The structure of dense sulphur layers on Ru(0001) I. The c(2 × 4) structure

Schwennicke, C.; Jürgens, D.; Held, Georg; Pfnür, H.

doi:10.1016/0039-6028(94)91130-4

Cited by 33 publications

(28 citation statements)

References 34 publications

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“…In the S/Ru͑0001͒p(2ϫ2) system again, the vibrations of the adsorbate itself do not contribute to the Debye-Waller effect, and the small increase of background intensity observed is compatible with vibrational excitations of only the substrate, which yielded ⌰ D ϭ540 K, in good agreement with the optimizations carried out in LEED-IV studies. 23 The data for the other two systems show that they are also compatible with this description far away from T c ͑the larger slope for Ni is due to ⌰ D,Ni ϭ270 K͒, but close to T c an S-like increase is seen. This increase is directly related to the thermally excited uncorrelated occupation of the second threefold site.…”

Section: A Debye-waller Factor and Thermal Diffuse Backgroundmentioning

confidence: 53%

“…Inserting for m the mass of a substrate atom, we obtain a Debye temperature of ⌰ D ϭ270Ϯ15 K. This Debye temperature agrees very well with other measurements. [21][22][23] Two conclusions can be drawn from this result: First, hydrogen vibrations are not excited to an appreciable extent at these temperatures, 24 i.e., even at and above the disordering temperature. Second, the main contribution to the background intensity is indeed thermal diffuse scattering.…”

Section: A Debye-waller Factor and Thermal Diffuse Backgroundmentioning

confidence: 88%

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Experimental determination of the phase-transition critical exponentsαandηby integrating methods

Voges

Pfnür

1998

Phys. Rev. B

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Integrating methods in low-energy electron diffraction-turning the instrument to low resolution in k ʈ -can reliably be used to study critical properties of continuous two-dimensional phase transitions and to determine critical exponents ␣ and . We performed systematic tests of the conditions under which an energylike power dependence of the diffracted intensity of superstructure beams can be observed in order-disorder phase transitions of adsorbed atomic layers belonging to three-and four-state Potts universality classes. As experimental examples, we studied the systems p(2ϫ2)-and (ͱ3ϫͱ3)R30°-S/Ru͑0001͒ and (2ϫ2)-2H/Ni͑111͒. We show that above T c the condition for an energylike singularity, K I ӷ1 (K I : radius of integration in k space, : correlation length͒ is already reached at K I Ͼ3, whereas below T c effective exponents ␣ are already obtained for K I Ͻ1. Therefore, in the temperature range below T c this method to determine ␣ turns out to be particularly easy to apply, and we concentrate on the determination of ␣ below T c in this study. Values of ␣ of 0.67Ϯ0.04 and 0.40Ϯ0.05 were obtained for four-state Potts and three-state Potts systems, respectively. The latter value indicates small crossover effects to the critical behavior of the peak intensity. These studies were then further extended to the order-disorder transition of p(2ϫ2)-O/Ni͑111͒, which is weakly first order, and to the effects of oxygen impurities in the system (2ϫ2)-2H/Ni͑111͒. We further show that in the limit kӷ1 the exponent can be determined from the k ʈ dependence of integrated ring intensities around positions of superstructure beams. With the systems mentioned, we demonstrate that the limit of a leading term of critical scattering which is independent of temperature can be reached by carrying out measurements going through the order-disorder phase transitions. Values of of 0.27Ϯ0.10 and of 0.30Ϯ0.10 were obtained for the four-state and the three-state Potts systems, in close agreement with theoretical expectations.

