title: Two-stage surface freezing of a single top layer in a smectic-A membrane.
abstract: The crystallization of a single liquid top layer of smectic membranes of the compound 4O.8 has been studied with grazing-incidence x-ray diffraction. As this process takes place in two steps, involving an intermediate hexatic smectic-B layer before the final crystalline-B surface structure is reached, it provides a model for melting in two dimensions. The positional order has been investigated quantitatively by measuring the scattering profiles and the associated correlation lengths. The surface liquid-hexatic phase transition is found to be continuous, while the hexatic-crystal transition is weakly first order with an abrupt change of the in-plane positional correlations. The surface phase transitions do not modify the liquid in-plane structure of the interior layers.
authors.affiliation: FOM-Institute AMOLF, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands. dejeu@amolf.nl
authors.forename: Wim H
authors.initials: WH
authors.lastname: de Jeu
authors.forename: Andrea
authors.initials: A
authors.lastname: Fera
authors.forename: Oleg
authors.initials: O
authors.lastname: Konovalov
authors.forename: Boris I
authors.initials: BI
authors.lastname: Ostrovskii