Narrow Results

This paper presents a comprehensive study of the optical properties of amorphous and crystalline MoO₃ thin films using spectroscopic ellipsometry. MoO₃ films were deposited on SiO₂/Si substrates with varying oxide thicknesses using the atomic layer deposition (ALD) method. The study utilized various optical oscillator models, including Lorentz, Tauc–Lorentz and Harmonic, to analyze the dielectric functions and identify midgap states resulting from oxygen deficiencies. The findings highlight significant differences in the optical properties between amorphous and crystalline MoO₃ films, demonstrating the impact of structural phases and substrate conditions. Specifically, amorphous films exhibited lower broadening and energy peaks compared to crystalline films, which showed distinct midgap states indicative of higher oxygen vacancy concentrations. These results enhance the understanding of the optical behavior of MoO₃ films and their potential applications in advanced optoelectronic devices.

We have applied spectroscopic ellipsometry to obtain the optical constants, i.e., refractive indices (n) and extinction coefficients (k) of a thin tris (8-hydroxyquinoline) aluminum (Alq₃) film evaporated on the top of 300-nm-thick SiO₂ layer on a silicon substrate. Using a spectroscopic ellipsometer we collected the ellipsometric data of Ψ and Δ at 3 incident angles of 65°, 70° and 75° and 226 energies of 1.5 eV to 6.0 eV. For the organic sample, we adopted a simple two-film model consisting of ambient/organic film/SiO₂ film/silicon substrate. Using the multiple oscillators of Tauc-Lorentz (TL) dispersion function and the two-film model, we obtained the thickness of the Alq₃ film. By data inversion technique, the spectra of n and k for the Alq₃ film are calculated from measured Ψ and Δ at each photon energy when the film thickness is fixed to a value obtained by the TL dispersion fitting. The extrapolation of optical function near band gap yields the band gap of 2.64 eV for Alq₃ film.

To determine the optical parameters of crude oil and seawater systems, we carried out spectral investigations using the ellipsometry method, which is a highly sensitive and accurate optical method for studying the surfaces and interfaces of various media. This method is based on studying the change in the polarization state of reflected light after its interaction with the surface of interfaces of these media. Crude oil and seawater from different regions of Caspian Sea were accessed by spectroscopic ellipsometry over the 200–1700 nm spectral range at room-temperature. Optical constants and dielectric function were obtained for massive samples of each substance, as well as for ultrathin layers of the oil spilled over the sea surface. Dielectric function, when completely determined in the frequency regions corresponding to electronic transitions and excitation of atomic or molecular vibrations in the object, is a unique dielectric fingerprint of this object. Oils with even miserable difference in type and concentration of biomarkers and heterocomponents will have different dielectric functions. The possibility to use dielectric function as a unique optical fingerprint for oil identification is figured out.

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

In this paper, we have performed a study on the optical properties of single crystals ZnGa₂S₄ by method of density functional theory (DFT) and ellipsometry measurements. The calculated results for the real ${\epsilon }_r$ and imaginary ${\epsilon }_i$ parts of the dielectric function are compared with the measured experimental spectroscopic ellipsometry (SE) spectra in the 0.7–6.5 eV spectral region. Absorption coefficient-photon energy dependency revealed the existence of direct bandgap transitions with energy 3.5 eV. This result is very close to bandgap obtained from our theoretical calculation.

ITO thin films were coated on unheated glass and Si-wafer (100) substrates by ion-assisted evaporation. The effects of post annealing, in vacuum at 250°C and 350°C for 1 h, on the structural, optical and electrical properties were studied. The structure was characterized by X-ray diffraction (XRD). The surface morphology of the films was investigated by atomic force microscopy (AFM). The optical properties were evaluated by spectrophotometer and spectroscopic ellipsometry (SE). The resistivity was measured by the four-point probes method. It was found that the increase of post-annealing temperature would improve the film crystallinity and electrical properties. The preferred orientation of ITO thin film after annealing is (222). The resistivity of the as-deposited film is found to be 5.52 × 10^-4 Ωcm and decreases to 2.11 × 10^-4 Ωcm after annealing at 350°C. The AFM image reveals that the surface roughness decreases with increasing annealing temperature. The uniqueness test based on SE analysis data has been applied for ITO modeling. This modeling indicates that the film microstructure consists of three layers including the higher-index ITO layer, the effective medium approximation (EMA) layer to represent a slightly lower optical index, and the surface roughness layer on top. The EMA thickness and its relative composition decrease with increasing annealing temperature. The extinction coefficient in the IR region increases whereas the refractive index decreases with increasing annealing temperature.

