Structure of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>c</mml:mi><mml:mo>(</mml:mo><mml:mn>2</mml:mn><mml:mn /><mml:mo>×</mml:mo><mml:mn>2</mml:mn><mml:mo>)</mml:mo></mml:math>-Br/Pt(110) surface

Blüm, Volker; Hammer, Lutz; Heinz, K.; Franchini, Cesare; Redinger, Josef; Swamy, K.; Deisl, C.; Bertel, E.

doi:10.1103/physrevb.65.165408

Cited by 45 publications

(39 citation statements)

References 87 publications

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“…At room temperature and 0.5 ML coverage, the c(2 × 2) structure is well-ordered and stable for Br/Pt(110), 22 I/Pt(110), 23 Cl/ Pd(110), I/Pd(110), 12 Cl/Cu(110), 24,25 and I/Cu(110). 18 The exceptions are Cl/Pt(110) 14 and Br/Pd(110).…”

Section: ■ Resultsmentioning

confidence: 97%

Halogen Phases on Pd(110): Compression Structures, Domain Walls, and Corrosion

et al. 2015

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Halogens are used as modifiers in catalytic processes, notably including photocatalytic watersplitting; as redox-active species in dye-sensitized solar cells; and as etchants in device fabrication. Atomically resolved studies of the adsorption and reactivity of halogens on Pt and Pd surfaces are scarce in view of the prominent role these metals play in the mentioned applications. The present study reports phases of halogens on Pd(110) in the submonolayer coverage range as monitored by temperature-programmed desorption, low-energy electron diffraction, scanning tunneling microscopy, and density functional calculations. Domain wall and compression structures are observed, as is typical for halogens (except fluorine) on transition and noble metals, but not on Pt, where the bonding is much more site-specific and a different succession of phases is found. The reactivity of Br toward Pd(110) is greater than that of Cl, as judged by the corrosive attack and by the bond strength derived from the thermal desorption temperature. The results confirm that an ionic-bonding picture based on a large metal-to-halogen charge transfer is not valid for Pd and Pt. Rather, the bonding is predominantly covalent, and the reactivity does not obey simple intuitive rules. ■ INTRODUCTIONHalogen−transition-metal interactions are of considerable relevance in catalysis, device engineering, and corrosion. In catalysis, halogens serve to modify the selectivity of catalytic processes. In device fabrication, halogens are widely used as mobilizing agents for transition metals in both deposition and ablation (dry-etching) processes. 1,2 Whereas an abundance of studies concerning the dry etching of silicon surfaces by exposure to halogen-containing species have been published, the halogen−metal interaction is much less studied. Halogen− platinum and halogen−palladium interaction is of particular interest because of the relevance of these metals in catalysis and as electrodes in microelectronic devices. Recently, the topic has acquired additional relevance in sustainable-energy research, because Pt and Pd are used as electrodes and cocatalysts in photocatalytic water splitting 3 and in dye-sensitized solar cells. 4,5 Halogens, in particular iodine, are used as redox shuttles and as catalytic modifiers in these applications.In the present study, we investigate the phases formed by halogens on Pd(110) at submonolayer coverage and compare the results with the halogen/Pt(110) and other halogen/ transition-metal systems. The phases of halogens on Pd (110) were investigated by temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density functional theory (DFT) calculations using both the local density approximation (LDA) and the generalized gradient approximation (GGA). Angle-resolved (UV) photoemission spectroscopy (ARPES) measurements were also carried out, but these results will be discussed elsewhere.

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Section: ■ Resultsmentioning

confidence: 97%

Halogen Phases on Pd(110): Compression Structures, Domain Walls, and Corrosion

et al. 2015

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“…More computational details have been given previously. 9 Clean Pt(110) exhibits a missing-row reconstruction with a (1 × 2) surface unit cell 10 (Figure 1a). After a dose of 0.5 monolayers [ML; 1 ML is defined by the atom density of the (1 × 1) Pt(110) surface] of Br or Cle atoms is applied, the missingrow reconstruction is lifted and a c(2 × 2) Br/Pt(110) or (2 × 1) Cl/Pt(110) structure, respectively, is formed (Figure 1b a slight indication of a (4 × 2) periodicity (Figure 2b).…”

