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To better understand the growth mechanism of diamond films via low-temperature chemical vapor deposition in a C-H-F atmosphere, this paper employed density functional theory based on first principle. It calculated the adsorption energy, reaction heat, and reaction energy barrier of H and F atoms undergoing extraction reactions on the hydrogen-terminated diamond surface. Additionally, the analysis included the adsorption of CF3, CF2, and CF growth groups on the active site substrate. The results show that compared with H atoms, F atoms are more likely to extract H from the surface of hydrogen terminated diamond and desorb it in the form of HF. This process is advantageous for generating more active sites at low temperatures in a C-H-F atmosphere. Both the structure and the absolute value of the adsorption energy of CF3, CF2, and CF groups are more favorable for the generation of the diamond phase after adsorption. Increasing the concentration of CF3, CF2, and CF growth groups appropriately can facilitate the growth of diamond phase at a higher rate.

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Janus particles are known to be useful to various fields such as biomolecule-probing sensors, reaction catalysts, surfactants, and so on. They have two chemically different surfaces which possess contradictory characteristics such as polarity, hydrophobicity, etc. Here, a simple fabrication of dumbbell-shaped Janus microparticles was tested by the chemical reaction of carboxyl groups and amino groups to form amide bonds. They were distributed to the interface between polyethylene glycol (PEG)-rich phase and dextran (DEX)-rich phase, while the unreacted particles having carboxyl groups located at the top PEG-rich phase and particles having amine ligands went to the bottom DEX-rich phase of an aqueous two-phase system (ATPS). The fabrication procedures, observations, and possible applications of results are discussed. [ABSTRACT FROM AUTHOR]

Hydrophobic characteristics are widely used in the development of new materials, especially to be applied to the surface coating of materials. This involves amplification of the light exposure on the hydrophobic surface for energy-efficient buildings and photovoltaic energy harvesting systems. The paper discusses the role super-hydrophobic nature of light dispersion falling on the water droplet of the taro leaf surface. Camera and video modes were used to get infrared ray images shot at the water droplet, in dark and bright spaces, with variations in the angle of rays incidence and the volume of droplet. The result shows that the waxy layer surface of the taro leaf has the main structure of alkanes/alkyne with active phenol and aldehydes groups, that peak in 2,648/cm. These active groups bind the atoms (free) of the leaf surface when the leaf surface is in normal conditions. The presence of water bubbles on the surface of the taro leaf causes air to be trapped in the cavity of the lump, forms a silvery layer, resulting in chemical reactions with Mg and K atoms, and dehydrogenation of hydrocarbons. These reactions form metal oxides and hydrogen gas. When the bubble is hit by light, the dispersion tends to strengthen at the light angle greater than 40°, due to the silvery coating of magnesium and potassium oxides and the activity of hydrogen gas, that lead to stronger surface tension and the electron mobility and strengthening water molecules bonds. The activities of these products accelerate atomic movement that amplifies the light energy into white light. This study is expected to be a consideration for the new hydrophobic materials design. Applications for surface coating that can amplify light irradiated on the super-hydrophobic surface are promising for energy-efficient buildings and photovoltaic energy harvesting. [ABSTRACT FROM AUTHOR]

Highlights • Electroviscous effect on pressure driven flow and heat transfer is studied. • The surface chemical reaction in microchannels is considered. • The boundary slip is considered. • Three different electrical boundary conditions are compared. Abstract This study investigates the fluidic flow and related heat transfer in a microchannel formed by two parallel plates. Uniform heat flux is applied at the walls with considering the surface chemical reaction, which determines the surface charge on the wall of the microchannel. Our results show that the pH and ionic concentration apparently affect the surface chemical reaction and the subsequent fluidic behavior and heat transfer in the microchannel, especially with the boundary slip. The dimensionless velocity and temperature increase with the ionic concentration. The difference of the dimensionless flow rate and the Nusselt number is obvious under three different electrical boundary conditions: constant surface charge density, constant zeta potential and MI model. Under the boundary slip, the dimensionless flow rate and Nusselt number decrease by 50% and 12%, respectively, with increasing pH under the MI model, but keep unchanged under constant zeta potential or surface charge model. The dimensionless flow rate and Nusselt number also increase with the ionic concentration due to weakened electroviscous effect. Meanwhile, the slip increases the influence of ionic concentration on the dimensionless flow rate and Nusselt number. The results of this work may guide the design and optimization of microfluidic devices. [ABSTRACT FROM AUTHOR]

