Distribution by Scientific Domains
Distribution within Physics and Astronomy

Kinds of Ellipsometry

  • angle spectroscopic ellipsometry
  • spectroscopic ellipsometry
  • variable angle spectroscopic ellipsometry

  • Selected Abstracts

    Optical properties of TiO2 thin films prepared by chemical spray pyrolysis from aqueous solutions

    R. Ayouchi
    Abstract Titanium dioxide (TiO2) is known to have three different kinds of polymorphous crystalline forms: rutile, anatase, and brookite. The rutile phase is always formed at higher temperatures, while the anatase phase is formed at lower temperatures and transformed into rutile phase above 800 ºC. Various deposition techniques have been developed for depositing TiO2 thin films, including evaporation, sputtering, chemical vapour deposition and thermal oxidation of titanium. Among them, the Chemical Spray Pyrolysis (CSP) technique has many advantages, such as good conformal coverage, the possibility of epitaxial growth and the application to large area deposition. Also, this method is low cost and it is easy to control the deposition growth parameters. In the present work, TiO2 thin films have been deposited on p-Si (001) and fused silica substrates by Chemical Spray Pyrolysis (CSP) method from aqueous solution containing titanium (IV) isopropoxide (Ti[OCH(CH3)2]4. As-deposited thin films show anatase polycrystalline structure, and rutile phase formed for films annealed at 750ºC. SEM images have confirmed a smooth and crack-free surface with low surface roughness. X-ray photoelectron spectroscopy (XPS) combined with 4 keV Ar+ depth profiling has shown that crystallized films correspond to TiO2. Residual carbon coming from the organic precursor solution is only detected at the surface of the film. Thin films deposited on fused silica were highly transparent (more than 85%), with an indirect optical band gap of 3,43 and 3,33 eV for as-deposited and annealed films, respectively, and refractive indexes in the range between 2.01,2.29. Spectroscopic Ellipsometry (SE) also has been used to extract optical parameters. SE data fitted to triple-layer physical model revealed the same tendency to increase refractive index in annealed films. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Ellipsometric studies of diamond like carbon films prepared by PECVD using pulsed DC power supply

    D. K. Rai
    Abstract Diamonds like carbon (DLC) films were deposited by DC and pulsed DC glow discharge plasma enhanced chemical vapor deposition technique (PECVD). High deposition rates and uniform thin film were obtained using pulsed DC PECVD glow discharge deposition technique. The optical and surface properties of these films were investigated using transmission spectroscopy, spectroscopic Ellipsometry and atomic force microscopy. Fourier transform infrared spectroscopy was employed to examine the compositional properties and sp3/sp2 ratio in our films. Phase modulated Spectroscopic Ellipsometry (SE) in wide range of 300-1650 nm was used to determine the complex refractive index (ñ (,) = n (,) +ik (,)) using Forouhi-Bloomer amorphous model in the analyses of SE data. The extracted parameters are reported. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Cu underpotential deposition on Au controlled by in situ Spectroscopic Ellipsometry

    Mirko Prato
    Abstract We have studied Cu electrodeposition on well defined Au films using real time Spectroscopic Ellipsometry (SE). SE allows to discriminate the under-potential (UP) and over-potential (OP) regimes. In the UP regime, tiny yet reproducible variations of , and , parameters indicate the formation of two phases with slightly different optical behavior. The phase at the largest coverage is assigned to a Cu monolayer. The SE response in the OP regime shows a marked dependence on the potential scan rate. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Ultra-thin silicon solar cell: Modelling and characterisation

    L. Danos
    Abstract An ultra-thin crystalline silicon solar cell with an active silicon layer of 200 nm has been fabricated and fully characterised electrically (I-V characteristic, spectral response) and optically (Variable Angle Spectroscopic Ellipsometry). Interference effects were observed in the spectral response of the cell due to multiple reflections from the layers within the cell. A mathematical model was developed to account for the different reflections and transmission within the cell which reproduced excellently the essential features of the experimental spectral response. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Sulphur passivation of GaSb, InGaAsSb and AlGaAsSb surfaces

