Quantitative ARXPS investigation of systems with ultrathin aluminium oxide layers

Angle‐resolved x‐ray photoelectron spectroscopy (ARXPS) is a non‐destructive method to investigate the near‐surface structure of specimens with a flat surface. For interpretation of the electron intensities emitted from different depth regions, model calculations are necessary. Based on an earlier algorithm we have developed a program for ARXPS studies of thin multilayers. In our model calculation the sample structure is treated as consisting of several layers (one to three) on the substrate, whereas the top layer can be incomplete. Emitted electrons are assumed to be attenuated exponentially in the layers. Different atomic volumes, electron attenuation lengths (including consideration of elastic scattering) and assumptions on stoichiometry are taken into account for the particular layers. As an application of our model calculations we present a study of a set of Al samples that were oxidized by different methods, i.e. natural and plasma oxidation (plasma obtained by electron cyclotron resonance). The oxide layers produced by plasma oxidation were protected by a 2 nm thick Co film, before exposing the samples to the air. Additionally, in order to check our results of the ARXPS model calculation, x‐ray reflectometry (XRR) analysis was used. Copyright © 2004 John Wiley & Sons, Ltd.     

The structure of the water–propane interface investigated by x‐ray reflectivity measurements

We present an x‐ray reflectivity study of the water–propane interface. The vertical structure of the interface is analyzed and the adsorption of thin layers of propane on the water surface is observed. An increase of layer thickness with rising pressure is found. The electron density of the thin films is identical with the corresponding value of bulk liquid propane. From the adsorption isotherm we determine the Hamaker constant of the system, which shows a considerably higher value compared to calculations based on the Lifshitz theory. The surface tension of the molecularly thin layer is reduced in comparison to the bulk value. The measured surface roughness is in good agreement with a modified model based on capillary wave fluctuations of the water‐propane–gas interfaces. Copyright © 2008 John Wiley & Sons, Ltd.     

Formation of a tetragonal Cu3Au alloy at gold/copper interfaces

A gold–copper alloy with a nominal composition of Cu₃Au but with a tetragonal (c = 4a) structure is observed to form at Au/Cu interfaces of gold/copper multilayers deposited on amorphous substrates by d.c. magnetron sputtering. The formation of this non‐equilibrium structure (tentatively D0₂₃) under‐ambient conditions is detected by secondary ion mass spectrometry, x‐ray diffraction and high‐resolution cross‐sectional transmission electron microscopy. Co‐sputtering of Au and Cu under similar conditions produces only conventional fcc Cu₃Au alloy phases, suggesting that interfacial confinement plays a significant role in producing the novel Cu₃Au alloy phase in gold/copper multilayers. Copyright © 2003 John Wiley & Sons, Ltd.     

Conformational Properties of Arenicins: From the Bulk to the Air–Water Interface

The structures of two antimicrobial peptides (arenicin Ar‐1 and its linear derivative C/S‐Ar‐1) are studied in different solutions and at the air–water interface using spectroscopic methods such as circular dichroism (CD) and infrared reflection absorption spectroscopy (IRRAS) as well as grazing incidence X‐ray diffraction (GIXD) and specular X‐ray reflectivity (XR). Both peptides exhibit similar structures in solution. In the buffer used for most of the experiments the main secondary structure elements are 22 % β‐turn, 38 % β‐sheet and 38 % random coil. The amphiphilic peptides are surface‐active and form a Gibbs monolayer at the air–buffer interface. The surface activity is drastically increased by increasing the ionic strength of the subphase. The β‐sheet layer is quite stable and can be compressed to higher surface pressures. This adsorption layer is very crystalline. Bragg peaks corresponding to an interstrand distance of 4.78 Å and to an end‐to‐end distance have been observed. This end‐to‐end distance can be connected with the observed differences in the layer thickness leading to the assumption that the peptides form a hairpin which is bended depending on the interactions with the counterions.     

