Noncatalytic Surfaces Research Articles

Self-Aligned Thin-Film Patterning by Area-Selective Etching of Polymers

Patterning of thin films with lithography techniques for making semiconductor devices has been facing increasing difficulties with feature sizes shrinking to the sub-10 nm range, and alternatives have been actively sought from area-selective thin film deposition processes. Here, an entirely new method is introduced to self-aligned thin-film patterning: area-selective gas-phase etching of polymers. The etching reactions are selective to the materials underneath the polymers. Either O2 or H2 can be used as an etchant gas. After diffusing through the polymer film to the catalytic surfaces, the etchant gas molecules are dissociated into their respective atoms, which then readily react with the polymer, etching it away. On noncatalytic surfaces, the polymer film remains. For example, polyimide and poly(methyl methacrylate) (PMMA) were selectively oxidatively removed at 300 °C from Pt and Ru, while on SiO2 they stayed. CeO2 also showed a clear catalytic effect for the oxidative removal of PMMA. In H2, the most active surfaces catalysing the hydrogenolysis of PMMA were Cu and Ti. The area-selective etching of polyimide from Pt was followed by area-selective atomic layer deposition of iridium using the patterned polymer as a growth-inhibiting layer on SiO2, eventually resulting in dual side-by-side self-aligned formation of metal-on-metal and insulator (polymer)-on-insulator. This demonstrates that when innovatively combined with area-selective thin film deposition and, for example, lift-off patterning processes, self-aligned etching processes will open entirely new possibilities for the fabrication of the most advanced and challenging semiconductor devices.

Elucidation of Ionomer-Pt Interactions By Operando Vibrational Spectroscopy

Operando vibrational spectroscopy of the membrane electrode assembly (MEA) of Pt catalyzed fuel cell cathodes elucidates potential dependent adsorptive properties of ionomers upon Pt surfaces. These include direct evidence of sulfonate group adsorption at fuel cell potentials of 700 mV. An increase in the ionomer state-of-hydration, from oxygen reduction at the cathode, transitions ion exchange sites from the sulfonic acid to the dissociated sulfonate form. C1 and C3V modes correlate to the sulfonic acid and sulfonate forms respectively. The gradual transition of the MEA spectra from C1 to C3V modes, from the fuel cell open circuit voltage to the short circuit current respectively, demonstrate the utility of vibrational group mode assignments in terms of exchange site local symmetry. Operando vibrational spectroscopy coupled with polarization modulated IR spectroscopy of Nafion coated Pt also confirms adsorption of the Nafion -CF3 group upon Pt. At the anode side of the operando spectroscopy cell, Stark tuning of CO stretching modes are observed and discussed. The absence of Stark tuning is evidence of metal based materials as non-catalytic surfaces.

Assembly of B4GALT1/ST6GAL1 heteromers in the Golgi membranes involves lateral interactions via highly charged surface domains

β-1,4-Galactosyltransferase 1 (B4GALT1) and ST6 β-galactoside α-2,6-sialyltransferase 1 (ST6GAL1) catalyze the successive addition of terminal β-1,4-linked galactose and α-2,6-linked sialic acid to N-glycans. Their exclusive interaction in the Golgi compartment is a prerequisite for their full catalytic activity, whereas a lack of this interaction is associated with cancers and hypoxia. To date, no structural information exists that shows how glycosyltransferases functionally assemble with each other. Using molecular docking simulations to predict interaction surfaces, along with mutagenesis screens and high-throughput FRET analyses in live cells to validate these predictions, we show here that B4GALT1 and ST6GAL1 interact via highly charged noncatalytic surfaces, leaving the active sites exposed and accessible for donor and acceptor substrate binding. Moreover, we found that the assembly of ST6GAL1 homomers in the endoplasmic reticulum before ST6GAL1 activation in the Golgi utilizes the same noncatalytic surface, whereas B4GALT1 uses its active-site surface for assembly, which silences its catalytic activity. Last, we show that the homomeric and heteromeric B4GALT1/ST6GAL1 complexes can assemble laterally in the Golgi membranes without forming cross-cisternal contacts between enzyme molecules residing in the opposite membranes of each Golgi cisterna. Our results provide detailed mechanistic insights into the regulation of glycosyltransferase interactions, the transitions between B4GALT1 and ST6GAL1 homo- and heteromers in the Golgi, and cooperative B4GALT1/ST6GAL1 function in N-glycan synthesis.