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confidence: 99%

Halogen-Induced Corrosion of Platinum

et al. 2009

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The interaction of halogens with platinum surfaces is an extremely interesting problem in catalysis and semiconductor technology. Halogens serve as platinum mobilizers in both deposition and corrosion or etching processes. [PtCl 4 ] 2-adsorption from an electrolyte and subsequent reduction to metallic Pt clusters is an electrochemical pathway for obtaining highly dispersed, catalytically active Pt surfaces. 1 Halogen-induced etching of platinum surfaces is widely applied in device fabrication, where platinum functions as the electrode metal. 2,3 Cl 2 is routinely used in the etch gas, but its role is not clear. 4,5 Enhancement of etching by addition of CO in the Cl 2 etching plasma was attributed to the formation of volatile species. 6 Here we investigate the halogen-platinum surface interaction in an ultrahigh vacuum (UHV) environment by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density functional theory (DFT) calculations. We show that the dry deposition of Cl 2 in vacuo on the initially clean Pt(110) surface yields an array of Cl and PtCl 4 almost identical to that from direct deposition of [PtCl 4 ] 2-onto Au(100) in an aqueous environment, as described by Kolb and co-workers. 1 Furthermore, coadsorption of other less reactive species is observed to promote corrosion by converting adsorbed chlorine into PtCl 4 . This indicates that the highly ordered Cl/PtCl 4 /metal system reported here is a universal transition state in both erosion and deposition. In addition, the results provide new insights into the role of promoters of the etching process.To study the platinum-halogen interaction, we chose the Pt(110) surface. Baking in oxygen, Ar ion sputtering, and finally cycles of low-temperature oxygen adsorption (T < 140 K) and flash desorption yielded an extremely clean (1 × 2) missing-row reconstructed surface ( Figure 1a). Halogen adsorption was carried out by means of solid-state electrolysis of AgBr or AgCl. The silver halide pellet was kept in a heated glass collimator tube, and the amount of halide molecules produced during electrolysis was calculated from the time-integrated electrolysis current. The sample was positioned in front of the collimator, thereby avoiding contamination and corrosion of the UHV chamber.First-principles DFT calculations served to determine the Br and Cl bond energies on different adsorption sites and the optimum bonding geometries. The calculations were performed using both the all-electron full-potential linearized augmented plane-wave method (as implemented in the FLAIR package) 7 and the Vienna ab initio simulation package (VASP) 8 within the local density approximation (LDA) and the generalized gradient approximation (GGA). The surface was modeled either by a single slab (FLAIR) or repeated slabs (VASP) up to 11 layers thick. In VASP, the repeated slabs were separated by vacuum layers at least 1 nm thick.The geometry was optimized until all of the forces were less than 0.01 eV/Å. More computational details have been given previously. 9...

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“…In addition, there is now a growing set of simulations for halogens on metallic surfaces (e.g. chlorine [7][8][9] , bromine 10,11 or iodine 12 ). Both for alkali metals and for halogens as adsorbates, there are general questions such as the geometry, binding energies, diffusion barriers, charge transfer and the binding mechanism.…”

Section: Introductionmentioning

confidence: 99%

Density functional study of Ni bulk, surfaces and the adsorbate systems Ni(111)R30°–Cl, and Ni(111)(2×2)–K

Doll

2003

Surface Science

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Nickel bulk, the low index surfaces and the adsorbate systems Ni(111) ( √ 3 × √ 3)R30 • -Cl, and Ni(111)(2 × 2)-K are studied with gradient corrected density functional calculations. It is demonstrated that an approach based on Gaussian type orbitals is capable of describing these systems. The preferred adsorption sites and geometries are in good agreement with the experiments. Compared to non-magnetic substrates, there does not appear to be a huge difference concerning the structural data and charge distribution. The magnetic moment of the nickel atoms closest to the adsorbate is reduced, and oscillations of the magnetic moments within the first few layers are observed in the case of chlorine as an adsorbate. The trends observed for the Mulliken populations of the adsorbates are consistent with changes in the core levels.

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Structure of thec(2×2)-Br/Pt(110) surface

Cited by 45 publications

References 87 publications

Halogen Phases on Pd(110): Compression Structures, Domain Walls, and Corrosion

Halogen Phases on Pd(110): Compression Structures, Domain Walls, and Corrosion

Halogen-Induced Corrosion of Platinum

Density functional study of Ni bulk, surfaces and the adsorbate systems Ni(111)R30°–Cl, and Ni(111)(2×2)–K

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