Sulfur Interaction with Cu(100) and Cu(111) Surfaces: A Photoemission Study

Results of a high-resolution synchrotron photoemission study of sulfur adsorption on Cu(100) and Cu(111) surfaces are reported. Sulfur adsorption was performed by immersion of pristine samples into aqueous Na₂S, which provokes strong sulfidation of copper. Annealing leads to partial elimination of S and progressive formation of well-ordered surface sulfur phases followed here by LEED. This translates into sizable Cu 2p core level binding energy (CLBE) shifts as well as changes in the S 2p binding energies. For Cu(111) we see evolution at the higher temperature to the (√7 × √7)<i>R</i>19.1° phase as identified by LEED, with a S 2p_3/2 binding energy of 161.45 eV. An intermediate phase with an S 2p_3/2, binding energy of 161.15 eV appears at lower temperatures. For Cu(100) at 300 °C we see the appearance of the known 0.47 ML S coverage (√17 × √17)<i>R</i>14° structure, with S 2p_3/2 CLBE of 161.15, 161.62, and 162.10 eV. At higher temperatures some S atom loss occurs, and we observe a p(2 × 2)-S phase, with S 2p_3/2 CLBE of 161.05 eV and a smaller component at 164.45 eV that could correspond to local c(4 × 2) domain boundaries as identified in earlier studies. The core level binding energies of Cu 2p are reported along with valence band characteristics

Chalcogen Atom Interaction with Palladium and the Complex Molecule–Metal Interface in Thiol Self Assembly

In the case of reactive metals, on adsorption of organic chalcogenide molecules like thiols, chalcogenide-C bond scission can occur. Thus, the high reactivity of Pd leads to initial thiol dissociation and formation of a complex PdS interface layer on which thereafter thiol self-assembled monolayers (SAM) can form. In this context we investigate in detail the adsorption of S, Se, alkanethiols, and aromatic dithiols on Pd by photoemission with synchrotron radiation. The nature of the PdS and PdSe layers formed is studied, and thiol adsorption on Pd(111), PdS, and PdSe surfaces is investigated, along with interface characteristics. After initial strong sulfidation (selenization) in Na2S(Se) solutions, a well-ordered surface PdS (PdSe) layer can be obtained by annealing. For S, annealing leads to formation of a PdS (root 7 x root 7)R19.1 degrees layer, whereas for Se, large domains of this structure are formed. Experiments suggest that in thiol adsorption the Pdsulfide interface is not simply similar to the (root 7 x root 7)R19.1 degrees PdS layer but that modifications in this surface sulfide layer are induced. A similar effect is observed on the selenide interface layer. In addition, 1,4-benzenedimethanethiol adsorption on Pd is investigated with the aim of creation of thiol-terminated dithiol molecular layers. Unlike the case of surfaces like Au, no clear indication of a standing-up, thiol-terminated SAM was found. X-ray radiation damage effects are reported

Selenium adsorption on Au(111) and Ag(111) surfaces: adsorbed selenium and selenide films

Results of a high resolution photoemission and electrochemistry study of Se adsorption Au(111) and Ag(111) surfaces performed by immersion of pristine samples into an aqeuous solution of Na2Se are presented. Cyclic voltammetry on Au shows formation of selenium adsorbed species and the structures observed in reductive desorption are to the atomic and polymeric species observed in XPS. In the case of Au(111) XPS spectra in the Se(3d) region indeed show two main features attributed to Se chemisorbed atomically and polymeric Se-8 features.' Smaller structures due to other types of Se conformations were also observed. The Au(4f) peak line, shape does not show core level, shifts: indicative of Au selenide formation the case of silver, XPS spectra for the Ag(3d) show a broadening of the peak and a deconvolution into Ag-B bulk like Ag-Se components shows that the Ag-Se is located at a lower binding energy, an effect similar to oxidation and sulfidation of Ag. The Se(3d) XPS spectrum is found to be substantially different from the Au case and dominated by atomic type Se due to the selenide, though a smaller intensity Se structure at an energy similar to the Se-8 structure for Au is also observed. Changes in the valence band region. related to Se adsorption are reported

Properties of NTCDA Thin Films on Ag(110): Scanning Tunneling Microscopy, Photoemission, Near-Edge X-ray Fine Structure, and Density Functional Theory Investigations

It is well proven that the properties of organic/metal interfaces play an utmost role in the performance of organic devices. Here we present a study on structural and electronic properties of high-quality 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) films grown on an Ag(110) surface. High-resolution scanning tunneling microscopy and low-energy electron diffraction show the presence of two molecular domains. Density functional theory calculations indicate that the most stable location of NTCDA corresponds to anhydride oxygen attached to the Ag atoms along the [110] direction. Photoemission results of the C 1s and O 1s core levels demonstrate a strong interfacial bonding, inducing a charge transfer from the Ag metal to the molecular monolayer. An angular-dependent study of the C K-edge near-edge X-ray fine structure spectra provides detailed information concerning the evolution of the NTCDA orientation with the film thickness.Fil: Tong, Yongfeng. Université Paris Sud; Francia. Synchrotron SOLEIL; FranciaFil: Fuhr, Javier Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Martiarena, María Luz. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Oughaddou, Hamid. Université Paris Sud; FranciaFil: Enriquez, Hanna. Université Paris Sud; FranciaFil: Nicolas, François. Synchrotron SOLEIL; FranciaFil: Chaouchi, Karine. Synchrotron SOLEIL; FranciaFil: Kubsky, Stefan. Synchrotron SOLEIL; FranciaFil: Bendounan, Azzedine. Synchrotron SOLEIL; Franci

