Displacive phase transition at the 5/3 monolayer of Pb on Ge(001)

Journal Article · Fri Jul 15 00:00:00 EDT 2005 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.72.045404· OSTI ID:20719166

Cvetko, D ^[1]; Ratto, F ^[2]; Cossaro, A; Floreano, L ^[2]; Bavdek, G ^[2]; Morgante, A ^[2]

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1. Department of Physics, University of Ljubljana, Ljubljana (Slovenia)
2. Laboratorio TASC dell'Istituto Nazionale per la Fisica della Materia, Trieste (Italy)

At a coverage of 5/3 monolayer (ML), Pb adsorbed on Ge(001) forms a ground phase displaying a ((2 1/0 6)) symmetry. This phase undergoes two reversible phase transitions ((2 1/0 6)){r_reversible}((2 1/0 3)){r_reversible}(2x1) at the critical temperatures T{sub c{sub 1}}{approx}178 K and T{sub c{sub 2}}{approx}375 K, respectively. We investigated the behavior of the relevant order parameters at the critical temperatures by means of He and in-plane x-ray diffraction (HAS and XRD, respectively). Both phase transitions at the critical temperature put in evidence a clear order-disorder behavior, in agreement with the universality class expected for the corresponding symmetry group transformation. The low-temperature transition yields the critical exponent of the two-dimensional (2-D) Ising universality class, whereas the three-state Potts' critical exponents are found for the high-temperature transition. By out-of-plane XRD measurements, the low-temperature phase transition is observed to be accompanied by a static surface distortion at room temperature. A complementary HAS study of the temperature evolution of the surface charge corrugation reveals that the complete ((2 1/0 6)){r_reversible}((2 1/0 3)) transition is of the displacive type. On the contrary, the high-temperature phase transition does not show any change of the surface corrugation up to its irreversible decomposition, thus pointing to a pure order-disorder character.

• OSTI ID: 20719166
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 4 Vol. 72; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ADSORPTION
CRITICAL TEMPERATURE
DECOMPOSITION
GERMANIUM
LAYERS
LEAD
ORDER PARAMETERS
ORDER-DISORDER TRANSFORMATIONS
SEMICONDUCTOR MATERIALS
SURFACES
SYMMETRY
SYMMETRY GROUPS
TEMPERATURE DEPENDENCE
X-RAY DIFFRACTION