Effect Of Chemisorption Research Articles

Tight-binding Ising-model study of chemisorption effects on surface segregation in transition-metal alloys

The tight-binding Ising model is generalized for the system consisting of a transition-metal alloy with chemisorbed adatoms. The effect of chemisorption on the surface segregation is calculated within the scope of a semi-infinite linear chain model for hydrogen chemisorbed on a Cu-Ni alloy. The charge-neutrality condition is incorporated into the model and its effect on the calculated surface segregation is demonstrated.

Anomalous effects of weak chemisorption on desorption kinetics of alkenes: The desorption of propylene and propane from Ag(110)

Temperature programmed desorption (TPD), using x-ray photoelectron spectroscopy for absolute coverage determinations, was used to compare the desorption kinetics of weakly bound propane and propylene from Ag(110). The dependence of the activation energy on coverage was quantified by a linear relationship obtained from a leading edge analysis of the TPD curves. Whereas propane shows very weak attractive lateral interactions, propylene shows clear evidence for repulsive interactions in desorption. Weak attractive interactions are expected for both the propane and propylene based on theories of physical adsorption, since the second virial coefficients for both in the gas phase are negative below 550 K. Adsorption of propylene introduces repulsive intermolecular forces that are not present in the gas phase. We suggest that these repulsive forces originate in local interactions resulting from weak chemical bonding interactions between the surface and adsorbed propylene, which give rise to a preferred orientation of the double bond perpendicular to the surface. Fourier transform infrared spectroscopy results indicate that two adsorption states of propylene exist on the surface simultaneously. In the high coverage region the increase in repulsive interactions gives rise to a change in the dominant binding configuration as crowding increases.

Surface chemistry of V–Sb–oxide in relation to the mechanism of acrylonitrile synthesis from propane. Part 1.—Chemisorption and transformation of possible intermediates

The mechanism of propane ammoxidation to acrylonitrile on V–Sb–oxide is analysed by IR spectroscopy in three papers dealing with the study of (i) the reaction network in propane conversion, (ii) the relationship between ammonia chemisorbed species and catalytic behaviour and (iii) the effect of ammonia chemisorption on the surface reactivity. This first part deals with the study of the nature of surface adspecies formed by chemisorption of acetone, isopropyl alcohol, acrylic acid, ally alcohol, propene, propionic acid, acetic acid, propane and acrylonitrile on a vanadium antimonate catalyst (V/Sb = 1.0) and subsequent thermal treatment. The results indicate that the catalyst is characterized by multifunctional properties (H-abstraction, O-insertion and oxidative cleavage properties), the relevance of which for the mechanism and catalytic behaviour in acrylonitrile synthesis from propane is discussed. A surface reaction network in propane oxidation is also proposed involving multiple possible pathways of transformation. The main route of propane conversion is through the formation of propene as an intermediate, although a side reaction of acrylate formation via a propionate intermediate is possible. Propene may be oxidized according to two routes, the first leading to acetone which undergoes quick oxidative cleavage to an acetate species and a C1 fragment, and the second to the formation of an allyl alcoholate adspecies which transforms to acrolein which quickly further converts to an acrylate species. The acrylate species strongly interacts with the surface and is thermally stable up to relatively high temperatures.

Infrared spectroscopy of model electrochemical interfaces in ultrahigh vacuum: Surface–cation solvation in the Pt(111)/K+–methanol system

Infrared reflection–absorption spectroscopic (IRAS) measurements are reported for methanol dosed onto Pt(111) in ultrahigh vacuum (UHV) in both the presence and absence of adsorbed potassium atoms at 90 K with the objective of elucidating the nature of sequential cation solvation at this model electrochemical interface. Corresponding variations in the metal-UHV work-function (Φ), evaluated with a Kelvin probe, yield additional insight into the interfacial electrostatic environment as a function of the alkali and methanol dosages. Methanol forms a particularly suitable solvent for such a ‘‘double-layer modeling’’ study since both the O–H stretching (νOH) and C–OH stretching (νC–OH) vibrations are sensitive to the local coordination environment. In addition, comparisons are made with the detailed infrared spectral data available for progressive methanol solvation of gas-phase alkali cations [(a) A. J. Draves, Z. Luthey-Schulten, W.-L. Liu, and J. M. Lisy, J. Chem. Phys. 93, 4589 (1990); (b) T. J. Selegue, N. Moe, J. A. Draves, and J. M. Lisy, ibid. 96, 7268 (1992)], allowing unprecedented insight into the manner and extent to which cation solvation is affected by the metal surface. The initial stage of methanol solvation of interfacial K+ is signaled by substantially downshifted and relatively sharp νOH and νC–OH bands at ∼3100 and 1010 cm−1, respectively, which are not observed in the absence of K+. This spectral behavior is consistent with the formation of a primary solvation shell featuring methanol–cation coordination via the oxygen along with –OH hydrogen bonding to the metal surface. The significant (∼0.5–1 eV) Φ increases observed under these conditions support the presence of primary solvation methanol with a negative-outward δ−O–Hδ+ dipole orientation. The second solvation stage, referring to K+–methanol stoichiometries above ∼3, is accompanied by the appearance of markedly upshifted νOH and νC–OH bands, at ∼3300 and 1050 cm−1, respectively, suggesting the occurrence of extensive first–second shell H-bonding. Marked Φ decreases are observed in this dosage regime, more closely akin to the behavior observed in the absence of adsorbed alkali. The methanol dosage-dependent interfacial νC–OH behavior is markedly different to that observed in the gas phase, highlighting the role of the metal in modifying the nature of both the primary and second-shell solvation structure. The structure of methanol on uncharged (i.e., K+-free) Pt(111) is also addressed by combined IRAS and work-function measurements. The H-bonded structures even within multilayer methanol films differ significantly from the analogous bulk phases. The effects of competitive CO chemisorption on K+ solvation are also considered.

