Surface vs. bulk order/disorder transition in a binary alloy. A He diffraction study of the surface*
Istituto Nazionale di Fisica della Materia (INFM) and
Dipartimento di Fisica, Università di Genova
via Dodecaneso 33, I-16146, Genova, Italy
Accepted: 14 January 1999
We present a helium diffraction study of the order/disorder phase transition at the (001) surface of . We have measured the specular and the superlattice (-1, 0) Bragg intensities in the 140 K K temperature range. We have performed an accurate determination of the Debye-Waller factor, including anharmonic contributions. Thanks to the extreme surface sensitivity of helium diffraction, the superlattice peak intensity provides an experimental determination of the long-range order parameter M at the topmost surface layer. The surface critical temperature is found to be = . The value of the critical exponent = 0.45 ± 0.05 is in good agreement with theoretical predictions within the surface-induced disorder model.
PACS: 68.35.Rh – Phase transitions and critical phenomena / 34.50.-s – Scattering of atoms, molecules, and ions
© EDP Sciences, 1999