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Contour maps of distributions of electronic density as a function of distance between oxygen atoms in the top-bridgetop configuration on the Pt(111) surface, shown in the normal plane containing the oxygen atoms.
Source publication
Mechanism of the associative desorption of oxygen from the Pt(111) surface
has been studied on atomic level by means of DFT/GGA calculations and
kinetic Monte Carlo simulations. It has been found that two oxygen adatoms
can occur, with sufficient probability, in neighboring on-top sites, which
is essential for formation and subsequent evaporati...
Contexts in source publication
Context 1
... course of formation of the molecule can be illus- trated by contour maps of calculated distributions of the electronic density in the normal plane drawn through the oxygen atoms (Fig. 3). The distributions shown in Fig- ure 3 have been obtained by means of the "cold" Broyden optimization (that is, oxygen atoms were allowed to move by the action of forces estimated from the gradients of the potential energy). Starting position (Fig. 3a) corresponds to oxygen atoms, slightly shifted from on-top sites. In the course of ...
Context 2
... course of formation of the molecule can be illus- trated by contour maps of calculated distributions of the electronic density in the normal plane drawn through the oxygen atoms (Fig. 3). The distributions shown in Fig- ure 3 have been obtained by means of the "cold" Broyden optimization (that is, oxygen atoms were allowed to move by the action of forces estimated from the gradients of the potential energy). Starting position (Fig. 3a) corresponds to oxygen atoms, slightly shifted from on-top sites. ...
Context 3
... distributions of the electronic density in the normal plane drawn through the oxygen atoms (Fig. 3). The distributions shown in Fig- ure 3 have been obtained by means of the "cold" Broyden optimization (that is, oxygen atoms were allowed to move by the action of forces estimated from the gradients of the potential energy). Starting position (Fig. 3a) corresponds to oxygen atoms, slightly shifted from on-top sites. In the course of optimization, O atoms move towards each other until the molecule is formed (Fig. 3c). Desorption of the formed molecule requires some ∼0.8 eV energy, and distri- butions of electron density, shown in Figures 3d-3f, were obtained by optimization of the ...
Context 4
... means of the "cold" Broyden optimization (that is, oxygen atoms were allowed to move by the action of forces estimated from the gradients of the potential energy). Starting position (Fig. 3a) corresponds to oxygen atoms, slightly shifted from on-top sites. In the course of optimization, O atoms move towards each other until the molecule is formed (Fig. 3c). Desorption of the formed molecule requires some ∼0.8 eV energy, and distri- butions of electron density, shown in Figures 3d-3f, were obtained by optimization of the bondlength d O−O for fixed distances z from the ...
Context 5
... the course of optimization, O atoms move towards each other until the molecule is formed (Fig. 3c). Desorption of the formed molecule requires some ∼0.8 eV energy, and distri- butions of electron density, shown in Figures 3d-3f, were obtained by optimization of the bondlength d O−O for fixed distances z from the surface. ...
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... It is important to notice that the growth of 2-MBT layer is accompanied by a continuous decrease of the oxygen signal. Oxygen is substituted by 2-MBT with dissociation of the initial 2D oxide layer, and it may desorb as gaseous O 2[98,99]. The results are in agreement with that obtained by AES[89], where a complete disappearance of oxygen was observed after about 25 L. The atomic ratios of S and N versus C were calculated, we obtain values close to the stoichiometry of the molecule, indicating the adsorption of 2-MBT in its molecular form on the pre-oxidized Cu(111) surface.Similarly, a high resolution XPS analysis of the molecular layer formed on pre-oxidized Cu(111) after different exposures was performed, and the results are shown inFig. ...