    E. Papis
    Abstract The effects of electrochemical treatment in either 21%(NH4)2S-H2O or 16%Na2S-C3H7OH solutions on the surface properties of GaSb, In0.23Ga77As0.18Sb0.82 and Al0.34Ga0.66As0.025Sb0.975 have been investigated by complementary use of Variable Angle Spectroscopic Ellipsometry (VASE) and X-ray Photoelectron Spectroscopy (XPS). We have shown that electrochemical sulphuration enables to produce 94,350 nm thick insulating overcoats with good surface morphology. The main components of the passivating layers are Ga2S3 and Sb2S5when formed on GaSb, while additional components of In2S3, admixture of Al2O3 and appearance of Al-As bond were observed on InGaAsSb and AlGaAsSb, respectively. The main feature distinguishing the effect of electrochemical treatment in Na2S,C3H7OH when comparing to those in (NH4)2S-H2O is that passivating layers contain additional components of Na2SO3 and/or Na2SO4. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Anisotropy of the ,-point effective mass and mobility in hexagonal InN

    T. Hofmann
    Abstract We determine the anisotropic electron effective mass and mobility parameters in wurtzite InN thin films with free electron concentration N from 1.8 × 1017 cm,3 to 9.5 × 1018 cm,3 using Infrared Magneto-optic Generalized Ellipsometry. The room-temperature measurements were carried out with magnetic fields up to 4.5 T. For the ,-point we estimate m*, = 0.047m0 and m*, = 0.039m0 for polarization perpendicular and parallel to the c -axis, respectively. Scattering by impurities or ionized donors may explain the decrease of mobility for polarization parallel to the c -axis from 1600 cm2/(Vs) to 800 cm2/(Vs) with increase in N , where the perpendicular mobility is further decreased, likely caused by additional grain boundary scattering. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Spectroscopic Ellipsometry as a Tool for Damage Profiling in Very Shallow Implanted Silicon

    Iordan Karmakov
    Abstract Summary: Ion implantation is still one of the key steps in Si integrated circuit technology. Spectroscopic Ellipsometry (SE) detects the defects created in the implanted Si. The successful application of SE for damage profiling depends on the quality of the algorithm used for evaluating the damage profile from SE data. In this work, we present retrieved SE damage depth profiles by our previously published algorithm in the as-implanted Si with very low energies Ge+ ions- from 2 keV to 20 keV and 1 keV B+ ions (1,×,1015 cm,2). The comparisons of the SE retrieved damage depth profiles with experimental atomic concentration depth profiles, or simulated by the state-of-the-art computer ATHENA code of Silvaco TCAD suits were made. The functional relation was obtained by proper fitting of measured by SE a/c depths, and the depths named "ends of damage" with the experimental or simulated ions concentration depth profiles. For reasons not understood, the damage profile of 5 keV Ge+ in c-Si is smoother in shape beyond the a/c depth, with a longer tail. The damage profiles measured by SE for 5 keV Ge+ in c-Si with two different doses: curve 1 - for 6,×,1013 cm,2 and curve 2 - for 1,×,1015 cm,2. Curve 3 - presents the damage profile simulated by ATHENA for Ge+ ions with 5 keV; 1,×,1015 cm,2. [source]

    Development of InN metalorganic vapor phase epitaxy using in-situ spectroscopic ellipsometry

    M. Drago
    Abstract Metalorganic vapor phase epitaxy of InN layers on sapphire was studied in-situ by spectroscopic ellipsometry (SE), ex-situ atomic force microscopy and optical microscopy. Surface morphology has been largely improved by using nitrogen instead of hydrogen as carrier gas during sapphire nitridation. Using the sensitivity of in-situ SE with respect to roughness we established a new growth procedure with low V/III ratio (104) at high temperature (580 °C) and growth rates as high as 350 nm/h, leading to improved electronic layer properties and allowing for growth of comparably thick layers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Growth and optical characterization of Cd1- xBexSe and Cd1- xMgxSe crystals

