Coexistence of {011} facets with {112} facets on W(111) induced by ultrathin films of Pd

Nien, C.-H.; Madey, Theodore E.; Tai, Yu-Ke; Leung, T. C.; G., J.; Chan, Che Ting

doi:10.1103/physrevb.59.10335

Cited by 53 publications

(41 citation statements)

References 31 publications

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“…This finding is consistent with a firstprinciples theory that indicates that a higher heat of adsorption provides both a strong thermodynamic driving force for faceting and a lower kinetic barrier to faceting (25,26).…”

Section: Synchrotron Radiation Studies Of Metals On Wsupporting

confidence: 91%

Nanoscale surface chemistry

Madey

Pelhos

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

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We report evidence in several experiments for nanometer-size effects in surface chemistry. The evidence concerns bimetallic systems, monolayer films of Pt or Pd on W(111) surfaces. Pyramidal facets with {211} faces are formed on annealing on physical monolayer of Pt, Pd on a W(111) substrate, and facet sizes increase with annealing temperature. We used synchrotron radiation-based soft x-ray photoemission to show that monolayer films of Pt, Pd, on W ''float'' on the outer surface, whereas multilayer films form alloys on annealing. Acetylene reactions over bimetallic planar and faceted Pd͞W surfaces exhibit size effects on the nanometer scale, that is, thermal desorption spectra of reactively formed benzene and ethylene (after acetylene adsorption) change systematically with facet size. In the second case, the decomposition of C 2H2 over planar and faceted Ir(210) surfaces also exhibits structure sensitivity; temperature programmed desorption of H 2 from C2H2 dissociation depends on the nanoscale surface structure. Finally, we have characterized interactions of Cu with the highly ordered S(4 ؋ 4)͞W(111) surface. The substrate is a sulfur-induced nanoscale reconstruction of W(111) with (4 ؋ 4) periodicity, having broad planar terraces (Ϸ30 nm in width). Fractional monolayers of vapordeposited Cu grow as threedimensional clusters on the S(4 ؋ 4) surface over a wide coverage range. At low Cu coverage (< 0.1 ML), Cu nanoclusters nucleate preferentially at characteristic 3-fold hollow sites; we find a clear energetic preference for one type of site over others, and evidence for self-limiting growth of nanoclusters.A n important issue in surface chemistry and catalysis is how surface structures and features with nanometer dimensions affect reactivity in heterogeneous systems (1-3). The focus of our work has been on several aspects of nanoscale phenomena that influence surface chemistry, including faceting of metallic and model bimetallic catalyst surfaces, and nucleation of subnanometer metallic clusters on sulfided surfaces. We study atomically rough substrates [bcc (111) surface of W, and fcc (210) surface of Ir] that are morphologically unstable, that is, the initially planar substrate becomes covered with nanoscale facets when covered with monolayer films of gases or other metals, and heated to elevated temperature. Major objectives of this work have been (i) to determine how the surface transition from planar to faceted affects the surface reactivity of metallic and bimetallic systems, and (ii) to characterize the nucleation and growth of metals on sulfided W surfaces. The three main components of this effort are surface structure, surface chemistry, and surface electronic properties.The importance of bimetallic catalysts based on Pt-group metals has been increasing in recent decades (4, 5). These catalysts display important advantages over classical reforming catalysts, including better stability, as well as improved activity and selectivity. In particular, refractory metals (W, Mo, Re, . . .) in combination with ...

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Section: Synchrotron Radiation Studies Of Metals On Wsupporting

confidence: 91%

Nanoscale surface chemistry

Madey

Pelhos

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

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“…Both types of facets have been accounted for by theory. [23][24][25] The ferromagnets Fe, Co, Ni, and Gd have been found not to induce such facetting. Surprisingly, relatively little work has been carried out on the ferromagnets on W͑111͒ beyond the issue of facetting, and the little that is known concerning structure does not touch at all on magnetism.…”

Section: Introductionmentioning

confidence: 98%

Growth morphology, structure, and magnetism of ultrathin Co films on W(111)

et al. 2003

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The growth morphology, structure, and magnetism of ultrathin Co films on the W͑111͒ surface are studied with conventional and spin polarized low energy electron microscopy and diffraction and first principles total energy calculations. Pseudo-layer-by-layer growth of thick pseudomorphic ͑ps͒ Co films is observed at 380 K, while Stranski-Krastanov growth and transformation to a ͑6ϫ6͒ closed-packed structure are observed at higher temperatures. On the basis of the calculations, only one ps Co monolayer is expected to be thermodynamically stable against three-dimensional island formation. Calculations also indicate that the magnetic moment on Co atoms at the interface is reduced due to strong hybridization with the substrate, but remains non-zero even for the single ps monolayer. Metastable ps Co/W͑111͒ is found experimentally to be ferromagnetically ordered at 380 K when film thickness exceeds 7.6 ps ML. Although only in-plane magnetization is observed, substrate atomic steps have a strong influence on the magnetization easy axis and magnetic domain structure, which suggests that the in-plane magnetocrystalline anisotropy is weak.

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“…This is most dramatically illustrated in the phenomenon of overlayer-induced faceting of bcc(111) surfaces (Ta, Mo, and W) [25][26][27][28][29][30][31][32][33][34][35][36]. Recently, more subtle overlayer-induced effects have been investigated.…”

Section: Introductionmentioning

confidence: 99%

Core-level spectroscopy of the Pd/W(110) interface: Evidence of long-range Pd-island–W interactions at submonolayer Pd coverages

et al. 2009

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We have measured W 4f 7/2 core-level photoemission spectra from W(110) in the presence of Pd overlayers for coverages up to ∼1 pseudomorphic monolayer (ML). At coverages close to 0.05 ML a striking change in the W core-level spectrum is observed, which we interpret as indicating a long-range lateral effect of 2D Pd islands upon the W electronic structure in both the first and second W layers. As the coverage increases the long-range effect weakens and finally vanishes near 0.85 ML. Above this coverage the W spectra are typical for a W-based bimetallic interface, with the first-layer W atoms exhibiting a small interfacial core-level shift (−95 ± 5 meV) compared to the bulk atoms.

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Coexistence of {011} facets with {112} facets on W(111) induced by ultrathin films of Pd

Cited by 53 publications

References 31 publications

Nanoscale surface chemistry

Nanoscale surface chemistry

Growth morphology, structure, and magnetism of ultrathin Co films on W(111)

Core-level spectroscopy of the Pd/W(110) interface: Evidence of long-range Pd-island–W interactions at submonolayer Pd coverages

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