Stoichiography for investigation of the functional materials composition,structure, and properties

Principles of the stoichiography and differential dissolution method (DD) providing deep insight into the composition of mixtures containing unknown chemical compounds are considered. Compounds can be identified using their primary feature — the stoichiometry of elemental composition; reference samples of the compounds are not needed. The DD method makes it possible to analyze mixtures of crystalline and/or amorphous phases with constant and/or variable composition in the form of dispersed powders, ceramics, crystals, thin films and nanosize objects. Various aspects of the stoichiography and DD method application to investigation of composition, structure and properties of the functional materials are discussed.     

Influence of electrostatic and chemical heterogeneity on the electric-field-induced destabilization of thin liquid films

A numerical model for thin liquid film (<100 nm) drainage in the presence of an external electric field is developed. Long-wave theory is applied to approximate and simplify the governing equations. A spatiotemporal film morphology evolution equation thus obtained is then solved using a combination of finite difference to resolve the spatial dimensions and an adaptive time step ODE solver for the temporal propagation. The effect of fluid properties, namely, viscosity and surface tension, on the film drainage time is observed for a homogeneous electric field, which leads to random dewetting spots. Electrically heterogeneous fields, achieved by modeling electrodes with various periodic patterns, are explored to identify their effect on the drainage time and behavior. Finally, the chemical heterogeneity of the substrate is coupled with the periodic electric heterogeneity to understand the implications of combined heterogeneity. It is observed that the introduction of any heterogeneity results in faster drainage of the film when compared to that of the homogeneous field. In all cases, the thin film is drained, leaving submicrometer-scale structures at the interface. Well-controlled surface patterns are found on the application of periodic heterogeneity. This study effectively demonstrates the immense potential of electrically induced thin film drainage as a means for faster de-emulsification and for the creation of ordered submicrometer-scale surface patterns on soft materials.     

Simultaneous growth of diamond and nanostructured graphite thin films by hot-filament chemical vapor deposition

Diamond and graphite films on silicon wafer were simultaneously synthesized at 850 °C without any additional catalyst. The synthesis was achieved in hot-filament chemical vapor deposition reactor by changing distance among filaments in traditional gas mixture. The inter-wire distance for diamond and graphite deposition was kept 5 and 15 mm, whereas kept constant from the substrate. The Raman spectroscopic analyses show that film deposited at 5 mm is good quality diamond and at 15 mm is nanostructured graphite and respective growths confirm by scanning auger electron microscopy. The scanning electron microscope results exhibit that black soot graphite is composed of needle-like nanostructures, whereas diamond with pyramidal featured structure. Transformation of diamond into graphite mainly attributes lacking in atomic hydrogen. The present study develops new trend in the field of carbon based coatings, where single substrate incorporate dual application can be utilized.     

Synthesis and characterization of nanostructured bismuth selenide thin films

Nanostructured bismuth selenide thin films have been successfully fabricated on a silicon substrate at low temperature by rational design of the precursor solution. Bi(2)Se(3) thin films were constructed of coalesced lamella in the thickness of 50-80 nm. The nucleation and growth process of Bi(2)Se(3) thin films, as well as the influence of solution chemistry on the film structure were investigated in detail. As one of the most promising thermoelectric materials, the thermoelectric properties of the prepared Bi(2)Se(3) thin films were also investigated. The power factor increased with increasing carrier mobility, coming from the enlarged crystallites and enhanced coalesced structure, and reached 1 μW cm(-1) K(-1).     

Evolution of crystalline structure in SnS thin films prepared by chemical deposition

Crystal structure and morphology undergo significant evolution in thin films of tin(II) sulfide prepared by chemical deposition, over a narrow interval of bath temperature of 20–40 °C, but has not been recognized in previous studies. The chemical bath is constituted using tin(II) chloride, triethanolamine, ammonia(aq.) and thioacetamide. At bath temperature of 20 °C, the deposition rate of the film is 10 nm/h; and at 24 h, a film of thickness 260 nm is obtained. This film is compact and with a predominantly cubic (Cub-) crystalline structure. At 40 °C, the deposition rate is 25 nm/h, and a film of 600 nm in thickness is deposited in 24 h. However, this film has evolved into vertically stacked platelets of orthorhombic (OR-) crystalline structure. The transition from compact-to-platelet morphology as well as from Cub-to-OR-crystalline structure is observed near a deposition temperature, 35 °C. The Cub-SnS has a characteristic high optical band gap, 1.67 eV (direct gap; forbidden transitions) with an electrical conductivity, 10⁻⁷(Ω cm)⁻¹; both properties being un-affected when films are heated at 300 °C in a nitrogen ambient. In OR-SnS, the band gap is 1.1 eV (indirect gap; allowed transitions). The electrical conductivity of such films is notably higher, 10⁻⁴ (Ω cm)⁻¹, which increases further by an order of magnitude when the films have been heated at 300 °C in nitrogen.     