    F. Firszt
    Abstract Cd1- xBexSe and Cd1- xMgxSe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence and photothermal properties of these materials were investigated. Spectroscopic ellipsometry was applied for determination of the spectral dependence of the complex dielectric function (E) and refractive index n(E) at room temperature in the photon energy range 0.75-6.5 eV for samples with optic axis (c-axis) perpendicular to the air-sample interface. The critical point (CP) parameters for E0 and E1 transitions were determined using a standard excitonic CP function to fit the numerically calculated differential spectra ,2,2/,E2. The dispersion of the refractive index of the alloys was modelled using a Sellmeier-type relation. The values of fundamental and exciton band-gap energies were estimated from the ellipsometric and photoluminescence measurements. The origin of luminescence in Cd1- xBexSe and Cd1- xMgxSe was discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    4-Aminothiophenol Self-Assembled Monolayer for the Development of a DNA Biosensor Aiming the Detection of Cylindrospermopsin Producing Cyanobacteria

    ELECTROANALYSIS, Issue 22 2008
    Elisabete Valério
    Abstract The development of a DNA biosensor for the detection of cylindrospermopsin, based on self-assembled monolayers (SAMs) of 4-aminothiophenol, is investigated. SAMs were characterized by electrochemical reductive desorption. Detection of probe immobilization and hybridization has been achieved by cyclic and square-wave voltammetry (SWV), using methylene blue (MB) as electroactive indicator. The SWV data obtained in phosphate buffer, with and without NaCl, after MB accumulation, revealed an increase of the redox indicator current peaks after the hybridization step. This behavior is consistent with MB intercalation into DNA, for high ionic strength media and attributed to electrostatic interactions in the absence of salt. Evidence for surface modification is also provided by atomic force microscopy and ellipsometry. [source]

    Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device.

    ELECTROANALYSIS, Issue 5 2007

    Abstract Quaternized poly(4-vinylpyridine) (QPVP) has been incorporated as an anion exchanger into sol-gel derived silica films for use in a spectroelectrochemical sensor. The preparation, characteristics and performance of these films are described. The films, which are spin-coated onto the surface of a planar optically transparent electrode, are optically transparent and uniform. Scanning electron microscopy and spectroscopic ellipsometry have been used to examine film structure, thickness and optical properties. These films have been shown both spectroscopically and electrochemically to preconcentrate ferrocyanide, a model analyte for the sensor. The films can be regenerated for multiple measurements by exposure to 1,M KNO3. The effects of polymer molecular weight and storage conditions on film performance are described. The overall response of this film is comparable to the poly(dimethyldiallylammonium chloride)-silica films previously used for this sensor. [source]

    A label-free protein microfluidic array for parallel immunoassays

    ELECTROPHORESIS, Issue 20 2006
    Zhan-Hui Wang
    Abstract A label-free protein microfluidic array for immunoassays based on the combination of imaging ellipsometry and an integrated microfluidic system is presented. Proteins can be patterned homogeneously on substrate in array format by the microfluidic system simultaneously. After preparation, the protein array can be packed in the microfluidic system which is full of buffer so that proteins are not exposed to denaturing conditions. With simple microfluidic channel junction, the protein microfluidic array can be used in serial or parallel format to analyze single or multiple samples simultaneously. Imaging ellipsometry is used for the protein array reading with a label-free format. The biological and medical applications of the label-free protein microfluidic array are demonstrated by screening for antibody,antigen interactions, measuring the concentration of the protein solution and detecting five markers of hepatitis,B. [source]

    Poly(2-(dimethylamino)ethyl methacrylate) Brushes with Incorporated Nanoparticles as a SERS Active Sensing Layer

