Evaluation of the stress-strain properties of surface layers in plasma-treated polymers

The surface treatment of poly(ethylene terephthalate) (PET) and poly(vinyl chloride) (PVC) films in cold plasma over 1–15 min was carried out. It was found that the subsequent deformation of the films is accompanied by a special type of surface structuring that has been previously observed for polymer films with a thin hard coating. It was shown that unlike metal coatings, the thickness of the modified surface layer slightly depends on the time of treatment in plasma. The previously developed approach to analysis of the emerging patterns makes it possible to evaluate the stress-strain properties of the coatings. It was first revealed that the tensile strength of the modified layer produced in PET by plasma treatment is ∼12.3 MPa and its elongation at break varies from 20 to 90%. The differences in the properties between the plasma-modified surface layers of the polymer and the metal coatings studied earlier are discussed.     

Corrosion crack enhancement during the cathodic activation of zirconium AB<Subscript>2</Subscript> alloys

The activation of zirconium nickel alloys with and without the addition of chromium and titanium is investigated through electrochemical and optical techniques. Recent investigations in aqueous 1 M KOH indicate oxide layer growth and occlusion of hydrogen species in the alloys during the application of different cathodic scan potential programmes currently used for the activation process. In this research, several techniques, such as voltammetry, ellipsometry, energy dispersive analysis of X-rays and scanning electron microscopy, are applied to three polished massive alloys, Zr_1−x Ni _x , x = 0.36 and 0.43, and Zr_0.9Ti_0.1NiCr. Data analysis shows that the stability, compactness and structure of the passive layers are strongly dependent on the applied potential programme. The alloy activation depends on the formation of deep crevices that remain after further polishing. The microscopic observation shows an increase in crevice thickness after cathodic sweep potential cycling, which produces fragmentation of the grains and oxide growth during the activation process. This indicates metal breaking and intergranular alloy dissolution that take place together with oxide and hydride formation. In some cases, the resultant crevice thickness is one or two orders higher than the growth of surface oxide indicating localised intergranular corrosion. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

Electrodeposition of Ir—Ru alloys from chloride melts: Steady-state potentials and cathodic processes

Steady-state potentials of Ir, Ru, and glassy carbon are measured at 500–700°C in eutectic NaCl-KCl-CsCl melts containing a mixture of Ir and Ru chlorides. The Ir and Ru steady-state potentials are more positive than their equilibrium values, due to the alloying in the metal surface layer. In the cathodic deposition of alloys, depolarization is observed. Before the limiting diffusion current, Ir-Ru alloys (solid solutions) are plated as compact layers; at higher current densities, the deposit is a powdered dendritic mixture of individual Ir and Ru crystals, rather than the alloy     

On the interfacial chemistry of aryl diazonium compounds in polymer science

This review emphasises the role of aryl diazonium compounds as a new class of coupling agents for grafting polymer thin layers onto carbon, diamond, metals, metal oxides, alloys, semi-conductors, ceramics, and polymers. Physical and chemical methods are first reported for anchoring aryl layers to the surfaces, then the review concentrates on the modification of the above substrates by thin polymer films via a range of the “grafting from” and “grafting onto” strategies. Some applications are described which highlight the important role that diazonium salts will continue to play in the near future in the polymer and surface sciences.     

Film growth and interface reaction of ultra thin 3d-transition metal oxide/metal layer structures

The interface reactions between transition metal oxide substrates and ultra thin metal layers of different thickness (<15 nm) have been investigated by using x-ray photoelectron spectroscopy (XPS). To a different extent oxidation of deposited metal and reduction of the oxidic substrate is visible for complementary layer systems. For the interface nickel oxide/manganese an enhanced reaction is found compared to the system manganeseoxide/nickel. Based on the experimental data a model of the evolving interface is proposed.     