The effect of Sn dopant on crystal structure and photocatalytic behavior of nanostructured titania thin films

In this study, preparation of Sn doped (0–30 mol % Sn) TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of Sn content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission SEM (FE-SEM), and high resolution transmission electron microscopy (HR-TEM). Surface topography and surface chemical state of thin films were examined by atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). XRD patterns showed an increase in peak intensities of the rutile crystalline phase by increasing the Sn dopant. The prepared Sn-doped TiO₂ photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue solution under UV irradiation. The result shows that doping an appropriate amount of Sn can effectively improve the photo-catalytic activity of TiO₂ thin films, and the optimum dopant amount is found to be 15 mol%. The Sn⁴⁺ dopants substituted Ti⁴⁺ in the lattice of TiO₂ and increased surface oxygen vacancies and the surface hydroxyl groups. TEM results showed small increase in planar spacing (was detected by HR-TEM caused by Sn dopants in titania based crystals).     

Effects of X-ray radiation on the surface chemical composition of plasma deposited thin fluorocarbon films

Different thin fluorocarbon (FC) films were deposited on Si(111) using plasma polymerisation and then exposed to X-ray radiation. Changes in the chemical composition of the deposited fluorocarbon films as a function of irradiation time were investigated in situ using X-ray photoelectron spectroscopy. The evaluation of the C1s and F1s core level induced emission as a function of exposure to X-ray radiation (Mg Kα, hν = 1253.6 eV) reveals changes in the surface chemical composition of the FC polymer structure. The presented results indicate a high defluorination under X-ray irradiation. Additionally, binding energy shifts of the F1s and C1s peaks during the exposure associated with surface charging effects were observed. With ongoing exposure the surface charging decreases continuously and the FC surfaces become more conductive due to changes in the polymer structure. Different models have been used to describe the decomposition kinetics and surface composition.     

On the effects of bath composition and ultrasound on structure and properties of Cu thin films

Copper thin films were prepared by sono-electrodeposition method at different acid concentrations in the electrolyte. A potential of ?450 mV (100 mV negative than the Nernst potential) was selected for the deposition procedure for all the conditions. The thickness of films was found to be in the range of 100–600 nm. Electrochemical analysis was performed by chronoamperometry. Films were characterized by XRD, SEM, AFM, and study of the mechanical properties was done by nanoindentation.     

Multiply doped nanostructured silicate sol-gel thin films: spatial segregation of dopants, energy transfer, and distance measurements

Physical and chemical strategies that place designed molecules in spatially separated regions of surfactant-templated mesostructured silicate thin films are used to prepare films containing rhodamine 6G (R6G), lanthanide complexes, and both simultaneously. Fluorescence and photoexcitation spectra of R6G in amorphous and structured thin films show that it is located inside the surfactant micelles of structured thin films. A silylated ligand that binds lanthanides condenses to form part of the silica framework and causes the lanthanide to localize in the silica. Luminescence and photoexcitation spectra show that energy transfer from the metal complex to R6G occurs in the films. R6G quenches Tb emission in a concentration-dependent manner. Energy transfer efficiency is calculated using the Tb luminescence lifetime, and this quantity is used to calculate the distance between Tb and R6G with the aid of Forster theory.     

Photocatalytic oxidation of pharmaceuticals on thin nanostructured Zinc Oxide films

The photocatalytic activity of thin ZnO films in the photocatalytic oxidation of the pharmaceuticals, paracetamol and chloramphenicol (Levomycetin) is reported. The films annealed at 500°C exhibit the highest activity. They have a wurtzite-like structure and consist of conducting branches, which are the spinodal decomposition products.     

