Equivalent Monolayers Research Articles

Polypyrrolic bipyridine bis(phenantrolinequinone) Ru(II) complex/carbon nanotube composites for NAD-dependent enzyme immobilization and wiring.

We report the synthesis and electrochemical characterization of a novel electropolymerizable Ru(II) complex containing two phenanthrolinequinone ligands, Ru(II)(PhQ)2(bpy-pyrrole)(PF6)2. This complex was electropolymerized on glassy carbon (GC) and multiwalled carbon nanotube (MWCNT) electrodes. Higher apparent surface concentrations (80 nmol cm(-2)) were obtained on MWCNTs than on GC electrodes and correspond to ∼1000 equivalent compact monolayers of Ru complex. Moreover, the nanostructured metallopolymer exhibits efficient electrocatalytic properties toward oxidation of NADH. This metallopolymer can be electrogenerated in water from the adsorbed Ru(II) monomer. This property was applied to the immobilization of enzymes by coadsorption of Ru complex and enzyme and then electropolymerization of coatings. This two-step procedure leads to the entrapment of 70%-90% of the deposited amount of enzyme in poly-Ru(II)(PhQ)2(bpy-pyrrole) films. Glucose dehydrogenase (GDH) was thus efficiently immobilized in the electrogenerated polymer matrix. In presence of NAD(+) (10 mM), the resulting enzyme electrode exhibits high current densities for glucose oxidation of 1.04 mA cm(-2) at low overpotentials (-0.1 V) with a detection limit of 1 μM of glucose.

Structural comparison between MgO/Fe(001) and MgO/Fe(001)–p(1×1)O interfaces for magnetic tunneling junctions: An Auger electron diffraction study

Abstract Magnetic tunnel junctions based on MgO(0 0 1) barriers and ferromagnetic electrodes, such as Fe/MgO/Fe, represent a very popular and widely investigated subject in the field of spin-electronics because of the large values of magnetoresistance shown by these systems. In this paper, the structural properties of MgO thin films grown onto Fe(0 0 1) and MgO/Fe(0 0 1)–p(1 × 1)O surfaces, with MgO thickness ranging from 2 to 14 equivalent monolayers, have been investigated by means of Auger electron diffraction. The structural order and the crystal quality of the MgO films result practically independent from the template, the latter being either the clean Fe(0 0 1) surface or the oxidized Fe(0 0 1)–p(1 × 1)O one. This is confirmed by numerical simulations, showing that, apart from the first two MgO layers close to the interface, the structure is unaffected by the choice of the starting surface. By a structural point of view, we can conclude that Fe(0 0 1)–p(1 × 1)O is a good candidate for the role of bottom electrode for the realization of MgO-based magnetic tunnelling junctions, also considering its higher chemical stability and reproducibility if compared to the clean Fe(0 0 1) surface.

In situ XAS and XRF study of nanoparticle nucleation during O3-based Pt deposition

X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF) were combined in situ to study the ALD-based synthesis of Pt catalysts. This first time combination of synchrotron-based techniques was applied during the (methylcyclopentadienyl)trimethylplatinum/ozone deposition process executed at 150°C on a silica support. A nucleation delay indicative for nanoparticle formation was observed for Pt loadings below 1 equivalent monolayer. XAS and XRF were recorded simultaneously at different catalyst loadings in this nucleation regime. Analysis of the combined in situ data yielded a quantitative picture of the evolution of the diameter, shape, lattice packing and density of the deposited Pt clusters. Additionally, the degree of oxidation at the cluster surface after the ozone pulse could be monitored. At the early start of the deposition process, Pt adatoms cluster together to form stable nuclei. A strong increase in the density of nuclei is seen below 0.16 equivalent monolayers, after which coalescence gradually occurs. From 0.04 to 0.71 equivalent monolayers, Pt clusters are fcc packed and correspond best to a hemispherical (111)-truncated cuboctahedral shape. By crosslinking the XRF and XAS data, a linear increase in cluster diameter with Pt loading is observed within this range. The surface of the Pt clusters is shown to be oxidized immediately after the ozone exposure. The degree of surface oxidation remains approximately constant for clusters with a 1–3nm diameter. This surface oxygen is shown to be crucial for further growth during deposition. The combined application of in situ XRF and XAS thus allowed for an advanced identification of the ALD-deposited Pt nanoparticles.