    Smrati Gupta
    Abstract A simple, fast, and versatile approach to the fabrication of outstanding surface enhanced Raman spectroscopy (SERS) substrates by exploiting the optical properties of the Ag nanoparticles and functional as well as organizational characteristics of the polymer brushes is reported. First, poly(2-(dimethylamino)ethyl methacrylate) brushes are synthesized directly on glassy carbon by self-initiated photografting and photopolymerization and thoroughly characterized in terms of their thickness, wettability, morphology, and chemical structure by means of ellipsometry, contact angle, AFM, and XPS, respectively. Second, Ag nanoparticles are homogeneously immobilized into the brush layer, resulting in a sensor platform for the detection of organic molecules by SERS. The surface enhancement factor (SEF) as determined by the detection of Rhodamine 6G is calculated as 6,×,106. [source]

    Vapor-Phase Deposition of Monofunctional Alkoxysilanes for Sub-Nanometer-Level Biointerfacing on Silicon Oxide Surfaces

    Brian Dorvel
    Abstract Improving the performance and lowering the analyte detection limits of optical and electronic biosensors is essential for advancing wide ranging applications in diagnostics and drug discovery. Most sensing methods require direct linkage of a recognition element and a sensor, which is commonly accomplished through an organic monolayer interface. Alkoxyorganosilanes are typically used to prepare sensor surfaces on dielectric oxides. However, many silanes lead to roughened or thick interfaces that degrade device sensitivity. Here, controlled vapor phase deposition of monoalkoxysilanes is found to lead to monolayers resistant to elevated temperatures and extreme pH conditions. The formation of high density, subnanometer monolayers is demonstrated by ellipsometry, XPS, and AFM. The uniform attachment of these monofunctional silanes to such biosensing platforms as microarrays, field effect devices, and the formation of surface enhanced Raman spectroscopy substrates is demonstrated. The advantages of using this silane deposition protocol for the above technologies are also discussed. [source]

    Perfluorinated Subphthalocyanine as a New Acceptor Material in a Small-Molecule Bilayer Organic Solar Cell

    Hans Gommans
    Abstract The complex refractive index of fluorinated subphthalocyanines (SubPcs) deposited by vacuum sublimation is determined by spectral ellipsometry. Their performance as acceptor material is characterized in a range of donor/acceptor heterojunctions in organic photovoltaic cells (OPVCs) by current,voltage measurements under 1,sun AM 1.5D simulated solar illumination and spectral response. Both electron and hole transfer between donor and acceptor materials is demonstrated. Power conversion efficiencies of 0.96% are found with an open-circuit bias of 940,mV. Hence, it is shown that fluorinated SubPcs can be considered as an acceptor material in OPVCs with an absorption in the visible comparable to that of well-known metallophthalocyanines. [source]

    Layer-By-Layer Dendritic Growth of Hyperbranched Thin Films for Surface Sol,Gel Syntheses of Conformal, Functional, Nanocrystalline Oxide Coatings on Complex 3D (Bio)silica Templates

    Guojie Wang
    Abstract Here, a straightforward and general method for the rapid dendritic amplification of accessible surface functional groups on hydroxylated surfaces is described, with focus on its application to 3D biomineral surfaces. Reaction of hydroxyl-bearing silica surfaces with an aminosilane, followed by alternating exposure to a dipentaerythritol-derived polyacrylate solution and a polyamine solution, allows the rapid, layer-by-layer (LBL) build-up of hyperbranched polyamine/polyacrylate thin films. Characterization of such LBL-grown thin films by AFM, ellipsometry, XPS, and contact angle analyses reveals a stepwise and spatially homogeneous increase in film thickness with the number of applied layers. UV,Vis absorption analyses after fluorescein isothiocyanate labeling indicate that significant amine amplification is achieved after the deposition of only 2 layers with saturation achieved after 3,5 layers. Use of this thin-film surface amplification technique for hydroxyl-enrichment of biosilica templates facilitates the conformal surface sol,gel deposition of iron oxide that, upon controlled thermal treatment, is converted into a nanocrystalline (,9.5,nm) magnetite (Fe3O4) coating. The specific adsorption of arsenic onto such magnetite-coated frustules from flowing, arsenic-bearing aqueous solutions is significantly higher than for commercial magnetite nanoparticles (,50,nm in diameter). [source]

    Block-Copolymer-Templated Synthesis of Electroactive RuO2 -Based Mesoporous Thin Films