Chemisorption effect on K-shell XANES in N 2 and CO molecules on surfaces

Using the quasi-atomic approach the appearance of a new σ-resonance features in K-shell XANES of diatomic adsorbates due to their chemisorption is shown.

Angular and vibrational effects in the direct dissociative chemisorption of deuterated methane and ethane on Ir(110)

We have measured the initial probability of dissociative chemisorption of deuterated methane and ethane on the reconstructed Ir(110) surface as a function of polar angle of incidence using vibrationally hot supersonic molecular beams. The probability of chemisorption scales Approximately with the component of translational energy normal to the surface ( E icos 2 θ i) for deuterated ethane and methane, with slight systematic deviations. These deviations are explained in terms of the translational energy distribution of the incident molecular beam. We conclude that in the limit of a monoenergetic beam, normal-energy scaling is obeyed at a constant vibrational energy.

Alkali-metal chemisorption on Ta(110).

The effect of alkali-metal chemisorption on the surface electronic structure of Ta(110) is presented. A [ital d]-derived surface state on clean Ta(110) is strongly modified, as manifested by a level shift and lateral delocalization. Strong mixing between alkali-metal and substrate valence bands is observed. It is suggested that alkali-metal overlayers on the more complex metals have fundamentally different behavior than on simple metal substrates.

Confinement, surface, and chemisorption effects on the optical properties of Si quantum wires.

We have used the empirical pseudopotential method to study the electronic and optical properties of [001] Si quantum wires with (110)--([bar 1]10) square cross sections ranging from 4[times]4 to 14[times]14 monolayers (7.7[times]7.7 to 26.9[times]26.9 A, respectively). We present energy levels, band gaps, oscillator-strength, and charge-density distributions. To understand the electronic structure of these systems we calculate their properties in a stepwise process, considering (1) wires with a free surface but without hydrogen and (2) wires with hydrogen chemisorption on the surface. We find that (i) in both cases, the band gap between bulklike states increases as the wire size is reduced (due to quantum confinement). However, (ii) hydrogen chemisorption acts to reduce the gap. (iii) Whereas the low-energy states near the valence-band [ital minimum] are effective-mass-like, the near-band-gap states with or without H on the surface can be decisively non-effective-mass-like. The lowest conduction states are pseudodirect, not direct. (iv) The calculated energy dependence of the transition lifetimes is too strong to explain the observed low-energy slow'' emission band in porous Si purely in terms of transitions in an ideal wire. However, an alternative model, which introduces a mixture of wires and boxes, can account for the experimental slope.

Molecular Bonding and Adhesion at Polymer-Metal Interphases

Abstract The purpose of this review is to demonstrate that there are well established molecular bonding and strong interactions between monomers or polymers and metals. We discuss both theoretical and experimental work related to adsorption and adhesion at polymer-metal interphases. Firstly, we briefly describe the fractal nature of polymer-metal interphases, and the effect of chemisorption on fractal dimension. Secondly, we mention several theoretical studies related to the models and the conformation of polymer segments to metal surfaces. Recent theoretical work by others with molecular modeling has provided some insight about the interfaces; however, this type of work is still at an early stage. Thirdly, we cite the experimental work by others with XPS, SERS (surface-enhanced Raman scattering spectroscopy), Mössbauer emission spectroscopy, etc., on chemisorption, molecular bonding, redox interaction, restructuring of polar groups, and contact oxidation of polymers on metal surfaces. Among them, SERS and XPS are capable of describing chemical composition and conformation right at the interfaces. These results appear very valuable in understanding the formation of the architectural framework of a functional interphase beyond the superficial blending. In general, some preliminary data indicate that adhesion of polymers is greatly improved by various forms of strong interactions, e.g., chemisorption and molecular bonding at polymer-metal interphases. However, strong chemical reactions at the interphases may not be always beneficial to adhesion and physical properties.