Influence of surface contaminations on the hydrogen storage behaviour of metal hydride alloys

Hydrogen storage in metal hydrides is a promising alternative to common storage methods. The surface of a metal hydride plays an important part in the absorption of hydrogen, since important partial reaction steps take place here. The development of surface contaminations and their influence on hydrogen absorption is examined by means of absorption experiments and surface analysis, using X-ray photoelectron spectroscopy (XPS), thermal desorption mass spectrometry (TDMS) and secondary neutral mass spectrometry (SNMS), in this work. All investigations were carried out on a modern AB₂ metal hydride alloy, namely Ti_0.96Zr_0.04Mn_1.43V_0.45Fe_0.08. Surface analysis (SNMS, XPS) shows that long-term air storage (several months) leads to oxide layers about 15 nm thick, with complete oxidation of all main alloy components. By means of in situ oxygen exposure at room temperature and XPS analysis, it can be shown that an oxygen dose of about 100 Langmuirs produces an oxide layer comparable to that after air storage. Manganese enrichment (segregation) is also clearly observed and is theoretically described here. This oxide layer hinders hydrogen absorption, so an activation procedure is necessary in order to use the full capacity of the metal hydride. This procedure consists of heating (T = 120° C) in vacuum and hydrogen flushing at pressures like p = 18 bar. During the activation process the alloy is pulverized to particles of ∼20 μm through lattice stretches. It is shown that this pulverization of the metal hydride (creating clean surface) during hydrogen flushing is essential for complete activation of the material. Re-activation of powder contaminated by small doses of air (p ≈ 0.1 bar) does not lead to full absorption capacity. In ultrahigh vacuum, hydrogen is only taken up by the alloy after sputtering of the surface (which is done in order to remove oxide layers from it), thus creating adsorption sites for the hydrogen. This is shown by TDMS measurements with and without sputtering and oxygen exposure. Figure Investigated metal hydride before and after activation     

Oxide and nitride protective layers on stainless steel studied by AES,WDS and XPS

Protective surface layers on AISI 321 stainless steel were prepared by thermal treatments at two different temperatures in air and two controlled atmospheres. Different oxide and/or nitride layers were formed. Surface morphology of the layers was investigated by scanning electron microscopy (SEM). Auger electron spectroscopy (AES) depth profiling of the samples was performed. Since depth profiling suggested layer thicknesses of the order of hundreds of nanometres, an attempt was made to obtain some fast, averaged information about the layer compositions using wavelength dispersive spectroscopy (WDS) at two different beam energies to obtain probing depths best suited to the layer thickness. X‐ray photoelectron spectroscopy (XPS) profiling of one layer was also performed to obtain information about the chemical states of the elements inside the layer. The analysed samples showed considerable differences with respect to their surface morphology, oxide/nitride layer thicknesses, compositions and layer–metal interface thickness. Copyright © 2007 John Wiley & Sons, Ltd.     

Oberfl?chensegregation an Au-Pd-Legierungen

Summary Measurements of the surface composition of Au-Pd binary alloys performed by Ion Scattering Spectroscopy (ISS) and X-ray Photoelectron-Spectroscopy (XPS) are presented. A set of 11 alloys with different bulk composition was used for these studies. Argon bombardment induced alternation of the surface composition due to preferential sputtering effects and surface segregation due to temperature excursions up to 500 °C have been studied. For quantitative evaluation of the ISS spectra pure metal standards and also calculated scattering cross sections were used. In general, little gold enrichment due to preferential sputtering and strong surface segregation of gold at elevated temperature was found by ISS measurements. The thickness of the altered layer is about 1 or 2 monolayers.     

Bulk and surface composition, amorphous structure, and thermocrystallization of electrodeposited alloys of tungsten with iron, nickel, and cobalt

It has been shown for iron-group alloys of tungsten, using ESCA spectroscopy of samples sputtered with argon ions and SEM/EDS analysis, that no oxygen is present in the alloy bulk. A very weak internal organization in the alloys, which follows from low and wide diffractograms usually obtained for electrodeposited layers, is thought to be a heavily distorted structure of the major metal component of the alloy. Thermal crystallization of thin layers of the amorphous tungsten alloys does not lead to formation of well-known intermetallic crystal structures. Received: 19 January 1998 / Accepted: 17 July 1998     