In current research, surface reaction phenomena in several packed bed reactors have been considered. Flow field through several fractal Sierpinski carpet porous media have been simulate, using LBM. The endothermic Isopropanol dehydrogenization reaction has been considered as basic reaction mechanism and two major parameters: non-homogeneity and specific area in catalytic surface reaction have been investigated. To validate our numerical method, our results have been compared to a recent benchmark study, which adopted very well. In both cases, the porosity factor retained constant (ε=0.79). The results show that, by three times increase in specific area, the reactant conversion rate is increased significantly (approximately one order of magnitude) and the pressure drop is increased (nearly 5 times). Also, to consider non-homogeneity arrangement, the particle arrangements from small to large and from large to small have been considered. In both cases, the pressure drop is approximately the same. At low Re, reactant conversion of both arrangement are the same, but by increasing Re, the packed bed reactor with large to small arrangement has a little more reactant conversion. [ABSTRACT FROM AUTHOR]

To better understand chalcopyrite leach mechanisms and kinetics, for improved Cu extraction during hydrometallurgical processing, chalcopyrite leaching has been conducted at solution redox potential 750 mV, 35–75 °C, and pH 1.0 with and without aqueous iron addition, and pH 1.5 and 2.0 without aqueous iron addition. The activation energy (Ea) values derived indicate chalcopyrite dissolution is initially surface chemical reaction controlled, which is associated with the activities of Fe3+ and H+ with reaction orders of 0.12 and −0.28, respectively. A surface diffusion controlled mechanism is proposed for the later leaching stage with correspondingly low Ea values. Surface analyses indicate surface products (predominantly Sn2− and S0) did not inhibit chalcopyrite dissolution, consistent with the increased surface area normalised leach rate during the later stage. The addition of aqueous iron plays an important role in accelerating Cu leaching rates, especially at lower temperature, primarily by reducing the length of time of the initial surface chemical reaction controlled stage. [ABSTRACT FROM AUTHOR]

The leaching of naturally occurring magnesite in dilute ethanoic acid is achieved to optimize the reaction conditions affecting the reaction kinetics. In the current study effect of various reaction parameters (The particle size of ore, concentration of leaching agent, the reaction temperature and rate of stirring) on the dissolution of magnesium carbonate ore with aqueous solutions of acetic acid is probed. It is inferred that the rate of leaching reaction of magnesium carbonate ore in the aqueous solutions of acetic acid rises with a rise in temperature of reaction medium, acetic acid solution strength and decreases with the increase in particle size of the magnesite ore samples. The analysis of kinetic data done by the application of graphical and statistical approaches reveals that the leaching kinetics of magnesite ore in dilute solutions of acetic acid follows a surface chemically controlled mechanism. The calculated value of energy of activation for the dissolution reaction of magnesium carbonate in acetic acid is 46.39 kJ mol. [ABSTRACT FROM AUTHOR]

The extraction of tungsten from scheelite concentrate using phosphoric acid as chelating agent in nitric acid solutions was investigated. The effects of the leaching parameters, such as stirring speed, temperature, concentrations of HNO 3 and H 3 PO 4 as well as particle size were examined in order to model the kinetics of scheelite dissolution. It was determined that the leaching rate was practically independent of stirring speed and H 3 PO 4 concentration at an investigated range, while increased with increasing temperature and HNO 3 concentration. The leaching data agreed quite well with the shrinking core model, with surface chemical reaction as the rate-controlling step. The apparent activation energy was calculated as 52.91 kJ/mol, and the reaction order with respect to HNO 3 concentrations was determined to be 0.23. The leaching process using the shrinking sphere model was established as: 1 − 1 − x 1 / 3 = 3.2 × 10 2 C H N O 3 0.23 r 0 − 1 exp − 52910 R T . [ABSTRACT FROM AUTHOR]