Effect of Pretreatment on Magnetic Nanoparticle Growth on Graphene Surface and Magnetic Performance in Electroless Plating

Electroless plating involves sensitization, activation, and plating processes. Sensitization and activation are conducted by dipping the substrate in SnCl2 solution and PdCl2 solution, respectively. These pretreatment processes are required to plate the substrate with noncatalytic surfaces. We investigated the effect of sensitization on the magnetic properties of FeCoNi@graphene hybrids prepared via electroless plating. The solution concentrations during sensitization were varied to observe changes in the structural, morphological, and magnetic properties of FeCoNi@graphene using XRD, TEM, and VSM, respectively. Sensitization under high concentration produced a large amount of SnO2, resulting in low saturation magnetization. Further, the FeCoNi@graphene hybrid prepared via electroless plating without sensitization also exhibited low saturation magnetization owing to the formation of oxides and hydroxides. We prepared FeCoNi@graphene with a saturation magnetization of 40.8 emu/g under sensitization at low concentration; this is the highest saturation magnetization among the reported magnetic material@graphene hybrids prepared via electroless plating. This study provides guidelines for the pretreatment of graphene via electroless plating and should contribute to future studies on the synthesis of magnetic material@graphene hybrids.

Mercury emission control: Phase II. Let’s now go passive

The US Environmental Protection Agency’s plan for a National set of standards limiting mercury emission from coal power plants has recently hit a setback. A decision by the US Supreme Court rejected this based on the two available methods having a burdensome cost basis. Moreover, even if the activated charcoal or bromine addition methods do become standard in the US, their cost may still inhibit global implementation. As a result it is timely to develop alternate methods. This paper outlines further development of such an approach. It is based on mercury’s own chemistry. Previous published work discovered that elemental mercury, although volatile, has a propensity for heterogeneous chemistry on warm non-catalytic surfaces. This paper now reports results of a second pilot plant test continuing its clarification, extension and further validation of practicality. It extends data to inexpensive base metal surfaces that can be used and indicates the extent of mercury control possible. This non-catalytic heterogeneous chemistry has been overlooked due to this disguising role of surfaces. It is this that now suggests a passive mitigation method, natural to the system. By providing inserted metal surfaces in the downstream flue gas flow, mercury can be chemically modified and controlled.

The Role of Supporting Electrolyte on the Electrocatalytic Reduction of Organic Halides on Nanostructured Silver Electrodes in Water

Over recent two decades, electrocatalytic reduction of halogenated organic compounds (HOCs) was successfully employed in electrosynthesis and abatement of environmental pollutants by their conversion to less harmful compounds [1, 2]. Halogenated organic compounds have been frequently used in industry and disposed into wastewater and air, despite their toxicity and suspected mutagenicity. Some of them, like chloroform, are also disinfection by-products commonly produced during the chlorination of water and wastewater. Due their refractoriness to typical oxidative water remediation techniques, HOCs became one of the most problematic group of pollutants. Electrocatalytic reduction was already proven as alternative, useful method of HOCs removal from organic solutions after prior water-based electrolyte exchange from aprotic medium. The scope of this study was to reduce HOCs in water environment/aqueous solutions and to examine the possibility of direct elimination of HOCs without a need for electrolyte change. The electrochemical reduction of organic halides in aprotic media generally proceeds via two-electron cleavage of the C–X bond, occurring at very negative potentials at non-catalytic electrode surfaces (e.g., glassy carbon), what is the biggest disadvantage of this process due to the high energy requirement. To shift the reduction threshold to less negative potentials and therefore lower the costs of the process, new materials with enhanced catalytic properties toward electrocatalytic reduction are intensively studied. Among them, silver attracted significant interest, due to the most powerful electrocatalytic properties toward reduction of a wide range of organic halides [3]. It is generally accepted that this effect is directly related with a strong affinity of halides to silver, by means of specific adsorption of halide atom to the Ag surface. It was reported in the literature that nanostructured silver particles exhibit similar or even better electrocatalytic properties toward reduction of HOCs than bulk Ag electrodes due to the increased surface to volume ratio [4, 5]. It is surprising that Ag nanowire arrays have only once been used as electrodes for electrocatalytic reduction of organic halides, namely chloropropane [6]. It is expected that silver nanowire array electrodes should exhibit at least similar or even better electrocatalytic properties as nanoparticles and offer better stability and efficiency. Therefore, the aim of this research was also to synthesize and investigate electrocatalytic behavior of nanostructured Ag electrodes with different morphologies, and compare the obtained results with a silver bulk electrode. The electrocatalytic measurements were performed in various supporting electrolytes in order to select the optimum one and assess its influence on the mechanism of electrocatalytic reduction of chloroform. The two-step anodization process in oxalic acid (H2C2O4) was used in order to obtain highly ordered anodic aluminum oxide (AAO) membranes that served as templates for the synthesis of silver nanowire arrays. The electrochemical anodization of aluminum is a cost-effective method that results in hexagonally arranged nanopores. The barrier layer at the pore bottoms was removed by using a potential-shock method that results in AAO membranes with through-hole pores. Then, a thin layer of Ag was sputter deposited, and finally, the electrodeposition of Ag nanostructures was carried out in a commercially available silver plating solution by applying a constant current density. The electrocatalytic properties of nanostructured Ag electrodes were investigated by various voltammetric techniques in aqueous solutions of several different supporting electrolytes, such as NaOH, KClO4, NaClO4, and NaH2PO4.