Superconductivity and structure of the multilayer Cu/Nb/Nb-Ti nanocomposites

The multilayer composite tapes containing layers of superconducting alloy of niobium with 31 or 50 wt % of Ti separated by niobium layers were investigated. The thickness of a layer is from ∼140 to ∼10 nm. Composites were produced by three-step rolling of multilayer packages. Effective fixation of the superconducting vortex filaments occurred at the interlayer boundaries of Nb-NbTi, as evidenced by the large anisotropy of the critical current density. The second critical magnetic field was found also dependent on the orientation of the plane of rolling of the composite relative to the external magnetic field, and decreases with decreasing thickness of the layers.     

Hydrogen-induced metal-oxide interaction studied on noble metal model catalysts

Summary The effect of hydrogen reduction on the structure and catalytic properties of “thin film”and “inverse”model systems for supported metal catalysts is discussed. Thin film model catalysts were obtained by epitaxial growth of Pt and Rh nanoparticles on NaCl(001), which were coated with amorphous or crystalline supports of alumina, silica, titania, ceria and vanadia. Structural and morphological changes upon hydrogen reduction between 473 and 973 K were examined by high resolution electron microscopy. Metal-oxide interaction sets in at a specific reduction temperature and is characterized by an initial “wetting”stage, followed by alloy formation at increasing temperature, in the order VO_x< TiO_x< SiO₂< CeO_x< Al₂O₃. “Inverse”model systems were prepared by deposition of oxides on a metal substrate, e.g. VO_x/Rh and VO_x/Pd. Reduction of inverse systems at elevated temperature induces subsurface alloy formation. In contrast to common bimetallic surfaces, the stable subsurface alloys of V/Rh and V/Pd have a purely noble metal-terminated surface, with V positioned in near-surface layers. The uniform composition of the metallic surface layer excludes catalytic ensemble effects in favor of ligand effects. Activity and selectivity, e.g. for CO and CO₂methanation and for partial oxidation of ethene, are mainly controlled by the temperature of annealing or reduction. Reduction above 573 K turned out to be beneficial for the catalytic activity of the subsurface alloys, but not for the corresponding thin film systems which tend to deactivate viaparticle encapsulation.</o:p>     

My Research History on the Chemical Standpoint—From Molecular Structure to Surface Science

The structure of molecules using gas electron diffraction (GED) was my graduate study. However, I was making a new apparatus for precise measurements by GED and formulated a scheme for the least‐squares analysis for a smooth continuous curve of scattering intensity. My research was completely shifted to the solid surface after moving to Gakushuin University, where I briefly studied the liquid structure of CCl₄ molecules, and I then moved to the Institute for Solid State Physics, the University of Tokyo. My studies of surface science were focused on the electronic properties and related phenomena, and various experimental methods were developed. The plasmon dispersions elucidated the initial oxidation of aluminum and one‐dimensional metal on Si(001)2 × 1–K. Irreversible phase transition was discovered on MgO(001) using the LEED Kikuchi pattern. The electronic structure of the dislocation was observed on MgO(001) by the electron time‐of‐flight method. The phase transition on Si(001) and the rotational epitaxy in a K monoatomic layer on Cu(001) were found. Next, I changed to studies of the dynamical phenomena on the surface, where very low energy reactive ion scattering on metal surfaces and laser‐induced desorption caused by electronic transition of NO and CO molecules from metal surfaces were observed, and the hydrogen atom location at the surface and interface was measured with a high depth resolution using a resonance nuclear reaction of ¹H + ¹⁵N²⁺ at 6.385 MeV. Finally, I moved to the University of Electro‐Communications and studied thin single‐crystal oxide layers on transition metals, in which the band‐gap narrowing was found, and then a Pt monoatomic layer was prepared on the α‐Al₂O₃ film.     

