Variation Of Optical Parameters Research Articles

Optical properties of alkaline earth borate glasses

Borate glasses containing fixed concentrations of heavy metal oxides (MO= ZnO, PbO, TeO2, Bi2O3) and alkaline earth oxides (R= Mg, Ca, Sr, Ba) are prepared by melt quenching technique. The optical band gap values are estimated from the optical absorption spectra using absorption spectrum fitting (ASF) method. The values of electronic polarizability, optical basicity and interaction parameters of the glass were discussed. The increment of refractive index values in each series is attributed to the substitution of alkaline earth oxides of increasing mass. Optical band gap (Eopt) values decreased with the replacement of RO oxides in the glass matrix. The cut-off wavelengths have shown a red shift with composition. The decrease in optical band gap values and consequently increase in Urbach’s energies confirms more extension of the localized states within the band gap. As a result there shall be an increase in the disorder of the glass network. The variation in optical parameters is owing to substitution of RO oxides in MO-B2O3 glass network.Keywords: alkaline earth borate glasses, optical band gap, Urbach energy, refractive index, electronic polarizability, molar refraction

Effect of thickness on optical properties of nickel vertical posts deposited by GLAD technique

Nickel (Ni) thin films of different thicknesses (25 nm to 150 nm) were deposited on glass substrates using Glancing Angle Deposition technique. Characterization of obtained Ni films was performed by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry and by four-point probe method. Variations in optical parameters with thickness correlated with structural, chemical and electrical properties of nanostructured nickel thin films were studied. The results showed that deposit is porous and consists of nano-scaled columns, which grow perpendicular to the substrate. It was found that the size of the columns and the surface roughness change with film thickness. Spectroscopic ellipsometry revealed that the refractive index and extinction coefficient varied with thickness, which can be correlated with changes in microstructure of Ni films. Additionally, the relationship between the film microstructure and its resistivity was also analyzed. It was found that the variations in Ni films resistivity could be attributed to the changes in the width of the columns. The increasing of layer thickness leads to overall decrease of optical resistivity of nickel thin films.

Optical methods for hydrogen degassing monitoring in urban conditions

Results of a study of variations in optical parameters of bioindicators that grow in the regions of hydrogen degassing in Samara are presented. Raman spectroscopy and confocal fluorescence microscopy were used as the main methods of the study. Features of Raman spectra of plants that grow in zones with presence/ absence of deep hydrogen emissions have been ascertained. The main variations have been recorded at wavenumbers of 1380, 1522, 1547, and 1600 cm–1, which are responsible for stretching vibrations in lignin and β-carotene and chlorophyll a and cellulose in plant leaves. Confocal fluorescence microscopy showed an increase in the chloroplasts in leaves of plants which grow at hydrogen degassing territories. An optical coefficient was introduced, on the basis of which the Samara region was monitored.

Argon irradiation effects on the structural and optical properties of reactively sputtered CrN films

The present study deals with CrN films irradiated at room temperature (RT) with 200 keV Ar+ ions. The CrN layers were deposited by d.c. reactive sputtering on Si (100) wafers, at nitrogen partial pressure of 5?10-4 mbar, to a total thickness of 280 nm. The substrates were held at 150?C during deposition. After deposition the CrN layers were irradiated with 200 keV Ar+ ions to the fluences of 5?1015 - 2?1016 ions/cm2. Structural characterization was performed with Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM) and X-ray diffraction (XRD). Spectroscopic ellipsometry measurements were carried out in order to study optical properties of the samples. The irradiations caused the microstructrual changes in CrN layers, but no amorphization even at the highest argon fluence of 2?1016 ions/cm2. Observed changes in microstructure were correlated with the variation in optical parameters. It was found that both refractive index and extinction coefficient are strongly dependent on the defect concentration in CrN layers.

