Adsorption-site mixing at a continuous order-disorder phase transition

Schwennicke, C.; Sandhoff, M.; Sklarek, W.; Jürgens, D.; Pfnür, H.

doi:10.1103/physrevb.52.2138

Cited by 12 publications

(2 citation statements)

References 21 publications

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“…A quantitative determination of the occupation probability of this site has been carried out recently by us. 25 Details are discussed there. Consistently, no occupation of the second threefold site has been found close to the phase transition in the S/ Ru͑0001͒-p(2ϫ2) system.…”

Section: A Debye-waller Factor and Thermal Diffuse Backgroundmentioning

confidence: 99%

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: 99%

Experimental determination of the phase-transition critical exponentsαandηby integrating methods

Voges

Pfnür

1998

Phys. Rev. B

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“…As explained in detail in ref. [17], this is indicative for a change of site during the order-disorder phase transition, which, however, does not influence the critical properties, as tested by Monte Carlo simulations [18]. This experimentally determined background was subtracted from the data shown below without further adjustments.…”

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confidence: 99%

Critical properties in two-dimensional order-disorder phase transitions: experimental determination of the exponents alpha and eta by integrating methods

Voges

Pfnür

1997

Europhys. Lett.

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Integrating methods in low-energy electron diffraction (LEED)—turning the instrument to low resolution in k∥—can reliably be used to study critical properties of continuous two-dimensional phase transitions and to determine critical exponents α and η. We performed systematic tests of the conditions under which an energy-like power dependence of the diffracted intensity of superstructure beams can be observed in order-disorder phase transitions of adsorbed atomic layers belonging to 3- and 4-state Potts universality classes. We further show that in the limit kξ ≫ 1 the exponent η can be determined reliably both below and above Tc using integrated intensities.

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Thermal Fluctuations in Equilibrium and Their Modification by Surface Defects

Pfnür

1997

Surface Diffusion

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Adsorption-site mixing at a continuous order-disorder phase transition

Cited by 12 publications

References 21 publications

Experimental determination of the phase-transition critical exponentsαandηby integrating methods

Experimental determination of the phase-transition critical exponentsαandηby integrating methods

Critical properties in two-dimensional order-disorder phase transitions: experimental determination of the exponents alpha and eta by integrating methods

Thermal Fluctuations in Equilibrium and Their Modification by Surface Defects

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