The adsorption of sulfide on a Au(100) electrode from a 0.01 M NaOH + 0.5 mM Na 2 S electrolyte was studied by in situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV). Starting with a sulfur free electrode surface at low potentials the subsequent formation of a p(2 × 2)-S, a c(2 × 6)-S and a c(2 × 2)-S phase was observed during potential increase. Only the p(2 × 2)-S (Θ S = 0.25 ML) phase appears as a single species phase; the c(2 × 6)-S (Θ S = 0.33 ML) and the c(2 × 2)-S (Θ S = 0. 5 ML) phase are accompanied by the simultaneous appearance of additional “dimer” particles. Concomitant changes of the step morphology and the results of the electrochemical characterization strongly suggest that these additional particles contain both, sulfur and gold atoms. Upon further potential increase the formation of a phase consisting of ring-like units was found, which is well known for Au(111) surfaces in the presence of sulfur. This phase is, by analogy, interpreted as a gold sulfide compound formed under electrochemical conditions. [ABSTRACT FROM AUTHOR]

Abstract: We studied femtosecond laser-induced desorption of CO from Ru(0001) using intense near-infrared and visible femtosecond laser pulses. We find a pronounced wavelength dependence with a factor 3–4 higher desorption yield at comparable fluence when desorption is induced via 400nm light, compared to 800nm and attribute this difference to the difference in penetration depth of the incident light. All our data can be described using empirical friction-modeling to determine the desorption mechanism with the same mechanism for both wavelengths. We find that both hot electrons and phonons contribute to the desorption process. [Copyright &y& Elsevier]

Abstract: The adsorption of small amount of Cu onto 1×1-Pb/Si (111) and √3×√3R30°-Pb/Si (111) coexisting phases was studied with variable temperature scanning tunnelling microscopy and spectroscopy. The most significant features connected with the deposition of copper at room temperature appeared as tiny clusters randomly scattered over smooth 1×1-Pb islands. Behaviour of the clusters at room at low temperature assumed that Cu penetrates through inert 1×1-Pb layer and mixes up with silicon. Moderate thermal treatment of (Cu, Pb)/Si (111) system induced the formation of shallow depressions of variable shape and size that are embedded into 1×1-Pb phase. Tunnelling spectra taken over a particular depression showed the peaks typical for the copper silicides. Moreover, the temperature rise causes the formation of large objects of distinctive hexagonal shape on neighbouring √3×√3R30°-Pb/Si (111) structure. Filled and empty state STM images of the hexagons differ strongly suggesting covalent bonding between constituent atoms. Detailed analysis of the hexagonal objects (and their agglomerates) reveals the specific features of quasi-commensurate 5×5-Cu structure. [Copyright &y& Elsevier]

A selective drug-release system was prepared for a controlled drug release between hydrophobic and hydrophilic drugs by using a prepared membrane. A membrane was constructed by electrospun carbon fibers. A porous structure was created in the carbon fibers by chemical activation to reduce the initial drug-burst phenomenon by drug storage in the pores. The surface of the activated carbon fibers was modified by the addition of hydrophobic/hydrophilic functional groups by oxyfluorination or fluorination treatments to allow the selective release of mixed hydrophobic and hydrophilic drugs. The in vitro drug permeation was studied under various applied electric voltages. The initial drug-release phenomenon was reduced due to the storage effect by the improved pore structure, and the drug-release rate was controlled by the intensity of the applied electric voltage. In addition, selective drug release was observed with the presence of the hydrophobic or hydrophilic functional groups introduced through oxyfluorination or fluorination treatments. [ABSTRACT FROM AUTHOR]

