Infrared Reflection Absorption Research Articles

Tyrosinase enzyme Langmuir monolayer: Surface chemistry and spectroscopic study

This study investigates the surface chemistry properties of the tyrosinase enzyme Langmuir monolayer at air-aqueous interface using sodium chloride in the subphase to induce the surface activity of the enzyme. Investigation of surface packing and stability of the tyrosinase Langmuir monolayer were performed using surface chemistry experiments while spectroscopic analysis was done to study enzyme conformation. It was found that the tyrosinase enzyme forms a fluid film at air-aqueous interface with good stability as shown by compression-decompression cycles experiments and stability measurements at various surface pressures. UV-vis absorption and fluorescence measurements at different surface pressures revealed that the Langmuir monolayer has good homogeneity with no evidence of aggregates during compression. To gain insight on the conformation of tyrosinase Langmuir monolayer p-polarized infrared-reflection absorption spectroscopy was used. It was found that at high surface pressures the predominant secondary structures were β-sheets while at lower surface pressure both α -helices and β-sheets were present. The circular dichroism spectra were obtained by transferring the Langmuir monolayer at 10 mN.m−1 to a solid quartz support (Langmuir-Blodgett film, LB film), which showed that the major conformation present were α-helices. Images from the immobilized LB films were obtained using atomic force microscopy which showed homogenous and regular deposition with a mean thickness ranging from 3 to 4 nm.

Liquid-Phase Epitaxial Growth of Highly Oriented and Multivariate Surface-Attached Metal-Organic Frameworks.

Multivariate metal-organic frameworks (MTV-MOFs) incorporating multiple chemical functionalities within single-phase crystalline materials show superior properties that arise from synergistic effects. Herein, we report an efficient and versatile method for the growth of highly oriented multivariate surface-attached MOFs (MTV-SURMOFs) by the combination of the liquid-epitaxial growth method (LPE) and the mixed-linker strategy. Twenty-six MTV-SURMOFs of the [M2L2P] type with a maximum of five different dicarboxylate linkers (L) were deposited onto suitably functionalized surfaces. Systematic studies by infrared reflection absorption (IRRA) spectroscopy and surface XRD provide evidence for the formation of highly oriented MTV-SURMOFs. Interestingly, the pKa's of the dicarboxylate linkers play a crucial role for the orientational quality of the MTV-SURMOFs. In addition, benzene uptake experiments showed that the MTV-SURMOFs exhibit up to 2.6 times higher adsorption capacity as compared to the single-linker SURMOFs, demonstrating the synergistic effects in these surface systems.

Optical Properties of Plasmonic Nanoantennas Based on Arrays of Interacting V-Shaped Structures in the Mid-IR Range

Polarization-selected IR transmission, IR reflection, and IR absorption spectra of arrays of V-shaped gold structures are experimentally studied for various structure periods. To form a local region of the enhanced electromagnetic field in subwavelength nanogaps, arrays with unit cells consisting of two V-shaped structures, facing each other by acute angles with gaps of 0, 50, 100 nm were also used. The results of comparison of spectral data with measurements of dimensional parameters using atomic-force microscopy and scanning electron microscopy are presented. The possibility of using the fabricated structures to achieve the effect of surface-enhanced IR absorption by quantum dots is shown.

Structural Evolution of Water on ZnO(10 0): From Isolated Monomers via Anisotropic H-Bonded 2D and 3D Structures to Isotropic Multilayers.

The surface chemistry of water on zinc oxides is an important topic in catalysis and photocatalysis. Interaction of D2O with anisotropic ZnO(101‾ 0) surfaces was studied by IR reflection absorption spectroscopy using s‐ and p‐polarized light incident along different directions. Interpretation of the experimental data is aided using isotopologues and DFT calculations. The presence of numerous species is revealed: intact monomers, a mixed 2D D2O/OD adlayer, an anisotropic bilayer, and H‐bonded 3D structures. The isolated water monomers are identified unambiguously at low temperatures. The thermally induced diffusion of water monomers occurs at elevated temperatures, forming dimers that undergo autocatalytic dissociation via proton transfer. Polarization‐ and azimuth‐resolved IR data provide information on the orientation and strength of H‐bonds within the 2D and 3D structures. Ab initio molecular dynamics simulations reveal strong anharmonic couplings within the H‐bond network.

