Phase transitions driven by competing interactions in low-dimensional systems

Cordin, Michael; Lechner, Baj; Amann, Peter; Menzel, A.; Bertel, E.; Franchini, Cesare; Zucca, Rinaldo; Redinger, Josef; Baranov, M. A.; Diehl, Sebastian

doi:10.1209/0295-5075/92/26004

Cited by 12 publications

(22 citation statements)

References 25 publications

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“…For Cl/Pt(110), a (2 × 1) structure is formed that is also the low-temperature phase (ground state) of Br/Pt(110). 15 Br/Pd(110) is the only system in which no well-ordered phase at all is formed at room temperature and 0.5 ML coverage. STM images and the combined evidence of LEED and TPD suggest that this is due to the instability of the Pd(110) surface against corrosion at even moderate temperatures.…”

Section: ■ Resultsmentioning

confidence: 99%

“…Because the Pt surface shows a significant buckling for all structures with Θ > 0.5 ML, we infer an active role of the substrate in forming these phases. 15,28,35 Of course, open questions remain. Although the similar succession of compression structures for Cl, Br, and I on Pd(110) suggest similar adsorption sites, the calculation predicts the sb site (i.e., adsorption on the ridges rather than in the troughs) to be preferred for Cl/Pd(110) in contrast to Br/Pd(110) and I/Pd(110).…”

Section: ■ Resultsmentioning

confidence: 99%

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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: 99%

Section: ■ Resultsmentioning

confidence: 99%

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

et al. 2015

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“…However, since the corresponding q vector is incommensurate, the CDW is not stable on the clean Pt(110) surface, at least not above 50 K. In the presence of 0.5 to 0.66 ML of Br, however, CDW fluctuations are observed. At a coverage of precisely 0.5 ML, the well ordered room temperature c(2ˆ2)-Br/Pt(110) structure shows a phase transition to a low-T (2ˆ1) structure at around 50 K [23,29]. Fluctuating (2ˆ1) domains can be imaged by STM in this case, since the fluctuations are rather sluggish at 50 K [29] (see Figure 5a).…”

Section: The Order-order Phase Transitionmentioning

confidence: 90%

“…A similar type of substrate induced order-order transition in the adsorbate layer has been explored on the Pt(110) surface with a coverage of 0.5 monolayers (ML) of Br [20,23,24]. Pt exhibits a strong Kohn anomaly in its phonon dispersion, signaling a coupling of the phonons to electronic excitations with finite wave vector q at E F .…”

Section: The Order-order Phase Transitionmentioning

confidence: 99%

“…The model contains a Landau expansion of the free energy in terms of the order parameter m to describe the substrate CDW order, an Ising type modeling of interadsorbate repulsion with interaction parameter, J , and a coupling term with coupling strength, g (<0), capturing the modulation of the adsorbate-substrate bond strength by the CDW: The model is illustrated in Figure 6 and discussed in more detail in [23]. Basically, in the high-T phase, the CDW order parameter is zero and the adsorbate structure is determined by the interadsorbate repulsion.…”

Section: The Order-order Phase Transitionmentioning

confidence: 99%

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Fluctuating Charge Order: A Universal Phenomenon in Unconventional Superconductivity?

Bertel

Menzel

2016

Symmetry

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Unconventional superconductors are characterized by various competing ordering phenomena in the normal state, such as antiferromagnetism, charge order, orbital order or nematicity. According to a widespread view, antiferromagnetic fluctuations are the dominant ordering phenomenon in cuprates and Fe based superconductors and are responsible for electron pairing. In contrast, charge order is believed to be subdominant and compete with superconductivity. Here, we argue that fluctuating charge order in the (0,π) direction is a feature shared by the cuprates and the Fe based superconductors alike. Recent data and theoretical models suggest that superconductivity is brought about by charge order excitations independently from spin fluctuations. Thus, quantum fluctuations of charge order may provide an alternative to spin fluctuations as a mechanism of electron pairing in unconventional superconductors.

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Halogen Adsorption on Metals

Andryushechkin

2015

Surface and Interface Science

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Phase transitions driven by competing interactions in low-dimensional systems

Cited by 12 publications

References 25 publications

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

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

Fluctuating Charge Order: A Universal Phenomenon in Unconventional Superconductivity?

Halogen Adsorption on Metals

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