Photon-Assisted CVD Growth of Graphene Using Metal Adatoms As Catalysts

A photon-assisted CVD growth scheme of graphene using metal adatoms as catalysts at the edge of a graphene seed on noncatalytic surfaces, such as silicon dioxide (SiO2), hexagonal boron nitride (h-BN), and graphene, is reported based on first-principles calculations. We systematically examine the possible graphene edge reactions with carbon precursors such as methane, ethylene, or acetylene, using Cu and Ni adatoms as catalysts. The metal atoms adsorbed at the graphene edge capture the ambient ethylene or acetylene molecules, and initiate a series of edge reactions that would be energetically unfavorable in the absence of metal adatoms catalysts. We also suggest that ultraviolet photons can be used to dissociate the stable metal–ethylene or metal–acetylene complex in order to sustain the catalytic reactions. The growth rate of the graphene seed is shown to be slightly higher when on an h-BN or graphene substrate. In principle, this process could also be used to heal graphene defects between flakes or impr...

Selective Deposition of a Cross-Linked Low-Permittivity Polycarbosilane on Copper

Differential scanning calorimetry studies of the reaction of a cyclolinear polycarbosilane [cyclo-(CH3Si(CH2)2SiCH3)-(CH2)6]n on air-exposed Cu surfaces reveal a substantial enhancement of the cross-linking rate compared to noncatalytic surfaces, e.g., Au, Ag, Al, Si. The increased rate is attributed to surface Cu(II)-catalyzed opening of the embedded disilacyclobutane rings in the polymer. This rate enhancement is used to selectively deposit a cross-linked polycarbosilane on copper patterns in exclusion to the silicon substrate surface. These results could be attractive for realizing metal-dielectric interfaces for applications in nanodevice wiring and packaging.

Interconnection of Micropad Electrodes by Controlled “Extraneous” Deposition of Electroless NiB Film

A method of interconnecting micropad electrodes was developed by using the electroless of NiB for application to the flip-chip bonding technology. The phenomenon of bridge formation by the so-called deposition was utilized as a technique to perform selective of NiB on noncatalytic surfaces. The process of extraneous electroless was controlled by optimizing conditions so that the deposit grew anisotropically along the surface between the facing pads. Practical feasibility of this technique was demonstrated by forming an interconnection between pads separated by 5 μm and measuring 5 μm in both height and width. This method was applied successfully to interconnecting the pads forming an array with a pitch of 20 μm.

Wavelet-based Spatiotemporal Multiscaling in Diffusion Problems with Chemically Reactive Boundary

Chemically reacting flows over catalytic and non-catalytic surfaces are one of the elementary operations in chemical processing plants. The underlying physical phenomena span time- and length-scales over several orders of magnitude, for which a robust and flexible modeling framework must efficiently account for. With this purpose as the eventual goal, we propose a wavelet-based multiscale numerical framework and demonstrate it on coupling of two prototype methods for the problem of species generated on a chemically reactive boundary and diffusing through the bulk. The two methods consider different time and length scales. The first method in this coupling, termed fine, models the chemical reactions on the reactive boundary stochastically by the kinetic Monte Carlo method (KMC) and the diffusion in the medium deterministically using relatively small time increments and small spatial discretization mesh size. The second method, termed coarse, models both the reaction and the diffusion deterministically and uses drastically larger time increments and spatial discretization size than the fine model. The two methods are coupled by forming a spatiotemporal Compound Wavelet Matrix (CWM) that combines information about the time and spatial scales contained in them.

Crystal structure of the apoptosis-inducing human granzyme A dimer.