硼酸系电结晶制[Co/Pt]_n(n≥40)金属多层膜的研究

于钝铜片及玻碳上采用双电解池恒电位结晶制取了［Ｃｏ（０．５ｎｍ～２．２ｎｍ）／Ｐｔ（２．０ｎｍ）］ｎ（ｎ≥４０）金属多层膜．低角度Ｘ射线衍射表明多层膜有良好的周期性调制结构,其Ｂｒａｇｇ峰的半幅值随着钴层电结晶电位的负移和铂层电结晶电位正移而减小．中角度Ｘ射线衍射表明界面上存在ＣｏＰｔ３金属化合物．多层膜的磁滞回线表明该多层膜的易磁化轴平行于膜面,表现出平面磁各向异性．以低过电位镀Ｃｏ（厚度约０．５ｎｍ）的多层膜的垂直方向磁滞回线形状较好,有望表现出垂直磁各向异性．     

Monte‐Carlo simulation of spatial distribution of characteristic x‐rays in multi‐film targets: source size of Al Kα x‐rays in W/Al film targets

A Monte‐Carlo simulation approach has been applied to describe the spatial distribution of characteristic x‐rays in W/Al film targets of different combinations of film thicknesses for the optimal design of a small‐sized x‐ray source having a high x‐ray intensity. The result has led to optimal combinations of W and Al film targets for 100 kV electrons, e.g. W(1 µm)/Al(20 µm), W(3 µm)/Al(15 µm) and W(5 µm)/Al(8 µm). These Al/W targets could be used as x‐ray sources for a medical instrument currently under development. Copyright © 2004 John Wiley & Sons, Ltd.     

X‐Ray Scattering and Imaging Studies of Electrode Structure and Dynamics

We will review structures and dynamics of electrode interfaces studied in situ using x‐ray scattering and imaging techniques. The examples cover single‐crystal and nanocrystal structures relevant to electrocatalytic activities, anodic oxidation and corrosion, aqueous dissolution reactions, surface reconstructions, and surface modifications by under potential deposition. The x‐ray techniques include the widely used traditional surface x‐ray scattering, such as crystal truncation rods and x‐ray reflectivity, as well as recently developed resonance surface scattering, coherent surface x‐ray photon correlation spectroscopy, coherent x‐ray Bragg diffraction imaging, and surface ptychography. Results relevant to various electrochemical phenomena will be highlighted.     

Monte‐Carlo simulation of spatial distribution of x‐rays in multi‐film targets. II: Spatial distribution of continuous x‐rays and temperature elevation in W/Al film targets

A Monte‐Carlo simulation written in C++ has been developed to describe spatial distributions of energy dissipation and x‐rays generated by penetrating kilovolt electrons in a multi‐film target. To evaluate the x‐ray source, especially its size and intensity, the use of brightness is proposed as a figure of merit. The Monte‐Carlo simulation approach was applied to a W (5 µm)/Al (200 µm) film target, which has been in practical use as an x‐ray source of small size with high emissivity. The result demonstrates that the experiment had considerable success. The optimum operating condition for the W (5 µm)/Al (200 µm) target in practical use has also been proposed by considering temperature elevation, spot size of electron beam, x‐ray source size and x‐ray intensity. Copyright © 2005 John Wiley & Sons, Ltd.     

Microstructure characteristics and shear properties of welding bonding of W/Al dissimilar metals with copper transitional layer

Commercial pure wrought tungsten and 1060 pure aluminum can be joined by using induction‐heat deposition (IHD) welding with commercial pure copper transitional layer. The microstructures of W/Cu/Al interfaces have been studied by means of scanning electron microscope, energy dispersive X‐ray, and X‐ray diffraction. Results show that copper as the transitional metal could form good interfaces with both tungsten and aluminum by IHD under proper processing parameters. The metallic bonding of W/Cu obtained by Cu and W mutual diffusing at a quite limited range without any intermetallic compounds, while eutectic of α(Al)/θ(CuAl₂) makes up Cu/Al interface. The average shear strength of W/Cu and Cu/Al interfaces are about 170 MPa and 55 Mpa, respectively, at room temperature. Copyright © 2012 John Wiley & Sons, Ltd.     

Improving the electro‐optical properties of bistable reflective cholesteric liquid crystal displays

We have improved the electro‐optical properties of a bistable cholesteric liquid crystal display (Ch‐LCD) that is driven by a 3+2 dynamic driving scheme (3+2 DDS). The best contrast ratio is achieved at the selection period of 1.2–1.5 ms/line and the temperature range 26–30°C. The suitable preparation period and evolution period for contrast ratio are 40 times and 20 times the selection time, respectively. In the 3+2 DDS, rubbing the homeotropic alignment layer increases reflectivity of the ON state and keeps the reflectivity of the OFF state at the same level, so reflectivity and contrast ratio alike increase as a result. However, in a delayed homeotropic reset driving method, when the homeotropic alignment layer is rubbed, the reflectivity of both the ON and OFF states increases, thus the contrast ratio decreases. The combination of driving method and aligned surface morphology influences the relaxation mechanism in the cholesteric texture. By optimizing panel condition, we have demonstrated an 8.4″ foldable VGA Ch‐LCD that exhibits high reflectivity and contrast ratio with an addressing speed of around 1.2 ms/line.     

