Visible Spectroscopic Ellipsometry Research Articles

Optical properties investigation of reactively sputtered tantalum oxynitride films

The coalescent behavior of metal oxide and metal nitride in metal oxynitride (MON) is making the material more conspicuous. Along with tunable optical properties, enhances mechanical properties, better chemical stability can be derived for MONs, which are of prime importance in the fields, such as photovoltaic, photo-chromatics, photocatalytic, protective and aesthetic coatings. In this paper, the optical properties of tantalum oxynitride thin film deposited through a reactive magnetron sputtering method were explored. Pure tantalum target was sputtered with argon gas in the presence of an optimized O2/N2 gas ratio. The chemical and physical properties of the film were investigated by X-ray diffraction technique, Scanning Electron Microscopy and AFM. Optical properties were explored with UV–visible spectroscopy and Spectroscopic Ellipsometry (SE). Transmittance and reflectance of the films show that the optical properties of the films have transparency (70–90%) and an absorption edge near 350 nm. For the analysis of SE data, the Tauc-Lorentz optical model with an additional Lorentz oscillator for semiconductor or insulator material were used. Here, the Ellipsometry technique has provided detailed optical nature of the film in terms of refractive index (n) ranging from 1.82 to 2.62, Energy Bandgap (Eg) 3.6 eV along with film thickness (∼200 nm) and surface roughness (∼6 nm).All these optical properties make the material a suitable candidate for antireflective coating, preparation of optical filters, photocatalytic agent, transparent coating for optical devices.

Spectro-ellipsometric modeling and optimization of two-dimensional Ge layer and three-dimensional Ge dot/island structures on SiO2 substrates

Morphological structures of two-dimensional (2D) Ge thin films and three-dimensional (3D) Ge dots/islands grown on SiO2 substrates were analyzed with UV–visible spectroscopic ellipsometry. The pseudo-dielectric functions (〈ε〉 = 〈ε 1〉 + i〈ε 2〉) were calculated under the Bruggeman effective medium approximation. The 〈ε〉 spectra of 2D films were well fitted with a simulation assuming a single-layer or two-layer model. The single-layer model has a mixture of c-Ge, a-Ge, and void components. The two-layer model has a base-layer consisting of 100% c-Ge and a surface-roughness layer consisting of a mixture of c-Ge, a-Ge, and voids. In the case of 3D films, the overall shape of the 〈ε〉 spectra could only be reproduced by using a two-layer model: a base-layer consisting of mixtures of c-Ge and a-Ge with a surface-roughness layer consisting of c-Ge, a-Ge, and voids. The degree of disagreement correlated with the root mean square surface roughness measured by atomic force microscopy.

Improvement of corrosion resistance of Zn-Ni alloy coatings by anodizing in selected alcoholic solutions

The subject of this investigation is the anodic treatment of galvanic Zn-Ni alloy coatings in alkaline solutions of selected alcohols and their characterization. The process was carried out galvanostatically at an anodic current density in the range 0.06–6.25 A/dm2 for 2–60 minutes. The characterization of the formed coatings was based on the morphological studies (OM), determination of the chemical and phase composition (XPS and GIXD), as well as film thickness (UV–vis spectroscopic ellipsometry) and corrosion investigations (EIS). It was found that the coatings have a mixed oxide-alkoxide passive character with the alkoxide-rich layer on the top. The anodic oxidation led to the coloration of the alloy; various colors (beige, blue, and violet) could be obtained depending on the process parameters. The colors were strongly related to the thickness of the films, which is similar to the passive layers found on valve metals (e.g. titanium). The thickest of the conversion coatings had ca. 250 nm. The EIS investigations showed the improvement of corrosion resistance of the substrate after the anodic treatment.

Cononsolvency Transition of Polymer Brushes: A Combined Experimental and Theoretical Study.

In this study, the cononsolvency transition of poly(N-isopropylacrylamide) (PNiPAAm) brushes in aqueous ethanol mixtures was studied by using Vis-spectroscopic ellipsometry (SE) discussed in conjunction with the adsorption-attraction model. We proved that the cononsolvency transition of PNiPAAm brushes showed features of a volume phase transition, such as a sharp collapse, reaching a maximum decrease in thickness for a very narrow ethanol volume composition range of 15% to 17%. These observations are in agreement with the recently published preferential adsorption model of the cononsolvency effect.