Structural Evolution of Water on ZnO(100): From Isolated Monomers via Anisotropic H‐Bonded 2D and 3D Structures to Isotropic Multilayers

AbstractThe surface chemistry of water on zinc oxides is an important topic in catalysis and photocatalysis. Interaction of D2O with anisotropic ZnO(10 0) surfaces was studied by IR reflection absorption spectroscopy using s‐ and p‐polarized light incident along different directions. Interpretation of the experimental data is aided using isotopologues and DFT calculations. The presence of numerous species is revealed: intact monomers, a mixed 2D D2O/OD adlayer, an anisotropic bilayer, and H‐bonded 3D structures. The isolated water monomers are identified unambiguously at low temperatures. The thermally induced diffusion of water monomers occurs at elevated temperatures, forming dimers that undergo autocatalytic dissociation via proton transfer. Polarization‐ and azimuth‐resolved IR data provide information on the orientation and strength of H‐bonds within the 2D and 3D structures. Ab initio molecular dynamics simulations reveal strong anharmonic couplings within the H‐bond network.

A Molecular Approach for Mitigation of Aluminum Pitting based on Films of Zinc(II) and Gallium(III) Metallosurfactants.

The use of metallosurfactants to prevent pitting corrosion of aluminum surfaces is discussed based on the behavior of the metallosurfactants [ZnII (LN2O2 )H2 O] (1) and [GaIII (LN2O3 )] (2). These species were deposited as multilayer Langmuir-Blodgett films and characterized by IR reflection absorption spectroscopy and UV/Vis spectroscopy. Scanning electron microscopy images, potentiodynamic polarization experiments, and electrochemical impedance spectroscopy were used to assess corrosion mitigation. Both metallosurfactants demonstrate superior anticorrosion activity due to the presence of redox-inactive 3d10 metal ions that enhance the structural resistance of the ordered molecular films and limit chloride mobility and electron transfer.

Low‐Temperature Synthesis of Oxides in Ionic Liquids: Ozone‐Mediated Formation of Co3O4 Nanoparticles Monitored by In Situ Infrared Spectroscopy

AbstractFor most functional oxides, structure‐selective synthesis is the key for the task‐specific production of nanomaterials. Herein, the low‐temperature synthesis in ionic liquids (ILs) is an attractive strategy to produce nanomaterials which are not accessible otherwise is described. In this study, a bench‐scale synthesis route toward Co3O4 by applying O3 on the molecular precursor Co2(CO)8 in IL medium is reported. The Co3O4 nanoparticles (NPs) are characterized by infrared (IR) spectroscopy, X‐ray diffraction (XRD), and transmission electron microscopy (TEM). This protocol yields Co3O4 with good crystallinity and narrow size distribution. In addition to conventional materials characterization, a new experimental approach is described in which the material synthesis in situ by IR reflection absorption spectroscopy (IRAS) (in situ IRAS) is followed. The in situ approach provides additional information on the growth mechanisms and kinetics and confirms that O3 treatment of Co2(CO)8 in IL exclusively yields pure Co3O4 without the formation of byproducts or intermediates.

Electrochemical Valorization of Glycerol on Ni-Rich Bimetallic NiPd Nanoparticles: Insight into Product Selectivity Using in Situ Polarization Modulation Infrared-Reflection Absorption Spectroscopy

Glycerol partial electrooxidation was studied on NixPd1–x (x = 100, 95, 90, and 80 atom %) nanoparticles synthesized using a polyol method. The shape-controlled urchin-like monometallic Ni and spherical NixPd1–x catalysts were synthesized. The morphology, crystal structure, and composition of Ni-rich catalysts were characterized using a number of physicochemical techniques. Detailed electrochemical characterizations showed that Ni and NixPd1–x NPs are active for GEOR and that the reaction follows either the direct electron transfer mechanism at low glycerol concentrations or the indirect electron transfer mechanism at high concentration. Among all investigated electrocatalysts, Ni80Pd20 exhibited the highest current density at lower overpotentials due to both a synergetic effect of Ni and Pd and the smaller particle size of Ni80Pd20. In situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) at various anodic potentials allowed discriminating the reaction products and intermediates directly on the electrode surface and in the electrolyte solution. PM-IRRAS showed that the main reaction products on NixPd1–x are glyceraldehyde, carbonyl groups for mesoxalate and tartronate ions, carboxylate ions, and traces of carbon dioxide. NixPd1–x catalysts are promising anode materials for glycerol oxidation to value added products and could be potentially combined with cathodic hydrogen production or CO2 electro-reduction processes in alkaline media.

Surfactant Charge Modulates Structure and Stability of Lipase-Embedded Monolayers at Marine-Relevant Aerosol Surfaces.