Effect of atmospheric nitrogen on the oxidation mechanism of aluminum alloys with rare-earth metals

Interaction (25–620°C) of aluminum and its alloys with an atmosphere saturated with nitrogen was studied to determine the role played by rare-earth metals in the mechanism by which nitride phases are formed in oxidation of Al + REM alloys in air. The ellipsometric method and Auger electron spectroscopy were used to determine that, under the given experimental conditions, metallic aluminum is subjected to the greatest extent to the nitridation process, which is competing with the oxidation process. The process is initiated by the conversion of the amorphous oxide film to γ-Al₂O₃. The surface of Al + REM alloys interacts with nitrogen at the outer part of the oxide layer. The rare-earth metal actively reacts with impurity oxygen present in the atmosphere under study and hinders formation of nitride/oxynitride layers.     

Freestanding Millimeter-Scale Porphyrin-Based Monoatomic Layers with 0.28 nm Thickness for CO2 Electrocatalysis

Developing two-dimensional (2D) and single atomic layered materials is a fascinating challenge. Here we successfully synthesize porphyrin-based monoatomic layer (PML), a freestanding 2D porphyrin-based material of monomer-unit thickness (2.8 Å). The solvothermal method provides a bottom-up approach for tailoring the monoatomic layer from the nanoscale to the milliscale. PMLs containing accurately tailorable M-N₄ units (M=Cu and Au) were synthesized, which present metal center-dependent performance for CO₂ electrocatalysis. PML with Cu-N₄ centers performs high faradaic efficiencies of HCOO⁻ and CH₄ (80.86 % and 11.51 % at −0.7 V, respectively) while PML with Au-N₄ centers generates HCOO⁻ and CO as major products (40.90 % and 34.40 % at −0.8 V, respectively). Irreversible restructuring behavior of Cu sites is also observed. Based on the graphene-like properties and metal center-selectivity relationships, we believe that PML will play a distinct role in various applications.     

Study of spin coated multilayer zirconia and silica films for non-quarterwavelength optical design based antireflection effect at 1,054 nm

A non-quarterwavelength optical design (design wavelength, λ_o = 1,054 nm) based antireflection (AR) coating was prepared by sol–gel spin coating technique. Two materials, zirconia and silica were chosen for the deposition of AR layers on borosilicate crown glass, refractive index (R. I. = 1.51). For this design, the bottom and middle layers were of zirconia with the R. I. range 1.941–1.958 while the top layer was of silica with R. I. 1.455. To understand the surface feature after each deposition, refractive index and physical thickness of the layers were measured ellipsometrically (λ = 632.8 nm) at different points over the area, 10 mm × 10 mm with an interval of 0.5 mm along the centre based perpendicular projection made on an imaginary chord. The surface feature was examined by plotting the measured values of the optical parameters against the displacement. The surface roughness decreased with increasing layers. This was verified by the study of AFM images of the layers. Specular reflection of the antireflection coated product at λ₀ was comparable to that of the theoretically simulated curve.     

Indirect Complexometric Determination of Mercury(II) Using Potassium Bromide as Selective Masking Agent

 A complexometric method for the determination of mercury in presence of other metal ions based on the selective masking ability of potassium bromide towards mercury is described. Mercury(II) present in a given sample solution is first complexed with a known excess of EDTA and the surplus EDTA is titrated against zinc sulfate solution at pH 5–6 using xylenol orange as the indicator. A known excess of 10% solution of potassium bromide is then added and the EDTA released from Hg-EDTA complex is titrated against standard zinc sulfate solution. Reproducible and accurate results are obtained for 8 mg to 250 mg of mercury(II) with a relative error ± 0.28% and standard deviations ≤0.5 mg. The interference of various ions is studied. This method was applied to the determination of mercury(II) in its alloys. Received April 18, 2001 Revision October 10, 2001     

Analysis of AlGaAs/GaAs superlattices by means of sputter-assisted AES,SEM and TEM