Abstract: A Cu(001) surface was exposed to products of an azomethane pyrolysis doser at varying temperatures. In addition to methyl radical adsorption, for certain doser conditions one or more doser emergent species can undergo an activated adsorption on the copper face. Directly after exposures, temperature programmed desorption between 170K and 500K was used to indicate the relative concentrations of adsorbed atomic hydrogen and methyl species, and thermally induced surface reactions. Two methane desorption features were invariably observed, indicating the presence of adsorbed methyl groups (CH3) and transient adsorbed atomic hydrogen. The deduced relative surface concentrations levels of both H and CH3 depend on the total exposures and the operating temperatures of the azomethane pyrolysis doser. The initial H concentrations apparent at surface temperatures between 275K and 375K are shown to arise from defect-related methyl decomposition and, at high operating doser temperatures, from the initial adsorption of one or more activated Cu incident species. It is proposed that the distributions of vibrational energies of emergent molecular hydrogen or methane species from higher temperature dosers are non-thermal. Hence, with doser temperatures of 800°C or above, the effects of subsequent dissociative molecular adsorption on the copper surface can dominate over Cu defect chemistries. [Copyright &y& Elsevier]

Abstract: An original physical route is proposed to organize size-selected bimetallic nanoparticles on graphite surfaces. This approach is based on the soft landing of preformed clusters and is demonstrated for bimetallic AuxPt1−x clusters of different compositions. Particle coalescence is avoided thanks to cluster surface reactivity, leading to a self-assembly with a well-defined inter-particle separation (~1nm). [Copyright &y& Elsevier]

Abstract: We present a new reaction model for ammonia oxidation on a Pt (533) surface and perform numerical simulations using mean field equations. Kinetic parameters were taken from experiments and Density Functional Theory (DFT) calculations. The model is based on an oxygen-activated ammonia decomposition and includes NHx (x=0, 1, 2) intermediates. Reaction rates and coverages obtained from calculations show semiquantitative agreement with values from kinetic and in-situ XPS measurements up to 0.1mbar pressures. Pathways for ammonia oxidation were analyzed by varying kinetic parameters in the model, which provides new insights into the relative importance of different reaction steps. [Copyright &y& Elsevier]

Abstract: We have studied desorption of 13CO and H2O and desorption and reaction of coadsorbed, 13CO and H2O on Au(310). From the clean surface, CO desorbs mainly in, two peaks centered near 140 and 200K. A complete analysis of desorption spectra, yields average binding energies of 21±2 and 37±4kJ/mol, respectively. Additional desorption states are observed near 95K and 110K. Post-adsorption of H2O displaces part of CO pre-adsorbed at step sites, but does not lead to CO oxidation or significant shifts in binding energies. However, in combination with electron irradiation, 13CO2 is formed during H2O desorption. Results suggest that electron-induced decomposition products of H2O are sheltered by hydration from direct reaction with CO. [Copyright &y& Elsevier]

Abstract: One to three layers of Ag grown on a Au(111) electrode were studied by cyclic voltammetry in chloride and bromide solutions and by ex-situ near-edge X-ray absorption fine structure spectroscopy at the Ag L3-edge (Ag L3-NEXAFS). The one and two layers obtained by underpotential deposition exhibited reduced intensity at the absorption edge in the Ag L3-NEXAFS spectra, which suggests the gain of d-electrons in these layers. The cyclic voltammograms and the Ag L3-NEXAFS spectra indicate that the second and third layers of Ag halogenated at positive potentials, whereas the first layer remained in metallic form. [Copyright &y& Elsevier]

Abstract: To understand the first polymerization steps between benzene-diboronic acid (BDBA) and hexahydroxy-triphenylene (HHTP) molecules, the peculiar self assemblies of HHTP molecules on an Ag(111) surface have been investigated in terms of substrate temperature during evaporation. Interaction of these different molecular structures with BDBA moieties has been researched. The results show that polymer tecton is based on an oligomer composed of one BDBA surrounded by two HHTPs, its shape being independent of the surrounding HHTP network. The geometry and functionality of this tecton determines the shape of the final structures obtained after covalent bonding. [Copyright &y& Elsevier]