Quantitative chemical composition of thin films with infrared spectroscopic ellipsometry: application to hydrated oxide films on aluminium

A method to quantify the composition of thin films using infrared spectroscopic ellipsometry (IRSE), supplemented by visible spectroscopic ellipsometry (VISSE), is proposed. Because ellipsometry measures the thickness and optical constants of a surface layer simultaneously, the absorption coefficient of the film as a function of wavelength can be obtained. Using values of the absorption coefficients for the pure components of the film, the percentages (mol.% or wt.%) of each component in the film can be calculated. The method is demonstrated in a study of the hydration of oxide films on electropolished aluminium and the anodically formed barrier oxide film. The IRSE technique shows that hydration of the films by immersion in boiling water results in the conversion of aluminium oxide to pseudoboehmite. Copyright © 2003 John Wiley & Sons, Ltd.     

X-ray photoelectron study of the structure and composition of organometal cluster systems

This paper gives the results of the study of the structure and composition of copper- and cobalt-containing complex compounds synthesized using acetylacetone and triethyleneglycoldimethacrylate as complexons. It was established by X-ray photoelectron, IR, UV, and ESR spectroscopy that the cluster nuclei differ in size from each other by about a factor of three. When acetylacetonate is used as a complexon, the nature of the metal determines the character of interactions during structure formation of cluster systems. In the case of triethyleneglycoldimethacrylate, the character of metal-complexon interactions is determined from the variation of the X-ray photoelectron spectrum of oxygen. Translated fromZhumal Struktumoi Khimii, Vol. 39, No. 6, pp. 1107–1112, November–December, 1998.     

Electrochemical reductive dechlorination of carbon tetrachloride on nanostructured Pd thin films

The nanostructured Pd thin films prepared via cyclic voltammetric deposition method are proved to be a promising electrocatalyst for electrochemical reductive dechlorination of carbon tetrachloride (CT). The use of as-prepared Pd thin films as the working electrode material provides a possibility to separately study the role of various forms of hydrogen in the dechlorination reactions. Electrochemical characterization and gas chromatography analysis clearly indicate for the first time that the adsorbed hydrogen has excellent ability to remove CT from acidic solutions through the surface reaction with the chemisorbed CT molecules, which is of fundamental importance to have a better understanding of the reaction mechanism of electrochemical dechlorination.     

Study of the structure of thin nanocrystalline films

Structure and phase composition of thin nanocrystalline films of semiconductors and insulators CdS, Cd_xZn_1?xS, SiC_xN_y, and BC_xN_y were studied using registration of weak diffraction intensities with synchrotron radiation. Three methods were developed and applied to obtain diffraction patterns, namely, θ—2-scan (Bragg—Brentano geometry); 2θ-scan (grazing incidence scheme); a scheme with an image plate as detector. The characteristic features of the diffraction patterns, obtained from the aforementioned samples, are discussed. The X-ray diffraction data are compared with the results obtained by HREM, SAED, electron spectroscopy, ellipsometry, IR and Raman spectroscopy. It is stated that: 1) the films are composed of nanocrystals, their size depending on the conditions of film deposition; 2) single crystalline substrate favors formation of oriented crystals, i.e., of the domains comprising uniformly oriented nanocrystals.     

An AFM, XPS and wettability study of the surface heterogeneity of PS/PMMA-r-PMAA demixed thin films

A series of homopolymer/random copolymer blends was used to produce heterogeneous surfaces by demixing in thin films. The chosen homopolymer is polystyrene (PS) and the random copolymer is poly(methyl methacrylate)-r-poly(methacrylic acid) (PMMA-r-PMAA), whose acidic functions could be used as reactive sites in view of further surface functionalization. The proportion of each polymer at the interface was deduced from X-ray photoelectron spectroscopy (XPS) data using, on the one hand, the O/C ratio, and on the other hand, decomposition of the carbon peak of the blends in two components corresponding to the carbon peaks of PS and PMMA-r-PMAA. Combining the information from XPS with atomic force microscopy (AFM) images, water contact angle measurements and PS selective dissolution, it appears that the surfaces obtained from blends with a high PS content (90/10 to 70/30) display pits with a bottom made of PMMA-r-PMAA, randomly distributed in a PS matrix. On the other hand, the surfaces obtained from blends with a low PS content (30/70 to 10/90) display randomly distributed PS islands surrounded by a PMMA-r-PMAA matrix. The characteristics of the heterogeneous films are thought to be governed by the higher affinity of PMMA-r-PMAA for the solvent (dioxane), which leads to the elevation of the PS phase compared to the PMMA-r-PMAA phase, and to surface enrichment in PMMA-r-PMAA.     

