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Hafnium dioxide (HfO 2) thin films are generally used as high refractive index layers in optical coating devices. Aging effects on optical and mechanical properties of the films are very crucial for long-standing performance and stability of the devices, therefore knowledge of the aging effects is very important. In the present work, HfO 2 thin film has been prepared using electron beam evaporation. The optical properties and residual stress of the film have been investigated in six months interval over a period of one-year in ambient condition to probe its aging behaviour. The measured refractive index increases with aging and its change is Δ n = 0.011 at wavelength of 550 nm. The dispersion parameters such as ε L , N / m *, ε s , and E d increase with aging, while E 0 decreases. The measured film residual stress is tensile in nature. The residual stress decreases with aging and the change in stress in the film is around 78% in a year. A simple model has been utilized to establish and explain a correlation between the measured stress and the film porosity which varies with aging time. The results suggest that the change in the residual stress is significant in contrast to a very small change in the refractive index with aging. [ABSTRACT FROM AUTHOR]

Abstract HfO 2 thin films were deposited by electron beam evaporation technique at different oxygen (O 2) partial pressures. The films are characterized using x-ray diffraction, x-ray reflectivity, spectrophotometry, atomic force microscopy, substrate curvature measurement and laser induced damage threshold (LIDT) measurement techniques. All the films show amorphous structure and are optically homogeneous. The film density decreases from 8.53 to 6.99 gm/cm3, while both the grain size and surface roughness increase with increasing oxygen partial pressure. Film refractive index decreases from 1.96 to 1.82, and the band gap increases from 5.59 eV to 5.67 eV with increasing O 2 partial pressure. The variation of refractive index is correlated with the grain size and density of the films. The measured residual stress for all the films is tensile in nature, and its variation with oxygen pressure is correlated with the film microstructure. The measured LIDT value decreases from 9.89 to 8.83 J/cm2 for 1064 nm laser and 5.97 to 4.52 J/cm2 for 532 nm laser, with increasing O 2 partial pressure. The variation of laser damage threshold with oxygen partial pressure has been explained through density of the film. Graphical abstract Image 1 Highlights • Amorphous HfO 2 thin films have been prepared using electron beam evaporation. • Effect of oxygen pressure on different properties of HfO 2 thin films has been investigated. • Correlation among density, refractive index and band gap has been established. • Variations of residual stress and LIDT with O 2 pressure are analyzed. [ABSTRACT FROM AUTHOR]

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]

One dimensional photonic crystal (1DPC) of TiO 2 /SiO 2 multilayer has been fabricated by sequential asymmetric bipolar pulsed dc magnetron sputtering of TiO 2 and radio frequency magnetron sputtering of SiO 2 to achieve wide omnidirectional photonic band in the visible region. The microstructure and optical response of the TiO 2 /SiO 2 photonic crystal have been characterized by atomic force microscopy, scanning electron microscopy and spectrophotometry respectively. The surface of the photonic crystal is very smooth having surface roughness of 2.6 nm. Reflection and transmission spectra have been measured in the wavelength range 300 to 1000 nm for both transverse electric and transverse magnetic waves. Wide high reflection photonic band gap (∆ λ = 245 nm) in the visible and near infrared regions (592–837 nm) at normal incidence has been achieved. The measured photonic band gap (PBG) is found well matching with the calculated photonic band gap of an infinite 1DPC. The experimentally observed omnidirectional photonic band 592–668 nm (∆ λ = 76 nm) in the visible region with band to mid-band ratio ∆ λ/λ = 12% for reflectivity R > 99% over the incident angle range of 0°–70° is found almost matching with the calculated omnidirectional PBG. The omnidirectional reflection band is found much wider as compared to the values reported in literature so far in the visible region for TiO 2 /SiO 2 periodic photonic crystal. [ABSTRACT FROM AUTHOR]