Structural, optical and electrical properties of argon implanted TiN thin films

Modification in structural, optical and electrical properties of titanium nitride (TiN) thin films induced by argon ion irradiation and thermal annealings was studied using various experimental techniques. TiN thin films deposited by dc reactive sputtering on Si substrate were implanted with argon ions at 200keV. As-implanted samples were annealed before or after ion irradiation at 600°C and 700°C, respectively. Rutherford backscattering spectrometry, X-ray diffraction, cross-sectional (high-resolution) transmission electron microscopy, spectroscopic ellipsometry and electrical measurements were carried out in order to study structural, optical and electrical properties of TiN/Si samples. After irradiation with 200keV Ar ions the columnar microstructure of TiN was changed and the presence of smaller crystalline grains was observed. Partial loss of columnar structure observed in implanted samples was completely recovered after annealing at 700°C. Observed changes in microstructure induced by ion irradiation and annealings were correlated with the variation in optical parameters obtained by spectroscopic ellipsometry. It was found that both refractive index and extinction coefficient are strongly dependent on the defects' concentration and size of the crystalline grains in TiN layers.

Effects of substituting P2O5 for B2O3 on the thermal and optical properties of sodium borophosphate glasses doped with Er

In this paper a set of (95-x) P2O5–xB2O3–4.9Na2O–0.1Er2O3 (x=5–10–15–20mol%) samples was prepared using a conventional melt-quenching technique. A glass ceramic phase was confirmed by X-ray diffraction. Small crystallites at the B2O3 addition were detected by Raman scattering. The glass containing 20mol% B2O3 shows a high thermal stability with a value ΔT=Tc–Tg exceeding 100°C, where Tg and Tc are the glass transition and crystallization onset temperatures. The Raman spectroscopy measurement shows that BOP bonds were present in the glasses.From the absorption edge studies, the value of the optical band gap Eopt has been evaluated. The decrease in optical band gap values and consequently the decrease in Urbach's energies confirm the less extension of the localized states within the band gap. As a result, there shall be an increase in the order of the glass network. The variation in optical parameters is owing to the substitution of B2O3 oxides in P2O5–Na2O–Er2O3 glass network. The fundamental absorption edge for all the glasses was analyzed and the Judd–Ofelt parameters (Ω2, Ω4 and Ω6) were obtained. The PL intensity, the PL life time and the quantum efficiency relative to the 4I13/2→4I15/2 (1530nm) transition of Er3+ were all found to decrease with the addition of B2O3.

Monitoring of glucose levels in mouse blood with noninvasive optical methods

We report the quantification/monitoring of glucose levels in a blood sample using optical diffuse reflectance (ODR) underlying variations in optical parameters with a white light source (at peak wavelength ∼600 nm and range 450–850 nm) and in blood in vivo using M-mode optical coherence tomography (OCT) in terms of the translational diffusion coefficient (DT). In the ODR experiments, we have investigated two types of mono-dispersive particles, i.e. polystyrene microspheres (PMSs) with diameters of 1.4 μm (variable concentrations) and 2.6 μm (fixed concentration) in a water phantom by observing changes in the reduced scattering coefficient. We believe that these differences in optical properties will be helpful for the understanding and optimal use of laser applications in blood glucometry without piercing the skin. In the OCT experiments, this idea of glucose monitoring was applied on an in vivo normal mouse without injection of glucose intravenously to provide the threshold levels by envisioning/identifying a blood vessel by speckle variance (SV-OCT) using a dorsal skinfold mouse windows chamber model. We report an average value of translation decorrelation time τT = 41.18 ± 1.92 ms and DT = 8.90 × 10−14 m2 s−1 underlying the dynamic light scattering (DLS). Our results have a potential application in the quantification of higher glucose levels in vivo administrated intravenously.