Optical Properties of Zn2Mo3O8: Combination of Theoretical and Experimental Study

We have investigated the electronic structure and optical properties of zinc molybdenum oxide (Zn2Mo3O8) by using both first-principle calculations and experiments. Optical properties of this material is very similar to other ternary oxides of tetravalent molybdenum (A2Mo3O8: A = Mg, Fe, Cd); therefore, this study provides meaningful insight into optical properties and possible phtotovoltaic applicability of these class of metal oxide cluster compounds. We use state-of-the-art methods, based on density functional theory and the GW approximation to the self-energy, to obtain the quasiparticle band structure and absorption spectra of the material. Our calculations shows that Zn2Mo3O8 is a near indirect gap semiconductor with an indirect gap of 3.14 eV. The direct gap of the material is 3.16 eV. We also calculate the optical absorption in the material. Calculated results compare well with UV–visible spectroscopy and spectroscopic ellipsometry measurements done on polycrystalline thin films of Zn2Mo3O8. We sh...

Effect of RF Power on the Structural and Optical Properties of Zinc Sulfide Films

Zinc sulfide (ZnS) films were prepared via a radio frequency (RF) magnetron sputtering technique using different RF powers (100, 120, 150, and 180 W), and the effects of the RF power on the structural and optical properties of the films were studied using x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, ultraviolet–visible spectroscopy, spectroscopic ellipsometry, and laser photoluminescence spectroscopy. It was found that the RF power has an important impact on the predominant phase formation and crystallinity of the ZnS films. The film thickness, refractive index, and film to bulk relative density increase systematically with an increase in the RF power. Among the various RF power values investigated, 150 W was optimal for the growth of highly crystalline ZnS films with a predominance of the cubic phase and enhanced photoluminescence emissions.

Effect of Nb doping on the structural, morphological, optical and electrical properties of RF magnetron sputtered In2O3 nanostructured films

Undoped and niobium (Nb) doped indium oxide (In2O3) thin films are prepared by radio frequency magnetron sputtering technique. The effect of Nb on the structural, morphological, optical and electrical properties of In2O3films are analyzed using techniques such as X‐ray diffraction (XRD), micro‐Raman spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy, UV–visible spectroscopy, spectroscopic ellipsometry, photoluminescence spectroscopy and Hall effect measurements. XRD analysis reveals that the as‐deposited undoped and Nb doped films are polycrystalline in nature with cubic bixbyite structure. Raman analysis supports the presence of cubic bixbyite structure of In2O3in the films. XPS analysis shows a decrease of oxygen deficiency due to Nb and the existence of Nb as Nb4+ in the In2O3lattice. The band gap energy of the films increases with increase in Nb concentration. PL spectra reveal intense UV and visible emissions in all the films. Optical constants of the films are determined using spectroscopic ellipsometry. The thickness of films estimated using FESEM and ellipsometry are in good agreement. The carrier concentration, mobility and nature of carriers are measured using Hall measurement technique in Van der Pauw configuration at room temperature.

Optical constants and band gap determination of Pb0.95La0.05Zr0.54Ti0.46O3 thin films using spectroscopic ellipsometry and UV–visible spectroscopy

We report the structural evolution and optical properties of lanthanum doped lead zirconate titanate (PLZT) thin films prepared on Pt/TiO2/SiO2/Si substrates by chemical solution deposition. X-ray diffraction demonstrates the post-deposition annealing induced crystallization for PLZT films annealed in a temperature (Ta) range of 550–750°C. PLZT films annealed at higher temperature exhibit polycrystalline structure along with larger grain size. Optical band gap (Eg) values determined from UV–visible spectroscopy and spectroscopic ellipsometry (SE) for PLZT films were found to be in the range of 3.5–3.8eV. Eg decreases with increasing Ta. The optical constants and their dispersion profiles for PLZT films were also determined from SE analyses. PLZT films show an index of refraction in the range of 2.46–2.50 (λ=632.8nm) with increase in Ta. The increase in refractive index at higher Ta is attributed to the improved packing density and crystallinity with the temperature.