HfO 2 thin films have been deposited on BK7 glass substrate by reactive RF sputtering technique at different oxygen/argon (O 2 /Ar) gas flow ratios. The films are polycrystalline in nature with (− 111) predominant monoclinic phase and the inter-planar spacing of the films is found to be decreasing with increasing O 2 /Ar flow ratio causing compressive strain in the films. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. The dispersion energy as well as the oscillator energy are correlated with the compressive strain in order to investigate the lattice strain effect on the optical properties of the films. The surface roughness and grain size of the films have been determined using atomic force microscopy. The residual mechanical stresses of the films probed by substrate curvature method are observed to be compressive in nature. The stress value decreases from 3.21 GPa for films deposited in pure argon gas ambient to 1.17 GPa for films deposited under O 2 /Ar flow ratio up to 0.3. The variation of the residual stress with O 2 /Ar flow ratio is explained through lattice expansion induced intrinsic compressive stress due to atomic peening and grain size dependent intrinsic tensile stress in the films. With respect to quality optical coating applications of reactively sputtered HfO 2 films, an optimum O 2 /Ar flow mixing ratio (0.1 in the present study) is needed in order to achieve a useful balance between the refractive index and the mechanical stress. [ABSTRACT FROM AUTHOR]

• TiO 2 /Ag/TiO 2 /Ag multilayer is prepared using asymmetric bipolar pulsed dc sputtering. • Annealing induced changes in transmission spectrum of the multilayer is investigated. • Reverse engineering of the spectrum is made to analyse and explain the observations. • Three different multilayer models are executed for reverse engineering of the spectrum. • Model suggests that interface roughness and absorption due to Ag varies with annealing. Measured optical transmission spectrum of photonic structure comprising TiO 2 /Ag/TiO 2 /Ag multilayer is reverse engineered by employing transfer matrix method with three different multilayer models to analyse the factors responsible for the annealing induced changes in the transmission. The multilayer is made to have a single peak or a passband in the visible region, so that the spectral changes due to annealing can be observed more vividly. Prior to the multilayer deposition, single layer thin film of Ag and TiO 2 are prepared using asymmetric bipolar pulsed dc sputtering and their optical constants such as refractive index and extinction co-efficient are determined. The multilayer is prepared by four-layer sequential deposition of Ag and TiO 2 on BK7 glass substrate. The deposited TiO 2 /Ag/TiO 2 /Ag multilayer is annealed in the temperature range 100–300 °C. The optical transmission of the annealed multilayers is measured using spectrophotometer. The measured peak transmission and spectral bandwidth of the multilayer filter decreases with annealing, which is ascribed to inter-diffusion at the interfaces, and increasing absorption at the interfaces and in the silver layers of the multilayer. The ascription is resolved from the layers properties and interface parameters obtained by reverse engineering the measured transmission spectra. The rough interfaces in the multilayer are modeled as thin homogeneous layers following Bruggeman effective medium approximation, and the interface parameters are found to be varying with annealing. [ABSTRACT FROM AUTHOR]

Abstract: Thin films of composite materials are being progressively explored for achieving tunability in the optical constants for application in multilayer optical devices. In the present study, a set of ZrO2–MgO binary mixed composite thin films have been prepared by reactive electron beam evaporation of solid solution of ZrO2 and MgO at different oxygen partial pressures. Since elastic properties of the thin films are very important for their environmental stability under high power laser application, elastic moduli (indentation moduli) of the films have been measured by atomic force acoustic microscopy measurements. The optical properties especially refractive index of such films has been determined from the optical transmission measurement using an inverse synthesis method, while the density of such films has been measured by grazing incidence X-ray reflectivity. The variation of the elastic moduli of the thin films as a function of oxygen partial pressure used during deposition has been studied and the above variation has been corroborated with the variation of density and refractive index of the thin films. [Copyright &y& Elsevier]