Influence of physical and chemical heterogeneity shape on thin film rupture

It is known that the breakup times for thin liquid films on solid surfaces can be substantially smaller if the surface is heterogeneous, either chemically or physically. In this paper we explore issues related to the effect of the shape of the physical and chemical heterogeneities on the breakup time and the thinning behavior. We consider two shapes, sinusoidal and exponential, for both physical and chemical gradients and compare the breakup times for these two different forms of gradients. Furthermore, the wavelength of the sinusoidal gradients and the length scale of the exponential gradients are varied and the effects of these on the breakup times and the film evolution are determined. For the sinusoidal gradients, we also obtain analytical results for shape evolution that are valid at short times and for small amplitude perturbation of the physical/chemical heterogeneities. The fastest growing modes are determined for spinodal breakup and also for both shapes (sinusoidal and exponential) of physical and chemical heterogeneities. The breakup times for the fastest growing modes from the linear and the nonlinear studies are compared for spinodal breakup and these results are also compared with those for both chemical and physical heterogeneities, of both sinusoidal and exponential shapes. Results show that the presence of heterogeneities, in general, accelerates the breakup of the film. In the linear regime, the growth rates are the same for the chemical and physical heterogeneities and spinodal breakup, and the effect of the heterogeneities is manifested as increased amplitude of initial perturbation. The effect of the chemical and physical heterogeneities dominate the film dynamics at early times, becoming less important at later times. The growth rates and equivalently the breakup times for the films on heterogeneous surfaces depend on the length scale over which physical/chemical gradients occur, and as the length scale approaches zero, which implies that the gradients become very steep, the effect of the heterogeneities on the breakup times becomes small.     

Photoinduced hydrophilic and photocatalytic response of hydrothermally grown TiO2 nanostructured thin films

It is demonstrated that nanostructured titanium (IV) oxide (TiO₂) films can be deposited on glass substrates at 95 °C using hydrothermal growth, their properties being greatly affected by the substrate materials. Anatase TiO₂ films grown on ITO for deposition period of 50 h were observed to exhibit a very efficient, reversible light-induced transition to super-hydrophilicity, reaching a nearly zero contact angle. Enhanced photocatalytic activity (65%) was found for the rutile TiO₂ samples grown on microscope glass, possibly due to their higher roughness with respect to anatase grown on ITO. The effect of the substrate material used is discussed in terms of the TiO₂ phase and morphology control, for the best photoinduced hydrophilic and photocatalytic performance of the samples.     

The chemical composition and bonding structure of B–C–N–H thin films deposited by reactive magnetron sputtering

The chemical composition and bonding structures of B–C–N–H films fabricated by medium frequency magnetron sputtering, with N₂+CH₄+Ar gas mixture sputtering the boron target, were investigated. XPS and FTIR spectrometric analyses show that the increase of CH₄ flow rate during deposition causes an increase of the C content in the films. The increase in the CH₄ flow rate promotes an increase in the B–C, C–N single and C?N double bonds which are the components of the hybridized B–C–N bonding structure. From the results of Raman spectroscopy analysis, it is seen that the intensity of the D band of the films' Raman spectrum decreases with increasing CH₄ flow rate, indicating a decrease of the sp²‐phase content or the sp² C cluster size. The decreases of I_D/I_G also reflect the formation of more boron‐ or nitrogen‐ bound sp³‐coordinated carbons in the films. Copyright © 2009 John Wiley & Sons, Ltd.     

High temperature X-ray diffraction studies of the crystallization process of thin amorphous films with the chemical composition CrSi2.57

The crystallization process of amorphous thin films with the chemical composition CrSi_2.57 has been investigated by means of high temperature X-ray diffractometry. The crystallization of the amorphous as-deposited films takes place in two stages; in the first stage CrSi₂ is formed and in the second Si, resulting in a two component nano-disperse structure. The results are in agreement with investigations of the thermopower and the electrical conductivity [5, 6].