Electric field assisted diffusion of hydrogen in a-Si:H thin films during hydrogen plasma etching

We exposed a hydrogenated amorphous silicon (a-Si:H) p–i junction to H2 plasma immediately after deposition. The H-induced modifications during hydrogen etching of the device were tracked by in situ UV–visible spectroscopic ellipsometry measurements. Against all odds and contrary to what occurs in a single thin a-Si:H layer, the plasma exposure leads to a thinner H-modified subsurface layer and a higher etch rate in the p-doped layer in comparison with the i-layer of the junction. Solution of the partial differential equation for electric field assisted diffusion of hydrogen, during the plasma etching process, provides the time-evolution of the mean diffusion distance of hydrogen and its relationship with the intensity of the electric field. These results, which emphasize the charged state of hydrogen diffusing into the p-layer and the role of the built-in electric field of the junction in counteracting it, can enable better control in manufacturing and processing of a-Si:H based devices.

Annealing temperature dependence on the structural and optical properties of sputtering-grown high-k HfO2 gate dielectrics

High-k gate dielectric HfO2 thin films have been deposited on Si and quartz substrates by radio frequency magnetron sputtering. The structural characteristics, surface morphology, and optical properties of the HfO2/Si gate stacks at various post-annealing temperatures were examined by X-ray diffraction (XRD), atomic force microscopy (AFM), fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis spectroscopy), and spectroscopic ellipsometry (SE). XRD measurement indicates that the 80 W-deposited HfO2 films demonstrate a polycrystalline structure. AFM measurements illustrate that the root mean square of the HfO2 thin films demonstrates an apparent increase with increasing the annealing temperature. Analysis from FTIR indicates that the Si–O–Si bonds vibration peak position shift toward lower wave numbers with increasing the annealing temperature. Combined with UV–Vis spectroscopy and SE measurements, it can be noted reduction in band gap with an increase in annealing temperature has been confirmed. Additionally, increase in refractive index (n) has been confirmed by SE.

Effects of germane flow rate in electrical properties of a-SiGe:H films for ambipolar thin-film transistors

In this work, the study of germane flow rate in electrical properties of a-SiGe:H films is presented. The a-SiGe:H films deposited by low frequency plasma-enhanced chemical vapor deposition at 300°C were characterized by Fourier transform infrared spectroscopy, measurements of temperature dependence of conductivity and UV–visible spectroscopic ellipsometry. After finding the optimum germane flow rate conditions, a-SiGe:H films were deposited at 200°C and analyzed. The use of a-SiGe:H films at 200°C as active layer of low-temperature ambipolar thin-film transistors (TFTs) was demonstrated. The inverted staggered a-SiGe:H TFTs with Spin-On Glass as gate insulator were fabricated. These results suggest that there is an optimal Ge content in the a-SiGe:H films that improves its electrical properties.

Optical and photocatalytic properties of Fe3+-doped TiO2 thin films prepared by a sol–gel spin coating

Various iron ion (Fe3+) doped titanium dioxide (TiO2) thin films (Fe3+-doped TiO2) have been successfully prepared on a glass substrate by a sol–gel spin coating route using titanium tetraisopropoxide and iron(III) nitrate nonahydrate as the initial materials. After the Fe3+-doped TiO2 thin films were calcined at 823K for 1h, the effect of Fe3+-doping on the optical properties and photocatalytic activity were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet– visible spectroscopy, spectroscopic ellipsometry and photocatalytic degradation of methylene blue. The XRD results showed that all Fe3+-doped TiO2 thin films contained only a single crystalline phase of anatase TiO2 after calcining at 823K for 1h. Moreover, the XRD results also revealed that the crystallinity and crystalline size decreased with increased Fe3+-doping due to worsening of the crystallization of anatase TiO2. FESEM micrographs showed that all Fe3+-doped TiO2 thin films have smooth surfaces containing granular nanocrystallines and are without cracks. The UV–vis absorption spectra showed that the absorption of the TiO2 thin films had a small red-shift as the Fe3+-doping increased. The direct band gap energy (Egd) and indirect band gap energy (Egind) of Fe3+-doped TiO2 films decreased with increasing Fe3+-doping. Moreover, the rate constant of methlylene blue decomposition increased from 0.018 to 0.038/h as the Fe3+-doped content increased from 0 to 25wt%.