Abstract: Composite thin films of HfO2:SiO2 with wide range of relative composition from 100:0 (pure HfO2) to 10:90 have been deposited on fused silica substrates by co-evaporation technique and the optical properties of the films have been studied by measuring the transmission spectra of the samples by spectrophotometer. Different important optical parameters viz., band gap, refractive index and absorption coefficients of the samples have been obtained by fitting the measured optical spectra with theoretically generated spectra and the variation of the optical constants as a function of SiO2 content in the films have been obtained. Two different dispersion models viz., the single effective oscillator model and the Tauc–Lorentz model have been used to generate the theoretical spectra in the above fitting procedure. X-ray reflectivity (XRR) measurement technique has been used to find the densities of the films in order to explain the observed variation in optical properties of the films with increase in SiO2 content. [Copyright &y& Elsevier]

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]

A new one-dimensional photonic crystal (1DPC) containing moderately doped silicon (m -Si) semiconductor is proposed and its tunable properties are theoretically investigated. The tunable complex permittivity of m -Si with temperature is the central idea that makes the 1DPC thermally tunable. The 1DPC systems such as (m -Si/SiO 2)12 and defective (m -Si/SiO 2)6D(m -Si/SiO 2)6 are examined in the spectral range of 0.4–0.8 THz with varying temperature from 40 to 100 K. Air and m -Si are considered as defect layer (D) in two different 1DPC systems. Our simulation shows that the photonic band gap (PBG) shifts to higher frequency and the omnidirectional PBG gets narrower with increasing temperature. The defect mode in both defective 1DPCs shifts to higher frequency with increasing temperature. The temperature sensitivity of peak transmission is found better in the air defective 1DPC, while that of defect frequency is better in the m -Si defective 1DPC. The angle of incidence and polarization dependency of the defect modes are studied in detail. The present work can be utilized for the development of tunable omnidirectional mirrors and narrow bandpass filters in the terahertz region as well as THz light based thermal sensors. • Tunability of 1DPC having moderately doped silicon (m -Si) has been investigated. • Photonic bandgap undergoes blueshift and gets narrower with temperature. • The omnidirectional PBG decreases with increasing temperature. • The defect mode shifts to higher frequency with increasing temperature. • Both defect frequency and resonant transmission are sensitive to temperature. [ABSTRACT FROM AUTHOR]

• 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]

Mechanical tunability of mid-infrared mirrors and filters made of one dimensional photonic crystal (1DPC) containing polymers has been theoretically investigated under hydrostatic compression. The elasto-optic properties of the polymer materials such as poly(methyl-methacrylate) (PMMA) and polystyrene (PS) are considered for tuning the properties of the 1DPCs. Studies on three multilayer 1DPCs viz., PS/SiO 2 , PMMA/SiO 2 , and PS/PMMA under varying hydrostatic pressures are presented in this paper. The calculation shows that the photonic band gap (PBG) of all the 1DPCs shifts to higher frequency with increasing hydrostatic pressure. The detailed variations in the size of PBG of the mirrors, and operating frequency and full width half maximum of the filters based on all the three 1DPCs have been studied. This study shows that the polymer based 1DPC mirrors and filters can be mechanically tuned, facilitating their applications in designing novel photonic devices. • Turnability of polymer based 1DPC mirrors and fitters have been investigated. • Photonic band gap of the 1DPCs undergoes blueshift with pressure. • The operating frequency of the filters shifts to higher frequency with pressure. • Mirror reflectivity and filter passband can be tuned by varying pressure. [ABSTRACT FROM AUTHOR]

The paper describes investigations into the correlation between the optical properties and the composition, structure and morphology of lanthanum fluoride films deposited at 373–473 K substrate temperatures by resistive heating of lanthanum fluoride powders. The composition of the films that includes depth profiling of fluorine has been determined non-destructively by ion beam analysis while their structure and morphology have been investigated by glancing incidence X-ray diffraction and atomic force microscopy respectively. The films are polycrystalline, exist in hexagonal phase and display substrate temperature dependent texturing. The substrate temperature has an important influence on composition as well. The films deposited at 373 K or 398 K substrate temperatures are deficient in fluorine but tend to acquire stoichiometric composition at 473 K. Possessing granular (∼100 nm) morphology, the films, in general, are UV transparent but their optical loss increases with texturing. Carbon and oxygen, present as impurities, lower the density and consequently the refractive index (1.47) of the films. Annealing in vacuum at 573 K brings about deterioration in the optical properties of the films which are related mainly to morphological changes and thermal stress. [ABSTRACT FROM AUTHOR]