A Comparison of Modifications Induced by Li3+and Ag14+Ion Beam in Spectroscopic Properties of Bismuth Alumino-Borosilicate Glass Thin Films

Ion irradiation effects on the glass network and structural units have been studied by irradiating borosilicate glass thin film samples with 50 MeV Li3+and 180 MeV Ag14+swift heavy ions (SHI) at different fluence rates ranging from 1012 ions/cm2to 1014 ions/cm2. Glass of the composition (65-x) Bi2O3-10Al2O3-(65-y) B2O3-25SiO2(x= 45, 40;y= 20, 25) has been prepared by melt quench technique. To study the effects of ionizing radiation, the glass thin films have been prepared from these glasses and characterized using XRD, FTIR, and UV-Vis spectroscopic techniques. IR spectra are used to study the structural arrangements in the glass before and after irradiation. The values of optical band gap, Urbach energy, and refractive index have been calculated from the UV-Vis measurements. The variation in optical parameters with increasing Bi2O3content has been analyzed and discussed in terms of changes occurring in the glass network. A comparative study of the influence of Li3+ion beam on structural and optical properties of the either glass system with Ag14+ion is done. The results have been explained in the light of the interaction that SHI undergo on entering the material.

The thermal–optical effect due to varying the angle of incidence used for designing a tunable filter in photonic crystals

Tunable devices based on photonic-crystal (PhC) structures are employed in optical sources, detectors, and filters. We present the design and optimization of a wavelength-selective tunable filter with potential applications to the wavelength-division-multiplexing (WDM) systems. We analyze the design of a 1D tunable photonic-crystal filter, where tunability is achieved either by changing the temperature or the angle of incidence. The device is designed in a multilayered structure of silicon/silica (Si/SiO2) with a defect in the middle. Based on the induced variation of optical parameters introduced by an external change of temperature, we analyze the effects of these changes in temperature on the transmission of the optical filter at different angles of incidence. We show that the position of the resonance peak has a linear dependence on temperature and the square of the angle of incidence. A linear regression provides a slope of dλ/dT = +0.06 nm/°C and dλ/dθ 2 = −0.104 nm/degree2 around the transmission wavelength λ = 1.55 μm. We obtain the corresponding field patterns and the transmission spectra using the transfer-matrix-method (TMM) simulations. We show the ability to tune the optical properties of the photonic-crystal filter elaborated by changing two parameters: the angle of incidence for selecting the wavelength and the temperature for fine tuning of the wavelength, which can be applied in integrated optics.

Spectroscopic ellipsometry studies of reactively sputtered nitrogen-rich GaAsN films

Nitrogen-rich GaAsN thin films have been deposited at 500°C by reactive rf sputtering of GaAs target in argon–nitrogen atmosphere. The arsenic content of the films was varied by changing the nitrogen percentage in the sputtering atmosphere and the As/Ga ratio in the films was estimated by X-ray fluorescence measurements. Spectroscopic ellipsometry measurements have been carried out on these films and the measured ellispometric spectra were fitted with theoretical spectra generated by using suitable model sample structures. From the best fit parameters of the dispersion model, band-gap values and variation of refractive index and extinction coefficient as a function of wavelength have been obtained for films deposited with different percentages of nitrogen in the sputtering atmosphere. The films deposited with 12% to 100% nitrogen in the sputtering atmosphere, which are of hexagonal GaN, exhibit GaN-like optical properties, though effects due to excess arsenic in amorphous phase are seen in the films deposited with less than 40% nitrogen. The films deposited with 5% to 12% nitrogen in sputtering atmosphere are dominantly polycrystalline GaAsxN1−x (x≈0.01 to 0.08) and exhibit variations in optical parameters, which are consistent with their structure and composition. The films deposited with less than 5% nitrogen in sputtering atmosphere are arsenic-rich and amorphous.

Kinetics of photostimulated changes of the refractive index in As-S amorphous films

The kinetics of photostimulated changes in the layers of non-crystalline chalcogenides AsxS1-x with different compositions has been studied be waveguiding techniques. The nature of both dynamic and irreversible components of photoinduced variations in optical parameters has been analyzed. Possible mechanisms of transformation have been proposed by which reversible (temporal) and irreversible components of changes in film parameters are set. The role a defective microstructure of films including the molecular-phase separation for optical effects have been discussed.