Study of the early stages of growth of Co oxides on oxide substrates

The growth of Cobalt oxides by reactive thermal evaporation of metallic Cobalt in an oxygen atmosphere on a series of oxide substrates, namely SiO2, Al2O3 and MgO, has been chemically and morphologically studied by means of XPS and atomic force microscopy (AFM). The XPS results reveal that cobalt oxide grows as CoO (Co2+) for coverages up to some tens of equivalent monolayers on all substrates. For larger coverages, the formation of the spinel oxide Co3O4 has been observed. AFM and XPS quantification allowed us to determine the way of growth of CoO on all substrates, being of Volmer–Weber (i.e. islands) mode for SiO2, whereas for Al2O3 and MgO, the growth follows the Frank‐van der Merwe (i.e. layer‐by‐layer) mode. The results are discussed in terms of the mismatch of the lattice parameters of the CoO adsorbates with the substrates. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of Mn and Cu Addition on Lithiation and SEI Formation on Model Anode Electrodes

The effect of addition of Mn2+ to the electrolyte on the lithiation of a model battery anode was studied using voltammetry, electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Cyclic voltammetry of a Au anode showed that the presence of one equivalent monolayer of Mn2+ in the electrolyte reduces the battery capacity by as much as 48%, a result which is recapitulated in SEM images of the anode surface after five cycles which show that the presence of Mn2+ blocks lithiation of the anode. AES demonstrates the presence or lack of Mn on the surface. EQCM analysis demonstrates greater initial mass gain on the anode with increasing concentration of Mn2+ in the electrolyte while MALDI-TOF MS shows no observable differences in the solid electrolyte interface (SEI) between the electrolyte with or without Mn2+. The addition of Cu2+ to the electrolyte exhibits an effect similar to Mn2+ addition.

Adsorption of Indole on Kaolinite in Nonaqueous Media: Organoclay Preparation and Characterization, and 3D-RISM-KH Molecular Theory of Solvation Investigation

Current oil sand mining operations in the Athabasca basin are predominantly aqueous-based. Extracts containing large amounts of fines lead to the formation of stable organoclay suspensions in froths giving lower yields and greater tailing wastes and making the development of more efficient extraction methods desirable from both economical and environmental perspectives. We examine an indole-kaolinite system as a model for these oil fines and their resistance to washing in nonaqueous solvents. The prepared organoclays show indole loading exclusively on the external surface of the clay. Micron-scaled vermicular structures, similar to natural kaolinite, are observed. Their formation is believed to be driven by strong adsorbate–adsorbate interactions. Indole is the primary adsorbate, as solvent adsorption is shown to be minimal based on both experimental and computational results. Isotherms are constructed and parameters calculated from linear regression analysis fitted to the Brunauer–Emmett–Teller equation. Monolayer quantities calculated match well to the theoretical amount calculated from surface areas measurements. Washing the organoclays with both toluene and isopropanol results in a 50% decrease of loaded organic material, leaving a monolayer equivalent of organic matter. The statistical-mechanical 3D-RISM-KH molecular theory of solvation is employed to perform full sampling of solvent orientations around a kaolinite platelet and gain insights into the preferred orientation and adsorption thermodynamics of indole on kaolinite in toluene and heptane solvents. In its preferred orientation, indole is hydrogen-bonded to one or two O atoms at the aluminum hydroxide surface of kaolinite. The calculated solvation free energy and potential of mean force for adsorption of indole and solvents on kaolinite in solution yield the increasing adsorption strength order of heptane < toluene < indole on the aluminum hydroxide surface. Multilayer adsorption profiles are predicted based on the integrated three-dimensional distribution functions of indole, toluene, and heptane.