Highlights: [•] SEIRA of uracil on AuNp film/glass slide using ATR geometry. [•] The deposition time of AuNp on glass slides varied to see its impact on SEIRA. [•] The small shift in SEIRA spectra indicates weak interaction of molecules with AuNp. [Copyright &y& Elsevier]

Highlights: [•] IR bands of carboxylate and sulphonate stretches show changes in the adsorbed state. [•] Multilayer formation of sodium benzoate and taurine. [•] Bottom layer chemically bound through carboxylate and sulphonate groups. [Copyright &y& Elsevier]

Abstract: Reactive evaporation technique has been used to deposit thin films of alumina (Al2O3) on crystalline Si substrates at ambient temperatures in an electron beam (e-beam) evaporation system using alumina granules as evaporant material. The loss of oxygen due to dissociation of alumina has been compensated by bleeding high purity oxygen gas into the system during evaporation. A set of samples were prepared at different flow rates of oxygen and the films have been characterized by Spectroscopic Ellipsometry (SE), Atomic Force Microscopy (AFM), Grazing Incidence X-ray Reflectivity (GIXR) and X-ray Photoelectron Spectroscopy (XPS) measurements. The density and optical properties of the films showed interesting variation with oxygen flow rates. [ABSTRACT FROM AUTHOR]

Abstract: An ion beam sputtering system, which uses a commercial ECR microwave based plasma ion source, has been designed and fabricated in-house for deposition of soft X-ray multilayer mirrors. To begin with, in the ion beam sputtering system W, Si thin films, W/Si bi-layer and W/Si/W tri-layer samples have been deposited on c-Si substrates as precursors to W/Si multilayer stack. The samples have been characterized by grazing incidence X-ray reflectivity (GIXR), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE) techniques. By analyzing the results, density, thickness, surface roughness of the single layer samples and interface width of the bi-layer and tri-layer samples have been estimated. [Copyright &y& Elsevier]

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: Diffuse reflectance or optical scattering in thin films and multilayers can pose serious limiting factors to their desired or ultimate performances. Besides, such studies provide valuable information related to the buried microstructures and interfaces. Synchrotron radiation is the most appropriate source to record wavelength dependent polarized light scattering in thin films and multilayers. In the present experiment several gadolinia, silica thin films and multilayers were studied for their light scattering using the white light synchrotron beam. Various thin film layer geometries were selected to probe the results due to different types and combinations of interfaces. Due to phase coherent delay in certain optical non-wedged component used in the experimental setup very interesting spectral interference were noticed as the modulations in the diffuse reflectance signal. Appropriate modeling approach utilizing Gaussian function de-convolution technique is used to compute the pulse delay between the back reflected and forward propagating scattering signals that lead to such spectral interference. Alternatively inverse fast Fourier transform (IFFT) and analytical techniques were adopted to determine the group delays. The diffuse reflectance spectra were finally compared with their specular counter part and a shift both in the wavelength and phase were noticed. This may be explained on the basis of thin film roughness factors, different polarizations and incident geometries used in the measurements. However, all most all the spectral scattering signals exhibited the features resembling their specular reflection characteristic. [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: Characteristic topographic parameters like fractals and superstructures contribute substantially to the thin film morphology, which directly or indirectly influences the physical, optical and mechanical properties. Fractal geometry and scaling concepts can concisely as well as more effectively describe the complex rough surface morphology. In the present study, such microstructural analysis has been carried out for gadolinia thin films, a most promising candidate to develop multilayer optical coatings in the deep ultraviolet spectral region. Extended power spectral density (PSD) spectra for these films acquired through atomic force measurements have been modeled and analyzed using several thin film morphological functions appropriately modified to suit the present requirements. Analysis results of the PSD functions have distinctly indicated the presence of Brownian fractals and uniformly distributed superstructures in the most experimental films deposited through reactive electron beam deposition technique. Process variables such as the rate of deposition and the oxygen partial pressure have affected the microstructural and related morphological evolutions very differently. The rate parameter strongly influenced the intrinsic microroughness, whereas the oxygen pressure influenced the grain sizes of the gadolinia films. One can advantageously use such information in tailoring a desired surface morphology in thin films by choosing appropriate combinations of process variables. [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]

