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In present work, structural, morphological and optical properties of glancing angle deposited (GLAD ~ 82°) ZrO 2 thin films by RF magnetron sputtering at different substrate rotation (ω) have been investigated and compared with normally deposited (ND ~ 0°) ZrO 2 films. Both GLAD and ND ZrO 2 films exhibit preferential structural growth of monoclinic phase oriented in different directions. GLAD films also depict a tetragonal peak which has been attributed to the presence of fine nano-crystallite size (~ 13 nm). Surface correlation length of such films decreases with the increase in ω. The decrease has been attributed to the change in columnar microstructure with ω. RMS roughness values for GLAD and ND ZrO2 films are 4.6–5.1 nm and 1 nm, respectively. Dominant atomic shadowing is responsible for high roughness of GLAD films. Refractive index derived from ellipsometric measurements manifests a decreasing trend with parameter, ω. The trend has also been explained in terms of varying columnar micro-structure. Refractive index for GLAD ZrO 2 films varies from 1.901 and 2.011 on varying ω from 0.50 to 4 rpm. ND ZrO 2 film exhibits refractive index value of 2.178 which is substantially greater than that of GLAD films. Lowering in refractive index of GLAD films has been attributed to dominant atomic shadowing at glancing angles. Residual stress switches from large compressive to small tensile as the deposition angle changes from 0° to 82°. For GLAD films, tensile stress increases with the increase in ω except for the film deposited at the highest substrate rotation. Lowering in stress for GLAD films compared to ND films and trend of stress with ω have been explained in terms of varying inter-molecular forces with inter-columnar distance. [ABSTRACT FROM AUTHOR]

Oblique angle deposited oxide thin films, in which refractive index profiles can be tailored across depth by tuning their microstructure using varying angle of deposition, have opened up new dimensions in fabrication of optical interference devices. Since surface morphology plays an important role for the qualification of these thin film devices for optical or other applications, it is important to investigate morphological properties of obliquely deposited thin films. In the present work, a set of HfO 2 thin films have been deposited at several oblique angles. Morphological parameters of such thin films viz., correlation length, intrinsic roughness, fractal spectral strength, etc., have been determined through suitable modelling of extended power spectral density measured by atomic force microscopy. It has been found that intrinsic roughness and fractal spectral strength show an interesting behaviour with deposition angle and the same has been discussed in the light of atomic shadowing and re-emission and diffusion of ad-atoms. Further refractive index and thickness of such thin films have been estimated from optical transmission spectra through suitable modelling. Refractive index of such thin film varies from 1.93 to 1.37 as the deposition angle varies from normal to glancing angle (80°). Further, refractive index and grain size depict an opposite trend with deposition angle. This variation has been explained in terms of varying film porosity and column slanting with angle of deposition. [ABSTRACT FROM AUTHOR]

Abstract: A comparative morphology, grain structure and optical properties studies of reactive electron beam co-evaporated mixed thin films of hafnia–silica (HfO2:SiO2) and zirconia–silica (ZrO2:SiO2) systems have been carried out using atomic force microscopy and phase modulated ellipsometry. The addition of silica, especially with small fractions, has demonstrated altogether different types of evolutions in the microstructure and morphology in these binary thin film systems possibly forming new solid solution phases. Such morphological evolutions are probed through RMS roughness, power spectral density, height–height correlation and autocorrelation analyses of the topographic data acquired through atomic force microscopy. The present investigations indicated that with composition-control morphological quality improvement is more favourable in composite hafnia–silica over the zirconia–silica films. So for ultraviolet optical coating applications which demand low light scattering thin film microstructure, hafnia–silica binary composite system has a definite edge over the zirconia–silica counterpart. [Copyright &y& Elsevier]

Abstract: Tailoring of the refractive index of optical thin films has been a very fascinating as well as challenging topic for developing new generation optical coatings. In the present work a novel Gd2O3/SiO2 composite system has been experimented and probed for its superior optical properties through phase modulated spectroscopic ellipsometry, spectrophotometry and atomic force microscopy. The optical parameters of the composite films have been evaluated using Tauc–Lorentz (TL) formulations. In order to derive the growth dependent refractive index profiles, each sample film has been modeled as an appropriate multilayer structure where each sub-layer was treated with the above TL parameterizations. All codeposited films demonstrated superiority with respect to the band gap and morphological measurements. At lower silica mixing compositions such as in 10–20% level, the composite films depicted superior spectral refractive index profile, band gap as well as the morphology. This aspect highlighted the fact that microstructural densifications in composite films can override the chemical compositions while deciding the refractive index and optical properties in such thin films. [Copyright &y& Elsevier]