    Capucine Sassoye
    Abstract RuO2 -based mesoporous thin films of optical quality are synthesized from ruthenium-peroxo-based sols using micelle templates made of amphiphilic polystyrene-polyethylene oxide block copolymers. The mesoporous structure and physical properties of the RuO2 films (mesoporous volume: 30%; pore diameter: ,30,nm) can be controlled by the careful tuning of both the precursor solution and thermal treatment (150,350,°C). The optimal temperature that allows control of both mesoporosity and nanocristallinity is strongly dependent on the substrate (silicon or fluorine-doped tin oxide). The structure of the resulting mesoporous films are investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. Mesoporous layers are additionally characterized by transmission and scanning electron microscopy and ellipsometry while their electrochemical properties are analyzed via cyclic voltammetry. Thick mesoporous films of ruthenium oxide hydrates, RuO2,·,xH2O, obtained using a thermal treatment at 280,°C, exhibit capacitances as high as 1000,±,100 F g,1 at a scan rate of 10,mV s,1, indicating their potential application as electrode materials. [source]

    Electropolymerized Self-Assembled Monolayers of a 3,4-Ethylenedioxythiophene-Thiophene Hybrid System,

    Maiténa Oçafrain
    Abstract Self-assembled monolayers (SAMs) of a conjugated bithiophenic system connected to an alkanethiol chain have been deposited on gold surface. The electroactive bithiophenic system involves a 3,4-ethylenedioxythiophene (EDOT) unit and a thiophene ring on which an alkanethiol is attached at the internal , -position via a sulfide linkage. The analysis of the structure of the SAMs by IR spectroscopy, ellipsometry, contact angle measurement and X-ray photoelectron spectroscopy (XPS) provides consistent results indicating compact monolayers in which the alkyl linkers are arranged in an almost vertical fashion while the bithiophenic-conjugated systems are essentially parallel to the surface. Cyclic voltammetry shows that application of a few potential scans to SAMs immersed in a medium containing only a supporting electrolyte leads to the typical electropolymerization curves while the CV of the electrooxized monolayer exhibits a reversible cyclic voltammogram characteristic of a stable electroactive extended conjugated system. The characterization of the electropolymerized monolayers by IR spectroscopy, ellipsometry, contact angle measurement, and XPS indicates compact monolayers. The analysis of the current voltage characteristics of the monolayers by conducting AFM before and after electrooxidation shows that the enhancement of the effective conjugation resulting from electropolymerization leads to a significant increase of the transport properties. [source]

    Colloidal Route for Preparing Optical Thin Films of Nanoporous Metal,Organic Frameworks

    ADVANCED MATERIALS, Issue 19 2009
    Patricia Horcajada
    Colloids of a highly flexible porous metal-organic framework (MOF) have been prepared using nontoxic and easily removable solvents. Furthermore, a simple dip-coating method for the preparation of optical-quality thin films of the MOF has been developed. The homogeneous thin film exhibits reversible flexibility, as has been proven by environmental ellipsometry. [source]

    Structural analysis of thin films of novel polynorbornene derivatives by grazing incidence X-ray scattering and specular X-ray reflectivity along with ellipsometry

    Taek Joon Lee
    In the present study, structural analyses using synchrotron grazing incidence X-ray scattering, specular reflectivity and ellipsometry were performed on thin films of two novel polynorbornene derivatives, chiral poly(norbornene acid methyl ester) and racemic poly(norbornene acid n -butyl ester), which are potential low dielectric constant materials for advanced microelectronic and display applications. These analyses provided important information on the structure, electron density gradient across the film thickness, chain orientation, refractive index and thermal expansion characteristics of the polymers in substrate-supported thin films. The structural characteristics and properties of the thin films depended on the tacticity of the polymer chain and were further influenced by the film thickness and thermal annealing history. [source]

    Low pressure plasma-based approaches to fluorocarbon polymer surface modification