Granzyme A (GzmA) belongs to a family of trypsin-like serine proteases localized in cytoplasmic granules of activated lymphocytes and natural killer (NK) cells. In contrast to the related granzyme B (GzmB), GzmA forms a stable disulfide-linked homodimer and triggers target-cell death in a caspase-independent way. Limited proteolysis of a high-molecular-mass complex containing SET (also named putative HLA-associated protein II or PHAPII), PHAPI (pp32, leucine-rich acidic nuclear protein) and HMG2 by GzmA liberates NM23-H1, a Mg2+-dependent DNase that causes single-stranded breaks in nuclear DNA. By analyzing the dimeric GzmA structure at a resolution of 2.5 A, we determined the substrate-binding constraints and selective advantages of the two domains arranged as a unique functional tandem. The active sites of the two subunits point in opposite directions and the nearby noncatalytic surfaces can function as exosites, presenting substrates to the active site region of the adjacent partner in a manner analogous to staphylokinase or streptokinase, which present plasminogen to the cofactor-plasmin and cofactor-plasminogen complexes.

Validation of Surface Chemistry Models Using Low Pressure Stagnation-Point Flames: Measurements of OH Above Platinum Surfaces

Near-surface laser-induced fluorescence (LIF) measurements of OH axe performed in the post-flame region of low pressure hydrogen/oxygen flames in stagnation flows above catalytic and non-catalytic surfaces. Measurements of the normalized gradient of the OH number density near the surface are shown to be sensitive to changes in surface reaction rates, and thus can be used as a test of surface chemical mechanisms. In addition, such measurements do not require an absolute calibration, which increases the accuracy of the comparison. A comparison of the observed results for varying substrate temperature, system pressure, and flame equivalence ratio suggests that the recombination probability of OH on platinum is overpredicted in general by current surface models, and that the dependence of recombination on pressure is stronger than predicted. The qualitative trends for OH recombination with temperature and equivalence ratio are similar to predicted trends.

Towards the electroreduction of very weak acids

In order to improve the understanding of the synthesis of electrogenerated bases (EGB), the electrochemical reduction of two weak acids, 2-pyrrolidone (p K a (DMSO)=24.2 and hexamethyldisilazane (HMDS, p K a (DMSO)=26), has been compared in DME+HMPA+Et 4 NBF 4 solution using the sacrificial magnesium anode method in an undivided cell under constant current. Both acids are reduced at transition metal cathodes to form dihydrogen and their conjugate base (as evidenced by their deprotonation abilities) whereas no gas evolution is observed at non-catalytic surfaces such as glassy carbon. Kinetic studies of dihydrogen evolution at Pt, stainless steel, Fe and Ni, throughout the electrolysis showed different behavior: a theoretical current efficiency (CE=1) characterizes 2-pyrrolidone, but HMDS needs a latency period with slow gas evolution mainly corresponding to reduction of HMPA, followed by a faster and linear evolution period during which HMDS is predominantly reduced (51<CE<64%). All these data are consistent with a direct dissociative discharge mechanism for the NH bond reduction giving an adsorbed hydrogen atom on the metal surface. But 2-pyrrolidone verifies Evans’ peak potential correlation with a p K a value for ‘category II acids’, which corresponds to a diffusion controlled process, while HMDS behaves differently without any observable reduction peak, probably showing a charge transfer controlled mechanism.

Estimation of the effect of vibrational excitation of diatomic molecules on their diffusional transport and dissociation in a boundary layer

Relations for the diffusion fluxes of vibrationally highly excited diatomic molecules are found by means of the Chapman-Enskog method. On the basis of these relations a quantitative estimate of the changes in the diffusion coefficients under vibrational excitation and the corresponding changes in the macroscopic dissociation rate is obtained under conditions of disequilibrium of the upper vibrational levels of the dissociating molecules caused by the diffusion processes. The diffusion relations obtained are used in deriving the boundary conditions for the equations of level vibrational kinetics. A simplified version of this derivation is presented for noncatalytic and catalytic surfaces.

Heat-transfer on yawed infinite cylinders in a hypersonic stream

Nonequilibrium air flow past the nose of a yawed infinite elliptical cylinder in flight at an altitudeH=66 km and velocityV??=6500 m/s is investigated on the basis of the thin viscous shock layer equations. The ellipticity coefficient δ and the yaw angle χ are varied and calculations are carried out for both absolutely catalytic and absolutely noncatalytic body surfaces. The values of the parameter δ corresponding to the lowest maximum surface temperature are determined.