Evidence of the Impact of Substitutions in Goethite on Rare Earth Element Adsorption

Since the 1980's the uses, and thus mining, of Rare EarthElements (REE) have grown exponentially. This has led toquestions about the impact of REE on the environment, and REEbeing designated emerging pollutants. Currently, knowledgeabout the behaviour of REE in the environment is stillincomplete. For example, there are few studies on REEadsorption on iron (Fe) (oxy)hydroxides, which are consideredkey carriers of metal pollution, and on the other factorscontrolling this adsorption [1-4]. Knowing that in natural(oxy)hydroxides, Fe is frequently substituted by other elementsin the environment in which they form, we were interested in theeffect of these substitutions on the adsorption capacity of(oxy)hydroxides towards REE.This study focusses on aluminium (Al, common in naturalenvironments and easily substituted into Fe-oxyhydroxides) andgallium (Ga, chemical analogue to Al) substitutions in goethite(Goe), representative of commonly found Fe-(oxy)hydroxideswhose well-defined structure allows for modelling of sorptionand surface interactions. For this purpose, experiments of REEwere conducted on pure and substituted goethites (Goe) withvarying Al and Ga content.A characterisation of these goethites, shows that thesubstitution does not affect the shape, size, and specific surfacearea significantly. Nevertheless, the REE adsorption patterns areaffected by substitutions: 5% substitution decreases the sorptioncapacity of the goethite, and at 10% substitution the preferredadsorption of the mid and heavy REE diminishes, resulting in a'flatter' pattern. Meanwhile, the Neodymium (Nd) L3-edgeEXAFS experiments show no modification of its binding modeto the Goe surfaces, forming corner sharing bidentate-binuclearcomplexes regardless of the substitution rate. However, TEMobservations and Cerium (Ce) L 3-edge XANES experimentsdemonstrate that the Ga substitution favours a higher Ce(IV)O2adsorption, while the Al substitution favours Ce(III) adsorptioncompared to the pure Goe.These results reveal the large impact of substitutions on thereactivity of goethite towards REE

Chalcogen Atom Interaction with Palladium and the Complex Molecule–Metal Interface in Thiol Self Assembly

In the case of reactive metals, on adsorption of organic chalcogenide molecules like thiols, chalcogenide-C bond scission can occur. Thus, the high reactivity of Pd leads to initial thiol dissociation and formation of a complex PdS interface layer on which thereafter thiol self-assembled monolayers (SAM) can form. In this context we investigate in detail the adsorption of S, Se, alkanethiols, and aromatic dithiols on Pd by photoemission with synchrotron radiation. The nature of the PdS and PdSe layers formed is studied, and thiol adsorption on Pd(111), PdS, and PdSe surfaces is investigated, along with interface characteristics. After initial strong sulfidation (selenization) in Na₂S­(Se) solutions, a well-ordered surface PdS (PdSe) layer can be obtained by annealing. For S, annealing leads to formation of a PdS (√7 × √7)­R19.1° layer, whereas for Se, large domains of this structure are formed. Experiments suggest that in thiol adsorption the Pd–sulfide interface is not simply similar to the (√7 × √7)­R19.1° PdS layer but that modifications in this surface sulfide layer are induced. A similar effect is observed on the selenide interface layer. In addition, 1,4-benzene­dimethanethiol adsorption on Pd is investigated with the aim of creation of thiol-terminated dithiol molecular layers. Unlike the case of surfaces like Au, no clear indication of a standing-up, thiol-terminated SAM was found. X-ray radiation damage effects are reported

Selenium Adsorption on Au(111) and Ag(111) Surfaces: Adsorbed Selenium and Selenide Films

Results of a high resolution photoemission and electrochemistry study of Se adsorption on Au(111) and Ag(111) surfaces performed by immersion of pristine samples into an aqeuous solution of Na₂Se are presented. Cyclic voltammetry on Au shows formation of selenium adsorbed species and the structures observed in reductive desorption are related to the atomic and polymeric species observed in XPS. In the case of Au(111) XPS spectra in the Se­(3d) region indeed show two main features attributed to Se chemisorbed atomically and polymeric Se₈ features. Smaller structures due to other types of Se conformations were also observed. The Au­(4f) peak line shape does not show core level shifts indicative of Au selenide formation. In the case of silver, XPS spectra for the Ag­(3d) show a broadening of the peak and a deconvolution into Ag_B bulk like and Ag_Se components shows that the Ag_Se is located at a lower binding energy, an effect similar to oxidation and sulfidation of Ag. The Se­(3d) XPS spectrum is found to be substantially different from the Au case and dominated by atomic type Se due to the selenide, though a smaller intensity Se structure at an energy similar to the Se₈ structure for Au is also observed. Changes in the valence band region related to Se adsorption are reported