in a constant state of motion. In this work, spectroscopic measurements on dynamic sand samples (sand that is falling through the optical beam path) show two Christiansen features seen previously in predicted and observed static sand measurements. Additionally, we characterize, for the first time, transmission around a Christiansen feature using a tunable laser and show results consistent with other spectroscopic measurements. [ABSTRACT FROM AUTHOR]

Regular wave patterns were created by a 2 kV gallium ion on Si(111) monocrystals at incidence angles between 60° and 80° with respect to the surface normal. The characteristic wavelength and surface roughness of the structured surfaces were determined to be between 35–75 nm and 0.5–2.5 nm. The local slope distribution of the created periodic structures was also studied. These topography results were compared with the predictions of the Bradley–Harper model. The amorphised surface layers were investigated by a spectroscopic ellipsometer. According to the results, the amorphised thicknesses were changed in the range of 8 nm to 4 nm as a function of ion incidence angles. The reflectance of the structured surfaces was simulated using ellipsometric results and measured with a reflectometer. Based on the spectra, a controlled modification of reflectance within 45% and 50% can be achieved on Si(111) at 460 nm wavelength. According to the measured results, the characteristic sizes (periodicity and amplitude) and optical property of silicon can be fine-tuned by low-energy focused ion irradiation at the given interval of incidence angles. [ABSTRACT FROM AUTHOR]

Optical sensors using zero‐reflection points (ZRPs) enable excellent sensitivity due to the accompanying phase singularities and the steepest slope of the reflectivity curve. Here, the collaborative manipulation of three ZRPs in a simple platform formed by a lithography‐free, metal‐dielectric‐metal structure with unsurpassed, experimentally demonstrated, limit of detection ≈2 × 10−8 refractive index unit is reported. The sensor relies on: i) strong coupling between p‐polarized surface plasmon polariton and photonic waveguide, leading to reflection suppression, Rabi splitting and phase singularities; ii) simultaneous implementation of two orthogonally polarized ZRPs, enabling spectral overlap of s‐polarized photonic modes (Rs) with the coupled p‐polarized resonances (Rp); and iii) ellipsometry‐based sensing where the s‐polarized ZRPs provide a stable reference to boost the sensor performance in terms of the amplitude ratio and phase difference of Rp and Rs thereby naturally forming a refinement measuring scale akin to a Vernier scale. Remarkably, the precise manipulation of ZRPs enables resetting the sensor to its optimal sensing point. The capability has been demonstrated for a biosensor of SARS‐CoV‐2 spike (S2) protein that can track the full functionalization process then reset to perform dose‐dependent detection of the S2 protein. This work provides a new strategy for the development of optical sensors and perfect light absorbers. [ABSTRACT FROM AUTHOR]

Hybrid strategies that combine conventional top-down lithography with bottom-up molecular assembly are of interest for a range of applications including nanolithography and sensors. Interest in these strategies stems from the ability to create complex architectures over large areas with molecular-scale control and precision. The molecular-ruler process typifies this approach where the sequential layer-by-layer assembly of mercaptoalkanoic acid molecules and metal ions are combined with conventional top-down lithography to create precise, registered nanogaps. However, the quality of the metal-ligated mercaptoalkanoic acid multilayer is a critical characteristic in generating reproducible and robust nanoscale structures via the molecular-ruler process. Therefore, we explore the assembly of alkanethiolate monolayers, mercaptohexadecanoic acid (MHDA) monolayers, and Cu-ligated MHDA multilayers on Au{111} substrates using atomic force microscopy and in situ dynamic spectroscopic ellipsometry. The chemical film thicknesses in situ dynamic spectroscopic ellipsometry agree with previous ex situ surface analytical methods. Moreover, in situ dynamic spectroscopic ellipsometry provides insight into the assembly process without interrupting the assembly process and potentially altering the characteristics of the resulting chemical film. By following the real-time dynamics of each deposition step, the assembly of the Cu-ligated MHDA multilayers can be optimized to minimize deposition time while having minimal impact to the quality of the chemical film. [ABSTRACT FROM AUTHOR]