    M. Nitschke
    Abstract A survey and comparison of several low pressure plasma-based approaches to fluorocarbon polymer surface modification is reported including "simple" plasma treatment, "grafting to" and "grafting from" plasma activated surfaces, plasma immobilization of predeposited molecules and the adsorption of charged macromolecules on plasma activated surfaces. Examples of each method are discussed in detail based on results from surface analytical experiments using X-ray photoelectron spectroscopy, ellipsometry, contact angle goniometry, and electrokinetic measurements. All reported examples refer to one and the same experimental setup. This makes the different approaches comparable and helps to exploit a wide range of plasma-based techniques for a particular goal and a given apparatus. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 100,109, 2007 [source]

    Distance dependence of long-range electron transfer through helical peptides,

    Minako Kai
    Abstract Helical peptides of 8mer, 16mer, and 24mer carrying a disulfide group at the N -terminal and a ferrocene moiety at the C -terminal were synthesized, and they were self-assembled on gold by a sulfur,gold linkage. Infrared reflection,absorption spectroscopy and ellipsometry confirmed that they formed a monolayer with upright orientation. Cyclic voltammetry showed that the electron transfer from the ferrocene moiety to gold occurred even with the longest 24mer peptide. Chronoamperometry and electrochemical impedance spectroscopy were carried out to determine the standard electron transfer rate constants. It was found that the dependence of the electron-transfer rates on the distance was significantly weak with the extension of the chain from 16mer to 24mer (decay constant , = 0.02,0.04). This dependence on distance cannot be explained by an electron tunneling mechanism even if increased hydrogen-bonding cooperativity or molecular dynamics is considered. It is thus concluded that this long-range electron transfer is operated by an electron hopping mechanism. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source]

    Solid-supported amphiphilic triblock copolymer membranes grafted from gold surface

    Ekaterina Rakhmatullina
    Abstract Gold-supported amphiphilic triblock copolymer brushes composed of two hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) blocks and a hydrophobic poly(n -butyl methacrylate) (PBMA) middle part were synthesized using a surface-initiated ATRP. Attenuated total reflectance Fourier transform infrared spectroscopy, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), ellipsometry, contact angle measurements, and atomic force microscopy were used for the characterization of PHEMA- co -PBMA- co -PHEMA brushes. The PM-IRRAS analysis revealed an increase of the chain tilt toward the gold surface during growth of the individual blocks. We suggest that the orientation of the amphiphilic polymer brushes is influenced by both the chain length and the interchain interactions. Additionally, a detachment of the polymer membranes from the solid support and subsequent gel permeation chromatography analyses allowed us to establish their compositions. We applied block-selective solvents (water and hexane) as well as a good solvent for the whole polymer chain (ethanol) to study the morphology and solvent responsive behavior of the amphiphilic brushes. The presented results could serve as a good starting point for the fabrication of functional solid-supported membranes for biosensing applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1,13, 2009 [source]

    Switchable thin-film surface prepared via a simple grafting-to method using a polystyrene- b -poly(2-vinylpyridine) copolymer

    Ying Wang
    Abstract A polystyrene- b -poly(2-vinylpyridine) block copolymer containing a methylhydridosilane linking group was chemically grafted to an 8-trichlorosilyloctene monolayer via a simple one-step hydrosilylation reaction. The resulting Y-shaped thin film exhibited a low grafting density, which was characteristic of the grafting-to technique. To further reduce the miscibility of the two arms, methyl iodide was reacted with the poly(2-vinylpyridine) block to produce quaternary ammonium groups. The surfaces before and after quaternization were both solvent-switchable when subjected to block-selective solvents. Tensiometry, ellipsometry, attenuated total reflection/Fourier transform infrared, and atomic force microscopy were used to characterize the properties and morphology of both unquaternized and quaternized samples. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5608,5617, 2006 [source]

    Photochemical attachment of polymers on planar surfaces with a covalently anchored monolayer of a novel naphthyl ketone photochemical radical generator