Characterization of multicomponent polymer trilayers with resonant soft X‐ray reflectivity

Resonant soft X‐ray reflectivity (RSoXR) has been used to quantify the layer thicknesses and the interfacial widths of a single, complex thin film with three polymeric layers supported on an inorganic substrate. By adjusting the photon energy, the sensitivity to particular interfaces within the trilayer can be selectively enhanced. The results significantly improve and broaden the capabilities of RSoXR, which has previously only been demonstrated and used for bilayers on silicon substrates. The capability of RSoXR to characterize polymer trilayers was not readily predictable from prior bilayer results, as the RSoXR characterization of bilayers benefits from a strong X‐ray reflection from the substrate that serves as a reference beam with which the reflections from the other interfaces interfere with. The impact of having the capability to investigate trilayers is exemplified by discussing the utility of RSoXR to characterize organic electronic light emitting multilayers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1291–1299, 2009     

Mechanical property and corrosion resistance of zirconia/polydopamine nanocomposite multilayer films fabricated via a novel non‐electrostatic layer‐by‐layer assembly technique

Zirconia/polydopamine (ZrO₂/PDA) nanocomposite multilayer films were constructed on Si substrate via a novel nonelectrostatic layer‐by‐layer (NELBL) assembly technique. The building block of this technique is the newly reported dopamine molecule, which can be attached to almost all material surfaces and undergo oxidation‐polymerization to form PDA layers; more importantly, the outer hydroxyl groups of the PDA layer can chelated with certain inorganic oxide nanoparticles to generate oxide films. Thus, ZrO₂/PDA nanocomposite multilayer films were fabricated by sequential NELBL deposition of PDA and ZrO₂ nanoparticles. The formation of the ZrO₂/PDA nanocomposite multilayer films was monitored by the water contact angle (WCA) and ellipsometric thickness measurements, while the microstructure of the fabricated films was analyzed by means of atomic force microscope (AFM), field emission scanning electron microscope (FESEM), X‐ray photoelectron spectrum (XPS), and X‐ray diffraction (XRD) analysis. The mechanical and anticorrosion behaviors of the annealed ZrO₂/PDA nanocomposite multilayers were found to be greatly enhanced as compared with that of the annealed homogeneous ZrO₂ film. The better mechanical and anticorrosion behaviors of the annealed ZrO₂/PDA nanocomposite multilayers than the annealed homogeneous ZrO₂ film may be closely related to their special microstructure. Namely, the organic–inorganic hybrid microstructure of the annealed ZrO₂/PDA nanocomposite multilayers may largely account for the increased nanohardness and corrosion resistance. Copyright © 2010 John Wiley & Sons, Ltd.     

Degradation of plasticized PVC for biomedical disposable device under soft x‐ray irradiation

Plasticized poly(vinyl chloride) (PVC) used for biomedical disposable devices was studied in the non‐sterilized state after different exposure times to soft x‐ray irradiation in a commercial photoelectron spectrometer (Al Kα, 15 kV/300 W; Mg Kα, 12 kV/240 W) by XPS surface analysis. The detailed spectra of C 1s, Cl 2p and O 1s have been recorded and processed. Irradiation with soft x‐rays induces a clear decrease of the total Cl 2p intensity, an increase of total C 1s intensity and a doubling of the O 1s intensity after 45 min of irradiation with Al Kα (300 W). Irradiation with Mg Kα (240 W) is slightly less damaging. These results can be interpreted with the classical PVC degradation model, e.g. bond cleavage with the formation of HCl gas, although the Cl 2p high‐resolution spectra reveal the formation of an additional side‐product, probably CaCl₂. For further studies of plasticized PVC using XPS surface analysis it can be concluded that a complete analysis of a polymer sample should not take >10 min of x‐ray exposure in order to avoid notable polymer degradation. Copyright © 2003 John Wiley & Sons, Ltd.     