• ZrO 2 Al 2 O 3 MgO thin films were deposited under varying oxygen pressure. • Indentation modulus of the films depicts a decreasing trend with oxygen pressure. • Density of the films shows an interesting trend with oxygen pressure. • Varying microstructure and different film components attributed the trends. Zirconia - Alumina – Magnesia (ZrO 2 Al 2 O 3 MgO) ternary composite thin films are used in the fabrication of interference multilayer thin film devices for lasers and photo-physical applications. Optical, structural and morphological properties of such thin films deposited under varying deposition parameters, are reported by researchers. Such thin films possess fascinating spectral stability and optical properties. However, reports on elastic properties that are crucial parameter to assess mechanical stability, are scanty for such thin films. In the present work, ZrO 2 Al 2 O 3 MgO thin films have been deposited by electron beam evaporation under varying oxygen (O 2) pressure. Atomic force acoustic microscopy, which is rather new technique, has been employed to estimate indentation modulus of the films. Indentation modulus exhibits a decreasing trend with deposition O 2 pressure. Film density measured by grazing incidence X-ray reflectivity, decreases monotonically with O 2 pressure. The variation of indentation modulus as well as density has been explained in terms of varying microstructure and mutual concentration of different components of ternary composite thin films. Correlation length, root mean square surface roughness and roughness exponents have been obtained through analysis of height-height correlation function measured by atomic force microscopy. Variation of correlation length corroborates the variation of indentation modulus and film density. [ABSTRACT FROM AUTHOR]

Abstract: Several powerful effective medium formulations/approximation (EMA) and associated theories with different origins and concepts have been discussed and utilized here in order to model the experimental refractive index evolutions of ZrO2–SiO2 and Gd2O3–SiO2 composite films with respect to their compositional mixings. Amongst these formulations, the Böttcher''s generalized theory has been noticed to have more versatility and can simulate varieties of experimental observations incorporating a form factor parameter to account for the grain structure and morphology to a great extent. The refractive index modeling results of most of the available theories were compared with respect to their functional evolutions and limitations. It was noticed that at higher silica fractions (>20%) in our composite films, the effective experimental refractive index parameters have remained close to the most modeling results and Böttcher''s expression has shown to fit the observable parameters very accurately. However, under low silica compositions (<20%) the refractive index values of the composite films depicted different functional evolutions. Such deviations have been attributed to the various morphological, grain structure and band gap supremacies observed in these specific composite films which are not accounted by the effective medium formulations and approximations. These observations are well supported by the atomic force microscopy results. [Copyright &y& Elsevier]

Abstract: Composites are pragmatic choices for tailoring the material to have a desired property. Besides, such thin films have scopes to display superior optical, microstructural and morphological properties which are otherwise not possible to obtain from the pure component films. Vapor-phase-mixed binary composite Gd2O3/SiO2 thin film is one such interesting system where band gap as well as refractive index superiority is observed simultaneously under certain compositional mixings. Such and similar observations in composites cannot be explained by Moss empirical rule. Our systematic study on the microstructure of this composite system based on ellipsometry and scanning probe microscopy has satisfactorily provided the information that can explain such optical properties supremacy. Morphological measurements and its derived parameters like autocorrelation and height–height correlation functions have provided several clues that represent the superior grain structures of the composites. Besides, refractive index modeling through effective single oscillator model has strongly supported such analysis results favoring the superior microstructure in composite films. [Copyright &y& Elsevier]

Abstract: Composite optical thin-film materials have received a significant amount of interest in order to relieve the material constraints on refractive indices as well as reducing the number of layers required in optical coating design. Amongst others binary zirconia–silica composite thin films have attracted considerable attentions due to their several favorable opto-mechanical properties. In the present studies such a composite system under certain compositional mixings displayed both refractive index and band gap supremacy over pure zirconia films violating the most popular Moss rule. This unexpected evolution has several practical applications one of which can be directly employed in extending the range of tunability of the refractive index. Besides, the probing of such a novel evolution through the analysis of ellipsometric refractive index modeling and morphological correlation functions has revealed several novel as well as superior microstructural properties in the composite thin film systems. All these characterization and analysis techniques distinctly indicate a strong interrelation between the microstructural ordering and superior optical properties of the present zirconia–silica codeposited composites. [Copyright &y& Elsevier]

Abstract: Aging-related multilayer spectral instabilities can pose severe performance limiting constraints to optical multilayer devices. In this study such instabilities of some periodic Gd2O3/SiO2 optical multilayer systems have been explored using scanning probe force–distance microscopy and spectrophotometric techniques. In the present case, a strong correlation between the spectral instabilities and the viscoelastic properties of the associated thin film layers has been distinctly noticed. From the experimental analysis it was quite evident that the spectral instability, which starts during the nucleation and growth stage in thin films, continues to persist at a much longer time scale following aging processes. In this study it is shown that the elastic properties of the constituent thin films, the layer design and the bilayer thickness have established a strong interrelation which ultimately contributes to the multilayer instabilities. These spectral instabilities also have strong interconnections with the morphological and viscoelastic changes in such multilayers. Other multilayer parameters like the total number of layers, the layer structure, the microroughness evolutions, related stiffness factors and the adhesion properties of the periodic layer systems contribute substantially to this instability process. [Copyright &y& Elsevier]