Ellipsometry is a well-known material analytical method widely used to measure thickness and optical properties of thin films and surfaces across a wide range of industrial and research applications including critical dimensions in chipmaking. The method employs the fact that light undergoes a change in polarization state upon reflection from or transmission through a material. The desired properties of the surface structure are related to measurements by the electromagnetic models expressed by Maxwell's equations as well as models of material properties. The work here demonstrates the use of artificial intelligence in the form of a multilayer perceptron artificial neural network to apply the electromagnetic model. The reflecting surface examined here is composed of indium tin oxide (ITO) films approximately 400 nm in thickness deposited on silicon substrates. Solutions are provided by 299 artificial neural networks, one per wavelength from 210 to 1700 nm across which ITO exhibits transparent as well as absorbing characteristics. Thus, it serves as a proxy for a wide range of other materials. To train the network, simulated measurements are computed at two thicknesses which differ randomly by 1–6 nm and at three different incidence angles of 55°, 65°, and 75°. Following training, results are obtained in less than one second on a conventional desktop computer. [ABSTRACT FROM AUTHOR]

The tailoring of the surface properties of cellulose nanocrystals (CNCs) to meet various requirements in environmental, food, and material areas has always been of great interest. In this study, the surface chemistry of CNCs was noncovalently modified by cetyltrimethylammonium bromide (CTAB), followed by characterizations and an investigation into its application as a coating material for interfacial interaction over various substrates. Due to the CTAB modification, the surface charge of the CNCs was neutralized, resulting in an increased size of each nanocrystal at the aqueous status and the aggregated microfibers when dried up. The CTAB modification not only decreased the crystallinity of the samples from 48.57% to 9.12%, but also reasonably hydrophobized the CNCs and decreased their total surface energy. Finally, the adsorption behavior of the CNCs and CTAB-CNCs over nonionic, anionic, and cationic polymers was investigated by ellipsometry. Based on the thickness of the CNC and CTAB-CNC layers over 2-Hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), and polyethyleneimine (PEI), we proposed that the adsorption behavior was overall influenced by electrostatic interaction, hydrogen bonding, and van der Waals forces, and the thickness of the adsorbed layers could be impacted by both the surface charge and the size of the crystals. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry and ultraviolet-visible (UV-VIS) spectrometry were utilized to study the optical properties of ferroelectric lead lanthanum zirconate titanate (PLZT) films. These films were deposited on platinized silicon [Si(100)/ SiO2/TiO2/Pt(111)] substrates using the chemical solution deposition method. Films were annealed at two different temperatures (650 and 750 °C) using rapid thermal annealing. Shimadzu UV-1800 UV-VIS spectrophotometer with a resolution of 1 nm was used to measure the reflectance data in the spectral range of 300–1000 nm with a step size of 1 nm. The bandgap values were determined from the reflectance spectra using appropriate equations. A J.A. Woollam RC2 small spot spectroscopic ellipsometer was used to obtain the change in amplitude (Ψ) and phase (Δ) of polarized light upon reflection from the film surface. The spectra were recorded in the wavelength range of 210–1500 nm at an incident angle of 65°. Refractive index (n) and extinction coefficient (k) were obtained by fitting the spectra (Ψ, Δ) with the appropriate models. No significant changes were observed in the optical constants of PLZT films annealed at 650 and 750 °C. The optical transparency and the strong absorption in the ultraviolet (UV) region of PLZT films make them an attractive material for optoelectronic and UV sensing applications. [ABSTRACT FROM AUTHOR]