An effective-substrate method was presented to obtain the optical constants of an iron native oxide layer with unknown optical constants and film thickness on an iron substrate with unknown optical constants by using spectroscopic ellipsometry (SE). "Thick" iron films were deposited on silicon wafer by magnetron sputtering and were exposed to air at room temperature. They were measured by spectroscopic ellipsometry during this procedure at different time points from ten minutes to seven months. Pseudo optical constants were calculated from the initially measured data and were introduced into the modeling work of subsequent measurements as an effective substrate in order to obtain the optical constants and film thickness of the native oxide layer. After obtaining the optical constants of the subsequent native oxide layer, they were employed in the modeling work of the initially measured data and the optical constants of the iron substrate and the film thickness of the initial native oxide layer was obtained.

In this study, undoped and cobalt (Co)-doped zinc oxide (ZnO) films were successfully produced by ultrasonic spray pyrolysis (USP) technique at low temperature (350${}^{\circ }$C). The optical and surface properties were investigated as a function of Co content. The optical parameters (thickness, refractive index and extinction coefficient) were determined using spectroscopic ellipsometry (SE) and it was seen that the refractive index and extinction coefficient values of Co-doped ZnO films decreased slightly depending on the increasing of Co doping. For investigation, the transmittance and photoluminescence (PL) spectra of the films, UV–Vis spectrophotometer and PL spectroscopy were used at room temperature. The transmittance spectra show that transmittance values decreased and Co${}^{+2}$ ions substitute Zn${}^{+2}$ ions of ZnO lattice. The optical band gap values decreased from 3.26 eV to 2.85 eV with the changing of Co content. The results of PL spectra exhibit the position of the different emission peaks unchanged but the intensity of peaks increased with increasing Co doping. Also, the surface properties of the films were obtained by atomic force microscopy (AFM) and these results indicated that the surface morphology and roughness values were prominently changed with Co doping.

TiO₂ films of different thickness are deposited on silicon substrate at low temperature and pressure by a Helicon-PECVD reactor. The evolution of film morphology and topography is observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), meanwhile the spectroscopic ellipsometry (SE) measurements are performed to investigate the film growth mechanism and optical constants. The SEM and AFM observations show that all the films exhibit a columnar structure, moreover all the columns are vertical grown and well-organized when the thickness below $\sim$80 nm. As the thickness is increased to $\sim$150 nm, 250 nm and 450 nm, the column size is increased in the top layers, the whole film morphology becomes inhomogeneous, which leads to a decreased density and rougher surface. By fitting the SE measurements, a suitable gradient physical model is found to describe the film morphologies, the model consists of a native SiO₂ layer on Si substrate, a mediate layer mixed TiO₂ with void whose concentration gradient changed from bottom to top, and a top roughness layer. For thick films ($\ge \sim$450 nm), the absorption and scattering on the rough surface is considered in order to keep the precision of SE fits. It is found that the optical index is decreased with film thickness, which is related to the evolution of structure in the top layers.

In this study, a sandwich-structured electrode composed of indium tin oxide (ITO)/metal silver layer/ITO was prepared by the radio frequency magnetron sputtering method. We used the Taguchi method and spectroscopic ellipsometry (SE) analysis to optimize the geometrical structures of the electrodes and the sputtering power for the silver layer. While the Taguchi method allows us to rapidly optimize the manufacturing parameters, SE analysis enables us to precisely evaluate the thickness of each layer of the electrodes, so that the whole optimization process is more precise and effective. When the silver layers of different samples are sputtered under the same conditions, the difference in their thickness is often $>1$ nm. Thus, it is difficult to understand the influences of the manufacturing parameters on the optoelectronic performance of the electrodes. Experimental results show that the thickness of the silver layer was the main factor affecting the transmittance and sheet resistance of the electrodes. However, the decisive factors for the Haacke index in the visible light range were the thickness of the bottom ITO film. Nonetheless, the signal-to-noise (S/N) ratios of some factors are quite close. Thus, further analyses are needed to understand this phenomenon. After optimization, the Haacke index is $20.17\times 10^{-3}{\mathrm{\Omega }}^{-1}$, which is better than the 19.45 of the best sample, suggesting that this experiment has improved the optoelectronic properties of the electrode.

