Narrow Results

Diamond-like carbon (DLC) films were deposited with a RF magnetron sputtering device. The target used was high purity graphite (99.999%) and n-type Si was used as the substrate. In order to get good anti-reflective films nitrogen gas was used to a small extent in addition to hydrogen gas thus resulting in a-C:H:N thin films. From the Ellipsometry studies it was found that the deposited films were good for optical coating. XPS studies indicate that film contains carbon in graphitic form, DLC form and CN bonding in sp² trigonal and sp³ tetrahedral structure. FT-IR spectra analysis agrees with the results of XPS data. AFM studies show that the surface roughness of the films depend on the film composition.

A set of AlN thin films was prepared by reactive magnetron sputtering at room temperature. The effect of oxygen impurities on the structural and optical properties of AlN films is discussed. The structural and optical properties were characterized using X-ray diffraction (XRD) and spectroscopic ellipsometry, respectively. Depending on the deposition conditions, films can grow hexagonal (würzite, P6₃m3) or cubic (zinc-blende, Fm3m) in microstructure. From the optical measurements, the ellipsometric parameters (ψ, Δ) and the real refractive index as a function of energy were obtained. From the ellipsometric measurements, a model of Lorentz single-oscillator was employed to estimate the optical band gap, E_g. In the theoretical part, a calculation of density of states (DOS) and band structure was performed to be compared with the experimental results.

Molybdenum nitride films γ-Mo₂N/Si have been fabricated with reactive magnetron sputtering in (N₂ + Ar) gas mixture. Phase composition of the films has been defined with reflection high energy electron diffraction. Refractive index and extinction coefficient of γ-Mo₂N have been evaluated with laser ellipsometry at λ = 632.8 and 488.0 nm. Upper limit of γ-Mo₂N film thickness measurable with laser ellipsometry has been found to be ~80 nm.

Titanium dioxide has been in close examination for application development due to its high index of refraction and transparency across the visible range. One of the most active researches is hydrophilicity and photocatalysis in TiO₂ films. In this study, a close investigation to TiO₂ films' microstructural transformation was examined. A number of thin film samples were prepared by ion-assisted electron-beam evaporation at 200-nm nominal thickness, 2.0 Å/s deposition rate and 250°C deposition temperature. The varying parameter was the oxygen flow rate at 2, 4, 6 and 8 sccm. The films were eventually annealed for three hours in air atmosphere. The crystalline structures of as-deposited (ASD) and annealed films were deduced by variable-angle spectroscopic ellipsometry (VASE), and supported by X-ray diffractometry (XRD) and atomic force microscopy (AFM). Film characterization based on VASE is desirable in order to understand physical and optical characteristics of the films. Transmittance spectra were derived from UV/Vis spectrophotometer. It was found that all as-deposited films were all amorphous with low luminous transmittance. Higher oxygen flow rate during the deposition, however, resulted in sub-oxide TiO₂ film. With this film, annealing at 300 and 500°C were presumed as transition temperatures for amorphous-to-anatase and anatase-to-rutile phases, respectively. The luminous transmittance also increased and was found to be the highest at 75.75% at 400°C annealing. The optical energy band gap for this film also increased up to 3.26 eV at 600°C annealing.

Amorphous zirconium oxide (a-ZrO₂) thin films were prepared onto fuzzed quartz substrates by ion beam sputtering deposition (IBSD) method in (Ar +O₂) gas mixture. Optical parameters of the films were evaluated by laser ellipsometry (λ = 632.8 nm) and optical transmission measurements. Structural parameters were studied by XRD measurements. Variation of refractive index and film thickness have been defined as a function of time of high-temperature annealing at T = 900°C. Formation of monoclinic zirconium oxide (m-ZrO₂) nanocrystals with diameter of ~60 nm embedded into a-ZrO₂ matrix has been found by XRD analysis after long-time annealing.

Optical characterization of TiAlON film applied in solar energy is presented in this paper. TiAlON-based films with different thicknesses have been deposited by magnetron sputtering. The spectrophotometer and spectroscopic ellipsometry (GES5) have been used to study the samples. Surface morphology and component of the films were investigated using scanning electron microscope (SEM), X-ray diffraction (XRD), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The optical constants and film thicknesses of TiAlON films with different thicknesses have been obtained by theoretical modeling analysis fitting (Cauchy model) and point-to-point analysis fitting. Results show that the refraction coefficient and extinction coefficient change with the film thickness increased. Those optical properties are useful for selecting the layers with adequate optical constants and thickness to design a solar selective absorber.

Optical properties of ${\mathrm{\text{Ga}}}_2\mathrm{\text{SeS}}$ crystals grown by Bridgman method were investigated by transmission, reflection and ellipsometry measurements. Analysis of the transmission and reflection measurements performed in the wavelength range of 400–1100 nm at room temperature indicated the presence of indirect and direct transitions with 2.28 eV and 2.38 eV band gap energies. Ellipsometry measurements were carried out in the 1.2–6.0 eV spectral region to get information about optical constants, real and imaginary parts of the pseudodielectric function. Moreover, the critical point (CP) analysis of the second derivative spectra of the pseudodielectric constant in the above band gap region was accomplished. The analysis revealed the presence of five CPs with energies of 3.87, 4.16, 4.41, 4.67 and 5.34 eV.