This paper reports the developments of evaluation methods on epitaxially grown superlattices by means of sputterassisted Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). AlGaAs/GaAs semiconductor superlattics were grown epitaxially by metal–organic chemical vapour deposition (MOCVD). The layer thickness of the superlattices ranged from a few to ten nanometers. Firstly, developments of Auger depth profiling were tried by using: (1) a differential pumping-type ion gun instead of a static pressure type to reduce the oxygen adsorbates on the AlGaAs layer; (2) low-energy Auger signals instead of high-energy ones to shorten the escape depth; and (3) the lowest ion etching energy of 0.2 keV instead of 1 keV to reduce the surface roughening effects. It is shown that the depth resolution of sputter-assisted AES is attainable to 1.5 nm. Secondly, high-resolution SEM can be used as an easy evaluation method by observing the cleaved surface of superlattices, since the layers can be distinguished by signal contrast. Also, TEM can be used as an evaluation method by observing the (110) cross-section thinned sample. The dark field image has a high contrast between AlGaAs and GaAs using the (002) diffraction. It is confirmed from these AES, SEM and TEM evaluations that the hetero-interface abruptness of AlGaAs/GaAs superlattices grown by MOCVD is of the order of one monoatomic layer.     

Sol–gel titania coating on unmodified and surface-modified polyimide films

Sol–gel coating of metal oxides on polymer substrates is a useful process to fabricate various organic–inorganic hybrid materials under mild conditions. However, this process is hardly applicable to pristine polyimide (PI) films because their surfaces do not display effective functional groups for metal oxide coatings. In this study, we firstly examined direct sol–gel coating of titania thin layers on unmodified PI film surfaces. The results confirmed homogeneous, ultrathin titania layer coating and showed that the thickness and microscopic morphology of the titania layers were affected by titanium alkoxide concentrations in the spin coating solutions. We next investigated titania layer coating on surface-modified PI films that prepared using alkaline hydrolysis, which generated carboxylic acid groups on the film surfaces. Optimal hydrolysis time was determined using FT-IR spectroscopy and contact angle measurements. After sol–gel titania coating on the hydrolyzed PI film surfaces, the Scotch tape test was conducted to evaluate adhesion strength between the titania layers and PI film surfaces. Morphological observations of the sample surfaces after the tests clearly showed that surface modification of PI films increased titania layer adhesions. Effect of hydrothermal treatments on film formability and adhesion strength between titania-PI film interfaces was also evaluated.     

Ellipsometric and IR spectroscopic study of the surface interaction of binary Al-REM alloys with water

The effect of Al-REM binary alloys’ composition on the kinetics of their surface oxidation by water is studied by means of ellipsometry and IR spectroscopy. Intermetallides with ～21 at % rare-earth metal in aluminum are oxidized in distilled water at 100°C, along with alloys of eutectic composition (Al-～2 at % REM) in solid and disperse state. It is found that the kinetic dependences of the thickness of films formed on pollycrystalline alloy samples and the IR transmission spectra of dispersed samples show that increasing the quantity of dopant REM in aluminum lowers the reactive capability of aluminum under certain conditions. It is found that the experimental ellipsometric results are described by a two-layer model consisting of a substrate, an inner oxide layer and an outer layer of hydroxide.     

Comparative Analysis of a Solar Control Coating on Glass by AES, EPMA, SNMS and SIMS

 A solar control coating was analysed by different methods of surface analysis with respect to the layer sequence and the composition and thickness of each sublayer. The methods used for depth profiling were Auger electron spectroscopy, electron probe microanalysis, secondary neutral mass spectroscopy and secondary ion mass spectroscopy based on MCs⁺. The structure of the coating was unknown at first. All methods found a system of two metallic Ag layers, embedded between dielectric SnO_X layers. Additionally, thin Ni-Cr layers of 1–2 nm were detected on top of the Ag layers. Thus the detected layer sequence is SnO_X/Ni-Cr/Ag/SnO_X/Ni-Cr/Ag/SnO_X/glass. The Ni:Cr ratio in the nm-thin layers could be quantified by every method, the Cr fraction corresponding to less than one monolayer. We compare the capabilities and limitations of each method in routinely investigating this solar control coating. Importance was attached to an effective investigation. Nevertheless, by combining all methods, measuring artefacts could be uncovered and a comprehensive characterisation of the system was obtained.