Surface modification of carbonyl iron powders with silicone polymers in supercritical fluid to get higher dispersibility and higher thermal stability

The surface of carbonyl iron powder (CIP) was modified in supercritical fluid with silicone polymers containing reactive Si‐OCH₃ groups. Fourier‐transformed infrared spectroscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, and thermo gravimetric analysis were adopted to characterize CIP. The dispersibility of CIP in epoxy resin matrix was evaluated by castor oil absorption factor, dynamic viscosity, Mooney viscosity, and scanning electric micrograph. The electromagnetic reflectivity of the CIP‐filled epoxy resin coatings was also checked. It was confirmed that comparing with those treated at atmosphere, the supercritical treated CIP presented higher surface carbon content, higher dispersibility, higher thermal stability, and its original crystalline structure did not change greatly. Even though it experienced a high temperature and a high pressure (250 °C, 7.8 Mpa) during supercritical treatment, it was not oxidized, and its electromagnetic reflectivity did not decrease. Copyright © 2016 John Wiley & Sons, Ltd.     

Physical–Chemical Properties and Transfection Activity of Cationic Lipid/DNA Complexes

Investigation of DNA interactions with cationic lipids is of particular importance for the fabrication of biosensors and nanodevices. Furthermore, lipid/DNA complexes can be applied for direct delivery of DNA‐based biopharmaceuticals to damaged cells as non‐viral vectors. To obtain more effective and safer DNA vectors, the new cationic lipids 2‐tetradecylhexadecanoic acid‐{2‐[(2‐aminoethyl)amino]ethyl}amide (C I ) and 2‐tetradecylhexadecanoic acid‐2‐[bis(2‐aminoethyl)amino]ethylamide (C II ) were synthesized and characterized. The synthesis, physical–chemical properties and first transfection and toxicity experiments are reported. Special attention was focused on the capability of C I and C II to complex DNA at low and high subphase pH values. Langmuir monolayers at the air/water interface represent a well‐defined model system to study the lipid/DNA complexes. Interactions and ordering of DNA under Langmuir monolayers of the new cationic lipids were studied using film balance measurements, grazing incidence X‐ray diffraction (GIXD) and X‐ray reflectivity (XR). The results obtained demonstrate the ability of these cationic lipids to couple with DNA at low as well as at high pH value. Moreover, the observed DNA structuring seems not to depend on subphase pH conditions. An influence of the chemical structure of the lipid head group on the DNA binding ability was clearly observed. Both compounds show good transfection efficacy and low toxicity in the in vitro experiments indicating that lipids with such structures are promising candidates for successful gene delivery systems.     

Formation of PdNiZn thin film at oil‐water interface: XPS study and application as Suzuki‐Miyaura catalyst

Nanosheet of PdNiZn and nanosphere of PdNiZn/reduced‐graphene oxide (RGO) with sub‐3 nm spheres have been successfully synthesized through a facile oil‐water interfacial strategy. The morphology and composition of the films were determined by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive analysis of X‐ray (EDAX) and elemental mapping. In the present study, we have developed a method to minimize the usage of precious Pd element. Due to the special structure and intermetallic synergies, the PdNiZn and PdNiZn/RGO nanoalloys exhibited enhanced catalytic activity and durability relative to Pd nanoparticles in Suzuki‐Miyaura C‐C cross‐coupling reaction. Compared to classical cross‐coupling reactions, this method has the advantages of a green solvent, short reaction times, low catalyst loading, high yields and reusability of the catalysts.     

Topological “interfacial” polymer chemistry: Dependency of polymer “shape” on surface morphology and stability of layer structures when heating organized molecular films of cyclic and linear block copolymers of n‐butyl acrylate‐ethylene oxide