Extended X-ray absorption fine structure (EXAFS) and atomic force microscopy (AFM) studies are carried out on yttrium oxide (Y 2 O 3 ) thin films deposited by radio frequency plasma assisted metalorganic chemical vapor deposition (MOCVD) process at different RF self-bias (−50 V to −175 V with a step of −25 V) on silicon substrates. A (2,2,6,6-tetramethyl-3,5-heptanedionate) yttrium (commonly known as Y(thd) 3 ) precursor is used in a plasma of argon and oxygen gases at a substrate temperature of 350 °C for deposition. To gain profound understanding about influence of RF self-bias on the properties of the deposited Y 2 O 3 thin films, the films are characterized by EXAFS and AFM measurements. From the EXAFS measurements it is observed that oxygen co-ordination is high for the film deposited at the lowest self bias (−50 V) which is due to presence of higher amount of hydroxyl group in the sample. Oxygen coordination however decrease to lower values for the films deposited at self bias of −75 V. Y O bond length decreases gradually with increase in self bias indicating reduction in hydroxyl content. However there is reduction in bond length for the film deposited at −100 V as compared to other films resulting from structural changes. The disorder factor obtained from EXAFS measurement increases for films deposited at voltages beyond −125 V due to degradation in crystallinity of the films caused by increased bombardment by incident ions. From AFM measurements, it is observed that the surface morphology of the films also change with self bias. The root mean square roughness value and the entropy factor are found to be low for films deposited at lower bias values and increase for films deposited at bias voltages above −100 V. [ABSTRACT FROM AUTHOR]

Abstract: Top-contact organic field-effect transistors based on poly(3-hexylthiophene) (P3HT) active layer were fabricated using gate dielectric (SiO2) modified with 3-aminopropyltrimethoxysilane (APTMS) multilayers. It has been demonstrated that the treatment of dielectric with APTMS enhances the field-effect mobility as well as the on/off ratio of the devices by nearly two orders of magnitude. This is attributed to conformational changes as well as to an improved uniformity of the spin coat P3HT films on the APTMS-modified substrate as revealed by atomic force microscopy, Fourier transform infrared spectroscopy and UV–Vis measurements. [Copyright &y& Elsevier]

Abstract: Electrochemical behavior of pitting corrosion of a Ni film, grown on Si substrate by sputtering, prepassivated in a chloride-free sulfuric acid solution and subsequently exposed to chloride above the pitting potential is reported. Specular and off-specular unpolarized neutron reflectometry and Atomic Force Microscopy (AFM) techniques have been used to determine the depth profile of scattering length density and morphology of as-deposited as well as corroded sample. Specular neutron reflectometry measurement of the film after corrosion shows density degradation along the thickness of film. The density profile as a function of depth, maps the growth of pitting and void networks due to corrosion. The AFM and off-specular neutron reflectivity measurements has suggested that the morphology of the film remains same after exposure of the film in chloride solution. [Copyright &y& Elsevier]

Abstract: Diamond like carbon (DLC) films were deposited at room temperature on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) process using plasma of methane diluted with argon gas. During deposition, dc self bias (−25 V to −200 V) on substrate was varied by application of RF power to the substrate. The influence of substrate bias on density of the deposited films was studied by X-ray reflectivity (XRR). The results from these measurements are further correlated with the results from UV and visible Raman spectroscopy. DLC film is modeled as a structure having three different layers such as low density surface, bulk and interface with the substrate. This three-layer model is used to fit the measured XRR data to evaluate the surface, interface and interlayer roughness, thickness and density of these films. The surface roughness obtained from XRR is correlated with the results from Atomic Force Microscopy (AFM) measurements. The observed results are explained based on the subplantation model for DLC film growth. [Copyright &y& Elsevier]

Abstract: Diamond like carbon (DLC) coatings were deposited on silicon(111) substrates by microwave electron cyclotron resonance (ECR) plasma CVD process using a plasma of Ar and CH4 gases under the influence of DC self bias generated on the substrates by application of RF (13.56MHz) power. DLC coatings were deposited under the varying influence of DC bias (−60V to −150V) on the Si substrates. Deposited films were analyzed by different techniques like: X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), Hardness and elastic modulus determination technique, Raman spectroscopy, scanning electron microscopy (SEM) and contact angle measurement. The results indicate that the film grown at −100V bias has optimised properties like high sp3/sp2 ratio of carbon bonding, high refractive index (2.26–2.17) over wide spectral range 400–1200nm, low roughness of 0.8nm, high contact angle (80°) compared to the films deposited at other bias voltages (−60V and −150V). The results are consistent with each other and find august explanation under the subplantation model for DLC growth. [Copyright &y& Elsevier]