Multi-layer graphene obtained by high temperature carbon implantation into nickel films

We present a study of carbon implantation in a stacked layered substrate made of Ni(200nm)/SiO2(300nm)/Si(100). The carbon atoms have energy of 20keV. Simultaneous or subsequent heat treatment is performed in the 450–600°C range. The carbon dose was set to be 4 equivalent graphene monolayers (EGM). Most of the carbon implanted diffuses directly to the surface, forming multi-layer graphene (MLG). A progressive structuration of these graphitic fragments occurs with the increase of the implantation temperature. However, this structuration is more pronounced if the thermal treatment is performed in situ following the carbon implantation at room temperature. The mean MLG thickness, corresponding to around 4–5 EGM, was measured by angular X-ray Photoemission Spectroscopy. Moreover, the overall carbon concentration inside and at the limits of the nickel films, determined by nuclear reaction analysis (NRA), is in the 7–10 EGM range. This concentration depends on the temperature but it exceeds surprisingly the expected carbon concentration. This discrepancy shows that some carbon is incorporated along the different steps. NRA analyses of the preparation confirm this point. To obtain large film, the presented results stress the interest to better understand the full system carbon–nickel in the preparation of MLG at each step of the process.

THU0033 SET7/9 and SIRT1 induce promoter-driven collagen 2ALPHA1 expression in 3D cultured human chodrocytes

BackgroundOsteoarthritis (OA) is characterized by disrupted balance between extracellular matrix (ECM) synthesis and breakdown, leading to loss of articular cartilage (AC) and severe joint pain-dysfunction. Collagen type IIα1 (Col2α1) is...

CO2-selective methanol steam reforming on In-doped Pd studied by in situ X-ray photoelectron spectroscopy

In situ X-ray photoelectron spectroscopy (in situ XPS) was used to study the structural and catalytic properties of Pd–In near-surface intermetallic phases in correlation with previously studied PdZn and PdGa.Room temperature deposition of ∼4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453K in vacuum yields a ∼1:1 Pd/In near-surface multilayer intermetallic phase. This Pd1In1 phase exhibits a similar “Cu-like” electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd1Zn1 counterpart.Catalytic characterization of the multilayer Pd1In1 phase in MSR yielded a CO2-selectivity of almost 100% between 493 and 550K. In contrast to previously studied In2O3-supported PdIn nanoparticles and pure In2O3, intermediate formaldehyde is only partially converted to CO2 using this Pd1In1 phase. Strongly correlated with PdZn, on an In-diluted PdIn intermetallic phase with “Pd-like” electronic structure, prepared by thermal annealing at 623K, methanol steam reforming is suppressed and enhanced CO formation via full methanol dehydrogenation is observed.To achieve CO2-TOF values on the isolated Pd1In1 intermetallic phase as high as on supported PdIn/In2O3, at least 593K reaction temperature is required. A bimetal-oxide synergism, with both bimetallic and oxide synergistically contributing to the observed catalytic activity and selectivity, manifests itself by accelerated formaldehyde-to-CO2 conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd1In1 inhibited inverse water–gas-shift reaction on In2O3 and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO2-selectivity of the supported catalyst.

Configuration of electrofusion-derived human insulin-secreting cell line as pseudoislets enhances functionality and therapeutic utility

Formation of pseudoislets from rodent cell lines has provided a particularly useful model to study homotypic islet cell interactions and insulin secretion. This study aimed to extend this research to generate and characterize, for the first time, functional human pseudoislets comprising the recently described electrofusion-derived insulin-secreting 1.1B4 human β-cell line. Structural pseudoislets formed readily over 3-7 days in culture using ultra-low-attachment plastic, attaining a static size of 100-200 μm in diameter, corresponding to ~6000 β cells. This was achieved by decreases in cell proliferation and integrity as assessed by BrdU ELISA, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, and lactate dehydrogenase assays. Insulin content was comparable between monolayers and pseudoislets. However, pseudoislet formation enhanced insulin secretion by 1·7- to 12·5-fold in response to acute stimulation with glucose, amino acids, incretin hormones, or drugs compared with equivalent cell monolayers. Western blot and RT-PCR showed expression of key genes involved in cell communication and the stimulus-secretion pathway. Expression of E-Cadherin and connexin 36 and 43 was greatly enhanced in pseudoislets with no appreciable connexin 43 protein expression in monolayers. Comparable levels of insulin, glucokinase, and GLUT1 were found in both cell populations. The improved secretory function of human 1.1B4 cell pseudoislets over monolayers results from improved cellular interactions mediated through gap junction communication. Pseudoislets comprising engineered electrofusion-derived human β cells provide an attractive model for islet research and drug testing as well as offering novel therapeutic application through transplantation.