Effect of environment and heat treatment on the optical properties of RF-sputtered SnO 2 thin films

Thin films of SnO 2 were deposited by RF-magnetron sputtering on quartz substrates at room temperature in an environment of Ar and O 2. The XRD pattern shows amorphous nature of the as-deposited films. The optical properties were studied using the reflectance and transmittance spectra. The estimated optical band gap ( E g) values increase from 4.15 to 4.3 eV as the Ar gas content decreases in the process gas environment. The refractive index exhibits an oscillatory behavior that is strongly dependent on the sputtering gas environment. The Urbach energy is found to decrease with increase in band gap. The band gap is found to decrease on annealing the film. The role of oxygen defects is explored in explaining the variation of optical parameters.

Investigation on the temperature-dependence of absorption properties of solar cells with micro-structured surfaces

The temperature of a solar cell will increase when it is exposed to the sunlight, which results in variations of optical parameters and thermal expansion coefficient of the cell, thus affecting its spectral absorption feature. This paper is aimed to investigate the effects of temperature on the absorption property of solar cells with micro-structured surfaces. By taking hemispherical, cylindrical and spherical surfaces as models, numerical computation is conducted to obtain spectral distribution of absorptance of such surfaces with different structural parameters by means of the finite difference time domain (FDTD) method. Furthermore, the effects of material properties and structural period on the absorption property are also investigated.

Heterogeneous crystallization and composition dependence of optical parameters in Sn–Sb–Bi–Se chalcogenides

Bulk samples of Sn10Sb20−xBixSe70 (0 ≤ x ≤ 8) chalcogenide alloys were prepared by the conventional melt quenching technique. Thin films were prepared on well-cleaned glass substrates by thermal evaporation technique. X-ray diffraction studies revealed that the alloys with x = 0 and 2 at.% of Bi were amorphous, whereas the alloys with x = 4, 6, 8 at.% were crystalline. The crystalline phases are identified as due to the formation of Bi2Se3 and BiSe2 phases. The microstructural and differential scanning calorimetric studies show the presence of these phases. A simple, straight forward procedure suggested by Swanepoel has been used to calculate the optical parameters, refractive index, and extinction coefficient. The optical gap for all the samples has been obtained from the Tauc plots. The variation in optical parameters for different Bi concentration has been explained on the basis of presence of defect states and the change in stoichiometry with the change in Bi concentration.

Monte Carlo model to describe depth selective fluorescence spectra of epithelial tissue: applications for diagnosis of oral precancer

We present a Monte Carlo model to predict fluorescence spectra of the oral mucosa obtained with a depth-selective fiber optic probe as a function of tissue optical properties. A model sensitivity analysis determines how variations in optical parameters associated with neoplastic development influence the intensity and shape of spectra, and elucidates the biological basis for differences in spectra from normal and premalignant oral sites. Predictions indicate that spectra of oral mucosa collected with a depth-selective probe are affected by variations in epithelial optical properties, and to a lesser extent, by changes in superficial stromal parameters, but not by changes in the optical properties of deeper stroma. The depth selective probe offers enhanced detection of epithelial fluorescence, with 90% of the detected signal originating from the epithelium and superficial stroma. Predicted depth-selective spectra are in good agreement with measured average spectra from normal and dysplastic oral sites. Changes in parameters associated with dysplastic progression lead to a decreased fluorescence intensity and a shift of the spectra to longer emission wavelengths. Decreased fluorescence is due to a drop in detected stromal photons, whereas the shift of spectral shape is attributed to an increased fraction of detected photons arising in the epithelium.