Abstract: Removal of toxic species such as As, Se, and S is critical to the successful implementation of high efficiency Integrated Gasification Combined Cycle (IGCC) processes for coal utilization. In this work we study the initial low-coverage surface reactions of AsH3, H2Se and H2S with a regenerable sorbent, zinc orthotitanate (Zn2TiO4), using first principles density functional theory. AsH3 adsorbs more preferentially on oxygen-rich (010) surfaces, while H2Se and H2S are more favorably bound to metal-rich (010) surfaces. We calculated the dissociation pathways and rates for each adsorbed species, finding that dehydrogenation of AsH3, H2Se, and H2S should be facile on these surfaces at the high temperatures relevant for IGCC processes. [Copyright &y& Elsevier]

Abstract: We have calculated chemisorption energies for different sorbates on cluster models for a number of sites on pure and subsurface rhenium-doped cobalt surfaces. Bonding energies follow the trend water

Abstract: The substrate reactions of three common oxygen sources for gate oxide deposition on the group III rich InAs(0 0 1)-(4×2)/c(8×2) surface are compared: water, hydrogen peroxide (HOOH), and isopropyl alcohol (IPA). Scanning tunneling microscopy reveals that surface atom displacement occurs in all cases, but via different mechanisms for each oxygen precursor. The reactions are examined as a function of post-deposition annealing temperature. Water reaction shows displacement of surface As atoms, but it does not fully oxidize the As; the reaction is reversed by high temperature (450°C) annealing. Exposure to IPA and subsequent low-temperature annealing (100°C) show the preferential reaction on the row features of InAs(0 0 1)-(4×2)/c(8×2), but higher temperature anneals result in permanent surface atom displacement/etching. Etching of the substrate is observed with HOOH exposure for all annealing temperatures. While nearly all oxidation reactions on group IV semiconductors are irreversible, the group III rich surface of InAs(0 0 1) shows that oxidation displacement reactions can be reversible at low temperature, thereby providing a mechanism of self-healing during oxidation reactions. [Copyright &y& Elsevier]

Abstract: Temperature programmed desorption (TPD), electron energy loss spectroscopy (ELS) and low energy electron diffraction (LEED) were used to study the interaction of molecular oxygen with the (2×1) reconstructed surface of hematite α-Fe2O3(011­2) under UHV conditions. The (2×1) surface is formed from vacuum annealing of the ‘ideal’ (1×1) surface and possesses Fe2+ surface sites based on ELS. While O2 does not stick to the (1×1) surface at 120K, the amount of O2 that can be reversibly adsorbed at 120K on the (2×1) surface was estimated to be ∼0.5 ML (where 1 ML is defined as the Fe3+ surface coverage on the ideal (1×1) surface), with additional O2 that is irreversibly adsorbed based on subsequent H2O TPD. Molecularly and dissociatively adsorbed O2 modifies the surface chemistry of H2O both in terms of enhanced OH stability (relative to either the (1×1) or (2×1) surfaces) and in the blocking of H2O adsorption sites. While O2 adsorption at 120 to 300K does not transform the (2×1) surface into the (1×1) surface, the influence of O2 on the (2×1) surface involves both charge transfer from surface Fe2+ sites and formation of an ordered c(2×2) structure resulting from O2 dissociation. [Copyright &y& Elsevier]

Abstract: The kinetics of NO desorption and its decomposition on Rh(111) surfaces have been simulated by using a dynamic Monte Carlo method. During the simulations, we used a triangular lattice that mimics the Rh(111) phase. NO decomposition was studied at low pressure and temperatures ranging from 120 to 1000K. The present analysis incorporates recent experimental evidence showing that N2 production occurs either from the classical N+N recombination step or by the formation and successive decay of an (N–NO)* intermediate species. Moreover, N2 and NO desorption rates are enhanced and the NO dissociation rate is inhibited by coadsorbed NO, N, and O species as nearest neighbors. These effects are taken into account in this study, along with the experimental adsorption, desorption, dissociation, and diffusion rates of the reactants. Our simulations are consistent with the experimental results of TPD spectra and can explain the formation of two peaks, δ-N2 and β-N2, as a natural consequence of the reaction mechanism herein proposed. Comparisons with different mechanisms used by other authors are also made. [Copyright &y& Elsevier]