In this paper, the effect of dewetted gold nanoparticles (AuNPs) on hexagonal boron nitride (hBN) is discussed along with the changes in surface plasmon resonance (SPR). Au is sputtered on monolayer hBN/SiO₂/Si substrate for a varied duration and subjected to thermal annealing. Monolayer hBN is verified by spectroscopic ellipsometry using the Tauc–Lorentz model, while the AuNPs are modeled using a combination of Gauss, Cody–Lorentz, and Tanguy dispersion laws. Sputtering of Au on hBN/SiO₂/Si results in a film-like layer compared to the one on SiO₂/Si. Before annealing, the improved uniformity of Au on hBN/SiO₂/Si diminished the SPR wavelength, ${\lambda }_{\mathrm{\text{spr}}}$, when the sputter duration exceeded 30 s, much sooner compared to 120 s from the one on SiO₂/Si. After annealing, the ${\lambda }_{\mathrm{\text{spr}}}$ is vibrant for all samples around 2.3 eV. Au dewetted more on hBN due to higher surface tension. Large dewetted AuNPs supported by hBN result in higher photon extinction at ${\lambda }_{\mathrm{\text{spr}}}$. The longest sputter duration of 120 s on hBN/SiO₂/Si (mean size 53 nm) exhibited an 11.2% higher extinction coefficient compared to the one on SiO₂/Si (mean size 39.6 nm). Findings support the advantages of preparing plasmonic AuNPs by dewetting on monolayer hBN.

The intrinsic absorption edge of a $\beta -{\mathrm{\text{Ga}}}_2{\mathrm{\text{O}}}_3$ single crystal is examined by spectroscopic ellipsometry. An absorption model consisting of five parameters including absorption amplitude, bandgap energy, Urbach energy and two power exponents is developed to describe the absorption characteristics of the $\beta -{\mathrm{\text{Ga}}}_2{\mathrm{\text{O}}}_3$ single crystal. The anisotropic bandgap energies obtained from the model are 4.938, 5.030 and 5.100 eV, respectively. These values obtained from the model agree well with values derived from the first derivative maximum of k and maximum of n method.

Silicon nitride and silicon oxynitride are materials used extensively in mechanical and electronic devices due to their outstanding properties. Thin films of silicon nitride and silicon oxynitride can be deposited on a silicon surface. In this study, nitridation of silicon wafers by a rapid thermal heating process with both nitrogen and ammonia as precursors was investigated by transmission electron microscopy, electron energy loss spectroscopy, and ellipsometry analyses. It was found that, under ammonia gas, the growth of nitride film was limited to 0.5 nm, whilst under the nitrogen atmosphere, a nitride film of 5–10 nm could be formed at 1200°C. The limited growth in ammonia suggests formation of high-quality passivating layer.

Undoped and phosphorus doped nanocrystalline nickel oxide thin films have been synthesized on silicon and glass substrates by RF magnetron sputtering technique in pure Ar atmosphere. Proper phase formation was confirmed by X-ray diffraction analysis. Energy band gaps were determined using UV-Vis spectra. Formation of NiO nanoparticle of dimension ~15 nm was confirmed using HRTEM. Doping of phosphorus as an impurity was confirmed from EDX spectra and XPS studies. Spectroscopic ellipsometric studies were performed on such films and the spectra were analyzed with a suitable model. Optical constants were determined and refractive indices were found to increase with increase of phosphorus doping percentages.

Attachment of synthetic analogs of natural tetrapyrroles to electroactive surfaces enables physicochemical interrogation and may provide material for use in catalysis, diagnostics, and energy conversion. Six synthetic zinc chlorins and one free base bacteriochlorin, tailored analogs of chlorophyll and bacteriochlorophyll, respectively, have been attached to Si(100) via a high-temperature (400°C) baking method. The hydroporphyrins bear diverse functional groups that enable surface attachment (vinyl, acetyl, triisopropylsilylethynyl, pentafluorophenyl, and hydroxymethylphenyl) and a geminal dimethyl group in each reduced ring for stabilization toward adventitious dehydrogenation. The films were examined by cyclic voltammetry, FTIR spectroscopy, X-ray photoelectron spectroscopy, and ellipsometry. Monofunctionalized and difunctionalized hydroporphyrins gave monolayer and multilayer films, respectively, indicating robustness of the hydroporphyrin molecules, but in each case the film was more heterogeneous than observed with comparable porphyrins. The data suggest that some amount of unattached molecules remain intercalated with surface-attached molecules. Additional molecular designs will need to be examined to develop a deep understanding of the structure-activity relationship for formation of homogeneous monolayers and multilayers of synthetic hydroporphyrins.

