Core level shifts of undercoordinated Pt atoms

We present the results of high-energy resolution core level photoelectron spectroscopy experiments paralleled by density functional theory calculations to investigate the electronic structure of highly undercoordinated Pt atoms adsorbed on Pt(111) and its correlation with chemical activity. Pt4f(7/2) core level binding energies corresponding to atoms in different configurations are shown to be very sensitive not only to the local atomic coordination number but also to the interatomic bond lengths. Our results are rationalized by introducing an indicator, the effective coordination, which includes both contributions. The calculated energy center of the valence 5d-band density of states, which is a well known depicter of the surface chemical reactivity, shows a noteworthy correlation with the Pt4f(7/2) core level shifts and with the effective coordination

Highly under-coordinated atoms at Rh surfaces: interplay of strain and coordination effects on core level shift

The electronic structure of highly under-coordinated Rh atoms, namely adatoms and ad-dimers, on homo-metallic surfaces has been probed by combining high-energy resolution core level photoelectron spectroscopy and density functional theory calculations. The Rh3d5/2 core level shifts are shown to be proportional to the number of Rh nearest-neighbours (n = 3, 4 and 5). A more refined analysis shows that the energy position of the different core level components is correlated with the calculated changes of the individual inter-atomic bond length and to the energy changes of the d-band centre, which is known to be a reliable descriptor of local chemical reactivity

Epitaxial growth of ultrathin palladium films on Re{0001}

Ultrathin bimetallic layers create unusual magnetic and surface chemical effects through the modification of electronic structure brought on by low dimensionality, polymorphism, reduced screening, and epitaxial strain. Previous studies have related valence and core-level shifts to surface reactivity through the d-band model of Hammer and Nørskov, and in heteroepitaxial films this band position is determined by competing effects of coordination, strain, and hybridization of substrate and overlayer states. In this study we employ the epitaxially matched Pd on Re{0001} system to grow films with no lateral strain. We use a recent advancement in low-energy electron diffraction to expand the data range sufficiently for a reliable determination of the growth sequence and out-of-plane surface relaxation as a function of film thickness. The results are supported by scanning tunneling microscopy and X-ray photoemission spectroscopy, which show that the growth is layer-by-layer with significant core-level shifts due to changes in film structure, morphology, and bonding

Role of MicroRNA Profile Modifications in Hepatitis C Virus-Related Mixed Cryoglobulinemia

Hepatitis C virus infection is closely related to lymphoproliferative disorders (LPDs), including mixed cryoglobulinemia (MC) and some lymphomas. Modification of the expression of specific microRNAs (miRNAs) has been associated with different autoimmune diseases and/or LPDs. No data exist about the modifications in miRNA expression in HCV-associated LPDs. The aim of this study was to analyze the expression levels of a panel of miRNAs previously associated with autoimmune/LPDs in a large population of HCV patients with and without MC or non-Hodgkin’s lymphoma (NHL), to identify potential markers of evolution of HCV infection. PBMC expression of miR-Let-7d, miR-16, miR-21, miR-26b, miR-146a and miR-155 was evaluated by real-time PCR in 167 HCV patients (75 with MC [MC-HCV], 11 with HCV-associated NHL [NHL-HCV], 81 without LPD [HCV]) and in 35 healthy subjects (HS). A significant increase in miR-21 (p<0.001), miR-16 (p<0.01) and miR-155 (p<0.01) expression was detected in PBMCs from only NHL patients whereas a significant decrease in miR-26b was detected in both MC and NHL subjects (p<0.01) when compared to HS and HCV groups. A restoration of miR-26b levels was observed in the post-treatment PBMCs of 35 HCV-MC patients experiencing complete virological and clinical response following antiviral therapy. This study, for the first time, shows that specific microRNAs in PBMC from HCV patients who developed MC and/or NHL are modulated differently. The specific, reversible downregulation of miR-26b strongly suggests the key role it plays in the pathogenesis of HCV-related LPDs and its usefulness as a biomarker of the evolution of HCV infection to these disorders

Geometric and electronic structure of the N/Rh(100) system by core-level photoelectron spectroscopy: Experiment and Theory

The nitrogen interaction with Rh(100) was studied by combining high-energy resolution core level photoelectron spectroscopy and density functional calculations. Nitrogen-induced Rh3d(5/2) surface core level shifts depend on the N-Rh local geometrical configuration. The core level shifts are dominated by initial state effects and correlate strongly with the variation of the energy position of the surface atom-projected d-band center

The Ni3Al(111) surface structure: experiment and theory

The structure of the Ni(3)Al(111) terminal layers has been studied by means of x-ray photoelectron diffraction and density functional theory. The analysis of the diffraction patterns, combined with multiple-scattering simulations, yields structural parameters which are in good agreement with the ab initio theoretical results. We find that the first-layer Al atoms move outwards with respect to the Ni atom plane, as previously found by low energy electron diffraction experiments and ab initio calculations. The experimentally (theoretically) determined distance between the outermost three layers is reduced by 0.07 +/- 0.07 angstrom (0.06 +/- 0.01 angstrom) and by 0.04 +/- 0.08 angstrom (0.01 +/- 0.01 angstrom) for the first-to-second-layer and second-to-third-layer distances with respect to the bulk value, respectively

Highly under-coordinated atoms at Rh surfaces: interplay of strain and coordination effects on core level shift

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The (1x1)-> hexagonal structural transition on Pt(100) studied by high-energy resolution core level photoemission

The (1 x 1)-> quasihexagonal (HEX) phase transition on a clean Pt(100) surface was investigated by monitoring the time evolution of the Pt4f(7/2) core level photoemission spectra. The spectral component originating from the atoms forming the (1 x .1) metastable unreconstructed surface was found at -570 +/- 20 meV with respect to the bulk peak. Ab initio calculations based on density functional theory confirmed the experimental assignment. At temperatures above 370 K, the (1 x 1) phase irreversibly reverts to the more stable HEX phase, characterized by a surface core level shifted component at -185 +/- 40 meV. By analyzing the intensity evolution of the core level components, measured at different temperatures in the range of 393-475 K, we determined the activation energy of the phase transformation, E=0.76 +/- 0.04 eV. This value is considerably lower than the one previously determined by means of low energy electron diffraction. Possible reasons for this discrepancy are discusse

Surface core level shift: High sensitive probe to oxygen-induced reconstruction of Rh(100)

Oxygen-induced Rh3d(5/2) surface core level shifts were used to probe the local electronic structure of first layer Rh atoms in the (2 x 2)pg reconstructed phase formed upon oxygen adsorption. By comparison of the computed shifts for differently reconstructed geometries with the experimental shifts obtained from high-energy resolution photoemission measurements, we confirm that the reconstructed phase is formed by Rh atoms single- and double-bonded to oxygen, yielding a shift from the bulk component of -185 and +140 meV, respectively. We find that the core level shifts are affected by the local rhomboidal distortion of the surface lattice, Moreover, we show that, on Rh(100), the oxygen-induced surface core level shifts are dominated by initial state effects and proportional to the calculated shift of the d-band center. The latter is therefore correlated to the local surface chemical reactivity, as already found for other adsorbate systems on transition metals