A computational study of methane-air combustion over heated catalytic and non-catalytic surfaces

A boundary layer model for the combustion of methane-air mixtures over a heated catalytic and noncatalytic surface maintained at constant temperature has been developed. Finite differences and a modified damped Newton's method were implemented to solve the coupled nonlinear parabolic partial differential equations for the conservation of total mass, momentum, energy, and chemical species. Adaptive gridding was used to obtain high resolution into the boundary layer and at the flame front. Detailed gas-phase chemistry was included in the model. The effect of different surface reaction boundary conditions on flame propagation and on the development of unstable species profiles in the gas-phase has been studied. An inert surface and a surface promoting gas-phase oxidation of the fuel to stable products have been simulated. In addition, the effect of desorption of hydroxyl radicals from the wall during the oxidation of the fuel on the unstable species profiles and on the propagation of the flame into the boundary layer was studied. The results illustrate the sensitivity of the predicted methane flame propagation on the surface boundary conditions used, which is more pronounced than for a hydrogen flame studied earlier.

The influence of catalytic activity on the ignition of boundary layer flows. Part III: Hydroxyl radical measurements in low-pressure boundary layer flows

The boundary layer ignition of fuel/air mixtures by heated catalytic (platinum) and noncatalytic (quartz) surfaces was studied through spatially resolved measurement of hydroxyl radicals at total pressures from 40 to 175 torr. Subatmospheric pressure operation increases both length scales and the ratio of surface/gas-phase reaction contribution to ignition, facilitating the study of the effect of surface catalytic activity on the initiation of gas-phase combustion. Fuels studied include ethane, acetylene, hydrogen, and methane, usually premixed in air. Ethane ignition was promoted by catalytic reaction at all equivalence ratios studied. This was a wider range of equivalence ratios evidencing catalytic enhancement than noted at atmospheric pressure in previous studies. At 70 torr, this enhancement was observed from 0.015 < Φ ≤ 0.5. Surface hydroxyl radical production rates were estimated for preignition conditions in the gas phase for ethane in air over both quartz and platinum surfaces. Combustion of hydrogen or acetylene in air at these conditions was not significantly affected by the catalytic activity of the surface, because for the reactions studied, gas-phase reaction was significant near the leading edge of the plate. N 2O substitution for O 2 severely inhibited the gaseous ignition of the ethane, hydrogen, and acetylene over platinum surfaces, and suppressed preignition OH concentrations to below our detection limits.

The influence of catalytic activity on the gas phase ignition of boundary layer flows Part II. Oxygen atom measurements

The process of gas phase ignition in a fuel-air boundary layer overa heated catalytic surface has been investigated using two-photon laser-induced fluorescence (LIF) measurement of oxygen atoms. The boundary layer was formed by flowing fuel-air mixtures over hot catalytic (platinum) and noncatalytic (quartz) surfaces, and simulates the entrance region of a catalytically stabilized thermal (CST) combustor. A unique optical design was required in order to eliminate interference with the fluorescence signal caused by thermal radiation from the hot surface of the plate. The O atom concentration profile data demonstrate that the platinum catalyst acts to promote the formation of oxygen atoms in the region adjacent to the surface. This effect is most apparent at lean equivalence ratios (Φ < 0.3 for ethane) where we have observed promotion of gas phase ignition by the catalytic surface. At higher equivalence ratios the ignition of ethane in air is inhibited by the platinum surface because of fuel depletion at the surface due to the mass transfer-limited catalytic oxidation reaction.

Gas Phase Ignition of a Premixed Combustible by Catalytic and Non-Catalytic Cylindrical Surfaces

Abstract An analysis is carried out of the gas phase ignition of a premixed combustible gas flowing under mixed convective conditions over a hot, non-catalytic or catalytic, cylindrical surface. The surface temperature of the cylinder is assumed to be constant. In the case of the catalytic surface it is also assumed that the catalytic reaction is infinitely fast so that chemical equilibrium is reached along the surface of the cylinder. In the gas, a finite rate chemical reaction with a large activation energy is considered. The analysis makes use of the boundary layer approximation to describe the gas flow and of first order matched asymptotic expansions to define ignition. Explicit expressions are derived for the critical gas phase Damkohler number for ignition as a function of the angular location. The results show that the value of the angular coordinate at which ignition takes place increases as the convective velocity and activation energy increase and as the initial temperature and initial fuci conc...

Effects of slip and chemical reaction models on three-dimensional nonequilibrium viscous shock-layer flows

Three-dimensional finite rate chemically reacting viscous shock-layer flows over complex geometries have been analyzed using seven- and eleven-species air models. The viscous shock-layer code for analyzing nonequilibrium flow over multiconics using a seven-species air model has been modified to include an elevenspecies air model. The viscous shock-layer code with seven-species model has been modified to include wall-slip conditions, and the results for fully catalytic and noncatalytic surfaces with slip are presented. For the cases under consideration, the surface-measurable quantities computed using the two models agree well with each other. Wall slip had negligible effect on electron number density, whereas with shock slip, an order of magnitude increase in electron density was predicted.