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  • 1
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 5238-5248 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 94 (1990), S. 6936-6939 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 9427-9439 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The properties of Zn, Au, and Zn–Au films on Ru(001) have been studied using thermal desorption mass spectroscopy (TDS) and core and valence-level photoemission. TDS spectra show desorption of Zn from Ru(001) at 450 (multilayer), 490 (second layer), and 720 K (first layer). The monolayer of Zn desorbs following zero-order kinetics with an activation energy for desorption of 36 kcal/mol. Photoemission studies show that the Zn(3s) and Zn(3d) levels of Zn bonded to Ru are shifted 0.5 eV toward lower binding energy with respect to the corresponding levels of pure metallic Zn. The direction of this binding-energy shift together with the results of CO-TDS indicate that Zn is withdrawing electrons from the Ru(001) surface. Such charge transfer is in part responsible for the large stability of the Ru–Zn bond. Au desorbs from Ru(001) at temperatures of 1175 (multilayer) and 1260 K (first layer). For a monolayer of Au deposited on Ru(001), the positions of the Au(4f ) and Au(5d) levels are very close to those of the surface atoms of Au(111), indicating that charge transfer between Au and Ru is minimal. A comparison of the desorption temperature for a monolayer of Zn or Au from Ru(001) with values previously reported for the desorption of monolayers of alkali (K and Cs), noble (Cu and Ag), and transition (Mn, Ni, and Pd) metals indicates that the strength of a metal–metal bond in a bimetallic surface depends on (1) the bulk cohesive energy of the individual metals (which gives an indication of the tendency of the element to form strong metal–metal bonds), and (2) the charge transfer within the bond. Zn and Au alloy when coadsorbed on Ru(001). Results for submonolayer coverages of Zn and Au show that the Zn–Ru and Zn–Au bonds in the trimetallic system are more stable than the corresponding bonds in Zn/Ru(001) or Zn–Au alloys. This phenomenon is probably caused by synergistic interactions in three center metal–metal bonding. The formation of ZnAu alloys induces a shift of ∼+1.0 eV in the Au(4f ) and Au(5d) levels, and −0.2 eV in the Zn(3s) and Zn(3d) levels. The shift in the core and valence levels of Au is caused by rehybridization of the Au(5d,6s,6p) levels, while the shift in the Zn levels comes from a contraction in volume.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 740-747 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The interaction between B and CO on Ru(0001) has been studied by means of thermal desorption mass spectroscopy, Fourier transform infrared reflection absorption spectroscopy, and x-ray photoelectron spectroscopy. Boron adatoms poison CO chemisorption approximately on a one-to-one basis. No reaction or direct bonding between B and CO was observed. The B⋅⋅⋅CO interaction is repulsive due to the electron-acceptor nature of both adsorbates. Boron adatoms modify the electronic and chemical properties of first and second nearest-neighbor metal atoms. In the presence of B, the CO desorption temperature decreases, whereas the O(1s) binding energy and CO stretching frequency increase. These trends are a consequence of (1) a reduction in 2π* back donation caused by competition for metal electrons between CO and B and (2) repulsive electrostatic interactions between the negative charges on CO and B. The infrared results indicate that metal atoms strongly affected by B are only occupied when no more unperturbed Ru sites are available on the surface, or when the high temperature of the system favors CO migration (due to entropic effects) onto these energetically less favorable sites.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7814-7825 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Adsorption of CO on ultrathin Cu films supported on Pt(111) has been studied using infrared reflection absorption spectroscopy (IRAS). Our results indicate that the infrared intensities of adsorbed CO are not representative of the relative composition of the Cu〈1.0/Pt(111) surfaces. The Cu-bonded CO molecules screen CO molecules bonded to Pt, making them invisible in the infrared spectrum. The "screening'' effect depends on the morphology and polarizability of the Cu overlayer. Changes in the morphology of the Cu adlayer produce large variations in the position and line shape of the Cu–CO signal in the infrared spectrum. CO molecules bonded to small Cu clusters show a higher (∼40 cm−1) C–O stretch frequency than CO molecules adsorbed on large Cu islands. The present results were compared with those reported in the literature for the CO/Cu/Ru(0001) and CO/Cu/Rh(100) systems. For CO adsorbed on supported monolayers of Cu, a correlation was found between the strength of the Cu–CO bond, the amount of π backdonation, and the C–O stretch frequency. This correlation cannot be explained using simple models of molecular orbital theory. On the bimetallic surfaces, the C–O stretch frequency is more sensitive to the charge on the metal center to which CO is bonded, than to the electron population of the CO(2π) orbitals.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1523-5378
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: In this study, we compared and evaluated the efficacy of five culture media for the primary isolation of Helicobacter pylori from gastric biopsies.〈section xml:id="abs1-2"〉〈title type="main"〉Materials and Methods.A total of 1,174 biopsies (antrum and corpus) taken from 587 patients were plated in parallel on two selective media—Skirrow’s medium and brain-heart infusion (BHI) agar supplemented with 10% sheep blood, polymyxin B, vancomycin, trimethoprim, and amphotericin B (HPA medium), and on three nonselective media—chocolate agar with Isovitalex, Columbia blood agar, and BHI-10% sheep blood agar.〈section xml:id="abs1-3"〉〈title type="main"〉Results.An isolation rate of 57.9% (680 of 1,174) was obtained with a combination of all media. HPA medium gave the highest isolation rate, 99.4% (676 of 680). Chocolate agar, Columbia blood agar, brain-heart blood agar, and Skirrow’s medium showed very poor performance (23.5%, 28.5%, 65.9%, and 71% of all isolates, respectively). The number of cultures in HPA medium discarded due to contamination was only 2 (0.32%). There was no difference in the positive rate of culture in HPA medium between the antrum and the corpus of the stomach.〈section xml:id="abs1-4"〉〈title type="main"〉Conclusions.The HPA medium is superior to Skirrow’s medium and nonselective media in promoting growth of H. pylori and, on the basis of these results, we recommended the use of HPA medium for primary isolation of H. pylori from gastric biopsies.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Langmuir 7 (1991), S. 1206-1214 
    ISSN: 1520-5827
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 11251-11255 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Accounts of chemical research 28 (1995), S. 477-478 
    ISSN: 1520-4898
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4279-4289 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: On platinum zinc surfaces at 150–300 K, CO adsorbs only on Pt sites. CO molecules bonded to these sites exhibit a significantly lower adsorption energy (4–8 kcal/mol) and a larger O 1s binding energy (0.2–0.4 eV) than molecules bonded to clean Pt(111). To explain these changes in the Pt↔CO interaction, we have examined the electronic properties of Zn/Pt(111) surfaces using core and valence level photoemission, and ab initio self-consistent-field calculations. At 80 K, Zn atoms deposited on Pt(111) remain on top of the surface. Above 400 K, alloy formation occurs. In general, the formation of Pt–Zn bonds produces a large depletion in the density of Pt 5d states around the Fermi level, with a shift in the centroid of the Pt 5d band and 4f core levels toward higher binding energy. This is accompanied by an important redistribution of charge, in which Pt loses 5d electrons and gains (6s,6p) electrons. The electronic perturbations induced by Zn on Pt reduce its CO-chemisorption ability by weakening the strength of the Pt(5d)–CO(2π*) bonding interactions. The changes in the Pt properties observed after bonding this metal to Zn are as large as those found for Pt bonded to early transition metals, and much larger than those found when Pt is bonded to late-transition metals. In the bimetallic surfaces, the perturbations in the Pt properties increase when the fraction of empty states in the valence band of the metal bonded to Pt rises.
    Materialart: Digitale Medien
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