A set of thin tantalum films was prepared by direct current (DC) magnetron sputtering using different substrate temperatures and sputtering power. In order to identify the optimal condition for hillock free thin tantalum (Ta) film deposition, AFM was employed to measure surface morphology of the Ta films and to research the effect of substrate temperatures and sputtering power on the films surface. The relationship between optical constants and film stress of thin Ta films was also investigated. The comparison of AFM results showed that thin Ta films deposited at 500 K with a sputtering power of 56 W produced a hillock free surface as well as minimum surface roughness. All films were also measured by spectroscopic ellipsometry (SE) to characterize their optical properties. Refractive index and extinction coefficient of thin Ta films obtained from SE results by using a 5-layer model increased simultaneously, when sputtering power increased and the substrate temperature remain unchanged. However when the power was a constant, the thin Ta film sputtered at 500 K had a lower refractive index and extinction coefficient than other samples sputtered with other substrate temperatures from 300 to 700 K.

Zinc Oxide thin films were deposited on glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, 2-methoxyethanol and monoethanolamine were used as precursor, solvent and stabilizer, respectively. Zinc acetate dihydrate was used with different molar concentrations of 0.15, 0.25 and 0.5 M. Optical properties of ZnO thin films such as dielectric constants, absorption coefficient, Urbach energy and optical band gap energy were calculated by spectroscopic ellipsometry (SE) method. The effect of zinc acetate concentration on optical properties of ZnO thin films is investigated. ZnO thin film with Zn concentration of 0.25 M had the highest optical band gap. Wemple DiDomenico oscillator model was used for calculation of the energy of effective dispersion oscillator, the dispersion energy, the high frequency dielectric constant, the long wavelength refractive index and the free carrier concentration.

In this work we investigate the effect of metal layer in the Al-doped ZnO (AZO)/Al/AZO structure. AZO and Al thin films are deposed successively at room temperature using DC magnetron sputtering by rotating the substrate holder without breaking the vacuum. The optical characterization of AZO/Al/AZO structure was performed by the spectroscopic ellipsometry under different incidence angles (55${}^{\circ }$, 65${}^{\circ }$ and 75${}^{\circ }$). For the AZO monolayer structure, it was found that the complex refractive index and the complex permittivity coefficient varied differently according to the incidence angle. The addition of Al layer (5nm thicknesses) in this monostructure reduces significantly this influence on the measurement, homogenizes the real refractive index variation and significantly reduces the real electrical coefficient permittivity in the visible range. In addition, the obtained depolarization values confirm the results of the AFM roughness revealing that the Al layer addition makes the surface smoother so that it meets the required conditions as the bottom electrode of organic light emitting diodes. The photoluminescence (PL) measurements indicate that the Al layer alters the PL emission. Actually, the Al layer enhances subsequently the PL emission and promotes the blue and red emission.

In the present work, zinc sulfide thin films were deposited on glass substrates by sol–gel process with different coating speeds 3600, 4800, 6000 and 7200rpm. Zinc acetate (Zn(CH₃COO)${}_2\cdot 2$H₂O) and thiourea (CH₄N₂S) were used as precursors. Two-methoxyethanol and monoethanolamine were used as solvent and stabilizer, respectively. The optical properties of ZnS thin films such as refractive index, extinction coefficient, dielectric function and optical band gap energy of the films were obtained by spectroscopic ellipsometry (SE) analysis method in the wavelength range of 300–800nm. The incidence angle of the layers was kept at 70^∘. The measured SE parameters ${\mathrm{\Psi }}_{\mathrm{\text{exp}}}$ and ${\mathrm{\Delta }}_{\mathrm{\text{exp}}}$ are fitted against the designed model by minimizing the mean square error (MSE). Considering the data obtained, it can be deduced that the optical properties of ZnS films are highly influenced by rotation rates. The extinction coefficients of the films were increased with increasing rotation rates of the films. From these results, it is found that the energy gap of the ZnS films increases with increasing rotation rates of the films in the range of 3.13–3.20eV.