A statistical approach to delta layer depth profiling

We present a simple statistical model describing the removal and relocation of material during a sputter depth profiling experiment. All input parameters are determined from low‐fluence molecular dynamics simulations, making the model de facto parameter free. The model can be used to extrapolate data from the molecular dynamics simulations to projectile fluences relevant to sputter depth profiling experiments. As a result, the erosion of the surface is calculated in terms of fluence‐dependent filling factors of different sample layers. Using input data determined for the 20‐keV C60 cluster bombardment of silicon, it is found that a steady‐state erosion profile is reached after removal of approximately 20 monolayer equivalents of material. Plotting the contribution of particles from a specific layer to the instantaneous sputtered flux, one can directly determine the delta layer response function predicted from such a model. It is shown that this function can be parameterized by the semiempirical Dowsett response function, and the resulting fitting parameters are compared with published depth profile data. The model is then used to study the role of different processes influencing the observed depth resolution. We find that the statistical nature of the sputtering process suffices to explain many features of experimentally measured delta layer depth profiles. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Oxygen‐deficient ordered phases of ultrathin BaTiO3 films on Pt(111)

The restructuring of epitaxial ultrathin BaTiO3 films on a Pt(111) substrate upon high‐temperature treatment has been studied by scanning tunneling microscopy, low‐energy electron diffraction, and XPS. Upon annealing ultrathin BaTiO3 films up to 4 monolayer equivalents in thickness at 1150 K in vacuum, BaTiO3 forms three‐dimensional islands surrounded by bare Pt. Annealing at 1250 K induces a two‐dimensional rewetting layer, which spreads around the three‐dimensional BaTiO3 islands. This rewetting layer consists of oxygen‐deficient BaTiO3. Within the rewetting layer, several long‐range ordered structures coexist. Their lattice constants vary between 11 and 46 Å. These rewetting structures are derived from a slightly modified BaTiO3(100) layer, which is stabilized by one direction of the Pt(111) lattice. The rewetting layer formation can be reversed by annealing in oxygen. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Comparison of Orientational Texture in Lipid Bilayers and Langmuir Monolayers

In solid ordered domains of lipid bilayers the lipids may have an in-plane orientational order associated with the tilted acyl chains. The variation of this orientation across the sample is denoted the texture. Although biological membrane normally only exist in the fluid phase, the gel phase is present, for instance in skin tissue and during apoptosis.The texture of monolayers has been investigated previously through the use of mainly Brewster Angle Microscopy (BAM) and AFM. For bilayers we have found that polarized two-photon fluorescence microscopy combined with image analysis is able to provide the orientational texture with single pixel resolution [1]. We have used this method to image the texture of solid ordered domains in lipid bilayers.In bilayers we typically observe texture patterns with splitting of the domain into 6 subdomains having different orientations. In contrast to monolayers we find a significant variation in the defect structure when going from the center of the domain to the edges. In an attempt to understand texture formation we have systematically compared results from bilayers with the texture of an equivalent monolayer system prepared at different temperatures.[1] JACS 131(40): p. 14130-14131 (2009)

Reversible oxidation of WO x and MoO x nano phases

WO x and MoO x nano phases were prepared on TiO 2(1 1 0) surfaces by a CVD procedure consisting of adsorption and decomposition of W(CO) 6 or Mo(CO) 6 precursors followed by annealing under UHV. Metal amount involved in each elaborated sample is in the fractional range from 0.1 to 0.35 equivalent monolayer (eqML) of W or Mo. Evolution of sample stoichiometry as a function of subsequent treatment is followed by valence band and core level photoemission as well as work function measurement. In each case, exposure of samples to molecular oxygen at room temperature induces an increase of sample work function in a range of several tenth of eV. Such a work function change is related to oxidation of sample involving both titanium and tungsten (or molybdenum) ions. Such an oxidation is reversible through an annealing under UHV at 470 K for molybdenum oxide and 670 K for tungsten oxide. Several cycles of exposure/annealing are possible without changes in work function or stoichiometry.