Lipases, as well as other enzymes, are present and active within the sea surface microlayer (SSML). Upon bubble bursting, lipases partition into sea spray aerosol (SSA) along with surface-active molecules such as lipids. Lipases are likely to be embedded in the lipid monolayer at the SSA surface and thus have the potential to influence SSA interfacial structure and chemistry. Elucidating the structure of the lipid monolayer at SSA interfaces and how this structure is altered upon interaction with a protein system like lipase is of interest, given the importance of how aerosols interact with sunlight, influence cloud formation, and provide surfaces for chemical reactions. Herein, we report an integrated experimental and computational study of Burkholderia cepacia lipase (BCL) embedded in a lipid monolayer and highlight the important role of electrostatic, rather than hydrophobic, interactions as a driver for monolayer stability. Specifically, we combine Langmuir film experiments and molecular dynamics (MD) simulations to examine the detailed interactions between the zwitterionic dipalmitoylphosphatidylcholine (DPPC) monolayer and BCL. Upon insertion of BCL from the underlying subphase into the lipid monolayer, it is shown that BCL permeates and largely disorders the monolayer while strongly interacting with zwitterionic DPPC molecules, as experimentally observed by Langmuir adsorption curves and infrared reflectance absorbance spectroscopy. Explicitly solvated, all-atom MD is then used to provide insights into inter- and intramolecular interactions that drive these observations, with specific attention to the formation of salt bridges or ionic-bonding interactions. We show that after insertion into the DPPC monolayer, lipase is maintained at high surface pressures and in large BCL concentrations by forming a salt-bridge-stabilized lipase-DPPC complex. In comparison, when embedded in an anionic monolayer at low surface pressures, BCL preferentially forms intramolecular salt bridges, reducing its total favorable interactions with the surfactant and partitioning out of the monolayer shortly after injection. Overall, this study shows that the structure and dynamics of lipase-embedded SSA surfaces vary based on surface charge and pressure and that these variations have the potential to differentially modulate the properties of marine aerosols.

Effect of silsesquioxane addition on the protective performance of fluoropolymer coatings for bronze surfaces

Two types of innovative coatings based on fluoroethylene/vinylether alternating copolymers are investigated as protective systems for bronze works-of-art. The influence of a polyhedral oligomeric silsesquioxane (POSS), i.e. open-cube trisilanol-heptaisooctyl-POSS, on the surface, mechanical, optical and electrochemical properties of coatings is examined. It is found that the isooctyl groups in the organic shell of POSS cause an increase in the hydrophobicity of the surface. On the other hand, nanoindentation tests show that the reduced modulus, hardness and plasticity index decrease with the addition of POSS, while abrasion resistance is slightly improved. Haze of coatings increases when POSS nanoparticles are present. More importantly, a beneficial effect of POSS addition on the protective efficiency against corrosion is assessed by exposure of coatings to acidic vapours and electrochemical treatments. In this regard, potentiodynamic polarisation clearly shows that the protective efficiency is systematically larger for coatings comprising POSS. The ex situ IR reflection-absorption spectroelectrochemistry shows that cuprous oxide can eventually form at the coating|bronze interface, which is identified through the spectroelectrochemistry of unprotected bronze.

Low-temperature V-oxide film for a flexible electrochromic device: Comparison of its electrochromic, IR and Raman properties to those of a crystalline V2O5 film

Manufacturing of flexible electrochromic (EC) devices requires the use of low-temperature films for deposition on electronically conductive foils. With this aim, low-temperature V-oxide films were spin-coated from a dispersion prepared by milling of crystalline V2O5 powder in vanadium(V) tri-n-propoxide oxide/isopropanol sol as dispersant. TEM images showed that the milling procedure enables the introduction of some V2O5 nanocrystallites into the matrix of the V-oxide pigmented film prepared at 150 °C. The electrochromic properties were analyzed using in situ UV–visible absorbance spectroelectrochemistry. The low transmittance values of as-prepared pigmented films revealed the presence of a greater amount of reduced V4+ centers compared to the crystalline sol-gel V2O5 model films. Significant bleaching of pigmented V-oxide films occurred during subsequent 521 cycles in the safe potential range.Three different types of vibrational spectroscopies were applied to examine the powdered V-oxide film, and the results were compared to the band changes for the sol-gel crystalline V2O5 films. For initial films, the modes in the IR reflection-absorption spectra were systematically shifted to higher wavenumbers with regard to the modes in the IR absorbance spectra. Both IR techniques confirmed the reversible shift of the vanadyl V-OA band to lower frequencies and the disappearance of the bridging V-OB-V mode upon intercalation. Raman spectra showed the appearance of two vanadyl stretching modes at 986 and 961 cm−1 that occurred simultaneously with the decrease in the intensity of the bands in the 750–400 cm−1 spectral region. After the deintercalation, the Raman spectra of the low-temperature films showed broad bands that remained after the second bleaching. Finally, a flexible NiO1-x/ormolyte/V-oxide EC device was constructed. The device was composed of two different pigmented films and demonstrated the practical applicability of the low-temperature pigmented films.

