Location of hydrogen adsorbed on palladium (111) studied by low-energy electron diffraction

Felter, T. E.; Sowa, Erik C.; Hove, M.A. Van

doi:10.1103/physrevb.40.891

Cited by 115 publications

(80 citation statements)

References 28 publications

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“…The positions of the surface and subsurface minima, r S and r SS , are bound to be close in absolute value. Felter et al [17] gave values from 1.5 to 1.6 for r S and from −2.2 to −2.3 for r SS , whereas our model PES has r S = 1.5 and r SS = −1.7. Also the subsurface absorption minimum (E SS ) always lies slightly below the surface adsorption minimum (E S ).…”

Section: Discussioncontrasting

confidence: 51%

Direct subsurface absorption of hydrogen on Pd(111)

Løvvik

Olsen

1996

The Journal of Chemical Physics

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We summarize and discuss some of the available experimental and theoretical data important for understanding the role played by subsurface sites in dissociative chemisorption calculations for the H 2 /Pd(111) system. Then we use a semi-empirical potential energy surface (PES) to model the interaction of a H 2 molecule impinging on a Pd(111) surface. The London-Eyring-Polanyi-Sato (LEPS) construction has been extended to make direct subsurface absorption possible. A 2-dimensional wave packet calculation is used to find qualitative trends in the direct subsurface absorption and to reveal the time scales involved. We suggest that a partial in-plane relaxation occurs for the slowest incoming particles, thus resulting in a higher direct subsurface absorption probability for low energies.

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Section: Discussioncontrasting

confidence: 51%

Direct subsurface absorption of hydrogen on Pd(111)

Løvvik

Olsen

1996

The Journal of Chemical Physics

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“…[60][61][62] For the work function, we find ⌽ = 5.30͑5.32͒ eV while experiment yields ⌽ = 5.60 eV. 63 At this level, one is led to conclude that a five-layer slab describes the structure of a Pd͑111͒ surface with good accuracy.…”

Section: A Bulk Metals and Pristine Surfacesmentioning

confidence: 88%

Magnetocrystalline anisotropy energy of Co and Fe adatoms on the (111) surfaces of Pd and Rh

et al. 2010

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We performed a combined theoretical and experimental investigation of the orbital magnetism and magnetocrystalline anisotropy of isolated Co and Fe adatoms on Pd͑111͒ and Rh͑111͒. Theoretical calculations of the spin and orbital moments are based on ab initio spin-polarized density-functional theory ͑DFT͒ including a self-consistent treatment of spin-orbit coupling. The calculations use a slab model to represent the adsorbate/ substrate complex and allow for a complete structural relaxation leading to a strong inward displacement of the adatom and modest vertical and lateral relaxations in the substrate atoms. Compared to an idealized geometry where the atoms are kept on bulk lattice positions up to the surface, relaxation leads to a much stronger adatom/ligand hybridization. This is also reflected in the results for orbital moments and magnetocrystalline anisotropy energy ͑MAE͒. The enhanced hybridization leads to strong quenching of the adatom orbital moments but also to the formation of large induced spin and orbital moments in the substrate. As a consequence, we find that the substrate contribution to the MAE is much more important than estimated before on the basis of studies using an idealized geometry. We also find the surprising result that the MAE strongly depends on the adsorption site. The magnitude and even the sign of the MAE change for adatoms on face-centered cubic with respect to the ones on hexagonal close-packed hollow sites on the ͑111͒ surface. The dependence of the MAE on the combination of adatom and substrate has been analyzed in terms of the electronic structure, leading to a sound physical picture of the origin of the MAE. A fundamental problem, however, is the correct prediction of the size of the orbital moments of the adatoms. We suggest that this problem can be solved only via post-DFT corrections introducing an orbital dependence of the exchange potential. The theoretical results are compared to site-averaged, element-specific x-ray magnetic circular dichroism ͑XMCD͒ measurements. Lowtemperature XMCD spectra and magnetization curves reveal weak out-of-plane anisotropy for Fe adatoms on both substrates. Interestingly, Co adatoms on Rh͑111͒ present in-plane anisotropy with MAE of about −0.6 meV, contrary to the known out-of-plane anisotropy of Co on Pd͑111͒ and Pt͑111͒. The orbital to spin magnetic-moment ratio measured by XMCD shows that the Co adatoms present much stronger orbital magnetization components compared to Fe. The connection between orbital moments and MAE is discussed at the theoretical level including the contribution of the induced substrate magnetization.

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“…Experimentally the H atoms on the surface are known to occupy the fcc sites. 7 Restricting ourselves to two degrees of freedom and dissociation above a bridge site means that the two hydrogen atoms move towards different surface sites, the fcc site and the hcp site. This we do not consider a serious shortcoming of our model.…”

Section: B the Lda And Gga Pess For H 2 On Pd(111)mentioning

confidence: 99%

“…The Pd͑111͒ surface is interesting because both experimental [1][2][3][4][5][6][7] and theoretical 2,3,[8][9][10][11][12][13][14][15][16] studies show the existence of a hydrogen absorption site located between the first and second metal layer. This so-called subsurface site is energetically more favorable than the bulk site and almost as favorable as the chemisorption site on the surface.…”

Section: Introductionmentioning

confidence: 99%

Direct subsurface absorption of hydrogen on Pd(111): Quantum mechanical calculations on a new two-dimensional potential energy surface

Olsen

Philipsen

Baerends

et al. 1997

The Journal of Chemical Physics

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We have calculated a two-dimensional ͑2D͒ potential energy surface ͑PES͒ for H 2 interacting with a Pd͑111͒ surface. The geometry considered is for H 2 approaching a bridge site and dissociating into neighboring hollow sites and the subsurface sites directly below these. Density functional calculations were performed using both the local density approximation ͑LDA͒ and the generalized gradient approximation ͑GGA͒. The LDA PES gives the usual overbinding and shows no barrier ͑relative to the bottom of the H 2 potential͒ to subsurface absorption, while the GGA PES agrees with the experimental adsorption energies and has a large barrier. We have performed quantum mechanical wave packet calculations on the GGA PES to obtain the direct subsurface absorption probability. We have also calculated the barrier height's dependence on a coordinate that can be associated with a local surface vibrational mode and the results suggest that this degree of freedom should be taken into account in the dynamical calculations.

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Location of hydrogen adsorbed on palladium (111) studied by low-energy electron diffraction

Cited by 115 publications

References 28 publications

Direct subsurface absorption of hydrogen on Pd(111)

Direct subsurface absorption of hydrogen on Pd(111)

Magnetocrystalline anisotropy energy of Co and Fe adatoms on the (111) surfaces of Pd and Rh

Direct subsurface absorption of hydrogen on Pd(111): Quantum mechanical calculations on a new two-dimensional potential energy surface

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