NO 2 uptake under practically relevant conditions on BaO/Pt(1 1 1)

The formation of nitrites and nitrates (Ba(NO x ) 2) under practically relevant conditions ( P NO 2 up to 1.0 Torr and T = 500 K) and their thermal decomposition on BaO (>20 monolayer equivalent (MLE))/Pt(1 1 1) were studied using temperature programmed desorption (TPD), infrared reflection absorption (IRA), and X-ray photoelectron (XP) spectroscopies. The exposure of BaO to 1.0 × 10 −8 Torr NO 2 at 500 K leads to the formation of a Ba(NO x ) 2 layer with small, disordered crystalline nitrate clusters. Under these conditions ( P NO 2 = 1.0 × 10 − 8 Torr and T = 500 K) only the top portion of the BaO layer converts to Ba(NO x ) 2 and the nitrites in this Ba(NO x ) 2 layer stay without converting completely to nitrates even after 100 min of NO 2 exposure. In the thermal decomposition of Ba(NO x ) 2, first nitrites decompose, releasing NO and then the decomposition of nitrates occurs via two pathways releasing NO 2 and NO + O 2. At 500 K and P NO 2 ≥ 1.0 × 10 − 7 Torr , first NO 2 reacts with BaO to form small disordered crystalline Ba(NO 3) 2 particles and then these particles agglomerate to form large, well-ordered (bulk-like) crystalline nitrates as the NO 2 exposure increases. The thermal decomposition of these well-ordered, bulk-like crystalline nitrate aggregates occurs in two steps releasing NO 2 and NO + O 2 in each step in two different temperature regions. NO 2 pressure ≥1.0 × 10 −5 Torr is required for the complete oxidation of initially formed nitrites to nitrates and the full nitration of the BaO layer at 500 K sample temperature.

Electronic exchanges between adsorbed Ni atoms and TiO 2(1 1 0) surface evidenced by resonant photoemission

Nickel was deposited on stoichiometric TiO 2(1 1 0) surface in the 0.02–2.1 equivalent monolayer (eqML) range and analyzed by means of photoemission and resonant photoemission. In the case of very low coverage (lower than 0.1 eqML), deposited nickel reacts with the surface through an electronic transfer from nickel atoms towards titanium ions. This exchange caused the filling of unoccupied Ti3d states leading to the increase of a peak in the TiO 2 band gap. These states can be better characterized through resonant photoemission experiments at the Ti 3p → 3d absorption edge: for very low coverage, these states in the TiO 2 band gap have resonant behavior of Ti3d electrons rather than Ni3d ones, confirming the filling of Ti3d states and thus electron transfer between nickel and titanium. For coverage higher than 0.14 eqML, nickel peaks (both Ni3p core level and valence band) should be related to the presence of metallic nickel in small clusters.

The 2-D growth of gold on single-layer graphene/Ru(0001): Enhancement of CO adsorption

The growth and morphology of two-dimensional (2-D) gold islands on a single-layer graphene supported on Ru(0001) have been studied by scanning tunneling microscopy (STM). Our findings show that gold exhibits 2-D structures up to a gold dosage of 0.75 equivalent monolayers, and that these 2-D gold islands are thermally stable at room temperature. Parallel polarization modulation infrared reflection absorption spectroscopic (PM-IRAS) and high resolution electron energy loss spectroscopic (HREELS) studies indicate that carbon monoxide (CO) adsorbs on these 2-D gold islands at 85 K, showing a characteristic CO stretching feature at 2095 cm − 1 for a saturation coverage of CO. The red shift of the CO stretching frequency compared to that on charge neutral gold is consistent with electron transfer from graphene to gold, i.e., an electron-rich gold overlayer. Preliminary data obtained by dosing molecular oxygen onto this CO pre-covered surface suggest that the 2-D gold islands catalyze the oxidation of CO.