Orientation of Oligopeptides in Self-Assembled Monolayers Inferred from Infrared Reflection-Absorption Spectroscopy.

A series of a single tryptophan containing oligo-alanine peptides were recently characterized as conductive molecules that enable electron transport between electrodes. IR reflection-absorption of self-assembled monolayers of such peptides on gold surfaces revealed that the relative intensities of amide I and II bands in the respective spectra depend on the tryptophan residue position in the oligopeptide sequence. This indicates different average peptide orientations with respect to the normal onto the carrying gold surface. We developed a model which calculates the polarized reflectivities of the amide I and II bands as function of the angle of the incident light, the average peptide orientation and the relative orientations of peptide group at the N-terminal. The orientation and strength of vibrational transition dipole moments were calculated by employing an excitonic coupling approach which considers probable conformational distributions of the disordered peptides. Our results revealed that the position of the tryptophan can affect the effective tilt angle of the peptide as well as the orientation of transition dipole moments with respect to the reflection plane. We have also calculated the average end to end distances of the examined peptides and found them to be in reasonable agreement with experimental values determined by ellipsometry. Some evidence is obtained for the notion that increasing the tilt angle of the investigated peptides reduces their conductivity.

Effect of the Interfacial Water Structure on the Hydrogen Evolution Reaction on Pt(111) Modified with Different Nickel Hydroxide Coverages in Alkaline Media.

The hydrogen evolution reaction (HER) constitutes one of the most important reactions in electrochemistry because of the value of hydrogen as a vector for energy storage and transport. Therefore, understanding the mechanism of this reaction in relation to its pH dependence is of crucial importance. While the HER on Pt(111) works efficiently in acid media, in alkaline media, the reaction is impeded and considerably larger applied overpotentials are necessary. The presence of Ni(OH)2 adsorbed on Pt(111) has been demonstrated to highly improve the rate of hydrogen evolution, decreasing the overpotential of this reaction in comparison to acid media. The way low coverages of Ni(OH)2 on the Pt surface improve HER is still under discussion. In this work, we have prepared different Ni(OH)2 coverages on Pt(111) to check how Ni(OH)2 deposited on Pt(111) influences the HER rate. To this end, the Ni(OH)2-Pt(111)|0.1 M NaOH interface was characterized with cyclic voltammetry, CO displacement technique, and Fourier transform infrared-reflection absorption spectroscopy. On the basis of the proposal made by Ledezma-Yanez et al. [ Nature Energy 2017, 2, 17031] to explain the HER in alkaline media, we also studied the effect of the different Ni(OH)2 coverages on the electric field using the laser-induced temperature jump technique. This technique revealed that introduction of nickel adlayers on the surface decreases the ordering of the water network at the interphase, a fact that has relevant implications for the HER mechanism.

Influence of silsesquioxane addition on polyurethane-based protective coatings for bronze surfaces

Two-component solvent-born polyurethane coatings for the protection of bronze from corrosion were prepared. Trisilanol-heptaisooctyl polyhedral oligomeric silsesquixane (POSS) nanoparticles were exploited to increase the coating protective efficiency. Its improvement was confirmed through a combination of characterisation techniques. In particular, the POSS addition caused an increase of the water contact angle, and an enhancement of the elastic connotation and abrasion resistance of the polyurethane coating. Potentiodynamic polarisation measurements also indicated that the coating containing POSS nanoparticles has an improved protection efficiency. Impedance spectroscopy revealed that the magnitude of low-frequency impedance of polyurethane coatings decreased more for the coating without POSS during exposure in electrolyte for thirty days. Ex situ IR reflection-absorption spectroelectrochemistry was exploited to get insight into the degradation of coatings during chronocoulometric charging at anodic potentials. IR reflection-absorption technique was also used to evaluate any possible effect of different stripper solutions on the bronze substrate.