Le cuivre est un métal mou et ductile qui présente une haute performance thermique et électrique. Cependant, il n'est pas totalement inerte. Pour les matériaux métalliques dans des conditions environnementales pour lesquelles l'autoprotection par passivation ne fonctionne pas, une méthode de protection consiste à utiliser des inhibiteurs de corrosion. Dans ce travail, l'effet des molécules inhibitrices 2-MBT et MBI sur le mécanisme d'oxydation du Cu(111) a été étudié, en utilisant une combinaison de techniques avancées de caractérisation de surface, y compris la microscopie à effet tunnel (STM), la spectrométrie photoélectronique X (XPS) et la spectrométrie de masse d'ions secondaires à temps de vol (ToF-SIMS). Ce travail apporte un nouvel éclairage sur la relation entre la structure locale de la surface du cuivre et l'efficacité de la molécule inhibitrice en présence d'oxydes.
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... A strong lateral interaction between O adatoms on Pt(1 1 1), which can be considered as superposition of the screened Coulomb and indirect interactions [8], complicates the association of O adatoms into O 2 molecules. A consistent picture of the associative oxygen desorption from Pt(1 1 1), based on DFT/GGA (Density functional theory with generalized gradient approximation) calculations and kinetic Monte Carlo simulations, was suggested in our recent study [9]. In particular, it was shown that when two oxygen adatoms occur in neighboring on-top sites, the formation and subsequent evaporation of oxygen molecules go spontaneously. ...
... However, the predominantly repulsive lateral interaction between oxygen atoms on the Pt(1 1 1) surface changes to attraction when the adatoms occupy on-top sites. The position of O adatoms in these sites is metastable and therefore, as follows from results of Monte Carlo simulations [9], the probability for two O atoms to occur in neighboring on-top sites is found to be sufficient for the explanation of the associative desorption. ...
... The cornerstone of the model [9] has been the change of the lateral interaction between adsorbed oxygen atoms excited to www.elsevier.com/locate/apsusc Available online at www.sciencedirect.com ...
Mechanism of the associative desorption of oxygen from the Pt(111) surface has been studied on atomic level by means of density-functional calculations. Key to the association of two oxygen adatoms into the O2 molecule is the excitation of one of the adatoms to on-top site, where it becomes essentially neutral. The related redistribution of the electronic density at the O adatom leads to the appearance of the lateral attraction with the other O atom, thus providing an efficient channel for associative desorption. Calculated local densities of states resemble the transformation of the electronic structure of adsorbed O adatoms from the reactive to bound state in the course of association.
... For the modeling of the formation of oxygen structures and the desorption from the Mo͑110͒ surface, we used our set of Monte Carlo programs, verified in simulations for various adsorption systems. [28][29][30][37][38][39] Briefly, the method, which explores the standard Metropolis algorithm for the lattice gas model, 40 takes into account the long-range dipole-dipole and indirect interactions between particles adsorbed on the 36 ϫ 60 lattice with periodic boundary conditions. Rearrangement of the particles ͑"surface diffusion"͒ was performed by movements ͑"jumps"͒ of randomly chosen adatoms to neighboring sites. ...
... For example, the binding energy for O on W͑112͒ is about 7 eV, 43 so that only atomic phase desorption is possible. In contrast, for O on Pt͑111͒, the binding energy is 3.7 eV, 30 and therefore, oxygen desorbs in a molecular form ͑associative de-sorption͒. ...
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We have investigated the interaction of oxygen with the Ag/Pt(111) surface alloy by thermal desorption spectroscopy (TDS). The surface alloy was formed during the deposition of sub-monolayer amounts of silver on Pt(111) at 800 K and subsequent cooling to 300 K. The low-temperature phase of the surface alloy is composed of nanometer-sized silver rich stripes, embedded within platinum-rich domains, which were characterized with spot profile analysis low energy electron diffraction. The TDS measurements show that oxygen adsorption is blocked on Ag sites: the saturation coverage of oxygen decreases with increasing Ag coverage. Also, the activation energy for desorption (E des ) decreases with Ag coverage. The analysis of the desorption spectra from clean Pt(111) shows a linear decay of E des with oxygen coverage, which indicates repulsive interactions between the adsorbed oxygen atoms. In contrast, adsorption on alloyed Ag/Pt(111) leads to an attractive interaction between adsorbed oxygen atoms.
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