Nanostructured Fe:SnO₂ thin films were deposited on glass substrates through sol–gel spin coating method. Films were synthesized with different iron quantities including 0%, 4%, 8% and 12% (wt.%). The effects of Fe concentration on optical properties of films were investigated by spectroscopic ellipsometry (SE) technique. SE measured ($\mathrm{\Psi },\mathrm{\Delta }$) parameters for films in the wavelength range between 300nm to 800nm. Optical properties including the refractive index, extinction coefficient, transmittance, dielectric constants and optical conductivity were determined by fitting the SE measured ($\mathrm{\Psi },\mathrm{\Delta }$) parameters and data obtained from the optical model-based analysis. Results showed that the transmittance values increase by increment of Fe concentration from 0% to 12%. The bandgap energy ($E_g)$ of prepared thin films was also calculated. $E_g$ values were between 3.44 and 3.58eV. Dispersion parameters including the high frequency dielectric constant (${\epsilon }_{\infty })$ and the ratio of free carrier concentration to effective mass (N/m${}^{\ast })$ were then obtained for the prepared films.

Spectroscopic ellipsometry was successfully applied in the evaluation of the thermal stability of thin films in air by detecting the changes in film optical properties and thickness. Tantalum nitride (Ta_xN_y) films with a nominal thickness of 30 nm were deposited on silicon wafer and annealed at different temperatures from 200°C to 700°C. Annealing-induced changes in thickness and optical properties of Ta_xN_y were detected and determined by spectroscopic ellipsometry. Different approaches were adopted in the modeling and analysis of spectroscopic ellipsometric data. The results are consistent with the findings from Fourier Transform Infrared Spectroscopy (FTIR).

Two sets of multilayer structures consisting of 44 alternating layers of a-SiN_x:H (~ 4 nm and 6 nm) and SiO₂ (5 nm) have been fabricated using the plasma-enhanced chemical vapor deposition (PECVD) technique. The a-SiN_x:H that has a lower bandgap forms the well layer, while the large bandgap SiO₂ forms the barrier layer. A single bulk layer of a-SiN_x:H has also been grown to serve as a reference for comparison with the multilayer structures. The samples were studied using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), spectroscopic ellipsometry (SE), and photoluminescence (PL) techniques. The SE data have been successfully fitted, and the complex refractive indices of the a-SiN_x:H in the bulk and multilayers have been determined. The effects of quantum confinement on the optical bandgap and refractive indices of a-SiN_x:H have been investigated. The results are correlated to the PL spectra of the samples.

In the present work, pure and Fe-doped ZnO thin films were deposited on glass substrates by sol–gel method. Zinc acetate and iron nitrate were used as the starting material and dopant source, respectively. The concentration of Fe doping was 6at.% and 8at.%. The optical and electronic properties of pure and Fe-doped ZnO thin films such as refraction index, extinction coefficient, dielectric function and optical band gap energy of the layers were obtained by spectroscopic ellipsometry method in the wavelength range of 300–900nm. The incidence angle of the layers kept 70${}^{\circ }$. Also data obtained by Kramers–Kronig relations were used for comparison. The influence of Fe-doping concentration on the optical and electronic properties of thin films was studied. The transmittance data of ZnO thin films showed that 6at.% Fe-doped ZnO thin film has the highest transmittance value. Dielectric function of pure ZnO films was found to be higher compared with Fe-doped ones. Also it can be deduced from the results that Fe doping influences the optical band gap energy of thin films.

In the present work, the optical response of CoPcF₁₆ films upon exposure to ammonia vapor in the concentration range 50 to 1000 ppm was measured by total internal reflection ellipsometry. It was demonstrated that the sorption of NH₃ molecules causes substantial shift of the Δ(λ) spectrum which is determined by the increase in film thickness and change of its optical parameters. It was found that the CoPcF₁₆ films deposited at substrate temperature of 220 °C are characterized by larger grains and more developed surface demonstrating higher optical response than films deposited at substrate temperature of 60 °C. In order to gain an insight into the sorption mechanism at molecular level, we have studied the interaction of ammonia vapor with hexadecafluorinated cobalt phthalocyanine using infrared spectroscopy. It was shown that the detection of ammonia was found to be governed primarily by coordination to the metal center.