Abstract: Surface properties of polycrystalline hydrogenated diamond produced by chemical vapour deposition upon oxidation under UV irradiation are studied. The diamond surfaces were cleaned in vacuum by thermal treatment. They were characterized estimating the electron affinity of the virgin surface by UV photoelectron spectroscopy and controlling the surface composition by X-ray photoelectron spectroscopy. The cleaned surfaces were then exposed to pure oxygen and UV radiation (deuterium lamp). Ozone induced surface oxidation was verified by XPS estimating the oxygen atomic concentration and the presence of specific chemical bonds. Surface oxidation was also verified analyzing the change in the diamond electron affinity. Oxygen was then removed in situ by a series of thermal treatments at increasing temperature. Already at ∼300°C a remarkable reduction of the oxygen concentration occurs which persists increasing the annealing temperature. Contemporary, a progressive recovery of the initial electron affinity is also obtained. These effects are observed up to 970°C, a temperature at which the electron affinity assumes a negative value. Specific chemical reactions are hypothesized to describe the oxidation process and to explain the electronic behaviour of the diamond surface. [Copyright &y& Elsevier]

Abstract: The influence of electric fields on the low temperature oxidation of individual nanoscale tungsten wires was investigated. In the experiments at room temperature, the nanowires were biased as anode opposite to a macroscopic cathode and H2O-vapor with a pressure of 10−7–101 mbar was provided as oxygen source. Under the influence of an electric field, a dramatic change of the oxidation behavior is observed with the formation of several 10nm thick oxide layers for electric fields exceeding a threshold. The chemical composition of the layers formed is determined with laser-assisted atom probe tomography to be slightly understoichiometric WO3. After an initial period of fast growth, the oxidation rate later rapidly decreases to immeasurable low values. Evaluation of the electric field distribution in the vicinity of the sample by the finite element method reveals that oxide formation only proceeds if a critical field in the range of 0.7–5.0V/nm, depending on the H2O-pressure, is present. This critical field is attributed to a field-activated reaction of H2O at the oxide–vapor interface. Besides for tungsten, field-induced oxidation is also observed for aluminum and p-doped silicon and thus apparently is a widely material independent phenomenon. [Copyright &y& Elsevier]

The thermal decomposition of dimethyl methylphosphonate (DMMP) on crystalline ceria thin films grown on Ru(0001) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and infrared absorption reflection spectroscopy (IRAS). TPD experiments show that methanol and formaldehyde desorb as the two main products at 575K, while water, formaldehyde and CO are produced above 800K. IRAS studies demonstrate that DMMP adsorbs via the phosphoryl oxygen at 200K, but the P=O bong converts to a bridging O—P—O species at 300K. DMMP decomposition initially occurs via P—OCH3 bond scission to form methyl methylphosphonate (MMP) and methyl phosphonate (MP) between 300 and 500K; XPS and IRAS data are consistent with a methoxy intermediate on the surface at these temperatures. The more stable P—CH3 bonds remain intact up to 700K, and the only surface intermediate at higher temperatures is believed to be POx. Although the presence of POx decreases activity for DMMP decomposition, some activity on the ceria surface remains even after 7 cycles of adsorption and reaction. The ceria films become reduced by multiple DMMP adsorption-reaction cycles, with the Ce+4 content dropping to 30% after seven cycles. Investigations of DMMP reaction on reduced ceria surfaces show that CO and H2 are produced in addition to methanol and formaldehyde. Furthermore, DMMP decomposition activity on the reduced ceria films is almost completely inhibited after only 3 adsorption-reaction cycles. Similarities between DMMP and methanol chemistry on the ceria films suggest that methoxy is a key surface intermediate in both reactions. [Copyright &y& Elsevier]