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Section: A Debye-waller Factor and Thermal Diffuse Backgroundmentioning

confidence: 53%

Section: A Debye-waller Factor and Thermal Diffuse Backgroundmentioning

confidence: 88%

Experimental determination of the phase-transition critical exponentsαandηby integrating methods

Voges

Pfnür

1998

Phys. Rev. B

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“…On the clean substrate a S monolayer was prepared by dosing 300 L of H 2 S with the substrate held at 550 K and subsequent annealing at 850 K for 30 s. With this procedure, H 2 S dissociates completely and the remaining sulfur forms a c͑4 ϫ 2͒ structure on Ru͑0001͒ with S atoms on hcp and fcc sites. 25 The specimen was exposed to synchrotron light at grazing incidence of 7°in two different geometries, with the electric field vector normal or parallel to the substrate surface. Figure 1 shows sketches of the setups.…”

Section: Methodsmentioning

confidence: 99%

Ultrafast charge transfer and atomic orbital polarization

Deppe

Föhlisch

Hennies

et al. 2007

The Journal of Chemical Physics

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The role of orbital polarization for ultrafast charge transfer between an atomic adsorbate and a substrate is explored. Core hole clock spectroscopy with linearly polarized x-ray radiation allows to selectively excite adsorbate resonance states with defined spatial orientation relative to the substrate surface. For c(4 x 2)S/Ru(0001) the charge transfer times between the sulfur 2s(-1)3p*+1 antibonding resonance and the ruthenium substrate have been studied, with the 2s electron excited into the 3p perpendicular* state along the surface normal and the 3p parallel* state in the surface plane. The charge transfer times are determined as 0.18+/-0.07 and 0.84+/-0.23 fs, respectively. This variation is the direct consequence of the different adsorbate-substrate orbital overlap.

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“…Above 0.33ML, a phase consisting on p(√3x√3)R30º domains separated by linear domain walls (DW) is observed [10,29]. Further deposition of S atoms leads to the reduction in the distance of the DW up to the critical Sulfur coverage of 0.43ML, for which the inter-wall distance reaches its minimum, i.e.…”

mentioning

confidence: 99%

“…We will refer to this phase, characterized by a (√3x7) primitive cell [8], as dense domain walls (DDW). Above 0.43 ML and up to the 0.5ML limit, a rectangular c(2x4) reconstruction is formed [10] ( Figure 1(c)). According to the literature, the higher coverage for this system is 0.6ML, while further S depositions result in the formation of second layer structures [10,11].…”

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confidence: 99%

Coverage evolution of the unoccupied Density of States in sulfur superstructures on Ru(0001)

Pisarra

Gavito

Navarro

et al. 2018

Applied Surface Science

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Sulfur adsorbed on Ru(0001) presents a large number of ordered structures. This characteristic makes S/Ru(0001) the ideal system to investigate the effect of different periodicities on the electronic properties of interfaces. We have performed scanning tunneling microscopy/spectroscopy experiments and density functional theory calculations showing that a sulfur adlayer generates interface states inside the Γ directional gap of Ru(0001) and that the position of such states varies monotonically with sulfur coverage. This is the result of the interplay between band folding effects arising from the new periodicity of the system and electron localization on the sulfur monolayer. As a consequence, by varying the amount of sulfur in S/Ru(0001) one can control the electronic properties of these interfacial materials.The structural properties of sulfur adlayers on transition metal surfaces have received a considerable attention due to the very rich phase diagram that results from the substratemediated long-range interaction between the surface adatoms [1][2][3][4]. For sulfur on Ru(0001) (S/Ru(0001)), experimental and theoretical studies [5-11] have reported the existence of different ordered structures of S atoms with commensurate unit cell with the Ru(0001) surface, each one characterized by a well-defined S/Ru ratio and periodicity. In addition to commensurate structures, a plethora of non-commensurate ordered structures, as well as disordered ones, has been found for non-optimal values of the S/Ru ratio. For this reason, S/Ru(0001) surfaces are ideal to analyze the effect of additional periodicities on the electronic properties of interfaces, e.g., through the folding of the electronic bands.Recently, the intercalation of atomic species between epitaxial graphene and various substrates has been used to break the hexagonal symmetry of graphene and to introduce superlattice perturbations to the graphene π electrons in the form of scalar and gauge potentials [15]. This has opened the possibility, e.g., to vary the density and effective

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The structure of dense sulphur layers on Ru(0001) I. The c(2 × 4) structure

Cited by 33 publications

References 34 publications

Experimental determination of the phase-transition critical exponentsαandηby integrating methods

Experimental determination of the phase-transition critical exponentsαandηby integrating methods

Ultrafast charge transfer and atomic orbital polarization

Coverage evolution of the unoccupied Density of States in sulfur superstructures on Ru(0001)

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