[Display omitted] • TiO 2 thin film electrodes prepared by rf magnetron sputtering on polished SS substrates. • Lithium Ion Batteries (LIB's) have been prepared with these samples as anodes. • LIB's show high value of capacity with increasing trend with charging/discharging cycles. • Synergy between TiO 2 films and Fe 2 O 3 layers present on the SS substrates leads to high capacity. • Results very important for development of thin film based all sold-state micro-batteries. TiO 2 thin film electrodes have been prepared using radio-frequency magnetron sputtering technique on polished stainless-steel substrates. Films with amorphous, anatase and rutile phases have been obtained by varying the preparation conditions and coin cell type Lithium Ion Batteries (LIB's) have been prepared with these samples as anodes. During the cycling test, all the samples show a gradual increase in capacity with increasing no. of charging/discharging cycles after an initial decrease with the cell containing the rutile phase TiO 2 showing the highest specific capacity of around 1.217 mAh.cm-2.μm−1 after 1000 cycles at a high current density of 0.127 mA.cm−2, which is better than any reported value so far. Structural and morphological investigations of the samples by various techniques show that a synergy between the deposited TiO 2 film and the Fe 2 O 3 layers present on the SS substrate alongwith an increase in porosity in the films during the charge–discharge cycling gives rise to the remarkably high capacity of the cells which increases gradually with cycling. The present study shows that LIB's with composite TiO 2 /Fe 2 O 3 anode having advantage of structural stability of TiO 2 and better diffusion kinetics of Fe 2 O 3 can be obtained by a simple, easily scalable, reproducible rf magnetron sputtering technique and specific capacities of the present LIB's are comparable to or better than that obtained through much more complicated and multi-step chemical processes and hence the results are important for large scale technological applications. [ABSTRACT FROM AUTHOR]

CuS, In 2 S 3 , CuInS 2 and CuGaS 2 semiconductors have been synthesised in powder form by precipitation reaction using Na 2 S·3H 2 O as a precipitating agent. Precipitated at about 313 K in aqueous medium, the powders of CuS crystallise in covellite (hexagonal) phase and those of In 2 S 3 , CuInS 2 and CuGaS 2 in tetragonal phase on heat treatment in argon atmosphere. The formation of CuS or In 2 S 3 takes place due to the reaction between the metal and bisulphide ions in aqueous phase while that of CuInS 2 or CuGaS 2 involves solid state reaction between CuS and In 2 S 3 or Ga x S y during heat treatment and is accompanied with the evolution of SO 2 gas. The powders are nearly monophasic, exhibit nanometric morphology and bear their respective stoichiometric compositions. The direct band gaps of CuS, In 2 S 3 , CuInS 2 and CuGaS 2 measure 2.06, 2.3, 1.34 and 2.38 eV respectively. The method is simple and is extended to the synthesis of CuIn 0.8 Ga 0.2 S 2 as well. [ABSTRACT FROM AUTHOR]

Thin films of Ti–Zr–V alloy have been deposited using an indigenously developed DC magnetron sputtering system. The microstructure of the deposited films investigated by GIXRD, AFM and FESEM exhibited a morphology that depended on substrate and deposition environment. Films deposited on stainless steel (SS) substrates in argon ambient exhibited a columnar growth with nanocrystalline grains of about 40 nm. The films were also studied using the X-ray photo-emission electron spectroscopy (XPS) after annealing them in-situ at different temperatures for two hours in ultra-high vacuum environment. The results observed through variations in the oxidation state showed that the heat treatment in vacuum leads to disappearance of the superficial oxide layer covering the Ti–V–Zr films. After heating at 180 °C the metal-oxides changed into metallic surface that was extremely conducive to adsorption of surrounding gaseous species followed by their absorption or chemical fixation. The studies suggest that the films deposited on SS substrates are suitable as a Non-Evaporable Getter (NEG) to achieve extreme high vacuum (XHV). [ABSTRACT FROM AUTHOR]