Abstract: The adsorption and thermal decomposition of N-methylaniline (NMA) on the Pt(111) surface has been studied with reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). NMA adsorbs molecularly at 85K through the nitrogen lone pair and is stable up to 300K. At temperatures of 300–350K it converts to two or more surface intermediates including the N-methyleneaniline (NMEA) species. This NMEA intermediate dissociates upon annealing to 450K, and further annealing leads to the desorption of HCN and H2, leaving only C on the surface at 800K. [Copyright &y& Elsevier]

Abstract: Seven soda-lime silicate glasses, each of which contains one of the following polyvalent metals: Fe, Mn, Cu, Ce, Ti, V, and Cr, are oxidized in air and reduced in H2/N2 (1/99) at their respective glass transition temperature for some period. A crystalline oxide surface layer is created on the glasses (except the vanadium-bearing glass) under the oxidizing condition, since the metallic ions are oxidized from lower to higher valence state, and thereby calcium ions diffuse outward and react with oxygen ions. In contrast, a silica-rich surface layer is created on the glasses under the reducing condition, since sodium and calcium ions diffuse inward. It is found that the extents of both outward and inward diffusions strongly depend on the type of the polyvalent ions for the same conditions of heat-treatment. Out of the seven polyvalent metals studied in this work, copper induces the highest extent of both the inward and outward diffusion, and hence, the thickest surface layer of both amorphous silica and crystalline alkaline earth oxides. The oxide layer lowers the onset temperature of the primary crystallization. The silica-rich surface layer enhances the chemical resistance of the glass in a hot basic solution. [Copyright &y& Elsevier]

Abstract: We discuss the interaction between adsorbing ammonia molecules and pre-adsorbed ammonia fragments on the Si(001) surface, searching for experimental evidence of a H-bonded precursor state predicted by modelling. While correlations along dimer rows have already been identified, these mix substrate-mediated effects due to dimer buckling with ammonia–adsorbate effects. Correlations between fragments on neighbouring dimer rows are not affected by substrate effects (in this system), allowing an analysis of direct ammonia–adsorbate effects. We present an analysis of cross-row correlations in existing high-coverage STM data which shows significant correlations between NH2 groups on neighbouring dimer rows over a significant range, providing evidence for the H-bonded precursor state with a range of around 10Å. We discuss implications for the interpretation of STM images of ammonia on Si(001). [Copyright &y& Elsevier]

Abstract: In this paper we review the preparation and reaction properties of ordered SmRh surface alloys and SmO x /Rh(100) model catalyst which have been systematically investigated by low energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS) and temperature desorption spectroscopy (TDS). The growth of Sm on Rh(100) at room temperature follows the Stranski-Krastanov mode. Thermal treatment of the Sm films on Rh(100) leads to the formation of ordered SmRh surface alloys. An “inverse” SmO x /Rh(100) model catalyst is produced under controlled oxidation of the SmRh surface alloy. CO adsorption on the SmRh alloy and SmO x /Rh(100) surfaces gives rise to five TDS characteristic features originating from different adsorption sites. Both the site blocking of SmO x and the electron transfer between SmO x and Rh substrate significantly affect the CO adsorption. Acetate decomposition on both Rh(100) and the SmO x /Rh(100) surfaces are found to undergo two competitive pathways that yields either (i) CO(a) and O(a) or (ii) CO2(g) and H2(g) at high temperature. The reactive desorption of acetic acid on SmO x /Rh(100) is dramatically different from that on Rh(100). A rapid decomposition of acetic acid to produce CO(g) and CO2(g) can be observed only on SmO x /Rh(100), where CO(g) becomes the predominant product at 225K, indicating a strong promotional effect of SmO x in the selective decomposition of acetate. Finally, we briefly describe the future outlook of research on rare earth oxide/metal model catalysts. [Copyright &y& Elsevier]