Spectroscopic ellipsometry studies of sol-gel-derived Cu-doped ZnO thin films

Undoped and Cu-doped ZnO (Zn1−xCuxO: x=0.00, 0.03, 0.06, 0.10) films were prepared on Si(100) substrates by the sol-gel method, and the effects of Cu content on the structural, and optical properties of these films were investigated by X-ray diffraction (XRD) and UV–visible spectroscopic ellipsometry (SE). XRD patterns revealed that all the films were monophasic and had wurtzite structure with (002) preferential orientation along c-axis, indicating there were not any secondary phases. The measured UV–visible SE spectra were analyzed with an appropriate procedure to accurately determine the thickness and the optical constants. We found that the refractive index and the extinction coefficient increase with Cu content increasing. The optical band gap (Eg) has been calculated by classical Tauc formula, and the Eg values decrease as Cu content increasing. The variation in Eg with different Cu content revealed that the Eg value was affected by doping Cu. These mean that we can control the optical properties of the ZnO films by varying Cu content, which might be important in view of designing integrated optic devices.

In situ spectroscopic ellipsometry of pH-responsive polymer brushes on gold substrates

The dynamic and reversible switching behaviour of polyelectrolyte brushes of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) toward changes of the pH value was studied by in situ VIS-spectroscopic ellipsometry (SE). For this, PDMAEMA brushes with three different molecular weights were synthesized via the "grafting from" method using surface initiated atom transfer radical polymerization. In detail, the applicability of different SE data modelling to describe the optical properties of the different brush layers in the swollen and collapsed state was investigated. Especially for the PDMAEMA brushes with a high molecular weight, an improved optical modelling of the experimental data could be achieved and revealed an exponential distribution of the PDMAEMA fraction in the brush layer.

Layer‐by‐layer assembled hydrogel nanocomposite film with a high loading capacity

ABSTRACTThe layer‐by‐layer assembly technique is a method that widely used in the preparation of nanostructured multilayer ultrathin films. We fabricated a hydrogel nanocomposite film by alternating the deposition of a core–shell poly[(dimethylimino)(2‐hydroxy‐1,3‐propanedily) chloride] (PDMIHPC)–laponite solution and poly(acrylic acid). The growth of the deposition procedure was proven by ultraviolet–visible spectroscopy and spectroscopic ellipsometry. The surface morphology of the films was observed by scanning electron microscopy. The films could reversibly load and release methylene blue (MB) dye, which was used as an indicator. It took about 4.5 h to reach loading equilibrium at pH 9.0. The loading capacity of the film for MB was as large as 4.48 μg/cm2 per bilayer because of the introduction of the core–shell PDMIHPC–laponite as a film component. Nearly 90% of MB was released at pH 3.0 or in a 300 mM NaCl solution within 2.5 h. The loading and release processes were greatly influenced by the ionic strength and pH value of the MB solution. The hydrogel nanocomposite film showed good pH‐triggered loading‐release reversibility and suggested potential applications in controlled drug‐delivery systems and smart materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39352.

Natural Organic UV-Absorbent Coatings Based on Cellulose and Lignin: Designed Effects on Spectroscopic Properties

Novel nanocomposite coatings composed of cellulose nanocrystals (CNCs) and lignin (either synthetic or fractionated from spruce and corn stalks) were prepared without chemical modification or functionalization (via covalent attachment) of one of the two biopolymers. The spectroscopic properties of these coatings were investigated by UV-visible spectrophotometry and spectroscopic ellipsometry. When using the appropriate weight ratio of CNC/lignin (R), these nanocomposite systems exhibited high-performance optical properties, high transmittance in the visible spectrum, and high blocking in the UV spectrum. Atomic force microscopy analysis demonstrated that these coatings were smooth and homogeneous, with visible dispersed lignin nodules in a cellulosic matrix. It was also demonstrated that the introduction of nanoparticles into the medium increases the weight ratio and the CNC-specific surface area, which allows better dispersion of the lignin molecules throughout the solid film. Consequently, the larger molecular expansion of these aromatic polymers on the surface of the cellulosic nanoparticles dislocates the π-π aromatic aggregates, which increases the extinction coefficient and decreases the transmittance in the UV region. These nanocomposite coatings were optically transparent at visible wavelengths.