A serum‐free chemically defined medium for the expansion of adult normal human dermal fibroblasts

Cultured dermal fibroblasts are used clinically for acute and chronic wound repair and as a source of collagen for cosmetic surgery. Typically cells are cultured in medium containing serum. The unknown components and variable nature of serum is a challenge in basic research and clinical applications. Alternatives to serum to supplement cell culture media is much sought after. We have developed a serum‐free chemically defined, fibroblast growth medium (TheraPEAKTM FGM‐CDTM), to propagate primary adult normal human dermal fibroblasts (NHDF). NHDFs from several donors grown in FGM‐CDTM, proliferated for multiple passages, maintained a fibroblast phenotype and expressed fibroblast‐specific markers comparable to serum‐containing control medium. NHDFs grown in FGM‐CDTM on several different plastic surfaces maintained equivalent monolayer growth, viability and fibroblast markers. The migration capacity of the fibroblasts in FGM‐CDTM was similar to migration in the control medium. Immunofluorescence staining showed that NHDFs synthesize more collagen I in FGM‐CDTM than in serum‐containing medium. Replacement of serum‐containing medium with TheraPEAKTM FGM‐CDTM for the in vitro expansion of fibroblasts provides a more defined environment for pharmacological manipulations for research studies and for clinical applications using fibroblasts. Source of research support: Lonza BioScience

Reactions of NO2 with BaO/Pt(111) model catalysts: the effects of BaO film thickness and NO2 pressure on the formation of Ba(NOx)2 species

The adsorption and reaction of NO(2) on BaO (<1, ∼3, and >20 monolayer equivalent (MLE))/Pt(111) model systems were studied with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRAS) under ultra-high vacuum (UHV) as well as elevated pressure conditions. NO(2) reacts with sub-monolayer BaO (<1 MLE) to form nitrites only, whereas the reaction of NO(2) with BaO (∼3 MLE)/Pt(111) produces mainly nitrites and a small amount of nitrates under UHV conditions (P(NO(2))≈ 1.0 × 10(-9) Torr) at 300 K. In contrast, a thick BaO (>20 MLE) layer on Pt(111) reacts with NO(2) to form nitrite-nitrate ion pairs under the same conditions. At elevated NO(2) pressures (≥1.0 × 10(-5) Torr), however, BaO layers at all these three coverages convert to amorphous barium nitrates at 300 K. Upon annealing to 500 K, these amorphous barium nitrate layers transform into crystalline phases. The thermal decomposition of the thus-formed Ba(NO(x))(2) species is also influenced by the coverage of BaO on the Pt(111) substrate: at low BaO coverages, these species decompose at significantly lower temperatures in comparison with those formed on thick BaO films due to the presence of a Ba(NO(x))(2)/Pt interface where the decomposition can proceed at lower temperatures. However, the thermal decomposition of the thick Ba(NO(3))(2) films follows that of bulk nitrates. Results obtained from these BaO/Pt(111) model systems under UHV and elevated pressure conditions clearly demonstrate that both the BaO film thickness and the applied NO(2) pressure are critical in the Ba(NO(x))(2) formation and subsequent thermal decomposition processes.

Modeling of water vapor adsorption isotherms onto polyacrylic polymer

The adsorbed amounts of water vapor onto polyacrylic polymer (polymer ×10) were measured using a thermogravimetry method as a function of pressure at 298 and 313 K. The adsorption isotherms are categorized to type II isotherms by IUPAC classification leading to a hysteresis loop between adsorption and desorption branches. The current study was completed by the measurement of the adsorption heats at 298 K using a differential scanning calorimetry. The calorimetric curves showed two adsorption heats domains. These domains have been attributed to the adsorption of “equivalent monolayer” and the condensation of water between polymeric chains. The correlation of experimental data to some chosen theoretical models shows that the GAB model is the most adequate to describe water vapor sorption isotherms.