Amyloid-β fibrils assembled on ganglioside-enriched membranes contain both parallel β-sheets and turns

Some protein and peptide aggregates, such as those of amyloid-β protein (Aβ), are neurotoxic and have been implicated in several neurodegenerative diseases. Aβ accumulates at nanoclusters enriched in neuronal lipids called gangliosides in the presynaptic neuronal membrane, and the resulting oligomeric and/or fibrous forms accelerate the development of Alzheimer's disease. Although the presence of Aβ deposits at such nanoclusters is known, the mechanism of their assembly and the relationship between Aβ secondary structure and topography are still unclear. Here, we first confirmed by atomic force microscopy that Aβ40 fibrils can be obtained by incubating seed-free Aβ40 monomers with a membrane composed of sphingomyelin, cholesterol, and the ganglioside GM1. Using Fourier transform infrared (FTIR) reflection-absorption spectroscopy, we then found that these lipid-associated fibrils contained parallel β-sheets, whereas self-assembled Aβ40 molecules formed antiparallel β-sheets. We also found that the fibrils obtained at GM1-rich nanoclusters were generated from turn Aβ40 Our findings indicate that Aβ generally self-assembles into antiparallel β-structures but can also form protofibrils with parallel β-sheets by interacting with ganglioside-bound Aβ. We concluded that by promoting the formation of parallel β-sheets, highly ganglioside-enriched nanoclusters help accelerate the elongation of Aβ fibrils. These results advance our understanding of ganglioside-induced Aβ fibril formation in neuronal membranes and may help inform the development of additional therapies for Alzheimer's disease.

Nanostructured Ni and Ni-Pd Catalysts for Glycerol Electro-Oxidation in Alkaline Media

The great interest of shifting towards biodiesel from vegetable oils or waste fats results in a tremendous increase of glycerol production as an inevitable by-product. This waste sparked the need for glycerol valorization to justify biodiesel as alternative for diesel from petroleum. Our research efforts are to partially electro-oxidize glycerol into value-added chemicals in order to make biodiesel production more environmentally benign with added financial benefits. The primary objective of this project is the identification of an active and stable electro-catalyst that can affect the selective electrooxidation of glycerol to value-added products without C-C-C bond cleavage leads to the formation of a large number of high value-added chemicals [1]. The control of catalyst selectivity and activity could be achieved through formulation of novel, nanostructured electrocatalysts [2]. Nickel is an attractive material for glycerol electrooxidation in alkaline media [3, 4], due to its natural abundance and good stability in alkaline media. Designing nanostructured 3D Ni electrodes could enhance the catalytic activity of Ni, whereas its selectivity could be altered by addition of small amounts of the second metal [5]. Monometallic Ni nanoparticles were synthesized using modified polyol method. Change of NaOH concentration resulted in the variation of Ni nanoparticles (NPs) shape: triangular NiNPs were synthesized at lower concentrations while Ni NPs of urchin-like structure were fabricated at higher NaOH concentration. Bi-metallic NixPdx-1 (x=95,90 and 80 at.%) were also synthesized by hydrazine reduction in the presence of ethylene glycol. The synthesised nanoparticles were characterized by XRD, SEM, TEM, EDS mapping and HAADF imaging. In this work, electro-oxidation of glycerol reaction (GEOR) is investigated in detail on mono- and bimetallic Ni nanoparticles in alkaline medium. In order to better understand the role of the nickel surface on GEOR, electrochemical measurements have been carried out on synthesized unsupported nickel nanoparticles using different electrochemical tests such as cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV). Results indicated that the Ni was able to catalyze the GEOR at the NiOOH surface, well known as the active species. Ni80Pd20 displays the highest activity toward glycerol electro-oxidation. Chronoamperommetry coupled with in-situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) for the simultaneous analysis of products on the Ni surface and in the bulk solution showed that the main reaction products on Ni surface are glyceraldehyde, carbonyl, carboxylate ions and some carbon dioxide. The correlation of electrocatalytic activity and selectivity with nanoparticle shape, size, surface and bulk composition, as well as structure of Ni-based nanoparticles will be discussed in terms of mass activities and product distribution during GEOR. References Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, Green Chemistry 10 (2008) 13.M. Simoes, S. Baranton, C. Coutanceau, Applied Catalysis B: Environmental110 (2011) 40.M.S.E. Houache, E. Cossar, S. Ntais, E.A. Baranova, J. Power Sources 375 (2018) 310.V.L. Oliveira, C. Morais, K. Servat, T.W. Napporn, G. Tremiliosi-Filho, K.B. Kokoh, Electrochim.Acta. 117 (2014) 255.M. Simoes, S. Baranton, C. Coutanceau, ChemSusChem 5 (2012) 2106.