Comparison of the optical responses of O-poor and O-rich thermochromic VOX films during semiconductor-to-metal transition

O-poor and O-rich thermochromic vanadium oxide (VOX) nanostructured thin films were prepared by applying reactive direct current magnetron sputtering and post-annealing in oxygen ambient. UV–visible spectrophotometer and spectroscopic ellipsometry were used to investigate the optical properties of films. It was found that, when the O-poor VOX thin film underwent semiconductor-to-metal transition, the values of optical conductivity and extinction coefficient in the visible region increased due to the existence of occupied band-gap states. This noticeable feature, however, was not observed for the O-rich film, which showed a similar optical behavior with the stoichiometric crystalline VO2 films reported in the literatures. Moreover, the O-poor VOX film exhibits consistent variations of transmission values in the visible/near-infrared region when it undergoes semiconductor-to-metal transition.

Structure and physical properties of colloidal crystals made of silica particles

The relationship between the particles size distribution of colloidal crystals and the structure and physical properties of the resulting 2D colloidal crystals is presented in this work. The colloids were constituted of silica sub-micron spheres with different size distributions comprised between 150 and 520nm, synthesized by the Stöber method and assembled in one monolayer through the Langmuir–Blodgett technique. Optical and wetting properties of the resulting crystals were studied by different techniques – UV–visible spectrometry, spectroscopic ellipsometry and contact angle measurements. They were related to the crystal structure which was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The conservation of orientational and translational orders over a large area is found for crystals with narrow particle size distribution. Optical interference bands in the transmittance spectra are linked to the crystal periodicity and the presence of optical anisotropy is attributed to distortions in the film generated by the deposition process. Moreover, large particle size distribution results in the most hydrophobic crystals. Thus the physical properties of the colloidal crystals can be tailored or tuned by controlling the particle size distribution and the deposition parameters.

Scanning Kelvin Probe Study of (Oxyhydr)oxide Surface of Aluminum Alloy

In this paper, the work function, referenced as electrode potential vs SHE, of modified (oxyhydr)oxide surfaces of AA1050 was studied upon exposure to different relative humidity (40% and 90%) and aging (40 and 240 min) by utilizing scanning Kelvin probe (SKP). Besides reference samples, different pretreatments (acid, alkaline, and immersion in boiling water) were applied in order to create variations in the surface properties (i.e., hydroxyl content, oxide thickness, surface morphology). The observed trend in the potential was correlated to the hydroxyl fraction and the oxide thickness of the modified surfaces, determined by X-ray photoelectron spectroscopy and visible spectroscopic ellipsometry , respectively. Fourier transform infrared spectroscopy was also used to investigate the chemical composition of the modified surfaces. It is presented how the surface potential of aluminum (oxyhydr)oxide is influenced by the oxide properties, such as hydroxyl fraction and thickness. This characterization work on...

Temperature responsive polymer brushes with clicked rhodamine B: synthesis, characterization and swelling dynamics studied by spectroscopic ellipsometry

Here, we report on a new temperature responsive polymer brush system with a terminal “click” functionality. Bifunctionalized poly(N-isopropylacrylamide) (PNiPAAm) with distinct functional end groups was synthesized by atom transfer radical polymerization (ATRP) and grafted to a modified silicon substrate. The presence of the active terminal alkyne functionality is validated using an azide-modified rhodamine B (N3-RhB) via copper(I) catalyzed alkyne–azide cycloaddition (CuAAC). The optical properties and swelling dynamics of an N3-RhB modified PNiPAAm brush are analyzed in dry state and in situ by VIS-spectroscopic ellipsometry (SE). The best-fit results are obtained using a Gaussian oscillator model and are confirmed by UV/VIS-spectroscopy. We observed evidence of interactions between the aromatic residues of the dye and the PNiPAAm amide groups, which significantly affect the swelling behavior of the modified polymer brush.