The values of the published dielectric constants of graphene determined on the basis of optical diagnostics methods differ significantly from each other. This is due, in particular, to contaminating layers on the surface of graphene or between the substrate and the graphene layer, the parameters of which are not generally known and which, therefore, are difficult to take into account. In this work, it is shown how to integrate ellipsometric and reflectance measurements so that the influence of contaminating layers on the determination of dielectric constants of graphene-like 2D materials is minimal or practically absent at all. The inversion problem is solved analytically within the long-wavelength approximation. The equations for determining the dielectric constants of graphene have only one definite solution and do not need the knowledge of the initial guesses. A thorough analysis has been made of the dependence of the method error on the parameters of the structure under study, the wavelength and angle of incidence of optical radiation.

We have investigated dielectric properties of aromatic polythiourea (ArPTU, a polar polymer containing high dipolar moments with very low defect levels) thin films that were developed on Pt/SiO₂ substrate. The detected response is compared to the response of commercially available polymers, such as high density polyethylene (HDPE) and polypropylene (PP), which are at present used in foil capacitors. Stable values of the dielectric constant ${\epsilon }^{\prime }\approx 5$ (being twice higher than in HDPE and PP) over broad temperature and frequency ranges and dielectric losses as low as in commercial systems suggest ArPTU as a promising candidate for future use in a variety of applications.

The research findings of the phase composition, nanostructure and optical properties of strontium–barium niobate thin films are discussed. ${\text{Sr}}_x$Ba${{}_{1-}}_x$Nb₂O₆ nanosized films ($x$ = 0.5 and 0.61) were characterized by XRD, SEM and AFM studies. Reflective multi-angle ellipsometry and spectrophotometry were used to determine the optical parameters (refractive index, its dispersion, and thickness of the damaged surface layer) of thin films. It was shown that SBN-50 and SBN-61 thin films were grown $c$-oriented on Al₂O₃ (0001) and heteroepitaxial on MgO (001) substrates. The increase of refractive index, approaching its maximum value in the bulk material for a given composition as the film thickness increases, is observed.

Ellipsometry is used to quantitatively evaluate the antigen-sensing capability of immuno-surfaces. The ellipsometric measurement is a rapid, label-free, and in situ detection; however, quantification of analytes by ellipsometry is not unambiguous. The proper use of the effective thickness as a measure for the amount of analytes is addressed in this article. Taking the effective thickness as the quantification reference, we find that employing protein A to immobilize antibodies makes the antigen capture two to three times higher than the covalent immobilization technique using N-succinimidyl 4-maleimidobutyrate (GMBS). Besides, the results also suggest a uniform orientation of antibodies achieved by protein A. Increasing the density of surface antibodies would improve the sensitivity as well; however, the effect is more crucial for the protein A immuno-surface and appears to be less important for the GMBS immuno-surface. Therefore, the optimal immobilization strategy should include an orientation layer, such as protein A, and maximize the amount of oriented antibodies on the surface to further improve the efficiency for antigen detection.

The problem of definition of parameters of thin anisotropic films used in a microelectronics on the basis of ellipsometrical measuring is explored. The method of definition of parameters of films with use of neuron networks is offered. The networks is trained in space of acceptable values of parameters of layered system. The algorithm of tutoring of a network grounded on a rule Widrow-Hoff. At tutoring the error of experimental data’s was taken into account. The neuron networks is applied for definition of parameters of uniaxial films of Langmuir-Blodgett dimethyl-3,4:9,10-perylene-bis(dicarboximide). The network has shown high performance, the results coincide with obtained other methods. The network can be applied for examination of layered systems.

The dielectric response functions of bulk ZnO for electric field polarizations parallel and perpendicular to the c-axis are obtained in the spectral range from 3 to 32 eV by analysis of ellipsometric data. Anisotropics are observed between ɛ_∥ and ɛ_⊥. Electronic transitions involving Zn-3d and O-2s bands are detected. Ab-initio band structure calculations performed at the DFT-LDA level help to interpret the observed transitions. The calculations are also extended to the GW approximation in order to determine the electronic bandgap. Finally, the plasmon frequency is found to be ħω_p=18.95eV for E ⊥ c and 18.12 eV for E ∥ c, respectively.

The experiment PVLAS studies the optical properties of the vacuum, that behaves much like a material medium when it is permeated by an external (electric or magnetic) field. Using a strong superconducting magnet and a very sensitive ellipsometer we have searched for modifications of the index of refraction of the vacuum due to the presence of a magnetic field. A birefringence is predicted to arise because of the vacuum fluctuations of the electromagnetic field, and a similar effect (dichroism) could be due to the presence of yet undiscovered low mass particles interacting with two photons.

At present PVLAS has set the best existing limits on such processes, its sensitivity being limited by external noise sources which have now been accounted for. A completely redesigned prototype apparatus is now under construction: it is based on rotating permanent magnets and an ellipsometer employing an ultra stable Fabry-Perot resonator. A 50-fold improvement in the sensitivity of the ellipsometer has now been achieved, and we hope to improve our best limits when the magnets system will be installed.