Yttria stabilized zirconia thin films have been deposited by RF plasma enhanced MOCVD technique on silicon substrates at substrate temperature of 400 °C. Plasma of precursor vapors of (2,7,7-trimethyl-3,5-octanedionate) yttrium (known as Y(tod) 3 ), (2,7,7-trimethyl-3,5-octanedionate) zirconium (known as Zr(tod) 4 ), oxygen and argon gases is used for deposition. To the best of our knowledge, plasma assisted MOCVD of YSZ films using octanediaonate precursors have not been reported in the literature so far. The deposited films have been characterized by GIXRD, FTIR, XPS, FESEM, AFM, XANES, EXAFS, EDAX and spectroscopic ellipsometry. Thickness of the films has been measured by stylus profilometer while tribological property measurement has been done to study mechanical behavior of the coatings. Characterization by different techniques indicates that properties of the films are dependent on the yttria content as well as on the structure of the films. [ABSTRACT FROM AUTHOR]

Glancing angle deposition of HfO 2 thin films by RF magnetron sputtering technique has been explored with respect to two vital deposition parameters visualizing angle of deposition (at 82° and 86° glancing angles) and target to substrate distance, D TS in the range 70–125 mm. AFM and spectroscopic ellipsometry measurements show that at optimum D TS of 110 mm and glancing angle 82°, the films exhibit nanostructures with an estimated lowest refractive index ∼1.63 at 550 nm. For both the deposition angles, with decrease in D TS the round shaped grains of the film surface as obtained from AFM images are found to coalesce and produce films with elliptical shaped grains at shorter target to substrate distance. With increase in D TS the deposition rate first decreases up to D TS = 110 mm and subsequently increases. The phenomenon has been ascribed to the competition between reduced deposition flux density and increased sticking coefficient due to decrease in adatom kinetic energy with the increase in D TS . GIXRD measurement reveals that all the films exhibit monoclinic crystal structure. At lower D TS , the crystallinity has improved with increase in deposition angle whereas at higher D TS (>90 mm) the crystallinity becomes poorer with increase in deposition angle. The fact has been explained in light of variation of shadowing effect and deposition rate. [ABSTRACT FROM AUTHOR]

Ni-aluminides are an important class of intermetallics from research and technological point of view. Ultrathin multilayers of Ni and Al with overall stoichiometric ratio as 3:1 (Ni rich) and 1:3 (Al rich), respectively, were characterized by X-ray diffraction, X-ray reflectivity and polarized neutron reflectivity after sequential annealing at 150 °C, 200 °C and 300 °C to track the structural changes at mesoscopic and microscopic length scales. Morphology of the as deposited and annealed states were examined by atomic force microscopy. The impact of stoichiometric difference on the diffusion mechanism and its influence on structural parameters like alloy layer thickness, magnetic moment and crystallite size was studied in detail for these systems. Activation energies for these systems were also obtained through Arrhenius plots extracted from reflectometry data. [ABSTRACT FROM AUTHOR]

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: The diffraction efficiencies of surface relief gratings formed in Slavich PFG-01 silver halide emulsion have been studied in the frequency range 300–1200grooves/mm in terms of relief depths and periods of the gratings. The relief depths generated in the gratings show a sudden decrease up to a certain frequency, then a slight increase and finally decrease with increasing grating frequency for a symmetrical geometry of holographic recording. Effect of grating period variation on the relief depth of the phase gratings is found to be similar to the correlation of diffraction efficiency and grating aspect ratio. Diffraction efficiency response of a grating with a fixed groove frequency has also been investigated in terms of relief depths. [Copyright &y& Elsevier]

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]