    K. Dayananda
    Abstract A monolayer of covalently anchored, novel, binaphthyl ketone is used as a surface-confined photochemical radical generator (PRG) for anchoring a variety of polymers to silicon surfaces. The precursor PRG is synthesized by the application of a facile and novel method for the oxidation of sterically hindered benzylic hydrocarbons to carbonyl compounds. Oxidation was carried out with a stoichiometric amount of potassium peroxydisulfate, in the presence of a catalytic amount of copper sulfate in an acetonitrile/water mixture. The PRG synthesized is characterized by 1H NMR, UV, and Fourier transform infrared (FTIR). The covalently attached monolayers are characterized by X-ray photoelectron spectroscopy, ellipsometry, and water contact angle measurements. The method developed is applicable to the preparation of a monolayer of a variety of polymers on a wide range of substrates carrying surface hydroxyl groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5413,5423, 2004 [source]

    Photoinitiated polymerization of styrene from self-assembled monolayers on gold.


    Abstract Ultrathin films of polystyrene (PS) were grown from self-assembled monolayers by the "grafting-from" technique. The initiating system consisted of a dithiol azobisisobutyronitrile-type free-radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform-reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 °C, and a water-jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 °C during extraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3284,3291, 2002 [source]

    Dielectric properties of (NH4)2SO4 crystals in the range of electronic excitations

    B. Andriyevsky
    Spectra of the real and imaginary parts of the pseudo-dielectric permittivity, ,,1,(E) and ,,2,(E), of ferroelectric ammonium sulfate crystals, (NH4)2SO4, have been measured in the range of electronic excitations 4.0 to 9.5,eV by ellipsometry using synchrotron radiation. Temperature dependences of the corresponding susceptibilities, ,,1,(T) and ,,2,(T), obtained for the photon energy E = 8.5,eV, related to excitations of oxygen p -electrons, reveal sharp peak-like temperature changes near the Curie point TC = 223,K. The large temperature-dependent increase of the imaginary part of the susceptibility ,2(T), together with a simultaneous decrease of the real part of the susceptibility ,1(T), take place at the phase transition. These anomalies have been ascribed mainly to the SO4 group of the crystal structure. [source]

    Synthesis and Characterization of Nanostructured Cerium Dioxide Thin Films Deposited by Ultrasonic Spray Pyrolysis

    Mario F. García-Sánchez
    Nanostructured thin films of cerium dioxide have been prepared on single-crystalline silicon substrates by ultrasonic spray pyrolysis using cerium acetylacetonate as a metal,organic precursor dissolved in anhydrous methanol and acetic acid as an additive. The morphology, structure, optical index, and electrical properties were studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, ellipsometry, and impedance spectroscopy. The use of additives is very important to obtain crack-free films. The substrate temperature and flow rate was optimized for obtaining smooth (Ra<0.4 nm), dense (n>2), and homogeneous nanocrystalline films with grain sizes as small as 10 nm. The influence of thermal annealing on the structural properties of films was studied. The low activation energy calculated for total conductivity (0.133 eV) is attributed to the nanometric size of the grains. [source]

    Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the Powder

    Liwu Wang
    A novel dispersant,O-(2-aminopropyl)-O,-(2-methoxyethyl)-polypropylene glycol (AMPG),was developed to disperse submicrometer-sized Si3N4 powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of >0.50) and colloidally stable nonaqueous Si3N4 suspensions can be realized using AMPG. [source]

    Poly(N -isopropylacrylamide) Brush Fabricated by Surface-Initiated Photopolymerization and its Response to Temperature

    Xinyan Jia
    Abstract A well-defined, high-density poly(N -isopropylacrylamide) (PNIPAM) brush was fabricated through a novel and reliable strategy by the combination of the self-assembly of a monolayer of dendritic photoinitiator and surface-initiated photopolymerization. The whole fabrication process of the PNIPAM brush was followed by water contact angles, X-ray photoelectron spectroscopy, and atomic force microscopy. Characterization of the PNIPAM brush, such as molecular weight and thickness determination, were measured by gel permeation chromatography, and ellipsometry, and the graft density was estimated. The temperature response of the PNIPAM brush was further investigated and the result verified the coil-to-globule transition of the PNIPAM chains in water from low to high temperature. [source]