The “topological polymer chemistry” of amphiphilic linear and cyclic block copolymers at an air/water interface was investigated. A cyclic copolymer and two linear copolymers (AB‐type diblock and ABA‐type triblock copolymers) synthesized from the same monomers were used in this study. Relatively stable monolayers of these three copolymers were observed to form at an air/water interface. Similar condensed‐phase temperature‐dependent behaviors were observed in surface pressure–area isotherms for these three monolayers. Molecular orientations at the air/water interface for the two linear block copolymers were similar to that of the cyclic block copolymer. Atomic force microscopic observations of transferred films for the three polymer types revealed the formation of monolayers with very similar morphologies at the mesoscopic scale at room temperature and constant compression speed. ABA‐type triblock linear copolymers adopted a fiber‐like surface morphology via two‐dimensional crystallization at low compression speeds. In contrast, the cyclic block copolymer formed a shapeless domain. Temperature‐controlled out‐of‐plane X‐ray diffraction (XRD) analysis of Langmuir–Blodgett (LB) films fabricated from both amphiphilic linear and cyclic block copolymers was performed to estimate the layer regularity at higher temperatures. Excellent heat‐resistant properties of organized molecular films created from the cyclic copolymer were confirmed. Both copolymer types showed clear diffraction peaks at room temperature, indicating the formation of highly ordered layer structures. However, the layer structures of the linear copolymers gradually disordered when heated. Conversely, the regularity of cyclic copolymer LB multilayers did not change with heating up to 50 °C. Higher‐order reflections (d₀₀₂, d₀₀₃) in the XRD patterns were also unchanged, indicative of a highly ordered structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 486–498     

Tungsten and nitrogen co‐doped TiO2 nanobelts with significant visible light photoactivity

Tungsten and nitrogen co‐doped TiO₂ nanobelts (W/N‐TNBs) have been successfully synthesized via 1‐step hydrothermal method. The structure, morphology, and composition of prepared samples were characterized by X‐ray diffraction, scanning electron microscopy, and X‐ray photoelectron spectroscopy, respectively. The prominent phase of all as‐prepared samples is anatase crystal. For samples with N doping, new energy states can be introduced on top of O 2p states which reduced the band gap by 1.1 eV. The reduced band gap leads to efficient visible light activity. The 3%‐W/N‐TNBs were found to exhibit the highest activity. The photocatalytic performance of 3%‐W/N‐TNBs under visible light is about 4.8 times than that of pure TiO₂ nanobelts, which emphasizes the synergistic effect of W and N co‐doping for effectively inhibiting the recombination of photogenerated electrons and holes. In addition, our results testify the different redox potentials of the photoelectrons at different final states.     

Heavy‐Atom Labeled Transmembrane β‐Peptides: Synthesis,CD‐Spectroscopy,and X‐ray Diffraction Studies in Model Lipid Multilayer

Transmembrane β‐peptides are promising candidates for the design of well‐controlled membrane anchors in lipid membranes. Here, we present the synthesis of transmembrane β‐peptides with and without tryptophan anchors, as well as a novel iodine‐labeled d ‐β³‐amino acid. By using one or more of the heavy‐atom labeled amino acids as markers, the orientation of the helical peptide was inferred based on the electron‐density profile determined by X‐ray reflectivity. The β‐peptides were synthesized through manual Fmoc‐based solid‐phase peptide synthesis (SPPS) and reconstituted in unilamellar vesicles forming a right‐handed 3₁₄‐helix secondary structure, as shown by circular dichroism spectroscopy. We then integrated the β‐peptide into solid‐supported membrane stacks and carried out X‐ray reflectivity and grazing incidence small‐angle X‐ray scattering to determine the β‐peptide orientation and its effect on the membrane bilayers. These β‐peptides adopt a well‐ordered transmembrane motif in the solid‐supported model membrane, maintaining the basic structure of the original bilayer with some distinct alterations. Notably, the helical tilt angle, which accommodates the positive hydrophobic mismatch, induces a tilt of the acyl chains. The tilted chains, in turn, lead to a membrane thinning effect.     

Crystallization of Celecoxib in Microemulsion Media

Celecoxib belongs to a new NSAID family specifically inhibiting cyclooxygenase‐2 (COX‐2). The present formulations require high dosage since the transmembrane transport fluctuates and is very difficult to control. We solubilized celecoxib in micelles of nonionic microemulsions and hydrophilic surfactant. The supersaturated solubilized drug was precipitated from the nano‐droplets to form a new solid structure with improved dissolution properties. The selected microemulsion systems loaded with celecoxib were characterized by SAXS, SD‐NMR, viscosity, and electrical conductivity techniques. Precipitation was conducted from W/O as well as from O/W U‐type microemulsions. The crystals obtained by the precipitation were characterized by x‐ray powder scattering, differential scanning calorimetry, FTIR measurements, and microscopic scans.