Abstract: Spectral microroughness is a performance-limiting factor for optical thin films like Gd2O3, which have dedicative applications in ultraviolet or deep ultraviolet region of the electromagnetic spectrum. Such a morphological parameter of a thin film surface can be very well characterized by power spectral density (PSD) functions. The PSD provides a more reliable description to the topography than the RMS roughness and imparts several useful information of the surface including fractal and superstructure contributions. Through the present study it has been noticed that deposition parameters like evaporation rate and oxygen pressure can play very definite, dominant and predictable roles in the evolution of fractal and superstructures in thin film topographies recorded through atomic force microscopy (AFM). In this work, the PSD functions derived from morphologies of various gadolinia thin films have been fitted with a novel multi peak-shifting Gaussian model along with fractal and k-correlation functions, to extract characteristic parameters of the precision surfaces. Using such information, roughness contributions of the fractal components (substrate dominated), pure film and the aggregates have been successfully extracted. Higher spectral fractal strengths have depicted lower refractive index values. The microroughness and grain sizes of the pure film have been influenced very differently with deposition rate and oxygen pressure. The oxygen pressure strongly influenced the grain sizes where as the deposition rate influenced the microroughness of the gadolinia films. [Copyright &y& Elsevier]

Abstract: Depositing optical coatings at ambient substrate temperature has been stimulating interest as it has a range of potential applications. However, developing such optical coatings especially using refractory oxides is challenging since they yield stable thin films mostly at elevated substrate temperatures. Gadolinia films (Gd2O3), in the present experiment, however, observed to form stable films even at ambient substrate temperatures when deposited through reactive electron beam deposition. In addition, the films exhibited interesting optical properties such as reasonably high refractive index and wide band gap, which are rarely obtainable with conventional oxide materials. During the deposition, rate and oxygen pressure have been systematically varied. The deposited films have subsequently been characterized for optical and band gap related properties using spectrophotometric as well as ellipsometric spectral measurements. Atomic force microscopy has also been employed to study the surface topography and morphological changes under various deposition conditions. Both oxygen pressure and rate of evaporation have observed to greatly influence both the optical constant and surface topography of the gadolinia films. [Copyright &y& Elsevier]

Abstract: Depositing optical coatings at ambient substrate temperature has been stimulating interest as it has a range of potential applications. However, developing such optical coatings especially using refractory oxides is challenging since they yield stable thin films mostly at elevated substrate temperatures. Gadolinia films (Gd2O3), in the present experiment, however, observed to form stable films at ambient substrate temperatures when deposited through reactive electron beam deposition. In addition, the films exhibited interesting optical properties such as reasonably high refractive index and wide band gap, which are rarely obtainable with conventional oxide materials. During the deposition, rate and oxygen pressure have been systematically varied. The deposited films have subsequently been characterized for optical and band gap related properties using spectroscopic phase modulated ellipsometric and spectrophotometric measurements. Atomic force microscopy has also been employed to study the surface topography and morphological changes under various deposition conditions. Both oxygen pressure and rate of evaporation have observed to greatly influence both the optical constant and surface topography of the gadolinia films. [Copyright &y& Elsevier]

Abstract: Silica films under present reactive electron beam deposition conditions have depicted a novel self-organized surface grain structures when probed through atomic force microscopy, 2D fast Fourier transform and glancing incidence X-ray diffraction techniques. The formation of such ordered surface grain structures is observed to be strongly correlated to the nucleation and growth process of the silica films. However, the nature of the substrate (amorphous or crystalline) and multilayer geometries have influenced the shapes, sizes and abundances in the grain structures and the ordering. The strain mediation of such ordered structures when buried under polycrystalline layers like Gd2O3 have shown to influence both the grain size as well as roughness. A variety of grain structure evolutions and morphological changes in silica layers were noticed in different multilayer geometries. It is, hence, inferred that by appropriately using combinations of these materials, it is possible to have a control over the multilayer morphology and grain structures, which is a very relevant factor in developing precision ultraviolet laser coatings. [Copyright &y& Elsevier]