Optimization and Modeling of Liquid Crystal Displays

The application of the LCD modeling and optimization system (MOUSE-LCD) for the design and development of the new advanced LCD configurations is demonstrated. The proposed new method of LCD optimization can be successfully applied for the design of the new advanced LCD configurations operating in various electrooptical nematic, cholesteric and ferroelectric LC modes, such as TN, STN, ECB, VAN, HAN, π-cell, book-shelf and others. We have found the conditions, which enable to realize perfect dark and bright states and wide viewing angles in LCDs for various LC physical characteritics, LC orientation in the cell and operating voltage as a function of the parameters of the phase compensators, anti-reflective layers, LC cell thickness and orientation of the polarizers. The optimization module allows for the spectral and angular averaging, thus enabling to produce LCD with wide viewing angles, achromatic (black/white) switching and fast response time. We have also shown, that some important LC elements of fiber optical systems, e.g., polarization controllers and polarization rotators can be designed and optimized. We demonstrate also 2D version, which enables to simulate the optical performance of LCD, as a function of the coordinate parallel to the LC layer. Liquid crystal (LC) structures in high resolution LCDs with a rapid lateral variation of optical parameters (microdisplays, multi-domain LCDs, IPS-LCDs) is characterized taking into account the effects of light diffraction. This software provides the simulation of various experimental tests with fine–structure LC cells. In particular, the simulation of LCD measurements with a polarizing microscope is performed.

5.4: Advanced Tools for Modeling of 2D-Optics of LCDs

Liquid crystal (LC) structures in high resolution LCDs with a rapid lateral variation of optical parameters (microdisplays, multi-domain LCDs, IPS-LCDs) must be characterized taking into account the effects of light diffraction. In addition to earlier reported MOUSE-LCD, we have developed a new software allowing estimation of diffraction effects in LCD optics. This software provides the simulation of various experimental tests with fine– structure LC cells. In particular, the simulation of LCD measurements with a polarizing microscope can be performed.

Ellipsometric studies of annealing of SiO2 layers during the formation of light-emitting Si nanocrystals in them

Annealing of SiO2 layers with excessive Si leading to the formation of silicon nanocrystals capable of fluorescing in the visible region owing to quantum-dimensional limitations is studied by the ellipsometry method. Excessive Si was introduced in SiO2 layers by ion implantation with an energy of 25 keV and a dose of 5× 1016 cm−2. Isochronous (103 s) annealings were carried out in a temperature interval of 200–1150°C with a step of 100°C. An LEF-2 ellipsometer with a 70° angle of incidence at a wavelength of 632.8 nm was used for the measurements. Fluorescence excited by a nitrogen laser was monitored concurrently. It is found that variations in optical constants of the layers at each step of annealing over the entire temperature range studied are clearly detected by ellipsometry. Variations in optical parameters of excessive Si are calculated in the Bruggeman approximation. They are found to correspond to individual stages of the formation of nanoprecipitates revealed earlier by other techniques. Nanocrystals proper producing intense visible photoluminescence are formed at annealing temperatures of 1000°C and higher.

Spectroscopic Ellipsometry of Ta2O5 ON Si

ABSTRACTIn this paper, we present the results of spectroscopic ellipsometry (SE) studies of Ta2O5 films on Si. Based on these results, we have experimentally determined an effective method for analyzing SE measurements of Ta2O5. A set of CVD-grown Ta2O5 films on silicon – with thicknesses ranging from below 10 nm to approximately 60 nm thick – was investigated by SE in an effort to improve optical film thickness metrology for Ta2O5. The samples were measured across the spectral range 1.5 eV to 6.0 eV by using a well-characterized, high-accuracy rotating-analyzer-type ellipsometer. We present an analysis method, based upon a Tauc-Lorentz parameterization of the optical properties of Ta2O5, that properly describes the SE data. We also demonstrate how optical properties are affected by the presence of an interlayer at the Si/Ta2O5 interface. Our results show small, but meaningful variations in optical parameters resulting from variations in deposition processes and annealing conditions. This work demonstrates that SE can be used successfully to characterize this category of alternate gate dielectrics.

Optical spectra of a conducting polymer (polymethyl-3-thiophene) at several stages of the electrodeposition process

The electrodeposition of polymethyl-3-thiophene on a platinum electrode was carried out potentiostatically. The variation in optical parameters was followed in situ in real time, by modulated ellipsometry at a fixed wavelength. On the contrary, ex-situ spectra were determined by spectroscopic ellipsometry, for doped and undoped films, at several stages of the film growth. The structure of the film for each stage was observed by atomic force manoscopy. Nucleation, first monolayer, thin dense fibrous layers and thicker granular layers were successively studied.