FTIR Spectroscopic Study of Thiophene, SO2, and CO Adsorption on Cu/Al2O3 Catalysts

Infrared spectra are reported of copper/alumina catalysts in various states of oxidation or reduction and exposed to carbon monoxide, thiophene, sulphur dioxide, co-adsorbed carbon monoxide and thiophene, and co-adsorbed carbon monoxide and sulphur dioxide. Available adsorption sites could be broadly divided into four groups: Cu2+, Cu+ in a matrix of Cu2+, Cu+ in a matrix of Cu+, and Cu0. Both site-blocking and electronic effects of thiophene on CO adsorption have been identified and are discussed in terms of the nature of the surface-adsorbate interactions, the oxidation state of the adsorption sites, and the specific effects of thiophene on the adsorption sites for CO. Sulphur dioxide blocked CO adsorption on Cu2+ sites. Adsorption of CO on Cu+ sites was not inhibited by adsorption of sulphur dioxide, the latter having an electronic effect on CO molecules at adjacent sites. Adsorption of sulphur dioxide on a reduced Cu0 surface caused surface oxidation giving Cu+ sites which were available for the subsequent adsorption of CO. The pre-adsorption of CO impeded but did not prevent the oxidative effects of sulphur dioxide chemisorption.

Monte Carlo studies of the chemisorption and work function temperature effects on noble metals

Monte Carlo simulations of some properties of the noble metals using the Morse, Rydberg and Varshni potentials with effective constants were carried out to select the proper interaction potentials for Cu, Ag and Au in their monocrystals. The extended coherent potential approximation with phonon-electron coupling was applied to compute the surface charge and work function temperature dependence. The influence of the lattice vibrations on the mechanism of chemisorption was also analysed.

Symmetry and rotational orientation effects in dissociative adsorption of diatomic molecules on metals: H2 and HD on Cu(111)

Following two previous quantum dynamics studies [J. Chem. Phys. 97, 6784 (1992); 99, 1373 (1993)], we present in this paper a more thorough investigation of the symmetry and rotational orientation effects in dissociative chemisorption of diatomic molecules on metals. Specifically, we extended our theoretical studies to calculate the sticking coefficients for H2 and its isotopomer HD on Cu from all angular momentum states (up to j=8). Our calculation shows a strong dependence of the dissociation probability P(jm) on both j and m rotation quantum numbers, and the increases of P(jm) are closely correlated with the increase of the quantum number m in a given j manifold. Also the dissociation of the diatomic rotational states whose quantum numbers satisfy j+m=odd is forbidden at low energies for the homonuclear H2 due to the selection rule. The present study provides further evidence that the effect of diatomic rotation on adsorption mainly arises from the effect of rotational orientation (m dependence) as found in previous studies. This m dependence predicts that at low kinetic energies, the degeneracy-averaged dissociation probability of hydrogen on Cu increases monotonically as the rotation quantum number j increases. However, at high kinetic energies, the adsorption probability first decreases as j increases from 0 to about 4–5 before increasing as j further increases above 4–5. The latter behavior is consistent with a recent experimental measurement by Michelsen et al. of the mean kinetic energy of the rotational states of D2 desorbed from Cu(111).

Electronical and structural effects in CO chemisorption on Cu 3Pt(111)

It is generally observed for CO adsorption on alloys composed of an sp-metal and a transition metal that the adsorption energy is decreased compared to adsorption on the pure transition metal, although the adsorption site is above a transition metal atom. We explain this behaviour for CO Cu 3Pt(111) by means of a model Hamiltonian investigation and compare to an earlier study of CO NiAl(110) . For the latter systems the decrease of the adsorption energy can be traced to the filling of the d-band and the change in sp-d hybridization, whereas for CO Cu 3Pt(111) the reduced density of Pt atoms in the surface decreases the heat of adsorption. The adsorption site is determined by different physical effects as well. On NiAl(110) the adsorption geometry is controlled by minimising 5σ-3d repulsion and on Cu 3Pt(111) sp-band corrugation is important for obtaining the right adsorption place.