Robust Surface Plasmon Resonance Chips for Repetitive and Accurate Analysis of Lignin-Peptide Interactions.

We have developed novel surface plasmon resonance (SPR) sensor chips whose surfaces bear newly synthesized functional self-assembled monolayer (SAM) anchoring lignin through covalent chemical bonds. The SPR sensor chips are remarkably robust and suitable for repetitive and accurate measurement of noncovalent lignin–peptide interactions, which is of significant interest in the chemical or biochemical conversion of renewable woody biomass to valuable chemical feedstocks. The lignin-anchored SAMs were prepared for the first time by click chemistry based on an azide–alkyne Huisgen cycloaddition: mixed SAMs are fabricated on gold thin film using a mixture of alkynyl and methyl thioalkyloligo(ethylene oxide) disulfides and then reacted with azidated milled wood lignins to furnish the functional SAMs anchoring lignins covalently. The resulting SAMs were characterized using infrared reflection–absorption, Raman, and X-ray photoelectron spectroscopies to confirm covalent immobilization of the lignins to the SAMs via triazole linkages and also to reveal that the SAM formation induces a helical conformation of the ethylene oxide chains. Further, SPR measurements of the noncovalent lignin–peptide interactions using lignin-binding peptides have demonstrated high reproducibility and durability of the prepared lignin-anchored sensor chips.

Ga-doping of nonpolar m-plane ZnMgO with high Mg contents

The electrical and optical properties of m-plane Ga-doped ZnMgO alloys are analyzed by capacitance-voltage profiling, Hall effect, and IR reflectance and UV-VIS absorption spectroscopies, spanning more than four orders of magnitude in electron concentration. Mg contents up to 50% are achieved while maintaining the wurtzite phase, with a measured band-edge energy of 4.41 eV. Despite the deterioration of the electrical properties with Mg incorporation, high electron concentrations (∼4.4×1019cm−3) are measured for Mg contents up to 35%, revealing doping efficiencies close to 100%. The potential physical origin for the drop of the electron concentration and mobility with Mg is analyzed and correlated to the absorption measurements. In ZnO:Ga epilayers band filling is observed, although upon alloying with Mg, bandgap shrinkage and Urbach tailing become evident. It is deduced that the observed carrier compensation arises from the presence of acceptor traps, such as VZn and VZn-GaZn complexes, whereas impurity scattering and electron trapping at extended defects are the mechanisms affecting the mobility.

Water on Atomically-Defined Cobalt Oxide Surfaces Studied by Temperature-Programmed IR Reflection Absorption Spectroscopy and Steady State Isotopic Exchange

In this work, we investigate the interaction of water with three different atomically defined cobalt oxide surfaces under ultrahigh vacuum (UHV) conditions using time-resolved and temperature-programmed infrared reflection–absorption spectroscopy (TR-IRAS, TP-IRAS) in combination with isotopic exchange experiments. The three surfaces, CoO(100), CoO(111), and Co3O4(111), are prepared in form of well-ordered films on Ir(100). Very different behavior is observed on the three surfaces, both with respect to D2O adsorption and desorption. On CoO(100), water adsorbs molecularly. It forms extended ice clusters even at low adsorption temperature (200 K) and which desorb molecularly at 200 K (Ea,des ∼ 60 kJ·mol–1). A very small amount of defect sites is observed at which D2O dissociates and forms strongly bound OD groups. On CoO(111), the interaction with ordered facets is very weak and no adsorption occurs at these sites at 200 K. The CoO(111) films expose, however, a higher density of defects as compared to the C...

Features of the Radiation-Stimulated Hydrogenation of an Aluminum Surface

By the methods of reflection-absorption IR (infrared) spectroscopy, electrical measurement and AFM microscopy, the process of the radiation-stimulated hydrogenation of the aluminum surface in the Al/ads n-hexane system under γ-irradiation at room temperate is studied. On the basis of the dose dependence of the Al surface specific resistance, two stages of the hydrogenation process in the absorbed dose range (0.5‒120 kGy) are revealed. It is established that the transition from the first to the second stage is accompanied by a decrease in the electrical conductivity of Al by 35 times and an increase in the hydride-nanolayer thickness by an order of magnitude. AFM studies of the aluminum surface relief showed that radiation-stimulated hydrogenation is accompanied by the formation of carbon-nanotube structures. A possible mechanism for the radiation-stimulated hydrogenation of aluminum is suggested.