Abstract: A recently published first-principles model for the ammonia synthesis on an unpromoted Ru-based catalyst is extended to also describe ammonia decomposition. In addition, further analysis concerning trends in ammonia productivity, surface conditions during the reaction, and macro-properties, such as apparent activation energies and reaction orders are provided. All observed trends in activity are captured by the model and the absolute value of ammonia synthesis/decomposition productivity is predicted to within a factor of 1–100 depending on the experimental conditions. Moreover it is shown: (i) that small changes in the relative adsorption potential energies are sufficient to get a quantitative agreement between theory and experiment () and (ii) that it is possible to reproduce results from the first-principles model by a simple micro-kinetic model (). [Copyright &y& Elsevier]

Abstract: The interaction of NO with the O-rich RuO2(110) surface, exposing coordinatively unsaturated O-bridge, O-cus, and Ru-cus atoms, was studied at 300K by thermal desorption spectroscopy (TDS) and high-resolution electron energy-loss spectroscopy (HREELS). The conclusions are validated by isotope substitution experiments with 18O. During exposure to NO an O···N–O surface group (NO2-cus) is formed with O-cus. Additionally, a smaller number of empty Ru-cus sites are filled by NO-cus. If one warms the sample to 400K, NO2-cus does not desorb but decomposes into O and NO again, the latter being either released into gas phase or adsorbed as NO-cus. With O-bridge such a surface group is not stable at 300K. Our experiments further prove that O-cus is more reactive than O-bridge. [Copyright &y& Elsevier]

Abstract: The most successful method to unravel the microscopic mechanisms governing reactions in heterogeneous catalysis is the “surface science” approach which is based on well-controlled studies on model catalysts (usually single crystal surfaces) under ultrahigh vacuum (UHV) conditions [G. Ertl, Angew. Chem. 47 (2008) 3524]. In this review our recent vibrational spectroscopic studies on selected model reactions at various single-crystalline metal oxide surfaces are summarized. Two vibrational spectroscopic methods, high resolution electron energy loss spectroscopy (HREELS) and Fourier-transform infrared spectroscopy (FTIRS), were applied to characterize the adsorbed species and to elucidate the elementary processes of chemical reactions at oxide surfaces ranging from well-defined single crystals to modified surfaces with deliberately introduced defects. The combination of both methods allows us to extend the vibrational spectroscopic studies from ideal to complex systems. [Copyright &y& Elsevier]

Abstract: Recent progress and future developments in angle-resolved measurements of desorbing surface reaction products are reviewed for the analysis of surface species. Spatial and energy distributions of desorbing products with hyperthermal energy deliver the most direct structural information of the transition state including active intermediates and product formation sites. Knowledge of the desorption mechanism is requisite to achieve structural information since the method is directly linked to the chemical process. Structural analyses are exemplified in photoinduced O2 desorption and CO oxidation, and compared with those from thermal N2O decomposition and CO oxidation as well as their applications to steady-state catalytic processes. [Copyright &y& Elsevier]

Abstract: A computer algorithm was developed to automatically track the displacement of straight step edges between sequential scanning probe microscopy images of single-crystal surfaces. The program utilizes the Canny edge detection algorithm followed by the Hough Transform of the edge map to identify step edges according to their direction, relative to the image axes, and according to their displacement, relative to the image origin. The tracking of individual steps is facilitated by the fact that straight edges in general maintain their direction and therefore, steps of similar displacement but different direction can be sorted. The algorithm is based on the assumption that the rate of image acquisition is much greater than the rate of (mono)layer growth/dissolution, requiring that changes in step displacement are small in successive images. The change in step displacement in sequential images leads directly to the calculation of the step speed. By tabulating all changes in step displacement through a sequence of images, a statistical representation of the step edge data is produced. The program was evaluated using a sequence of 20 atomic force microscopy images from a calcite (104) surface growing from a supersaturated aqueous solution. The program required, in total, 5 CPU-minutes running on a Pentium 4 processor to compute the mean step speed with 60% precision whereas the equivalent number of measurements performed “by hand” required 6 person-hours at 70% precision. For comparable output, the computer program therefore represents a factor of about 100 decrease in required effort. [Copyright &y& Elsevier]