Calculation of the chemisorption energy of H on a multilayer-segregated CuNi alloy

The chemisorption theory of Einstein and Schrieffer is used to calculate the chemisorption energy of hydrogen on a multilayer-segregated CuNi disordered binary alloy surface, in which the Green-function technique, based on the coherent-potential approximation, and the method of complex-energy integration are adopted. When the effect of chemisorption on the surface component is neglected, multilayer surface segregation of Cu leads to an increasein chemisorption energy ΔE as compared to the case of no surface segregation as well as monolayer segregation. In general cases, chemisorption-induced surface segregation can change the surface component and the chemisorption energy to varying degrees. The results show that the chemisorption energy depends sensitively on the adatom coverage θ, and decreases with increasing θ. The calculated result for θ = 0.41 agrees with the experiment of Takeuchi et al.

Effects of metal ion chemisorption on gallium arsenide surface recombination: picosecond luminescence decay measurements

n-GaAs/KOHSe^(-/2-)(aq) contacts have been studied using real time photoluminescence decay techniques. This system is of interest because metal ion chemisorption improves the steady-state current-voltage properties of GaAs/KOH-Se^(-/2-)(aq)/Pt cells, yielding 16% efficiency under simulated 1-sun illumination conditions. In this work, the luminescence decay dynamics of thin epilayer GaAs samples under high level injection conditions were monitored in contact with KOHSe^(-/2-)(aq) solutions. The photoluminescence signals decayed more rapidly after metal ion chemisorption than after a fresh etch, indicating that the metal ion treatment induced a more active recombination and/or charge-transfer process than the etch. A finite-difference simulation was used to model the decays and to extract a minority carrier surface recombination velocity, S_(min), for these systems. For etched GaAs surfaces, S_(min) = 5 X 10^3 cm s^(-1), while GaAs surfaces that had been etched and then exposed to 0.010 M Co(NH_3)_6^(3+) (pH = 11) solutions displayed S_(min) = 2 X 10^5 cm s^(-1). Qualitatively similar behavior was observed for Rh-, Ru-, and Os-treated GaAs surfaces as well. These data are fully consistent with prior suggestions that the primary effect of metal ion chemisorption is to increase the rate of hole transfer to the Se^(-/2-)(aq) electrolyte, as opposed to decreasing surface recombination processes at the GaAs/liquid contact.

Electrode potential-induced reconstruction of gold (100): effect of chemisorption on nanoscale dynamics as probed by in-situ scanning tunneling microscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectrode potential-induced reconstruction of gold (100): effect of chemisorption on nanoscale dynamics as probed by in-situ scanning tunneling microscopyXiaoping Gao and Michael J. WeaverCite this: J. Phys. Chem. 1993, 97, 34, 8685–8689Publication Date (Print):August 1, 1993Publication History Published online1 May 2002Published inissue 1 August 1993https://doi.org/10.1021/j100136a004RIGHTS & PERMISSIONSArticle Views194Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts

Rotational rainbows in NO scattering from Pt(111)

The interaction between NO and Pt(111) is dominated by the presence of a deep well corresponding to molecular chemisorption. To study the effect of a deep chemisorption well on the scattering dynamics we have performed measurements of rotational (J) excitation of NO in collisions with Pt(111). The measurements show surprisingly large rotational excitation and a clear rotational rainbow. Classical trajectory calculations were carried out to examine the origin of this rainbow. Using the potential of Haug et al. the observed energy dependence of the rainbow could not be reproduced. We have constructed another model potential, having a shallow well for the O end of the molecule. Trajectory calculations with this potential explain the experimental observations qualitatively. We suggest that the rotational excitation manifested in the rotational rainbow is a result of the anisotropy in the repulsive part of the interaction potential.

Chemisorption effects on the thin-film conductivity

An investigation of chemisorption effects on the electrical conductivity of thin, wide bandgap semiconductors is presented in the framework of the Volkenstein model. The controversially discussed problem of a neutral, weak-chemisorbed state is reconsidered on the basis of the one-electron theory of chemisorption (considered by Einstein and Schrieffer). An analytically tractable variational method is developed for the ground state in lattice space. It turns out that in case of atop-anion binding a stable, weak-chemisorbed state can arise. For the case of acceptor-like chemisorption the pressure dependence of the thin-film conductivity is derived, solving selfconsistently the one-dimensional Poisson equation. In a wide pressure region the conductivity shows a power-law behaviour. It is found that the power is determined by different, fundamental parameters and cannot be expressed by only one parameter, e.g., the constant, stochiometric exponent in the mass-action law. Furthermore, the theoretical values of the power vary between 0 and 1 in agreement with the variety of experimental results.

Chemisorption effects on the thin-film conductivity

Chemisorption effects on the thin-film conductivity

Interactional effects in corrosive chemisorption of chlorine and oxygen on iron(110)

Interactional effects in corrosive chemisorption of chlorine and oxygen on iron(110)