Chemisorption of atomic oxygen on Pd(111) studied by STM

Rose, M.; Borg, A.; Dunphy, J.C.; Mitsui, Toshiyuki; Ogletree, D. Frank; Salmerón, Miquel

doi:10.1016/j.susc.2004.04.037

Cited by 56 publications

(58 citation statements)

References 23 publications

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“…However, oxygen contamination of the tip introduces significant qualitative changes ͓see Fig. 4͑b͔͒: oxygen atoms are now imaged as bright protrusions located on top of the atom ͑images for this case, in agreement with this result, will be published elsewhere 19 ͒. These changes can be easily understood in terms of the I pq current components: while for the metal tip most of the current is associated with the apex atom, for the oxygenterminated tip, the apex atom contributes a very small fraction, and most of the current goes through the three metal atoms on the layer above the oxygen, a result in agreement with previous approximate calculations using a scattering formalism and the extended Debye-Huckel approximation 20 …”

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confidence: 80%

Origin of contrast in STM images of oxygen on Pd(111) and its dependence on tip structure and tunneling parameters

et al. 2005

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The dependence of the contrast and symmetry of scanning tunneling microscope images of O / Pd͑111͒ −2 ϫ 2 on the structure of the tunneling tip and on tunneling parameters is explained using first-principles density functional theory. Experimentally, the contrast changes in different ways when a metal-terminated tip over hcp and top sites changes its bias and tip-sample distance. These changes are also reflected in the symmetry of the image. A detailed analysis of the tunneling contributions indicates that for the metallic tips, the Pd d orbitals are determining the image symmetry at close range and low bias, while at larger separations and high bias the Pd p z orbitals are the ones that control the image contrast. For oxygen-terminated tips, we predict a positive image contrast, associated with the tip oxygen bonds, as opposed to the negative contrast images obtained with metallic tips.

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confidence: 80%

Origin of contrast in STM images of oxygen on Pd(111) and its dependence on tip structure and tunneling parameters

et al. 2005

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“…Oxygen molecules adsorb intact on the Pd(111) surface forming ordered (2×2) islands at low temperature but when the temperature is increased to 120 K thermal dissociation can be observed to occur on the time scale of minutes, and at 160 K all the molecules have dissociated, forming a (2×2) ordered phase [10,11].…”

Section: Introductionmentioning

confidence: 99%

Interactions of oxygen and hydrogen on Pd(111) surface

et al. 2008

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The coadsorption and interactions of oxygen and hydrogen on Pd(111) was studied by scanning tunneling microscopy and density functional theory calculations. In the absence of hydrogen oxygen forms a (2×2) ordered structure. Coadsorption of hydrogen leads to a structural transformation from the (2×2) to a (√3×√3)R30 o structure. In addition to this transformation, hydrogen enhances the mobility of oxygen. To explain these observations, the interaction of oxygen and hydrogen on Pd(111) was studied within the density functional theory. In agreement with the experiment the calculations find a total energy minimum for the oxygen (2×2) structure. The interaction between H and O atoms was found to be repulsive and short ranged, leading to a compression of the O islands from (2×2) to (√3×√3)R30 o ordered structure at high H coverage. The computed energy barriers for the oxygen diffusion were found to be reduced due to the coadsorption of hydrogen, in agreement with the experimentally observed enhancement of oxygen mobility. The calculations also support the finding that at low temperatures the water formation reaction does not occur on Pd(111).

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“…The vast majority of DFT calculations [4,6,7] as well as combined studies of both DFT and experimental data [2,3,8] support the viewpoint that oxygen reside on hollow three-fold fcc sites of Pd(1 1 1). An exception is the ion scattering study [9] which claims higher binding energy of the three-fold hcp sites.…”

Section: Introductionmentioning

confidence: 82%

“…The reaction rate was n r ¼ n r 0 expðÀE r a =k B TÞ. Parameters characterizing the hopping of oxygen were activation energy E O a ¼ 0:4 eV (which is the lower limit of that obtained by the STM measurements [8] and rather close to E O a on Pt(1 1 1) [19]) and pre-exponential factor n O 0 ¼ 10 12 s À1 [8]. The value for hopping of CO, E CO a ¼ 0:12 eV, was chosen in accordance with the STM result [13], but the pre-exponential factor n CO 0 ¼ 10 8 s À1 was four orders of magnitude lower than the experimental.…”

Section: The Choice Of Kinetic Parametersmentioning

confidence: 99%