Complex dielectric function (ɛ = ɛ1 + iɛ2) spectra of a heat treated single crystal yttria-stabilized zirconia (YSZ) have been determined over a spectral range of 0.03–8.5 eV using spectroscopic ellipsometry. Spectra are collected using three instruments covering different parts of the measured spectrum. The YSZ sample is modeled as a semi-infinite bulk crystal covered by a surface layer described by a Bruggeman effective medium approximation of equal parts YSZ and void. [ABSTRACT FROM AUTHOR]

The growth of an oxide film on the surface of polycrystalline β-rhombohedral boron during thermal oxidation in air at temperatures of 400, 500, 600, and 700°C was studied using in situ single-wave ellipsometry. At temperatures above the melting point of B2O3, the oxidation was significantly activated. Having reached its maximum at 500, 600, and 700°C, the thickness of the oxide film decreased. This is attributed to the dynamic equilibrium between the processes of evaporation of liquid oxide and film growth caused by the diffusion of boron and oxygen ions. The refractive index of the substrate (pure boron) decreased from 3.1 to 2.95 during the annealing due to a change in its porosity. It was established by Raman spectroscopy that after annealing at 700°C, the surface contained not only the oxide B2O3, but also traces of suboxide B6O, previously observed during the oxidation of boron at higher temperatures. [ABSTRACT FROM AUTHOR]

Amphiphilic silk fibroin (SF) forms stable adsorption layers at the air–water interface. The range of the investigated protein concentrations can be divided into two parts according to the peculiarities of the surface layer properties. At protein concentrations from 0.0005 to 0.01 mg/mL, the dynamic surface elasticity monotonically increases with the concentration and surface age and reaches values of up to 220 mN/m. In this range, the adsorption layer compression leads to a fast increase of the surface pressure. In the second part (>0.01 mg/mL), the surface elasticity decreases again and the kinetic dependences of the film thickness and adsorbed amount change only a little. In this case, the layer compression leads only to a slight increase of the surface pressure. These two types of behavior can be attributed to the distinctions in the protein aggregation in the surface layer. Atomic force microscopy (AFM) investigations of the layers transferred from the liquid surface onto a mica surface by the Langmuir–Schaefer method show some peculiarities of the layer morphology in the intermediate concentration range (~0.02 mg/mL). [ABSTRACT FROM AUTHOR]

A solution to the direct ellipsometry problem is presented for a single-layer model of an isotropic substrate–anisotropic film in the case of the orientation of the film optical axis in the plane of incidence. Analytical expressions for calculating the ellipsometric parameters of such a structure are obtained. A simple numerical algorithm is proposed for determining the ordinary () and extraordinary () refractive indices of a bulk crystal under various measurement conditions. The inverse problem of determining , , and the film thickness when changing the azimuth of the optical axis is considered. The correlation of the required parameters for such a problem is discussed. [ABSTRACT FROM AUTHOR]

The dielectric function evolution and electronic bandgap manipulation by silicon (Si) doping for Sb 2 Te 3 phase change films have been investigated by temperature dependent spectroscopic ellipsometry measurements. During the phase change from amorphous to rhombohedral structures, the significant contrast of electronic band structure for pure Sb 2 Te 3 and Si-doped Sb 2 Te 3 (SST) films as functions of temperature (210–620 K) and Si concentration (0%–12%) has been systematically studied by analyzing the dielectric functions, Tauc gap energy, and partial spectral weight integral. The distinct differences can be mainly attributed to the increment of structure order degree, originated from the change of local bonding arrangement. Based upon the evolutions of Tauc gap energy and partial spectral weight integral with increasing temperature for all four samples, it can be concluded that Si doping can inhibit the crystallization of amorphous films and accelerate the phase change process by serving as nanoscale heaters, which is helpful in improving the thermal stability of amorphous films. The elevated crystallization temperature and phase change rate by Si doping contribute to the dependability and endurance for SST-based phase change memory. The present data provide an important direction on the physical mechanism investigation of Si doping Sb 2 Te 3 by optical techniques. [ABSTRACT FROM AUTHOR]